Thesis for Master’s degree in chemistry Asfaw Gebretsadik Extent, sources and

Thesis for Master’s degree in chemistry Asfaw Gebretsadik Extent, sources and

Thesis for Master’s

degree in chemistry

Asfaw Gebretsadik

Extent, sources and evolution of groundwater salinization in Lower

Shire area, Malawi

60 study points

DEPARTEMENT OF CHEMISTRY

Faculty of mathematics and natural sciences

UNIVERSITY OF OSLO 08/2010

Acknowledgements

This master thesis has been carried out at the Department of Chemistry, University of Oslo, since autumn 2008.

First and foremost, I would like to express my sincere gratitude to my supervisor Professor

Rolf D. Vogt for his help and guidance throughout this study, not only in terms of academic supervision, but also for his words of encouragement.

I would like to give thanks to Professor Grethe Wibetoe and Professor Per Aaagard for providing me all support for chemical analysis. I am indebted to Professor Hans Martin Seip for his critical comments on my thesis.

Many thanks to Maurice Monjerezi, who helped to sharpen my research question and depth discussion, explained how to do the interpretation of data and field work. I am grateful to him, who always had the time to look into my problem, whenever I was stuck at some stage during this research period. I must give thanks to Cosmo Ngongondo, Boniface Chimwaza and

Dixon Mlelemba who personally accompanied me all the time during my field campaign.

Special thanks go to Dr. Mesay Mulugeta and Brian Lutz for helping me in analytical analysis of water samples. I am also grateful to Ingar Johansen for isotope analysis. I am thankful to

Anne-Marie Skramstad and Marita for helping me with instrumental difficulties and for providing analytical advice.

I would like to thanks to my fellow student, Christian W. Mohr at environmental chemistry group for the time that we spent together, assistance in computer, shared the knowledge and joy at UiO. I express my appreciation to all the members of the Environmental Chemistry group.

I gratefully acknowledge the International Student Office of Administration Department of

UiO and Quota Scheme from Norwegian Government for their financial support.

Last but not Least I stretch out my hands to my family and friends for always being there for me.

2

Table of Contents

Acknowledgements ................................................................................................................... 2

Figure of tables ......................................................................................................................... 5

List of tables .............................................................................................................................. 7

Abbreviations and symbols ..................................................................................................... 8

Abstract ..................................................................................................................................... 9

1. INTRODUCTION .............................................................................................................. 11

1.1

Objectives of the study .............................................................................................. 11

1.1.1 Main Objectives ............................................................................................................. 12

1.2

NUFU PROJECT ...................................................................................................... 13

2

THEORY ......................................................................................................................... 14

2.1

Groundwater salinity ................................................................................................. 14

2.2

Drinking water standards ........................................................................................... 14

2.3

Natural salt accumulation .......................................................................................... 15

2.4

Effects of salinity ....................................................................................................... 17

2.5

Ground water quality and availability ....................................................................... 18

2.6

Groundwater and aquifer systems ............................................................................. 20

2.7

Groundwater and surface water interaction ............................................................... 21

2.8

Borehole depth ........................................................................................................... 21

2.9

Floodplains around lower Shire River ....................................................................... 22

2.10

Irrigation-induced salinity ...................................................................................... 23

2.11

Alkaline earth metals in aquifer ............................................................................. 23

2.12

Heavy metals - origin and occurrence in groundwater .......................................... 23

2.12.1 Origin of heavy metals in groundwater ......................................................................... 24

2.13

Environmental isotopes .......................................................................................... 24

2.13.1 Isotope techniques ........................................................................................................ 25

2.13.2 Stable Isotope ................................................................................................................ 26

2.13.3 Strontium Isotopes ........................................................................................................ 26

2.14

Theoretical Background on Analytical techniques ................................................ 27

2.14.1 Alkalinity ........................................................................................................................ 27

2.14.2 Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) ........................ 28

2.14.3 Ion Exchange Chromatography(IC) ................................................................................ 28

3

MATERIAL AND METHODS ..................................................................................... 30

3.1

Introduction ............................................................................................................... 30

3.2

Description of the study area ..................................................................................... 31

3.2.1 Sampling areas .............................................................................................................. 31

3.2.2 Physiography, climate and land use .............................................................................. 32

3.3

Geology and Hydrogeology....................................................................................... 36

3.3.1 Geology .......................................................................................................................... 36

3.4

Sample analysis ......................................................................................................... 38

3.4.1 Cleaning ......................................................................................................................... 38

3

3.4.2 Water sampling procedure ............................................................................................ 38

3.4.3 Dilution .......................................................................................................................... 41

3.4.4 EC, pH and TDS .............................................................................................................. 41

3.4.5 Determination of Alkalinity ........................................................................................... 41

3.4.6 Determination of Heavy metals and major cations in water using ICP-AES ................. 41

3.4.7 IC method ...................................................................................................................... 42

3.4.8 Analytical Methods for Isotope samples ....................................................................... 42

3.5

Softwares for data processing .................................................................................... 43

3.5.1 Hierarchical cluster analysis .......................................................................................... 43

3.5.2 Principal Component Analysis ....................................................................................... 44

3.5.3 Piper diagram ................................................................................................................ 44

3.5.4 General about PHREEQC ............................................................................................... 44

4

Results and Discussions .................................................................................................. 45

4.1

Ground water quality ................................................................................................. 45

4.1.1 Physical parameters ...................................................................................................... 45

4.1.2 Major ions ...................................................................................................................... 47

4.1.3 Calculation of saturation indexes from PHREEQC ......................................................... 53

4.2

Minor ions in groundwater ........................................................................................ 54

4.2.1 Minor alkaline earths (Ba and Sr) .................................................................................. 56

4.3

Environmental Isotopes ............................................................................................. 57

4.3.1 Hydrogen and Oxygen isotopes..................................................................................... 57

4.3.2 Strontium isotopes ........................................................................................................ 59

4.4

Stastical Analysis ....................................................................................................... 60

4.4.1 Hierarchical cluster analysis .......................................................................................... 60

4.4.2 Principal Component Analysis ....................................................................................... 62

4.4.3 Concentrations of major ions in the four clusters ......................................................... 64

4.5

Validation and Quality control .................................................................................. 66

4.5.1 Accuracy of chemical analysis ....................................................................................... 66

4.5.2 Spike and Recovery ....................................................................................................... 66

5

CONCLUSIONS ............................................................................................................. 69

6

References ........................................................................................................................ 71

7

Appendices ....................................................................................................................... 74

4

Figure of tables

Figure 1. Global distribution of salt - affected soils (Schofield, 2001) .................................... 16

Figure 2. Salt deposition on the soil surface in the Lower Shire region, Photo Rolf D.Vogt,

University of Oslo .................................................................................................................... 17

Figure 3. Salt extraction from soil, Photo Rolf D.Vogt, University of Oslo ........................... 18

Figure 4. Abandoned borehole due to salinity around lower Shire area. ................................ 20

Figure 5. Number of boreholes drilled in Malawi (MER, 2002) . ........................................... 22

Figure 6. Map of Malawi including the study area ................................................................ 32

Figure 7. Annual rainfall and average min and max temperature for Lower Shire (MET,

2004) ......................................................................................................................................... 33

Figure 8 . Map of Lower Shire with location of sampling points indicated. ........................... 35

Figure 9. Geological map of Lower Shire in Malawi .............................................................. 37

Figure 10. Measuring conductivity of ground water directly from the well. .......................... 40

Figure 11 Values of electro conductivity (EC) in selected boreholes and surface water from 46

Figure 12 Variation of TDS with chlorides for the sampled borehole ..................................... 47

Figure 13 A plot of Ca vs. SO

4

2-

for the sampled surface water and boreholes. ...................... 48

Figure 14 Variation of major ions with chloride concentration for all waters analysed in the study ......................................................................................................................................... 49

Figure 15. Piper diagram of surface and ground water samples. ............................................. 50

Figure 16. Spatial variability of TDS and major cations in lower Shire area ......................... 52

Figure 17. A plot of Na ( meq/L) vs, Cl (meq/L) ................................................................... 53

Figure 18. Variation of Li and B with chloride concentration for the analysed ground and ... 55

Figure 19. Variation of Sr with chloride concentration for the analysed ground and .............. 56

Figure 20. A plot of Sr vs. Ca for the sampled surface and borehole waters. ........................ 57

Figure 21. Relationships between

2

H and

18

O in surface and groundwaters. The global water meteoric water line (GMWL) of Craig (1961), ∂

2 H=8 ∂ 18

O+10, is also shown ........... 58

Figure 22. Plot of

87

Sr/

86

Sr values vs Sr concentration for ground -and surface waters. ........ 59

Figure 23. Dendrogram for the ground and surface water samples based on similarities ....... 61

Figure 24. Dendrogram for the ground and surface water samples (S28 and S32) based on .. 62

Figure 25. Loading plot of first component (PC1) vs. second component (PC2) .................... 63

Figure 26. Score plot of first component (PC1) vs. second component (PC2). ....................... 64

5

Figure 27. Major ions distribution at the studied sites. Box range (25-75 th

............................ 65

Figure 28. Major and trace elements recoveries for Chamboko groundwater ......................... 68

Figure 29. Major and trace elements recoveries for Jasi 2 groundwater analyzed by IC-OES.

.................................................................................................................................................. 68

6

List of tables

Table 1. Drinking water standard .......................................................................15

Table 2. Application of isotope elements in salinity problems(Gaye, 2001) ........25

Table 3. Eigenanalysis of the Correlation Matrix for the water samples..............63

7

Abbreviations and symbols

CRM Certified Reference Material

GISP

EC

Greenland Ice Sheet Precipitation

Electro Conductivity

EL Evaporation Line

GIS Geographical Information System

GPS Geographical Positioning System

GMWL Global Meteoric Water line

HDPE High Density poly Ethylene

HCA

IAEA

Hierarchal Cluster Analysis

International Atomic Energy Agency

IC Ion Chromatography

ICP-OES Inductively Coupled Plasma Optical Emission Spectrometry

ISO

MS

International Organization for Standardization

Mass Spectrometry

NIST National Institute of Standards and Technology

NUFU Norwegian Programme for Development, Research and Education

PCA Principal Component Analysis ppm ppt parts per million parts per trillion

RA Residual alkalinity

SD Standard Deviation

TA-Ngabu Traditional Authority Ngabu

TDS Total Dissolved Solids

UIO

WHO

University of Oslo

World Health Organization

8

Abstract

Groundwater resources in the lower shire region in Malawi, Southern Africa, show high salinity. The sources of salinity and the mechanism of groundwater salinization in this inland region are not known. The main objective of this study is to clarify sources and extent of groundwater salinization in the lower Shire area.

A total of 33 water samples were collected from lower Shire area. Three of the samples are surface water samples including lower Shire River and the rest are groundwater samples.

Major ions, heavy metals,

2

H,

18

O, and Sr isotopes have been determined for surface water and groundwater in the lower Shire area, Malawi.

Sodium and magnesium are the dominant cations while chloride and/or bicarbonate are the dominant anions in the majority of the groundwater. The waters are mostly classified as sodium-chloride type as shown on the piper diagram whereas some of the groundwater are sodium bicarbonate dominant and characterised as a Na-HCO

3

-Cl water type. Seven groundwater samples and one surface water sample are Mg(Ca)HCO

3

water type. Elevated

Na

+ concentrations may be due to cation exchange where Ca

2+

from groundwater is adsorbed on clayed materials in exchange of Na

+

. Another possible reason for the higher Na

+ concentration could be dissolution of NaHCO

3

.

In overall the studied area concentration of Ag, B, Ba, Cr, and Li were below the drinking water standards and the concentration of Al in this study except in Jasi (0.4 mg/L) borehole, shows concentration well below the guideline. However Pb content of some samples surpassed the drinking water standard. The heavy metals concentration is less pronounced in lower Shire studied area, Malawi compared to the drinking water standard.

The majority water samples stable isotopic data cluster below the GMWL (∂

2

H=8 ∂

18

O+10).

The deviation of groundwater samples from the GMWL indicates that evaporation enrichment of heavy isotope concentrations has occurred, resulting in a slope of 6.3; somewhat less than the GMWL slope. These samples are characterized by comparatively high chloride contents.

Therefore evaporation has an impact on the groundwater salinity of the study area.

9

The Sr-isotope ratios measured in ground and surface water ranged from 0.708500 (Nyasa) to

0.714417 (Machilka). The average

87

Sr/

86

Sr ratio of 33 water samples is 0.7116. This average is higher than the ratio in sea water of 0.709, probably due to the weathering of minerals.

In conclusion, high spatial variability in groundwater compositions suggest that the groundwater salinity was caused by numerous factors including evaporation, dissolution of evaporates minerals and ion exchanges of Ca for Na. Particularly evaporation has an impact on the ground water of the study area.

Key words: Salinization, groundwater, lower Shire area, Malawi

10

CHAPTER 1

.

1. INTRODUCTION

Water is vital for all of us. We depend on its quality- and quantity for drinking, sanitation, agriculture, industry, urban development, hydropower generation, inland fisheries, transportation, recreation and many other human activities - all related to the economic, mental and physical health of a population. Therefore water scarcity is one of the major challenges in Africa which has resulted in the continent’s underdevelopment. About two thirds of the rural population and one quarter of the urban population in Sub-Saharan Africa lack safe drinking water and adequate sanitation. Pressure on water resource has been increasing over the years mainly due to increased water pollution, increased demand due to increased population and per capita water consumption, and through increased water abstractions for water supply and irrigation.

Fresh water makes up only about 2.5% of the total global water resource and the remainder is saltwater (Ranjan, Kazama, & Sawamoto, 2006). The renewable fresh water (40,000km

3

/yr) is only 0.3% of the total 15 billion km

3

. The importance of groundwater as a fresh water source for drinking, industrial and domestic purposes is growing in most parts of world

(Ranjan, et al., 2006). Like many other Africa countries, the climate in Malawi is characterized by long dry periods and short intense rainy seasons. Groundwater is the prime resource of raw water under such conditions. One of the most significant environmental problems in Malawi, particularly in lower Shire area is increasing salinity of the groundwater.

This thesis is meant to provide data on the chemistry of groundwater in the semi-arid climate in lower Shire area, Malawi and to assess the extent sources and evolution of groundwater salinization in the area.

1.1 Objectives of the study

The socio-economic development of the Lower Shire rural area relies on groundwater resources because this is the main source of water supply for domestic, agricultural and industrial purposes. However, groundwater resources are facing numerous problems and

11

challenges. Three problems dominate the use of the groundwater resources. First the water resources are depleted due to over exploitation; secondly there is water logging and salinization and thirdly the water ground resources face pollution due to agricultural, industrial and other human activities. Salinity in soil and groundwater is the main problem in lower Shire area, Malawi and the pollution problem is increasing.

Inhabitants in the lower Shire region depend on local groundwater, as their main source for drinking water and agriculture. The source of salinity and the mechanism of groundwater salinization in the lower Shire region of Malawi are not known. Ground water in this region shows high salinity to the extent that they are also mined for salts. This is a hot and dry area of Malawi that occasionally becomes flooded. Consequently there are several possible sources of salinity; solutes may be concentrated by evaporation of the flood water or the flow and groundwater seepage receives salt from geological deposits of evaporates such as halite.

Determining the source of salinity and the mechanism of groundwater salinization is vital for future water management plans, including the design and drilling of new wells (Marie &

Vengosh, 2001).

The chemical quality of groundwater in the aquifers of Malawi has been scarcely documented and there exists neither isotopic nor any minor elements data from the previous studies. In order to get an overview of the potential extent of the salinization problem, it has therefore been necessary to conduct analyses of both major and minor elements as well as some selected isotopes. In this paper we present these data and evaluate the possible sources of salinity in the groundwater by investigating the chemical composition of groundwater in the lower Shire area.

1.1.1 Main Objectives

The main objective of this study is to clarify sources and extent of groundwater salinization in the lower Shire area. To achieve the main objective, we concentrate on three sub-objectives:

The first sub-objective is to establish environmental isotopic signatures of groundwater and surface water from the lower Shire area.

The second is to map the lateral extent of groundwater salinization.

12

The third sub-objective is to elucidate major processes leading to groundwater salinity based on isotopic signatures and the water chemistry including all major and important minor ion data.

The isotopes that were measured were

18

O,

2

H,

87

Sr/

86

Sr. The major ions in solution included

Na

+

, Mg

2+

, Ca

2+

, K

+

, Cl

-

, NO

3

-

, and SO

4

2-

. Of the minor elements the following were determined: Zn, Pb, Cu, Al, B, Br , Sr

2+

, Li

+

, Cr, Cd

2+

, Fe, Mn.

1.2 NUFU PROJECT

This research is part of the NUFU project “Capacity Building in Water Sciences for Improved

Assessment and Management of Water Resources” (Geofag, 2009). NUFU is the Norwegian

Cooperation program for Development, Research and Higher Education. The NUFU program is for academic cooperation based on initiatives from researchers and institutions in the South

Africa countries and their partners in Norway. The project is funded by Norwegian Foreign aid NORAD. This project is a collaborative network research project between the University of Malawi, University of Botswana and the University of the Western Cape, South Africa and the University of Oslo. Within the project this study falls under theme 1 “Water quality and linkages to origin of water resource” with the main objective to improve the knowledge on the temporal and spatial aspects of the countrywide (Malawi) and regional water quality.

In this theme the main spatial and temporal variation in chemical composition of water will be assessed relative to its usage (drinking water, irrigation etc.) and related to their governing factors in the catchments. This study will be closely linked to the four other areas of research within the network project. Information developed from this study will be used to inform and facilitate development and sustainable management of water resources. This research is based on an initiative by the local people in the region that would like to know more about the source and process of the ground water and soil salinization.

13

CHAPTER 2

2 THEORY

2.1 Groundwater salinity

Salinity, a measure of the total amount of salts dissolved (TDS) in water, is a good indicator of its waters suitability for various uses. Salts in groundwater originate either from quantities dissolved in rain water, from the weathering of rocks or from direct connection to seawater.

Saline water in Malawi found mainly in the lower Shire region in southern part of the country.

Based on TDS (mg/L) values, groundwater may be classified into fresh, brackish and saline as follows below (Fetter, 1990) .

Fresh up to 1000 mg/L TDS is suitable for most uses.

Brackish 1000 to 20,000 mg/L TDS is too saline to be potable.

Saline more or equal to 35,000 mg/L TDS may be suitable only for industrial uses.

2.2 Drinking water standards

Drinking water standards are regulations set to control the level of contaminants in the nation’s drinking water. In the world Health organization (WHO), these standards are part of the safe Drinking Water Act’s “multiple barriers” approach to drinking water protection, which also includes assessing and protecting drinking water sources; protecting wells and collection system; making sure water is treated by qualified operators; ensuring the integrity of distribution systems; and making information available to the public on the quality of their drinking water. Table 1 shows standards for the composition of drinking water.

14

Table 1. Drinking water standard (WHO, 2004)

Constituent

Na

+

Mg

2+

Cl

-

SO

4

2-

NO

3

-

F

-

Al

Mn

Fe

Ni

Cu

Zn

Cd

Pb

Cr

Maximal admissible

concentration(meq/L)

8.69

4.17

7.04

5.20

0.81

0.08

0.02

0.002

0.007

6.7

10

-4

0.063

0.003

8.9

10

-5

9.7

10

-5

0.002

2.3 Natural salt accumulation

All natural water contains dissolved mineral salts, but the concentration and composition of the dissolved salts vary depending on the sources of the water. Salinization, due to physical and chemical processes, increases the concentrations of salt in soil and water (Salama, Otto,

& Fitzpatrick, 1999). The accumulated salts are primarily chlorides and sulphates of sodium, magnesium and calcium. They may be brought into solution during weathering of rocks and minerals especially evaporate, or brought to the soils through rainfall and irrigation .

Naturally, salts accumulate when there is a negative water balance so that evapotranspiration exceeds precipitation at least for part of the year.

Salt affected soils are categorised into saline and sodic. Saline soils refer to those showing a concentration of soluble salts which results in lowering the soil moisture potential due to osmotic effects. The distinction between saline and sodic is based primarily on their chemical properties, as a result of the salinisation/sodification pathway. There are two main pathways that can be delineated called the neutral and alkaline paths of salinization often referred to as salinization and alkalinization, respectively. The paths can be distinguished using residual

15

alkalinity (RA) (Condom, M, S, V, & J, 1999) defined with respect to the successive precipitation of minerals such as calcite (CaCO

3

), and gypsum (CaSO

4

.

2H

2

O) during evaporation. The RA is calculated as the alkalinity minus the cations and anions that are involved in mineral precipitation. Mostly salt-affected soils are found more frequently in the semiarid and arid regions of the world, they can be found within practically all climatic belts

(Figure 1), reflecting a diverse range of causal processes that can act to produce soil salinization.

Figure 1. Global distribution of salt - affected soils (Schofield, 2001)

In many areas, particularly in arid and semi-arid regions, salinization of water is a widespread problem that limits supply of drinking water (Gaye, 2001). The processes responsible for the development of saline land and water are complex and often intimately related to the transport of dissolved mass in groundwater flow systems. Salt accumulates on the soils surface (Figure

2) when there is a negative water balance so that mineralized water at or near the groundwater surface is transported to the soil surface where it continually evaporates and causes minerals to precipitate. Salinization is in such cases strongly related to surface soil and groundwater hydrological processes, as the movement of water is mainly responsible for the transport of salt (Xu & Shao, 2002). In other areas exposed seasonal flooding experience soil salinization

16

due to the evapotranspiration of the flood water leaving the salts behind. In areas where the flooding does not flush out old salt deposits, the depositions of salt may have occurred naturally in the top part of soil.

Figure 2. Salt deposition on the soil surface in the Lower Shire region, Photo Rolf D.Vogt,

University of Oslo

In addition to natural processes, anthropogenic activities can pollute groundwater resources.

Urbanization, industries, and agriculture are major causes for groundwater pollution (UNEP,

1996). Once polluted, groundwater reservoirs are extremely difficult to purify on account of its inaccessibility, huge volume and its slow flow rates.

2.4 Effects of salinity

High salinity causes detrimental effects to crops by reduction of the accessible water by reducing the osmotic potential of the soil solution (Hillel, 1980). If the salinity is severe, no plants can grow (Figure 2). Plants draw water through their roots, up to their leaves where it

17

evaporates to the atmosphere. This is called the evapotransporation process. Salinity restricts the availability of water to plants by lowering the total water potential in the soil.

In some areas of the floodplains of the Lower Shire River people are traditionally engaged in small scale salt production from the saline soils (Figure 3). To extract the salt the top-soil is scraped off by the villagers and the salt is then extracted by application of dissolution and evaporation.

Figure 3. Salt extraction from soil, Photo Rolf D.Vogt, University of Oslo

2.5 Ground water quality and availability

It is important to know the quality of groundwater because it is the major factor which decides its suitability for domestic, agriculture and industrial purposes (Raju, Ram, & Dey, 2009). The suitability of groundwater for drinking and other purposes may be assessed by comparing physical and chemical parameters of the study area with the guidelines recommended by

World Health Organization (WHO, 2004).

18

Groundwater in Malawi is an important source of water and the dominant source for domestic supply in many areas, especially the dry areas where surface water are scarce and seasonal, because it generally does not require any pretreatment (Sajidu, Masamba, Thole, &

Mwatseteza, 2008). In general the quality of groundwater in Malawi is mainly affected by the chemical composition of the rock in which the water is in contact with, ambient climatic condition and human activities in the watershed. Examples of the latter are agricultural activities, the presence and extent of human settlement, discharge of human effluents. Several studies have shown the presence of chemical and biological contaminants (Sajidu, Masamba,

Henry, & Kuyeli, 2007), but in general the chemical quality of ground water in Malawi has been poorly documented. The ground waters used for drinking purposes have in general a magnesium bicarbonate composition. Chloride also represents a water quality problem in some areas in Malawi, such as the Lower Shire, and the boreholes where chloride contents are above the tolerance limit of 250mg/L are progressively expanding in lower Shire area (Bath,

1980). This is of great importance as all villages use boreholes as the main source for drinking water supply. In the Lower Shire area the surface water are generally not potable.

Groundwater aquifers supply therefore the most reliable potable water supplies for the majority of rural communities (Saka, 2006). A few boreholes had to be abandoned because of adverse groundwater quality (Figure 4).

19

Figure 4. Abandoned borehole due to salinity around lower Shire area.

2.6 Groundwater and aquifer systems

Most groundwater is found in aquifers – underground layers of porous rock that are saturated from above or from structures sloping towards it. Aquifer capacity is determined by the porosity of the subsurface material and its area. There are two main types of aquifers: confined and unconfined. Confined aquifers exist where the groundwater system is between layers of clay, dense rock or other materials with very low permeability. It is therefore possibly under more pressure than unconfined aquifers. Thus when tapped by a well, water is forced up, sometimes above the soil surface. Unconfined aquifers are more common and do not have a low permeability deposit above it. In fact, the top layer of an unconfined aquifer is the water table.

20

2.7 Groundwater and surface water interaction

Groundwater and surface water are fundamentally interconnected in the hydrologic system. In fact it is often difficult to separate the two because they feed each other. This is why one can contaminate the other (Sophocleous, 2002). Thus, an understanding of the basic principles of interactions between groundwater and surface water is needed for effective management of water resources. The movement of groundwater and its interaction with surface water as linked components of a hydrologic continuum has important implications on the quality and the sustainability of the groundwater resources.

2.8 Borehole depth

The chemical and physical quality of groundwater resources depends on boreholes depth, permeability of sediments and chemical makeup of sediments through which groundwater moves, climatic variations and anthropogenic activities among other things (Harrison, 1996).

The depth of groundwater has therefore important implications on water quality. The water levels in an aquifer may also fluctuate during the year as a result of seasonal rainfall or drought. If pumping exceeds recharge over long-term, the water level may declines over time.

During field work the depths of the ground water were not available for all boreholes; and we found very few data for the depth of ground water. Data gathered by the Water Resources

Department on groundwater level are inconclusive. However, it could be assumed that groundwater resources are diminished.

21

250

200

150

100

50

0

1992 1993 1994 1995 1996 1997 1998 1999

Figure 5. Number of boreholes drilled in Malawi (MER, 2002) .

The longer time groundwater flows through the sediments, the more it may become mineralised. Water from deeper aquifers typically have had to travel much longer distance from the surface and thus deep groundwater is likely to have been in contact with mineral sediments and rocks for longer periods. Shallow groundwater aquifers have for the opposite reason in general a lower level of mineralization, or total dissolved solids (TDS), than deeper aquifers. However, shallow wells have higher levels of calcium, magnesium and iron than deeper wells, making the water hard whilst deeper wells have higher levels of sodium and lower levels of hardness, making the water softer. As water moves downward through the sediments and different rock formations, a natural ion exchange process occurs (Appelo &

Postma, 2005). Calcium, magnesium and iron in the groundwater are exchanged for sodium in the sediment. The result is groundwater with higher levels of sodium with little or no hardness.

2.9 Floodplains around lower Shire River

Seasonal changes in water flow make floodplain systems complex, dynamic and diverse habitats. The rain season in Malawi generally extends from December to March. Excessive rainfall can reduce crop yields perhaps through flooding. Lower Shire has experienced

22

frequent floods that might be transporting industrial and agro chemical pollutant of groundwater. The area comprises swampy and marshy areas along the Shire River that could be potential source of pollution of groundwater resources on interaction with surface water.

The climate is semi -arid and its temperature range from 20

0

C to 46

0

C. The temperature encourages very high rates of evaporation that might be leading to a build-up of salts in the soil.

2.10 Irrigation-induced salinity

Irrigation has contributed extensively to the growth in agricultural production in many developing countries. Irrigation waters, whether from upstream watersheds or underground pumping, may carry significant quantities of soluble salts. In areas where there is more precipitation than evapotranspiration the land is typically well drained. In addition if sufficient irrigation water is supplied than the water can percolate down through the soil and thereby leach the soluble salts from the upper soil layers. However if the permeability of soil is drained, the downward movement of the salts to the groundwater is impaired, and the salts are left in the soil surface. Instead ground water may be brought up to the surface as water evaporates. A saline soil is thus created. The more arid the region, the larger is the necessary quantity irrigation of water and therefore the salts applied, and the smaller is the quantity of rainfall that is available to leach away accumulating salts.

2.11 Alkaline earth metals in aquifer

Barium, calcium, magnesium and strontium are denoted alkaline earth metals. They belong to the same chemical group but they vary widely in their abundance and behaviour in groundwater. Calcium and magnesium are abundant in rocks and soil, particularly in limestone and dolomites. The parent materials are relatively soluble. Barium and strontium compounds are less soluble than those of calcium and magnesium.

2.12 Heavy metals - origin and occurrence in groundwater

Lack of clean freshwater will be one of the main global resource problems in the coming decades and a major effort is required to supply good quality drinking water for the world

23

population(Appelo & Postma, 2005) . Heavy metals are considered as a serious pollutant in the environment because of their environmental persistence, toxicity and ability to be transported to groundwater (Nas, Berktay, Aygun, Karabork, & Ekercin, 2009).

2.12.1 Origin of heavy metals in groundwater

Low levels of heavy metals exist naturally in soils due to erosion and weathering of parent rocks. Heavy metals are also introduced antropogenically into the environment, for example, by industrial waste or by agricultural activities like application of fertilizers and pesticides to farmlands. Heavy metals are severely limit the amount of useful water for domestic or industrial application (Petrus & Warchol, 2005). Soil represents a major sink for heavy metals ions, but some of the heavy metals are lost from the soil by entering the food chain through plants or by being leached into groundwater.

In soil solution most heavy metals exist as aqueous cations, complexed to organic and inorganic ligands or adsorbed to particles (Alloway, 1995). Due to their cationic charge adsorption to the soil depends on the negative charges on the surface of soil colloids.

2.13 Environmental isotopes

Isotopes are atoms of the same element that have the same number of protons and electrons but different number of neutrons. Stable isotopes are nuclei that do not appear to decay to other isotopes within geologic time scales, but may themselves be produced by the decay of radioactive isotopes. The environment isotope compositions of hydrogen ∂

2 H and oxygen ∂

18

O are excellent parameters for determining the origin of salinity in groundwater and widely used in studying natural water circulation and groundwater movement (Subyani, 2004). The stable isotopic compositions of low- mass elements are normally reported as “delta” (∂) values in parts per thousand enrichments or depletions relative to standard of known composition (R std

) (Kendall, 1998) . ∂ -values are calculated by:

∂ =

R sample

R std

R std

* 1000 (1)

For example, deuterium (

2

H) and

18

O are heavier and much rarer than the more abundant isotopes hydrogen-1 and oxygen-16. By definition the sea water standards has ∂

2

H – and ∂

18

O

– values equal to 0 ‰. Negative values characterize water isotopically depleted (“lighter”),

24

while positive values correspond to water samples isotopically enriched (“heavier”) with respect to the standard. The most important natural processes that cause variations of the stable isotopic composition of natural waters are evaporation and condensation.

2.13.1 Isotope techniques

Environmental isotopes provide information about the history of water that cannot be obtained in any other way. Environmental isotopes, at concentrations set by natural and anthropogenic processes, give a “finger print” to a body of water which can be used as a trace of the water even as it moves from one system to another. Isotope assessment techniques are therefore especially useful for identifying the sources of salinity and the inflow of fresh groundwater (Gaye, 2001).

Isotope techniques have been used for identifying the sources of salinity and recharge rate of groundwater (Gaye, 2001). There is a wide range of stable isotope techniques used to study groundwater salinizaton. The scope of this project is limited to an overview of two of the most widely used isotope techniques. These techniques include the doubly labelled water technique of using deuterium (

2

H) and oxygen-18 (

18

O) together with strontium isotope measurements. The stable isotopes are excellent indicators of the circulation of water and the strontium isotopes

87/86

Sr provide additional constraints regarding the geochemical evolution of ground water. Moreover, the application of these techniques in the case of arid and semiarid zones, where the available water resources are often limited to groundwater, has proved to be a good tool for the identification of recharge and quantitative evaluation of the groundwater system (IAEA, 1980, 1983).

Table 2. Application of isotope elements in salinity problems(Gaye, 2001)

Isotopic tool

18

O, ∂

2

H

Role of evaluating salinity

Excellent indicators (together with chloride) of evaporative enrichment, evaporation rates precipitation in shallow groundwater environments. and

87/86

Sr

Provide additional constraints regarding the geochemical evolution of ground water and source of groundwater salinity especially in carbonate environments.

25

2.13.2 Stable Isotope

Isotope analysis is the identification of isotopic signature, i.e. the ratio of certain stable isotopes of chemical elements within chemical compounds. Isotope ratios are measured using mass spectrometry, which separates the different isotopes of an element on the basis of mass- to-charge ratio.

Different environmental processes influence the isotopic composition of a substance through fractionation, or preferential incorporation, of a particular isotope of an element in one species or phase over another. The ratios

2

H/

1

H and

18

O/

16

O in water are of special interest to geochemists. The stable isotopes are excellent indicators of the circulation of water. Various isotopic forms of water have slightly different vapour pressures and freezing temperatures.

This causes a difference in the

2

H and

18

O concentrations in water in various parts of hydrologic cycle. The process whereby the isotope content of a substance changes as a result of evaporation, condensation and freezing is known as isotopic fractionation. Water samples which fall below the global water meteoric line of slope 8 (Appelo & Postma, 2005) and a slope of between 4 and 6 have been subjected to evaporation (Terwey, 1984). (Meteroric: relating to or denoting water derived from the atmosphere by precipitation or condensation.)

2.13.3 Strontium Isotopes

The alkaline earth metal strontium (Sr) has four naturally occurring stable isotopes:

84

Sr,

86

Sr,

87

Sr, and

88

Sr. Of these,

87

Sr is the only radiogenic isotope, produced through the beta decay of

87

Rb. The geochemistry dissolved Sr is very similar to that of calcium in all natural waters.

Strontium is a divalent cation that readily substitutes for Ca

2+

in carbonates, sulphates and other rock-forming minerals. Like Ca

2+

, it participates in water-rock reactions (Lyons, Tyler,

Gaudette, & Long, 1995) and is a minor component of most groundwater.

The Sr isotope ratios in natural waters are therefore controlled in large part by rock-water interactions. Chemical reactions such as ion exchange and mineral dissolution determine the

Sr isotopic value of the water sample, and mineral precipitation affects the strontium concentration. Results of Sr-isotope studies are normally reported as the absolute

87

Sr/

86

Sr ratio. Like many other isotopes, variation in the Sr isotope system can be also expressed using

26

delta notation. The isotope ratio of sea water (0.7092) is used as the reference because it is globally uniform. Because of the small difference for

87

Sr/

86

Sr the value of Sr isotopes do not fractionate appreciably in nature. Therefore the measured

87

Sr/

86

Sr is not changed significantly when Sr is removed from water as a result of precipitation, cation exchange

(Gosselin, Harvey, Frost, Stotler, & Macfarlane, 2004). However the chemistry of water (the

Sr concentration) may possibly alter as a result of the above mentioned processes, but not the isotopic composition. As a result, Sr isotopes can give information about the source of the solute in water.

The

87

Sr/

86

Sr ratios in minerals relate to the Rb/Sr values (Franklyn, McNutt, Kamineni,

Gascoyne, & Frape, 1991). As a result of production of

87

Sr through decay of

87

Rb the isotopic ratio increases. K-rich rocks have significant

87

Rb and

87

Sr contents and this is reflected in the

87

Sr/

86

Sr ratio of water with which they have equilibrated. Thus, ground waters that have geochemically evolved in different geological terrains will have contrasting strontium isotope ratios. The

87

Sr/

86

Sr ratio of groundwater is thus a useful indicator of waterrock interaction (Franklyn, et al., 1991) and as a tracer for groundwater movement and the origin of salinity.

2.14 Theoretical Background on Analytical techniques

2.14.1 Alkalinity

Alkalinity is a measure of the capacity of water to neutralize or “buffer” acids. This measure of acid neutralizing capacity is important in figuring out how “buffered” the water is against changes in pH. The most important compounds in water that determine alkalinity include the carbonate (CO

3

2-

) and bicarbonate (HCO

3

-

) ions. Carbonate ions are able to react with and neutralize two hydrogen ions (H

+

) and the bicarbonate ions are able to neutralize H

+

or hydroxide ions (OH

-

) present in water. The ability to resist changes in pH by neutralizing acids or bases is called buffering.

Alkalinity increases typically together with the pH, when the alkalinity comes from weathering of a carbonate such as calcium carbonate (CaCO

3

). When CaCO

3

dissolves in water, the carbonate (CO

3

2-

) can react with water to form bicarbonate (HCO

3

-

), which produces hydroxide (OH

-

):

27

CaCO

3

(s)

Ca

2+

+ CO

3

2-

CO

3

2-

+ H

2

O

HCO

3

-

+ OH

-

2.14.2 Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)

Inductively coupled plasma optical emission spectroscopy (ICP-OES) is a well established spectroscopic method with large linear dynamic range, low detection limits, high precision and accuracy, which offers rapid multi-element analysis for the determination of major, minor and trace elements in water samples (Boss & Fredeen, 2004).

In Inductively Couples Plasma-Optical Emission Spectroscopy (ICP-OES), samples mostly in the liquid form, are nebulised to aerosols and then transported to the plasma by argon flow

(Boss & Fredeen, 2004) where desolvation, vaporization, atomization or ionization of the aerosol occur. The processes are followed by excitation of the atoms or ions.

ICP-OES works by the emission of photons from analytes that are brought to an excited state by the use of high-energy plasma. The plasma source is induced when passing argon gas through an alternating electric field that is created by an inductively couple coil. When the analyte is excited, the electrons dissipate the induced energy moving to a ground state of lower energy, in doing this they emit the excess energy in the form of light. The wavelength of light emitted depends on the energy gap between the excited energy level and the ground state. In this way the wavelength of light can be used to determine what elements are present by detection of the light at specific wavelengths. Consequently the characteristic radiations emitted from the excited species at several wavelengths are separated and converted to the electrical signals in the spectrometer that are converted into concentration information for the analyst. The intensity of the spectral signal is indicative of the concentration of the elements that is present.

2.14.3 Ion Exchange Chromatography(IC)

The ion chromatography is used for analysis of aqueous samples in parts-per-million (ppm) quantities of common anions (such as fluorides, chlorides, nitrate, and sulphate and common cations like, sodium, ammonium, and potassium) using conductivity detectors. In Ion chromatography, the analyte ions in the mobile phase solution are separated by selective

28

retention to the stationary phase caused by electrostatic forces. The affinity to the stationary phase varies among the different ions, and they will be detected at specific moments in time after injection into the column (Skoog, Holler, & Nieman, 1998).

29

CHAPTER 3

3 MATERIAL AND METHODS

3.1

Introduction

This chapter provides a description of the study area, geology and hydrogeology of the study area, sampling, analyses of samples, and softwares for data processing that were used in carrying out this study.

Surface Water

Malawi has a network of rivers and four major lakes. Lake Malawi, with a total surface area of approximately 28,750 km

2

and 700 meters deep , is the largest lake in the country and is the third largest lake in Africa. The mean lake level is 474.4m above sea level and the average annual outflow through Shire River is estimated to be 395m

3

/s. Other lakes include Chilwa,

Malombe, and Chiuta. The major rivers include Shire, Ruo, Buo, South Rukuru, Linthipe,

Songwe, and Dwangwa.

Malawi receives sufficient rainfall in most years to ensure an adequate supply in total to meet the numerous and varied needs for water. However, precipitation is concentrated in a short and well defined rainy season, which is followed by a dry season, hence the availability of water varies strongly with seasons, and dry-season water scarcity is common.

The chemistry of the vast majority of surface water resources is characterized by alkaline earth metals (calcium and magnesium) in the cation group and by the carbonate system in the anion group. Malawi’s economy is heavily reliant on agriculture and poor agricultural practice is one of the major causes of surface water resources degradation. Agricultural activities are important source of sulphates, phosphates, nitrates and heavy metal pollutants such as cadmium, lead, and iron from phosphate fertilisers, an omnipresent source of cadmium since the rock phosphates used in the manufacture of fertilisers have relatively high

30

concentrations of cadmium. Furthermore, poorly managed agricultural expansion has led to high rates of deforestation.

Groundwater

Groundwater resources are also widespread throughout the country. Malawi has three major groundwater zones, which are distinguished by the major physio-graphic units (Saka, 2006): the Rift Valley Zone, which includes the Lake Malawi rift and the upper and lower sections of the Shire Valley, and is separated by the Rift Escarpment zone of tectonic origin from the

High Plateau; the High Plateau zone with weathered rock products and fractured rock, and the rift escarpment.

The development of ground water resources in Malawi has been primarily for drinking water supply for both rural and per-urban areas. This supply has steadily increased as reflected by the number of boreholes drilled between 1992 and 1999 (Figure 5).

The Groundwater occurrences are associated with two types of aquifers: the extensive but relatively low yielding weathered Precambrian basement complex formations, which accounts for about 85% of the country geology and the relative high yielding quaternary alluvial deposits occurring in the lakeshore plains and the Shire valley. The basement complex aquifers can yield up to 2 litres per second, while alluvial aquifers can yield up to 20 litres per second. Naturally, water in the basement complex aquifer has a relatively low concentration of salts, while in alluvial aquifers the water is highly mineralised.

3.2 Description of the study area

3.2.1 Sampling areas

The study area in this research is the Lower Shire Valley in Malawi (Figure 6), about 400km south of the capital Lilongwe. The area is bounded between latitudes 9 o

and 18 o

S, and longitudes 33

0 and 36

0

E. Malawi is located in Southeast Africa and is boarded by Tanzania in the north and north–east, Mozambique in the south and east, and Zambia in the west.

31

Figure 6. Map of Malawi including the study area

3.2.2 Physiography, climate and land use

Physiography

Malawi is situated at the southern end of the East African Rift Valley system which dominates the topography of the country. There is a wide range in relief, which has a great influence on the climate, hydrology and occurrence of groundwater; thus the water resource areas are defined largely based on the topography. The distribution of the population, and

32

hence the demand for water supplies, is also largely controlled by the topography. Malawi can be dividing into four main topographic zones: plateau areas, upland areas, rift valley escarpment and rift valley plains (Saka, 2006).

Climate

Malawi lies entirely within the tropics, and has a sub-tropical climate. There are three seasons, the dry and hot period from August to November, the wet and hot period from

December to April, and the cool and drizzly period from May to August. The rainy season lasts from December to March. Annual rainfall varies considerably from year to year (Figure

7). Normally the lower the rainfall the greater is the variability and vice versa. The spatial distribution of the rainfall is strongly affected by topography and prevailing-wind direction.

1600.0

1400.0

1200.0

1000.0

Total rainfall

(mm)

800.0

600.0

400.0

200.0

0.0

`

35.0

30.0

25.0

20.0

15.0

AvgeTemp ( o

C)

10.0

5.0

0.0

Total annual rainfall Maximum average temperature Minimum average temperature

Figure 7. Annual rainfall and average min and max temperature for Lower Shire (MET,

2004)

Malawi receives in total sufficient rainfall in most years to ensure an adequate supply to meet the many and varied needs for water. However, precipitation is concentrated to three months which is followed by a prolonged dry season. Hence the availability of water has a strong dependency on seasons, and dry-season water scarcity is commonplace. Management of water supply through conservation dams or reservoirs is relatively undeveloped – nationally around

700 dams have a combined storage capacity of less than 0.1% of annual precipitation. A result

33

of this is that while the total supply should be more than adequate, most of what is not lost through evaporation simply runs off the land into the river systems and enters the lakes and leaves the country via the Shire River.

Therefore climate has multi-dimensional impact on the economy. It affects various sectors, namely agriculture, energy, forestry, health, fisheries and many more. The extreme climate events that cause floods, drought and other weather and climate related disasters have negative repercussion on the national economy.

The lower Shire area is comparatively arid, with a maximum temperature of around 33 o

C and minimum temperature of about 20 o

C (annual average) (Figure 7). The area experiences an average annual moisture deficit but is also prone to annual flooding.

34

Figure 8 . Map of Lower Shire with location of sampling points indicated.

35

The Shire River is the only outlet from Lake Malawi (500 m above sea level ) from which it meanders southwards for a distance of approximately 700km to its confluence with Zambezi

River. About 95% of the Shire river is located in Malawi and the rest in Mozambique. The lower river covers a distance of 213km from Maganga to the Zambezi confluence, with elevation in Malawi dropping to 37m above sea level at the Mozambique border.

Vegetation and landuse

The Shire high lands, floodplains and the elephant marsh form part of the landscape of

Chikwawa district. To a great extent, these geographical and physical characteristics correspond to different types of land uses in the district. The principal land use is agriculture which includes crop farming (horticulture, vegetables and fruits) around lower Shire area.

The introduction of cultivation could have resulted in increased soil erosion and incision of drainage channels, increased total runoff and peak flood flows, and a decrease in dry season river flows. The agricultural potential is directly linked to climate, particularly rainfall and to a lesser extent the temperature, which helps to define which crops is suitable.

3.3 Geology and Hydrogeology

3.3.1 Geology

There are two main types of aquifers in Malawi: the extensive but relatively low yielding basement aquifers and high yielding alluvial aquifers. Figure 9 shows simplified geological features .

The investigation site is largely composed of alluvial deposits. Most of the alluvium aquifers are unconfined although some thick clay sequences are semi-confined (GOM-UNDP,

1986)

36

Figure 9. Geological map of Lower Shire in Malawi

37

The larger part of lower Shire is underlain by crystal metamorphic and igneous rocks of

Precambrian to lower Palaeozoic origin referred to as the basement complex (Figure 9). This comprises mainly gneisses and granulites which have been highly metamorphosed. Biotite and hornblende gneisses are most commonly encountered, although other rock types are often interbanded with them. The gneisses are commonly rich in graphite and frequently also contain sulphide minerals, notably pyrite and pyrrhotite. The basement aquifers are low yielding aquifers because of the less porous nature of igneous and metamorphic rocks that do not allow a lot of water to pass through them.

The alluvial aquifers are mostly situated in the rift valley floor areas on the western side of

Shire River valley, which includes lower Shire valley. These aquifers are relatively high yielding in comparison with basement complex aquifers.

The alluvial aquifers are fluvial and lacustrine sediments which are variable in character both in vertical and lateral extent. The major lithological components of these aquifers are clay with significant occurrences of poorly sorted sands (GOM-UNDP, 1986). The lower Shire areas primarily have the alluvial aquifers chiefly in the floodplain and are with colluviums and alluvium geological formations (Figure 9).

3.4 Sample analysis

3.4.1 Cleaning

All glassware and polypropylene flasks were washed in the washing machine with temperature 85 and 60 o

C, respectively and kept clean. The volumetric flasks were filled with

5% HNO

3

solution overnight. Before use, all the equipments were rinsed repeatedly with type

2 water and given a final rinse with type 1 water.

3.4.2 Water sampling procedure

Field investigation was carried out during the dry season in June 2009. A total of 33 water samples were collected in the first sampling campaign from the lower Shire region and other selected sites (Figure 8). The sites were selected based on available EC data. Three of the

38

samples are surface water samples including lower Shire River and the rest are groundwater samples. At each site, three water parallel samples were collected carefully; two of them were collected in new 500mL polyethylene bottles of which one of them was acidified with 1%

HNO

3

just after collection.

At Chancellor College laboratory, Malawi, the samples were filtered through 0.45µm membrane filters. The acidified sample was transferred into two unused 125mL HDPE bottles for cation-and trace element analysis, and strontium isotope using ICP-OES and Delta+XP

Mass Spectrometry respectively. The unacidified sample was also transferred into 125 mL unused HDPE bottles for analysis of major anions using IC and total alkalinity. The third sample was collected directly from the borehole in 125mL HDPE for

2

H and

18

O isotope analysis.

39

Figure 10. Measuring conductivity of ground water directly from the well.

Care was taken to ensure little or no head space was present in the sample bottles to avoid degassing and stored in chest cooler soon after collection for transportation to the Chancellor

College, Malawi and then stored cool and dark until analysis. A few of the bottles were broken during transport due to that the water sample froze to ice. The samples were again stored cool at 4

0

C at UiO prior to chemical analysis.

40

3.4.3 Dilution

The water samples with highest levels of Na

+

, Ca

2+,

and Mg

2+

needed to be diluted to fit within the working range of the calibration standard. Due to high concentration in the samples lead to large standard deviations in the first preliminary test. This was solved by diluting the samples that contained high concentrations of the above elements from 10 to 250 times (few of samples were diluted two hundred times).

Water samples were also diluted for analysis of major anions (F

-

, Cl

-

, NO

3

-

, and SO

4

2-

) based on EC data. Samples having >5000 μs/cm EC were diluted twenty times and samples having

< 5000 μs/cm EC data were diluted ten times.

3.4.4 EC, pH and TDS

Physical parameters such as electrical conductivity (EC), pH, temperature, total dissolved solids (TDS) and GPS were measured in the field; pH of water sample was done at sampling points using Martin instruments pH 55 after calibration with pH 4.00 and 7.00 buffer solutions. EC and temperature was measured using an EcoScan CON 5 EC meter (Figure10).

3.4.5 Determination of Alkalinity

Alkalinity was measured using an auto titrator model 775 dosimat, manufactured by Metrohm at Chancellor College. In addition, the alkalinity of the water samples was determined at environmental chemistry laboratory, University of Oslo based on ISO-9963-1. Procedure equation for calculation and results are given in appendix D.

3.4.6 Determination of Heavy metals and major cations in water using ICP-AES

Analyses was performed using varian (Ausralia) Vista AX CCD simultaneous axial view ICP-

OES (Varian Ltd, Australia) equipped with V-groove nebulizer with Sturman Master spray chamber. The Ar gas (99.99%) was from AGA, Oslo; Norway. The instrument was calibrated using five calibration solutions ranging 0-5 mg/L for Al, Cd, Cu, Fe, Zn, Pb, Cr, Mn, B, Be ,

Li, K, Ag, Sr and 0-25 mg/L for Na, Mg, and Ca . The standards prepared for the ICP-OES

41

analysis were applied for calibration curve. Calibration curve and results are given in appendix B. Table B1 shows the operating conditions of the instrument.

3.4.7 IC method

Major anions (F

-

, Cl

-

, NO

3

-

, SO

4

2-

) were determined with a DIONEX 2000 IC. Stock solution was used to prepare the calibration standards so as to validate the IC method. The instrument was calibrated with five standard solutions in the range from 0.083-10 mg/L for F

-

, 0.833-100 mg/L for Cl

-

, 0.167-20 mg/L for NO

3

-

, and 1.667-200 for SO

4

2 – mg/L (Appendix A). The standards were run for every 12 sample to correct for possible instrumental drift. The measured concentration was not allowed to deviate from the known concentration more than

±5. In addition, the control standard was run for every 15 sample. The maximum deviation of the measure concentrations from the known concentrations was arbitrarily ±5.

3.4.8 Analytical Methods for Isotope samples

The analyses for stable isotopic composition were conducted by Institute for Energy

Technology (IFE), Norway.

2

H and

18

O were measured using Delta+XP stable isotope ratio mass spectrometry. The

87

Sr/

86

Sr ratios were measured using thermal ionization mass spectrometer (TIMS). Isotopic results are reported with an error margin of ± 1.07‰ for

2

H,

±0.15 ‰ for

18

O and ± 0.000009 ‰ for Sr

87

/

86

Sr.

Hydrogen isotope analyses: H

2

O

(l)

was equilibrated with H

2(g)

at 30 ºC for 24 hours.

Impurities were separated from H

2

on a Poraplot GC column before on-line determination of

2

H, using a Delta+XP isotope ratio mass spectrometer from Thermo Scientific, Germany.

Average value for GISP from IAEA during 2008-2009 is

D

VSMOW

= -189.57

1,07 ‰ (one standard deviation). “True” value is -189.73

0.9 ‰.

Oxygen isotope analyses: H

2

O

(l)

was equilibrated with CO

2(g)

at 30 ºC for 24 hours.

Impurities were separated from CO

2

on a Poraplot GC column before on-line determination of

18

O, using a Delta+XP isotope ratio mass spectrometer from Thermo Scientific, Germany.

Average value for GISP from IAEA during 2008-2009 is

18

O

VSMOW

= -24.78

0.15 ‰ (one standard deviation). “True” value is -24.78

0.08 ‰.

42

Sr isotope analyses: The samples were evaporated to dryness and the residue then dissolved in 200 µL 3M HNO

3

. Separation of Sr was done by ion exchange. Background levels of Sr will normally be 20-30 pg, and have not a significant influence on analytical results for different types of geological samples, inclusive water. The minimum sample amount for the mass spectrometric analysis is 100 ng Sr. A Finnigan MAT 261 solid source is used for the mass spectrometry analyses. The NBS-987 (now NIST 987) standard has routinely been analysed for every 12 th

sample. The average value in 2008-2009 is 0.710266

0.000009.

“True” value was 0.710248

0.000015.

3.5 Softwares for data processing

ArcGIS

Geographical Information system (GIS) was used to analyse digital information of the sample boreholes using ArcGIS software (GIS 9.2), which can be used to produce maps based on geodatabases. By applying the coordinates for each of the sampling sites in the lower Shire area, spatial distribution of groundwater quality and maps with marking of the sampling sites were prepared. In addition, sugar factory and rivers were plotted on the map (Figure 8).

Minitab 14

The Minitab statistical programme was used to perform Hierarchical cluster analyses, HCA and Principal Component Analyses, PCA.

3.5.1 Hierarchical cluster analysis

The HCA is a data classification technique and often used in the classification of hydrogeochemical data (Cloutier, Lefebvre, Therrien, & Savard, 2008). The purpose of these analyses is grouping of samples into the clusters from the data set. The results are visualized in a dendrogram, a two dimensional chart where the horizontal axis denotes the clusters and the vertical axis denotes the similarity between the clusters.

43

3.5.2 Principal Component Analysis

The PCA is a data transformation technique that attempts to reveal a simple underlying structure that assumed to exist within a multivariate dataset (Cloutier, et al., 2008). This study has 26 samples with complete dataset (i.e. omitted the missed variable in a few sample) of 12 variables (physical parameters and major ion concentrations). The first principal component,

PC1, is an axis through the most extended direction of the variance cloud in a 12 dimensional room. This component therefore describes the largest variability in the data set. The second component, PC2, is an axis extended perpendicularly to PC1 and explains the second largest variability in the data set.

3.5.3 Piper diagram

The percent contribution to the total cationic charge of the major cations Ca

2+

, (Na

+

+K

+

) and

Mg

2+

and major anions (Cl

-

, SO

4

2-

and carbonate (HCO

3

-

+ CO

3

2-

)) in each sample were used to construct triangle for cations and anions. The triangle for cations has 100 % Ca in the left corner, 100 % (Na +K) towards the right and 100 % Mg upwards where as the triangle for anions has 100 % carbonates (HCO

3

-

+ CO

3

2-

) to the left, Cl

-

to the right and SO

4

2-

on top.

The two data plots in the triangles were joined by drawing lines parallel to the outer boundary until they united in the central diamond shape with the relative chemical composition of the water sample indicated by a single point in the Piper diagram as shown in (Figure 15) .The main purpose of the Piper diagram is to show clustering of data points to indicate samples that have similar composition (Appelo & Postma, 2005).

3.5.4 General about PHREEQC

PHREEQC version 2 (Appelo & Postma, 2005) is a computer program for simulating chemical reactions and transport processes in natural or polluted water. The program is based on equilibrium chemistry of aqueous solutions interacting with minerals, gases, solid solutions, exchangers, and sorption surfaces, but also includes the capability to model kinetic reactions with rate equations that are completely user-specified in the form of Basic statements. Kinetic and equilibrium reactants can be interconnected(Appelo & Postma, 2005).

PHREEQC was used to set up some saturation indexes for water solutions according to the analytical data.

44

CHAPTER 4.

4 Results and Discussions

4.1 Ground water quality

4.1.1 Physical parameters

Physical parameters and major elements were determined for 30 groundwater and 3 river samples and the results are presented in Appendix B, table B 4. This table shows that pH values are from 7.2 – 9.8 and the water samples exhibit temperature ranging from 22-30

0

C.

The electrical conductivity (EC) of the groundwater shows that appreciable amounts of salts

. are present that may exceed the limit for a regular drinking water supply (Appelo & Postma,

2005). The EC values (Table B4) in the groundwater vary from 795 to 15540 µS/cm. The three surface water with the EC value ranging between 254-2269 µS/cm.

As mentioned above, the water quality varies considerably over short distances. The sample from Jasi 1 borehole has an EC value of 15540 µS/cm and a few hundred meters apart water from Jasi 2 borehole has about 6000 µS/cm (Figure 11). This may be attributed to differences in depth; the water may have penetrated different geological formations. Also the greater EC of the water is the result of solubilisation in the aquifers. In general the chemical quality for the majority groundwater is not widely suitable for domestic use.

45

Thumps lo dge

Tayakhasu river

Saindi F.P Scho o l

Nyasa

Nyada(shire river)

Nso mo

Nkhwangwa scho o l

Nkaru scho o l

Nibisi scho o l

M asnduko

M angulenje 2

M alemia

M akande

M afale I

Jasi 2

Jasi 1

Go nda

Go ma

Fo dya

Felo 2(B iliati)

Dzilo nzo

Chigweshe

0

254

2777

1428

2269

1847

1105

1148

2000

2227

1670

2245

1568

3240

2880

4000

6040

6000

6800

7110

8550

8160

8930

8070

8000 10000

EC (µS/cm)

11750

12000 14000

15540

16000 18000

Figure 11 Values of electro conductivity (EC) in selected boreholes and surface water from

the lower Shire

Total dissolved salts (TDS) also showed a wide variation from 127 (Shire river at Nyada) to

7770 mg/L (Jasi 1). Based on the classification mentioned in Section 2.1, we find that 33.3% of the groundwater samples are fresh water and 66.7% of the samples have brackish water quality. The three surface water samples collected including lower Shire river exhibit low to moderate brackish with TDS values ranging between 127-1128 mg/L. Two of them are fresh and one is brackish. Further it shows that 42.4% of water samples have values of total dissolved solid (TDS) ≥ 2000 mg/L. The limit for drinking water is 2000 mg/L. Sodium and bicarbonate (high alkalinity) are the dominant dissolved constituents. High concentrations of dissolved salts in the ground waters from the fluvial and lacustrine sediment formations are also common; as a result of reaction of the often abundant evaporate minerals. In these, high salinity may be manifested by high concentrations of sodium, chloride and/or bicarbonate in particular.

46

Figure 12 Variation of TDS with chlorides for the sampled borehole

The TDS is plotted against chloride concentrations in Figure 12. There is a correlation with chloride concentration. Chloride concentration is the most suitable parameter as a reference for the water because it is conservative (i.e. not lost from solution by precipitation) and shows the largest concentration range of any ion.

4.1.2 Major ions

Most samples have sulphate concentrations ≤ 4 meq/L. However, of the 30 water sample in the Lower Shire area, 76.67% of samples had sulphate levels of less than the WHO recommended limit of (5.2 meq/L). 23.33% of samples were above the recommended limit.

The occurrence of SO

4

can be associated with volcanic activities. Other sources of sulphate compounds include gypsum dissolution, oxidation of pyrite and agricultural fertilizers.

However the dissolution of gypsum is not supported by the Ca

2+

vs. SO

4

2-

relationship (Figure

13) which does not show a trend towards a slope of 1. Presumably, SO

4 bearing fertilizers is the most probable source as the positive relationship between Cl

-

vs. SO

4

2

suggests and in addition it could be from pyrite oxidation related to weathering.

47

Figure 13 A plot of Ca vs. SO

4

2-

for the sampled surface water and boreholes.

High concentrations of sulphate have been a cause of poor water quality. Waters with high sulphate contents, especially when in combination with magnesium, are unsuitable for human consumption because of their hardness and laxative effect.

There is a large variation in nitrate concentration from 0.007 to 1.22 meq/L. Data summarized by Bath (1980) showed that the concentrations of nitrate at the time of the study were usually much less than the WHO guideline value (0.81 meq/L, see table 1). Similarly the concentration of nitrate in this study, except in Goma, Makande and Miseu 4 (up to 1.04,

1.22 and 2.99 meq/L respectively) boreholes, show concentrations well below the guideline indicating that there was no hazard due to nitrates to the consumers. Such low values may indicate denitrification which is bacterial-mediated reduction of nitrate in groundwater in the alluvial aquifers under anaerobic conditions.

48

Figure 14 Variation of major ions with chloride concentration for all waters analysed in the study

The major ions to chloride ratio (Figure 14) of the samples show some differences. These variations most likely could be the result of dissolution of the minerals formed during evaporation processes, since the sampling campaign took place just after the rainy season.

The magnesium concentration appears to be much higher than Ca in the rock type that the water had been in contact with. However the plot Ca vs. Cl (Figure 14.) show less correlation

(r

2

=2.417) which indicates some Ca has removed from groundwater may be because of calcite precipitation (Appendix E).

49

Figure 15. Piper diagram of surface and ground water samples

.

The results of chemical analyses of groundwater and surface water samples are shown in the

Piper diagram (Figure 15). Sodium and magnesium are the dominant cations while chloride and/or bicarbonate are the dominant anions in the majority of the groundwater. The waters are mostly classified as sodium-chloride type as shown on the piper diagram (Figure 15), whereas some of the groundwater are sodium bicarbonate dominant and characterised as a Na-HCO

3

-

Cl water type. Seven groundwater samples and one surface water sample are Mg(Ca)HCO

3 water type.

50

In general the concentration of cations decreased in the orders Na > Mg > Ca > K and of anions Cl

-

> HCO

3

-

> SO4

2-

>NO

3-

. However, HCO

3

-

dominated over Cl

-

in some samples.

This order is due to lithologic composition of the region. A significant characteristic of the groundwater is very low K concentration ranging from 0.01 to 0.34 meq/L with a mean value of 0.08 meq/L. The low levels of potassium in ground waters are a consequence of its tendency to be retained in clay minerals and to contribute in the formation of secondary minerals (Zhu, Li, Su, Ma, & Zhang, 2007).

Na

+

concentrations are found to be higher than any of the other cations (Ca

2+,

Mg

2+

and K

+

) as shown appendix B, and are correlated with chloride concentrations. Elevated Na

+ concentrations may be due to cation exchange where Ca

2+

from groundwater is adsorbed on clayed materials in exchange of Na

+

. Another possible reason for the higher Na

+ concentration could be dissolution of NaHCO

3

.

51

Figure 16. Spatial variability of TDS and major cations in lower Shire area

There is a large variation of sodium and chloride concentrations from 0.88 (Shire rive at

Nyada) to 60.6 ( Jasi 1) and chloride from 0.23 (Shire river at Nyada) to 132.92 (Jasi 1) meq/

L with mean values 19.33 and 23.59 meq/ L. The scatter plot shows a high positive correlation between sodium and chloride (R

2

= 0.80, see Figure 17). Most samples show Na/Cl ratios far above the sea water relationship that is 0.858. The relative dominance of sodium over other ions in the majority sample sites (Appendix B, table B4) in the district could also be attributed to high temperatures that lead to high evaporation rates in the discharge area

(floodplain) that leaves behind a salt build up as inferred by the TDS concentration.

52

Figure 17. A plot of Na ( meq/L) vs, Cl (meq/L)

The spatial variability for TDS and major cations are shown in Figure 16. Particularly high concentrations of sodium and chloride are observed for ground waters from lower Shire area.

Some groundwater samples close to the Shire River have saline groundwater composition.

High spatial variability in groundwater compositions suggest that the groundwater salinity was caused by numerous factors including evaporation, dissolution of evaporate minerals, and ion exchanges of Ca for Na. Particularly evaporation had an impact on the ground water of the study area.

4.1.3 Calculation of saturation indexes from PHREEQC

From PHREEQC calculation, a list of relevant minerals and saturation indexes (SI) with respect to the given groundwater solution are obtained.

If the groundwater is saturated or super saturated (SI>0) with respect to a mineral, this mineral is prone to precipitation.

Conversely, if the groundwater is under saturated (SI<0) the mineral may dissolve into solution (Appelo & Postma, 2005). The PHREEQC calculations indicate that the samples, except at Chamboko and Kwadeka water samples, are much supersaturated with respect to calcite (Appendix E). This indicates that some Ca

2+

has been removed from groundwater due

53

to calcite precipitation (Raiber, Webb, & Bennetts, 2009). Therefore Na exchange for Ca

2+ and Mg

2+

.

4.2 Minor ions in groundwater

To the best of our knowledge, concentrations of heavy metals in the study area have not been previously reported. Appendix B, table B5, shows the concentrations of heavy metals in groundwater samples from the 33 boreholes that were sampled in lower Shire area.

Concentrations of heavy metals in ground water are as follows: Ag, 12.6 - 73.3 µg/L, Al, 8.91

- 403.53µg/L; B, 80.3 - 733.0 µg/L; Pb,11.67 – 1072.6 µg/L ; Cr, 2.26 – 103.33 µg/L; Li

148.4 - 227.9 µg/L. The average groundwater Ag, Al, B, Pb, Cr, and Li concentrations for the studied area showed 41.38, 45.07, 269.18, 340.49, 31.77 and 212.76 µg/L respectively.

The results indicates that the concentration of Al in this study except in Jasi 1(404 µg/L) borehole, shows concentration well below the WHO guideline value (0.02 meq/L, see Table 1). 18.52% of 27 water samples Cr are above WHO drinking water guideline. Al concentrations are often governed by equilibrium with clay minerals. The solubility of Al is low as the pH range from

7.2 to 9.8 and it is unlikely to find an Al concentration of more than 0.02 meq/L in a ground water. Except for one value of 0.4 mg/L this is in agreement with our observation

All lead values are above the guideline (0.97*10

-4 meq/L). The highest Pb concentration was observed in high salinity area (Jasi and Chigweshe region). The occurrence of Pb in groundwater may be from dust transported through atmosphere, precipitation and deposition of airborne aerosols. Another possible source of lead is from disposal of contaminated wastes, in particular lead batteries.

Most available analyses of iron in Malawian groundwater have yielded high concentration

Bath (1980) reported total iron concentrations in groundwater in the range 1-5 mg/L from alluvial sediments and much higher iron concentrations, up to 84mg/L, in lower Shire valley.

In the study area, except for four groundwater samples whose Fe and Mn concentration were not determined since their Fe and Mn contents were below detection limit (as the detection limit for Fe and Mn are 12.9 and 1.13 µg/L respectively). The reason for the low concentration may be the presence of dissolved oxygen, leading to oxidized conditions and the total iron concentration therefore low in ground waters where oxygen is present. As a result they are not detectable in almost all lower Shire ground waters and they are redox-

54

sensitive element. However for all groundwater samples whose Cd,Cu and Zn concentration were not determined since their contents were below detection limit of ICP-OES (Appendix

B). Most waters have trace element concentrations under the limits recommended by the

WHO (2004).

Li has relatively high concentrations with the average value 212.8 µg/L. Figure 18 shows that

Li does not correlate with chloride concentrations. Thus Li is most likely derived from waterrock interaction. Li is a common minor constitute of many silicate minerals (Cartwright et al.,

2004).

Figure 18. Variation of Li and B with chloride concentration for the analysed ground and

surface waters.

The concentration of B in water sample ranges from 0.01 to 0.08 meq/L, with a mean value

0.023meq/L. Since the pH is less than 9.88 for all the samples, it is likely that B is in the non-ionized state, i.e B (OH)

4

-

(Mondal, Singh, Puranik, & Singh, 2010). It is known that Cl behaves conservative as far as the salinization process is concerned, it can be compared with

B to analyse the distribution of B with respect to the sources, mixing and salinization processes. The concentration of B increases with increasing salinity as expected if the source is biotite and micas (Gascoyne, 2004).

55

4.2.1 Minor alkaline earths (Ba and Sr)

Barium (Ba): The highest concentration is 1822 µg/L, which is below WHO drinking water guideline and half of the samples have Ba concentrations below detection limit.

Strontium vs. Cl-content variation is illustrated in figure 19. The concentration varies from

950 - 8978 µg/L, with an average concentration of 2870 µg/L. The concentration of Sr is especially high in the lower Shire area, indicating that the source could be from water-rock interaction.

Figure 19. Variation of Sr with chloride concentration for the analysed ground and

surface waters

.

Strontium with similar properties as magnesium and calcium shows a clear correlation with both elements. However, the correlation is not very high (Figure 20). Carbonate precipitation may increase the concentration of strontium in the solution relative to calcium due to preferential removal of Ca (Faye et al., 2005). The main sources of strontium are supposed to be carbonate minerals and pyrite.

56

Figure 20. A plot of Sr vs. Ca for the sampled surface and borehole waters.

4.3 Environmental Isotopes

4.3.1 Hydrogen and Oxygen isotopes

The results of ∂

2 H and ∂ 18

O analyses are presented in Appendix C, table C1. Isotopic compositions of ground-and surface water range from 11.2 to - 46.9‰ for

2

H and 1.82 to –

7.36‰ for 18

O (Appendix C).

The relationship between the ∂

2

H and ∂

18

O values is shown in Figure 21 and define global meteoric-water line (GMWL; slope =8.0) with the relationship ∂

2

H=8 ∂

18

O+10. The samples from Tayakahsu River supplying water to lower Shire river, and Shire river at Nyada are distinctly enriched in their stable isotopic compositions by -3.5 and 11.2 ‰ for ∂

2

H and by -

0.75 and 1.82 ‰ for ∂

18

O (Table C1) and their evaporative trends deviate significantly from the GMWL values and thus all surface water show extensive evaporation (Figure 21). The other samples are mostly depleted in stable isotopes (Table C1).

A few water samples on the ∂

2 H vs ∂ 18

O diagram lie slightly above the global meteoricwater line and plot close to the GMWL, indicating that the groundwater is of meteoric origin and not strongly affected by evaporation (Negrel & Petelet-Giraud, 2005) or extensive oxygen isotopes exchanges between water and the rock matrix while the deuterium content has not

57

been greatly altered by exchange or fractionation process. Thus the origin of ground water with the lowest salinity is meteoric.

While the other groundwater isotopic data cluster below the GMWL (∂

2

H=8 ∂

18

O+10), defined by (Craig, 1961), which appears to be indistinguishable from the GMWL. The deviation of groundwater samples from the GMWL indicates that evaporation enrichment of heavy isotope concentrations has occurred, resulting in a slope of 6.3 (Figure 21); somewhat less than the GMWL slope (Faye, et al., 2005).

These samples are characterized by comparatively high chloride contents (Table B4). Therefore evaporation had an impact on the groundwater salinity of the study area.

The isotopic signatures of these ground waters indicate that the effects of evaporation, related either to the infiltration of surface waters affected by evaporation or the leaching salts previously formed by evaporation, are dominant for the lower lying, lower rainfall areas. The driving forces for the above-mentioned process are the periodic recharge events, coupled with a high evaporation and low-rainfall.

Figure 21. Relationships between

2

H and

18

O in surface and groundwaters. The global water meteoric water line (GMWL) of Craig (1961), ∂

2 H=8 ∂ 18

O+10, is also shown

58

4.3.2 Strontium isotopes

Strontium isotopes (

87

Sr/

86

Sr), unlike the stable oxygen and hydrogen isotopes, do not appreciably fractionate in natural environments (Kim et al., 2003) and thus Sr isotopes are not affected by evaporation. Sr may come from weathering and also be affected by exchange reactions. Natural variation in the abundance of

87

Sr/

86

Sr ratio can be used to trace strontium sources in surface and groundwater.

The

87

Sr/

86

Sr ratios measured by TIMS from these samples are presented in table C1. The Srisotope ratios measured in ground and surface water ranged from 0.7085 (Nyasa) to 0.7144

(Machilka). The average

87

Sr/

86

Sr ratio of 33 water samples is 0.7116. This average is higher than the ratio in modern sea water of 0.709 (Boger, Boger, Jones, & Faure, 1987), probably due to the weathering of minerals.

Figure 22. Plot of

87

Sr/

86

Sr values vs Sr concentration for ground -and surface waters.

The

87

Sr/

86

Sr ratios are plotted vs Sr in Figure 21 for ground and surface water. The Srisotope compositions of surface water do not vary widely and include

87

Sr/

86

Sr ratios of

0.173567 for Taykahsu River, 0.172378 for Nyakhamba River and 0.713078 for Shire River.

59

These high ratio values particularly in low-Cl samples (Table B4) suggest that the source of strontium load is predominantly weathering.

Some of the groundwater samples, mostly with high Sr concentrations (Table B2), have

87

Sr/

86

Sr ratios is more similar to the present-day sea water value of 0.7092 which is characterized by high TDS value. However the majority of the samples have higher than the present-day sea water value (more radiogenic). Therefore, the source of this extra

87

Sr must be from the direct weathering of geologic material in the study area. It is strongly indicating that the salinity of these ground waters originates from the weathering of minerals.

4.4 Stastical Analysis

Stastical Analysis of the ground and surface water samples.

4.4.1 Hierarchical cluster analysis

The cluster analyses were performed to discover similarities among the variables and among water samples. The main result of the HCA performed on the 26 ground and surface water samples are the dendrograms (Figure 23 and 24).

60

-3,58

Ward Linkage, Correlation Coefficient Distance

30,95

65,47

100,00

EC TDS Na Cl Mg Ca K pH NO3 CO3 HCO3 SO4

Figure 23. Dendrogram for the ground and surface water samples based on similarities

among major ions and other parameters

The classification of the parameters (Figure 23) and samples (Figure 24) into clusters is based on a visual observation of the dendrograms. There is high correlation between Na and Cl in groundwater samples (0.805). This is reflected in Figure 23. Ca and K are found to correlate very strongly (Figure 23) and having low levels in the water samples. In addition there is fairly high similarity between HCO

3

- and SO

4

2

. In Figure 24 the highest EC and TDS are in cluster 4

61

Ward Linkage, Euclidean Distance

-193,59

-95,73

2,14

100,00

S1

S1

1

S1

0

C1

S9

S3

0

S1

7

S4

S1

9

S7

S1

8

S1

3

C2

S3

1

S2

6

S1

6

S2

8

S2

0

S3

2

C3

S3

3

S2 S8 S5 S3 S6

S2

4

C4

S2

5

S2

1

Figure 24. Dendrogram for the ground and surface water samples (S28 and S32) based on

similarities on among observation.

In this study, the grouping into four clusters gave satisfactory results at forming geochemical distinct clusters. There is a very strong correlation between the two clusters (C2 and C3), which is also seen their high similarity in the dendrogram (Figure 24) and most samples from

C2 and C3 have low salinity. Samples in C1 are not very different from those in C2 and C3, while samples in C4 are rather different from the other sample water. This cluster has high salinity as the EC ranges from 6800-15540 µs/cm (Table B 4) and high values of chloride and sodium. C4 may thus be denoted the saline cluster.

4.4.2 Principal Component Analysis

The first principal component describes 46.1% of the variability in the data set while the second component explains 16.5% of the variability (Table 3). Thus PC1 and PC2 account for

62.6 % of the variation. As these two principal components explain a large part of the variation in the data, the discussion of the PCA results is mainly based on these components.

62

Table 3. Eigenanalysis of the Correlation Matrix for the water samples.

Eigenvalue 5,5306 1,9836 1,3825 1,0164 0,8792 0,6724 0,2628 0,1451

Proportion 0,461 0,165 0,115 0,085 0,073 0,056 0,022 0,012

Cumulative 0,461 0,626 0,741 0,826 0,899 0,955 0,977 0,989

Eigenvalue 0,0762 0,0331 0,0181 0,0000

Proportion 0,006 0,003 0,002 0,000

Cumulative 0,996 0,998 1,000 1,00

The loading plot in Figure 25 shows essential the same as the dendrogram (Figure 23). The 12 analysed parameters were clustered into four groups. Cluster 1 and 4 split essential along

PC1, while C2 and C3 split along PC2.

Cluster 4

Cluster 3

Cluster 2 Cluster 1

0,50

Ca

K

0,25

0,00

Na

Cl

Mg

SO4

-0,25

CO3

NO3 pH

-0,50 HCO3

-0,4 -0,3 -0,2

First Component

-0,1 0,0

Figure 25. Loading plot of first component (PC1) vs. second component (PC2)

The score plot of PC1 and PC2 (Figure 26) correspond well with the dendrogram in figure 24.

The same four clusters can be identified. Cluster 4 (samples S2, S3, S5, S6, S8, S21, S24, and

63

S25) have all negative PC1 values indicating high salinity although their PC1 values vary considerably.

Cluster 4

Cluster 3

Cluster 1

Cluster 2

3

2

S2

S5

S20

S32

S33

1

0

S8

"Salinity"

S24

S3

S10

S17

S4

S28

S31

S16

S11

S1

S18

S19

S26

S7

S13

-1

-2

S25

S21

S6

S9

S30

-3

-6 -5 -4 -3 -2 -1

First Component

0 1 2 3

Figure 26. Score plot of first component (PC1) vs. second component (PC2).

4.4.3 Concentrations of major ions in the four clusters

Medians and ranges for concentrations of the investigated major ions in the water samples at the studied sites are shown in box and whisker plots in figure 27. Except for HCO

3

-

the median is highest in C4 for all the shown ions. The differences are especially large for

Sodium and Chloride. Therefore C4 samples are sodium-chloride water type. The median bicarbonate concentration in C1 is slightly higher than C4 and clearly higher than in C2 and

C3.

64

Sodium

20

10

0

40

30

60

50

Magnesium

25

20

15

35

30

10

5

0

C1 C2 C3 C4

C1 C2 C3 C4

Calcium

Chloride

20

15

10

5

0

20

0

60

40

140

120

100

80

C1 C2 C3 C4 C1 C2 C3 C4

Sulphate

Bicarbonate

20

20

15

15

10

10

5

5

0

0

C1 C2 C3 C4 C1 C2 C3 C4

Figure 27. Major ions distribution at the studied sites. Box range (25-75

percentile),Whisker range (5-95 th th

percentile); median ( - ) values are shown.

65

4.5 Validation and Quality control

4.5.1 Accuracy of chemical analysis

A number of methods have been used to test and ensure the reliability of hydrogeochemical results. The accuracy of the analysis can for major ions be estimated from the electrical balance (E.B) since the sum of positive and negative charges in the water should be equal:

Electrical balance (E.B. %) =

(

Sumofcatio ns

(

Sumofcatio ns

Sumofanion s

)

Sumofanion s

)

* 100 (2)

Where cations and anions are expressed in meq/L and inserted without their charge sign.

Analysis of groundwater with E.B.< 5% are generally regarded as acceptable but in very dilute and in saline waters, up to 10% is acceptable. In dilute waters one must expect larger relative errors and concentrated waters must be diluted before analysis. However in this study, most of the water samples showed excess negative charge. This might be due to adsorption on iron oxides but some inversely in favour of an excess positive charge, could be from precipitation as the calculated SI for calcite and dolomite generally positive (Appendix E), suggesting that calcite tended to precipitate due to evaporation. This indicates that some Ca

2+ has removed from groundwater due to calcite precipitation.

4.5.2 Spike and Recovery

Spike and – recovery experiments are important methods for validating and assessing the accuracy of the ICP-OES method. Spike and – recovery is used to determine whether analyte detection is affected by matrix or not. To perform Spike and – recovery, a known amount of analyte is added (spiked) to the sample matrix and its response is measured (recovered) by comparison to an identical unspiked sample. The water sample were spiked with ±50% of sample concentration by adding 0.1 mg/L stock solution for trace element analysis and by adding 5 mg/L for major cations (Na, Mg Ca and K).

This experiment was performed on a separate days. The accuracy of the method was evaluated comparing the mean measured results on spiked sample and unspiked sample. The

66

recovery percentage was defined as the indicator to check the accuracy according to the equation below.

Recovery% =

(

Bmg

/

L

Amg

/

L

)

* 100 % (3)

Cmg

/

L

Where A is the amount in the original sample; B is the amount measured in the spiked sample and C is the amount added as a spike.

Spike and – recovery experiments are important methods for validating and assessing the accuracy of the method. Some representative samples were spiked based on pH and EC. The proposed methods were applied to check the methods that we used in ICP-OES and the equation 2 was used to calculate the recovery. The recovery achieved was between 85-110 %

(Figure 28 and 29) except for few trace elements. Unspiked samples were also analysed at the same time with spiked samples. The recovery percentage was used as indicator to check the accuracy.

Analysis of some selected samples for major cations and trace elements using ICP-OES resulted in acceptable recoveries for most of them (Figure 28 and 29). The recovery was in the range of 97.4- 129 % and 87.9-107.5 % for Chamboko and Jasi 2 groundwater respectively.

67

Figure 28. Major and trace elements recoveries for Chamboko groundwater

analyzed by IC-OES.

Figure 29. Major and trace elements recoveries for Jasi 2 groundwater analyzed by IC-OES.

Prior to making the first calibration solution/ controlled solution, the automatic pipettes were tested by comparing volume to weight. They were calibrated to show satisfactory relations between both least volume and weight and upper limit volume and weight.

The ISO standard method (ISO 11885:2007) was used as a guideline for the analytical procedure including selection of appropriate wavelengths for the elements. To correct for possible instrumental drift recalibration was recorded for every 18 samples.

As an additional validation of the method, control solution was run in every 12 sample. The measured concentration was accepted to deviate from the known concentration with less than

± 10 %.

68

CHAPTER 5

5 CONCLUSIONS

In the Lower Shire region (South of Malawi), salinization is one of the most serious long-term environmental problems that degrades water-quality and endangers future exploitation of groundwater resources.

The sampled groundwater in the study area is strongly affected by high salinity, and show high sodium, chloride and bicarbonate levels. Thus the groundwaters are mostly classified as sodium-chloride types whereas some of them are sodium bicarbonate.

Elevated Na

+ concentrations may be due to cation exchange where Ca

2+

from groundwater is adsorbed on clayed materials in exchange of Na

+

. Another possible reason for the higher Na

+ concentration could be dissolution of NaHCO

3

. High salinity in the Malawian groundwater in the Lower Shire area may also result from dissolution of minerals formed by evaporation and the influence of saline geochemical waters.

High spatial variability in groundwater compositions suggest that the groundwater salinity was caused by numerous factors including evaporation, dissolution of minerals, and ion exchanges of Ca for Na. Particularly evaporation has an impact on the ground water of the study area.

Some water samples show ∂

2

H and ∂

18

O values close to the global meteoric-water line

(GMWL) indicating that the groundwater originates from a meteoric origin with a composition not significantly affected by evaporation. However the isotopic signatures of the majority of ground waters indicate infiltration of surface waters concentrated by evaporation or the leaching of salts formed by evaporation salts in the lower lying, lower rainfall areas.

The driving forces for the above-mentioned process are the periodic recharge events, coupled with a high evaporation to low-rainfall ratio.

The strontium isotope ratio shows that the majority of the samples have higher than the present-day sea water value (more radiogenic). This extra

87

Sr must be from the direct weathering of geologic material in the study area, strongly indicating that the salinity of these groundwaters originates from the weathering of minerals.

69

In overall the studied area concentration of Ag, B, Ba, Cr, and Li were below the drinking water standards and the concentration of Al in this study except in Jasi (0.4 mg/L) borehole, shows concentration well below the guideline. However Pb content of some samples surpassed the drinking water standard. The heavy metals concentration is less pronounced in lower Shire studied area, Malawi compared to the drinking water standard.

The government should enforce a water management policy and economic policy that promotes efficient water resource use, e.g. appropriate pricing of irrigation of water. At the same time, agriculture strategies should incorporate measures to promote efficient water-use among farmers. Greater effort also has to be directed towards the analysis of the environmental impacts of projects that involve water resource use and development to ensure that only economically and environmentally sound projects are undertaken.

To reduce the salinization problem in the study area, lowering in the groundwater depth

(should be written in the borehole) and better management of use of water from wells are recommended. Besides, further and detailed studies of salinization in specific areas are recommended.

70

6 References

Alloway, B. J. (1995). Soil processes and the behaviour of metals. In Heavy Metals in

Soils.2nd edition (ed. B. J. Alloway): Blackie Akademic & Professional.

.

Appelo, C. A. J., & Postma, D. (2005). Geochemistry,groundwater and pollution (second ed.). Netherland: A.A Balkema.

Bath, A. H. (1980). Hydrochemistry in groundwater development: report on advisory visit to

Malawi (No. WD/OS/80/20).

Boger, P. D., Boger, J. L., Jones, L. M., & Faure, G. (1987). EFFECT OF CHEMICAL-

WEATHERING ON THE RB-SR DATE OF FELDSPAR IN NEOGENE TILL,

MOUNT FLEMING, SOUTH-VICTORIA-LAND, ANTARCTICA. Chemical

Geology, 65(1), 35-44.

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73

7 Appendices

Appendix A. Calibration and Methods.................................................................75

Appendix B . Results from IC and ICP-AES.......................................................80

Appendix C. Isotope Results from Mass spectrometry ........................................81

Appendix D. Determination of total alkalinity ................................................90

Appendix E. Saturation indices ..........................................................................91

Appendix F. Principal Component Analysis..........................................................92

Appendix G. Reagents, instruments and other equipment.....................................93

74

Appendix A. Calibration and Methods

A1. Preparation of calibration standards

In all calculation the dilution formula in equation A-1 was applied.

C

1

V

1

=C

2

V

2

(A-1)

The calibration standards were prepared from Dionex Seven Anion Standard II (Dionex,

Instrument Teknikk A.S, Oslo,Norway) To reference solutions were also prepared from the

Multielement Ion chromatography Anion Standard Solution (Fluka, Sigma-Aldrich, Buchs,

Switzerland)

A2 . Calibration curves for major ions and heavy metals determination.

Chloride calibration curve

75

Sulphate calibration curve

Nitrate calibration curve

76

Calibration Curves for major cation determination

77

Calibration Curves for minor and heavy metals determination

78

Table A-1 Instrumental conditions for IC

Anion

F

-

Cl

-

SO

4

2-

NO

3

-

PO

4

3-

Flow rate(mL/min) 1.0

Current (mA) 80

Temperatur of column(

0

C) 30

Temperatur of detector(

0

C) 30

Sample injection

Election with:

with auto- sampler AS40

32µM KOH

Table A 2. Anion calibration solutions with concentrations (mg/L)

Conc.Std

1

0,0833

0,833

1,667

0,1667

0,125

Conc.Std

2

0,41667

4,1667

8,333

0,833

0,25

Conc.Std

3

1,667

16,667

33,333

3,333

0,5

Conc.Std

4

5

50

100

10

1,5

Conc.Std

5

10

100

200

20

3

79

Appendix B. Results from ICP-OES and IC

Table B1: Instrumental ICP-OES conditions used for analysis

Parameter

RF power 1.20 kW

Plasma Ar flow

Auxilary Ar flow

Nebulizer Ar flow

Replicate read time

15 L min-1

1.5 L min-1

0.75 L min-1

1.00 s

Instrument stabilazation delay

Sample uptake delay

Sample flow rate

Rinse time

Replicates

15 s

30 s

1.5 ml min-1

10 s

10

Table B2 . The wavelength selected and LOD for all elements for ICP-OES

K

Li

Mn

Pb

Zn

Cd

Cr

Cu

Fe

Ag

Al

B

Ba

Element Wavelength(nm) LOD(µg/L)

Na

Ca

Mg

Sr

588.995

383.829

317.933

460.733

7.2

11.9

14.7

6.5

338.289

394.401

249.772

493.408

214.439

267.879

324.754

238.204

13.3

23

96.4

0.3

7.9

35.3

3.7

12.9

766.491

610.365

257.61

220.353

334.502

14.2

2.8

1.1

114.7

99.2

80

Method Development

Preliminary test of major cations and trace elements using ICP-OES

In the first preliminary test, we tried to find suitable wavelength for each element to analysis our sample based on freedom of interference and intensity value. In these experiments we could not get the linear calibration for the majority of the elements but the intensity value indicated that which element is going to be detected in the range given and some others need further dilution. As mentioned above, based on the intensity value we decided to classify the elements as follows:

Group1. High Concentration: Ca,Na, and Mg --- need further dilution

Group2. Low Concentration: Al, B, Br Mn, Cu, Sr, K, Li

Group3. Difficult to detect: Ag,Cr,Fe, Pb,Zn,and Cd

The second preliminary test was done again by following the same procedure to analysis for the second and the third group elements.

In the consecutive preliminary test, group 2 and 3 were analysed through changing the

Sturman Master Spray chamber by a cyclone spray chamber which gives higher sensitivity.

Finally we found the suitable wavelength (Appendix B, table B2) for almost all element to analyses our sample based on freedom of interference and intensity value and come up with the following concentration information.

Group1. High Concentration: Ca, Na, and Mg

Group2. Low Concentration: Al, B, K, Li, Sr , Cr Ba, Ag, Pb

Group3. Difficult to detect: Cu, Fe, Mn, Zn, and Cd

The water samples with highest levels of Na, Ca, and Mg needed to be diluted to fit within the working range of the calibration standards. High concentration in the samples leads to large standard deviations in the first preliminary test. After critical analysing the intensity value of each element for all samples and this was solved by diluting the samples that contained high concentrations of the above elements from 10 to 100 times (few of samples were diluted 100 times).

81

In the preliminary experiments, several wavelengths for each metal were selected for the analysis with ICP-OES, but because of interferences from the other components in the sample, good results were not achieved for all chosen wavelengths. The final wavelength for each metal was selected for the giving of data based on freedom of interferences and intensity of the line. The lines that were chosen are given in appendix B, table B2.

In order to determine the detection limit (LOD) in the ICP-OES analyses, the blank solution

(0 mg/L calibration solution) was analysed 10 and 11 times for major cations and trace elements respectively. Table B2 shows the selected wavelengths to report the major and heavy metal elements concentration.

The level of concentration of major (Na, K, Mg and Ca) and minor (Al, Cd, Cu, Fe, Zn, Pb,

Cr, Mn, B, Ba,Sr, Li, and Ag) elements in the water samples were determined. Selecting the best measuring conditions for ICP-OES constitutes a multivariate optimization problem. The aim was to ensure maximum sensitivity for the analysis major cations, minor and heavy metals, and to minimize matrix effects.

Limit of detection

The detection limit (also called the lower limit of detection) is the lowest quantity of analyte that is “significantly different” from the blank (Harris, 2003). The detection limit is estimated from the standard deviation of the blank.

LOD = 3*S blank

(4)

Where S blank is the standard deviation of a blank solution measured n times (n≥ 6).

82

Table B 4

. Major ions Concentrations of groundwater and surfacewater sample. All values in meq/l unless otherwise indicated.

No. Sample name

1 Chamboko

2 Chigweshe

3 Dzilonzo

4 Felo 2(Biliati)

5 Fodya

Sample

Id

S1

S2

S3

S4

S5

6 Goma S6

7 Gonda S7

8 Jasi 1 S8

9 Jasi 2

10 Jombo

11 Kwadeka

12 Kaluwa

13 Kholongo

S9

S10

S11

S12

S13

14 Kulima village S14

15 Machilka

16 Mafale I

17 Makande

S15

S16

S17

Temp.(˚C) EC(µS/cm) pH

29.6

28.2

29.4

29.1

28.6

1387

11750

7110

2880

8070

7.2

8.22

8.14

7.68

8.28

29.4

29.4

30.5

30.5

30

28.6

29

29.5

29.7

29.8

29.3

29.6

6800

1148

15540

6040

2042

1999

1932

>3900

967

>3900

1568

2245

8.31

8.02

9.3

7.69

8.48

8.63

8.08

8.2

7.2

7.2

7.9

8.57

TDS

(ppm) CO₃²⁻ HCO₃⁻ Cl- SO42- NO3- Na Mg Ca K

693 #NA

5875 #NA

3555 #NA

1445 #NA

4035 #NA

10.5 1.89

9.6 104

10 61.2

6.77 13.9

4.71 20.2

1.4

13.2

3.71 #NA

1.96

3.29

0.12 4.68

0.02 7.09

5.9 1.6 0.01

0.14 58.1 20.4 9.63 0.34

45.5 11.1 4.15 0.08

4.5 3.19 0.07

0.44 34.5 34.2 9.23 0.15

3400 #NA

573 #NA

7770 #NA

15.6 41.9 8.81 1.04 43.5 11.2 2.25 0.06

10.6 0.74 0.43 0.12 5.6 4.09 0.99 0.03

10.2 133 2.45 0.09 60.6 20 6.91 0.08

3020 #NA

1022 #NA

13.6 27.6 0.63 0.85 27 1.24 0.41 0.01

13.4 15.4 0.44 0.05 19.6 6.92 4.1 0.05

1000 #NA 9.2 0.91 0.58 0.45 6.86 4.89 1.8 0.01

966 #NA #NA #NA #NA #NA 13.5 2.87 0.61 0.02

7.96 1.14 0.23 0.18 4.39 2.51 1.63 0.03 507 #NA

>2000 #NA

>2000 #NA

810 #NA

1119 #NA

11.8 45.9

21.5 32.5

5.99 4.31

9.61 9.33

8.34

18.7

0.29

2.45

0.57 32.2 8.84 3.71 0.04

0.03 20.1 6.39 1.53 0.08

0.11 8.7 3.75 3.05 0.02

1.22 6.29 10.1 5.21 0.04

83

18 Malemia

19 Maluwa

20 Mangulenje 2

21 Masnduko

22 Miseu 4

S18

S19

S20

S21

S22

23 Mitubula

24 Nibisi school

25 Nkavu school

26

Nkhwangwa sch.

27

28

Nyada(shire river)

Nyakhamba river

29 Nyasa

30

Saindi F.P

School

S23

S24

S25

S26

S28

S29

S30

S31

31 Tayakhasu river S32

32 Thumps lodge S33

S34 33 Washeni

29

29.6

28.6

28.4

30.4

29.6

29.8

29.6

1670

795

3240

8930

>3900

>3900

8160

8550

29.1

23.5

1105

254

22.6

30.1

1269

1847

29

25.8

26.7

30.1

1428

2269

2777

>3900

8.38

8.1

7.8

8.28

8.33

8.1

8

8.57

858 #NA 10.1 6.07 0.32 0.13 8.8 3.91 1.56 0.03

398 #NA 5.34 0.24 0.07 0.23 1.25 3.51 2.41 0.01

1615 #NA 5.53 14.7 0.85 #NA 11.5 6.73 8.79 0.21

4465 1.26 11.9 29.8 14.1 #NA 52.7 20.8

>2000 #NA 5.95 19.4 4.01 2.99

1 0.04

23 13.2 2.88 0.01

>2000 #NA 8.84 6.73 7.32 0.32 10.7 3.37 1.52 0.02

4080 #NA 13.1 63.2 7.84 0.6 38.9 14.2 4.91 0.06

4275 #NA 20.2 51.8 20.5 #NA 49.8 13.2 0.62 0.19

8.88

9.88

7.5

9.18

553 #NA 9.04 1.28 0.61 0.36 3.51 5.35 2.43 0.02

127 #NA 2.35 0.23 0.03 0.02 0.88 0.49 0.67 0.1

633 #NA #NA #NA #NA #NA 2.57 4.36 4.97 0.08

956 #NA 16.1 3.34 0.13 0.69 10.1 1.39 0.75 0.04

8.5

7.99

8.52

7.75

713 #NA 7.77 3.14 3.52 0.01 3.45 4.03 2.24 0.05

1128 #NA 7.72 9.08 3.69 0.01 6.95 4.41 5.56 0.35

1388 #NA 5.63 14.6 3.62 #NA 14.4 4.56 4.48 0.24

>2000 #NA 3.22 23.1 0.13 0.02 23.8 9.82 15.5 0.09

84

Table B 5. Minor and Trace elemnent concentrations. All values in µg/l unless otherwise indicated

No. Sample name

1 Chamboko

2 Chigweshe

3 Dzilonzo

4 Felo 2(Biliati)

5 Fodya

7 Gonda

8 Jasi 1

9 Jasi 2

10 Jombo

11 Kwadeka

Sample

Id

S1

S2

S3

S4

S5

6 Goma S6

12 Kaluwa

13 Kholongo

14 Kulima village

15 Machilka

16 Mafale I

17 Makande

Sr Ag Al B Ba Pb Cr Li Cd

1226.1 43.11 14.2 255.3 #NA 89.47 5.87 148.36 #NA

5962.6 48.68 32.5 733 0.346 903.4 36.3 226.53 #NA

5769.1 52.65 28.2 457 34.21 743.2 39.2 218.88 #NA

1477.5 31.85 40.5 86.15 188 83.5 #NA 217.11 #NA

7666.9 45.69 18.3 246.9 1.768 667.1 61.8 221.98 #NA

5155.4 38.91 41.3 339.3 #NA 783.8 24.7 213.91 #NA

1071.3 42.71 16.8 137.5 #NA 149 #NA 214.95 #NA S7

S8

S9

S10

8997.7 40.64 404 182.7 359.6 1073 89.6 218.01 #NA

2032.8 39.34 23.8 428.7 33.83 398.7 8.44

1709 48.19 19.3 59.76 199.3 174.7 2.26

210.9 #NA

214.8 #NA

S11 1316 34.49 29.4 291.7 29.15 160.2 10.3 213.88 #NA

S12 940.25 16.68 9.03 383.9 #NA 332.6 #NA 199.14 #NA

S13

S14

1445 22.69 15.5 137 386.7 44.77 14.5

4092.4 16.82 13 219.1

201 #NA

#NA 273.3 2.93 201.65 #NA

S15

S16

2045.7 12.65 14.4 624.1 #NA 513.9

1658.9 16.73 21.1 80.25 550.8

#NA 203.52 #NA

#NA 4.13 201.38 #NA

S17 2218.3 17.88 10.4 233.5 95.95 70.13 3.46 204.15 #NA

Cu Fe Mn Zn

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

85

18 Malemia

19 Maluwa

20 Mangulenje 2

21 Masnduko

22 Miseu 4

23 Mitubula

S18 2015.1 27.03 8.91 134.9 531.5 74.37

S19 1126.8 60.24 32.7 193.4

#NA 198.91 #NA

#NA 76.11 25.7 221.51 #NA

S20

S21

2792.5 19.64 #NA 115 913.8 #NA

2152.7 20.61 10.1 421.5 #NA 790.4 59.6 203.35 #NA

#NA 215.34 #NA

S22 4272.6 18.67

S23 2141.2 20.84

#NA 307.1

#NA 373.9

#NA 341.7 34.2 207.08 #NA

#NA 82.84 12.5 215.61 #NA

24 Nibisi school

25 Nkavu school

26 Nkhwangwa sch.

S24 6403.1 61.86 40.8 350.2 6.638 621.8 103 226.16 #NA

S25 2188.6 60.53 31.8 347.6 #NA 728 48.8 218.51 #NA

S26 1082.5 65.08 55.9 190.6 #NA 56.78 20.4 221.78 #NA

27 Nyada(shire river) S28 950.21 53.64 143 89.64 70.49 96.37 15.8 216.73 #NA

28 Nyakhamba river S29 1241.5 60.84 42.5 146.9 49.32 64.21 31.4 224.68 #NA

29 Nyasa S30 1470.7 55.77 47.9 142.6 185.8 11.66 34.1 218.73 #NA

30 Saindi F.P School S31 1382.7 73.27 58.1 203.1 35.4 100.8 20 222.44 #NA

31 Tayakhasu river S32 1799 72.13 45.4 170.9 70.01 153.3 44 229.08 #NA

32 Thumps lodge S33 2066 59.66 31.3 556 166 376.3 55 223.18 #NA

33 Washeni S34 6853.2 65.97 51.9 243.1 1822 520.5 49.5 227.9 #NA

86

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

#NA #NA #NA #NA

B-6 Preparation for calibration standards

All the calibration standard solutions were prepared from high purity ICP 1000 mg/L stock standards. Multi-element standard (100 mg/L) stock solution was prepared from 1000 mg/L stock solutions of multi elements. Five multi-elements standard solutions which were 0.1, 0.5,

1.0, 25 and 50 mg/L concentration were prepared using C

1

V

1

=C

2

V

2

by adding 0.05, 0.25, 0.5,

12.5 and 25 mL volume of stock solution respectively. 0.5 mL p.a HNO

3 was added into the flasks. The blank solution was type 1.

In the second preliminary test, 0.5 1.0, 2.0 and 5.0 mg/L calibration standard solution were prepared from 100 mg/L stock solution (which was already prepared from 1000 stock standard solution). 0.5 mL p.a HNO

3

was added into the flasks including the blank.

In the consecutive preliminary test, ranging from 0 - 5.0 mg/L calibration standard solution were prepared from 100 mg/L stock solution (which was already prepared from 1000 stock standard solution) for trace elements and ranging from 0 – 25 mg/L calibration standard solution were prepared for Na, Mg, Ca and Sr. 0.5 mL p.a HNO

3

was added into the flasks including the blank. The calibration solutions were made by dilution of multi-element standards.

87

Appendix C. Isotope Results from Mass spectrometry.

Table C 1. D,

18

O and Sr isotope ratio value.

ID

S1

S2

S3

Sample name

Chamboko

Chigweshe

Dzilonzo

S4

Felo 2(Biliati)

S5

Fodya

S6

Goma

S7

Gonda

S8

Jasi 1

S9

Jasi 2

Temp.

(˚C)

29.6

28.2

29.40

29.10

28.60

29.40

29.40

30.50

30.50

30

28.6

EC( µS/cm)

1387

11750

7110

2880

8070

6800

1148

15540

6040

2042

1999

pH

7.2

7.1

6.9

S10 Jombo

S11 Kadeka

S12 Kaluwa

S13 Kholongo

S14 Kulima village

S15 Machilka

S16 Mafale I

29

29.50

29.70

29.80

29.30

1932

967

>3900

>3900

1568

6.7

7.4

7.2

7.2

7

6.4

2009.5486

2009.5487

7.2 2009.5488

7.30 2009.5489

2009.5490

2009.5491

2009.5492

2009.5493

7.9

6.9

6.7

7.3

7

IFE lab ID

D

2009.5483

2009.5484

2009.5485

2009.5494

2009.5495

2009.5496

2009.5497

2009.5498

VSMOW

-33.6

-9.1

-38.9

-35.8

-33.4

-35.4

-37.1

-41.3

-37.5

-39.6

-34.2

-35.4

-39.5

-34.0

-35.2

-46.9

18

O

VSMOW

87Sr/86Sr 2 sigma Comment

-5.57

-2.07

-6.48

-5.59

-4.32

-5.13

-5.59

-6.02

-5.44

-6.40

-4.68

-5.41

-6.47

-5.10

-5.41

-7.36

0.712121 0.000025

0.713250

0.709999

0.713761

0.710066

0.709288

0.711844

0.709463

0.709733

0.711378

0.711250

0.713865

0.711328

0.709820

0.714417

0.711121

0.000015

0.000008

0.000010

0.000008

0.000014

0.000009

0.000011

0.000008

0.000009

0.000007

0.000008

0.000008

0.000010

0.000015

0.000015

88

S17 Makande

S18 Malemia

S19 Maluwa

S20 Mangulenje 2

S21 Masnduko

S22 Miseu 4

S23 Mitubula

S24 Nibisi school

S25 Nkaru school

Nkhwangwa

S26

school 29.10

S27 Nsomo

S28 Nyada(shire river)

S29 Nyakhamba river

S30 Nyasa

29.5

23.5

22.6

30.10

S31 Saindi F.P School 29.00

S32 Tayakhasu river 25.80

S33 Thumps lodge

S34 Washeni

26.70

30.1

29.60

29.00

29.60

28.60

28.40

30.40

29.60

29.80

29.60

1105

2227

254

1269

1847

1428

2269

2777

>3900

2245

1670

795

3240

8930

>3900

>3900

8160

8550

6.7

7

6.7

6.9

7.1

7

7

6.6

7.2

2009.5499

2009.5500

2009.5501

2009.5502

2009.5503

2009.5504

2009.5505

2009.5506

2009.5507

7.2

8.1

7.3

6.6

7.20 2009.5508

7.5

8

2009.5509

2009.5510

7.5

7.4

2009.5511

2009.5512

2009.5513

2009.5514

2009.5515

2009.5516

-33.9

-43.1

-29.3

-33.3

-37.6

-35.3

-33.3

-32.5

-36.1

-35.7

11.2

-24.3

-34.3

-27.1

-3.5

-31.8

-37.4

89

-4.69

-6.81

-4.59

-5.11

-5.41

-5.14

-5.05

-4.35

-4.92

-5.45

1.82

-2.86

-4.42

-4.81

-0.75

-4.74

-5.95

0.712952 0.000026

0.710864 0.000009

0.711344 0.000009

0.713687 0.000008

0.714144 0.000020

0.710127 0.000012

0.710853 0.000011

0.709150 0.000009

0.711754 0.000011

0.713337 0.000010

0.713078 0.000016

0.712378 0.000013

0.708500 0.000015

0.711163 0.000014

0.713567 0.000021

0.712616 0.000016

0.710429 0.000024

No sample

Appendix D. Determination of total alkalinity

Procedures for determination of total alkalinity

The procedure for measurement of total alkalinity was according to ISO 9936-1.

The sample was titrated with standard acid solution (HCL) to fixed endpoint values of 8.3 and 4.5

(none of the samples had pH values above 8.3) using a 702 SM Titrino. The alkalinity was calculated with equation D-1 below.

Alkalinity =

c

(

HCl

)

V

V

1

2 * 1000

(D1)

Where C(HCl) = the actual concentration of HCl expressed in moles per liter

V1= volume (in ml) of the test portion

V2= volume (in mL) of HCl consumed to each pH 4.5

90

ApAppendix E. Saturation indices

Sample name

1 Chamboko

2 Chigweshe

3 Dzilonzo

4 Felo 2(Biliati)

5 Fodya

Id

S1

S2

S3

S4

S5

6 Goma S6

7 Gonda S7

8 Jasi 1

9 Jasi 2

S8

S9

10 Jombo

11 Kwadeka

13 Kholongo

14 Kulima village

15 Machilka

S10

S11

S13

S14

S15

16 Mafale I

17 Makande

18 Malemia

19 Maluwa

20 Mangulenje 2

21 Masnduko

22 Miseu 4

S16

S17

S18

S19

S20

S21

S22

23 Mitubula

24 Nibisi school

S23

S24

25 Nkavu school S25

26 Nkhwangwa sch. S26

28

Nyada(shire river) S28

30 Nyasa S30

31 Saindi F.P School S31

32 Tayakhasu river S32

33 Thumps lodge S33

34 Washeni S34

1.805

0.8334

1.0678

0.8076

0.9399

0.5978

1.0993

0.6507

1.0816

0.7216

1.6417

SI_calcite

-0.0852

1.3811

1.0649

0.5006

1.2056

1.2724

1.128

1.1567

0.4393

0.3477

-0.0697

1.2125

1.1976

0.7732

SI_gypsum

-2.2607

-1.0455

-1.783

-1.8617

-1.6012

-1.6997

-2.98

-1.8972

-2.9393

-2.5106

-2.5605

-2.9592

-1.18

-1.5061

-2.81

-1.6634

-2.9333

-3.244

-1.8959

-1.9019

-1.6355

-1.6504

-1.4287

-2.0942

-2.495

SI_dolomite

0.5387

3.2393

2.7101

1.2932

3.1323

3.4009

3.041

2.9355

1.4996

1.0701

0.4376

2.7756

2.913

2.306

3.9862

2.0975

2.6948

1.9249

1.91

2.6602

2.9123

1.7828

2.7748

3.0206

3.8069

1.3751

1.4794

1.2118

1.0811

1.3415

0.8393

2.8329

3.4646

2.8193

2.2037

2.8387

1.6297

-4.1484

-3.8141

-1.7318

-1.3919

-1.5263

-2.592

91

Appendix F: Principal Component Analysis

Eigenanalysis of the Correlation Matrix

Eigenvalue 5,5306 1,9836 1,3825 1,0164 0,8792 0,6724 0,2628 0,1451

Proportion 0,461 0,165 0,115 0,085 0,073 0,056 0,022 0,012

Cumulative 0,461 0,626 0,741 0,826 0,899 0,955 0,977 0,989

Eigenvalue 0,0762 0,0331 0,0181 0,0000

Proportion 0,006 0,003 0,002 0,000

Cumulative 0,996 0,998 1,000 1,000

Variable PC1 PC2 PC3 PC4

EC -0,413 -0,028 0,055 -0,027 pH 0,069 -0,084 -0,409 -0,641

TDS -0,413 -0,029 0,055 -0,028

CO3 -0,120 -0,265 -0,490 0,573

HCO3 -0,156 -0,535 0,156 -0,195

Cl -0,381 0,040 0,116 -0,182

SO4 -0,311 -0,206 -0,296 -0,108

NO3 0,004 -0,296 0,603 -0,086

Na -0,410 -0,127 -0,025 -0,040

Mg -0,350 0,099 0,033 0,266

Ca -0,220 0,539 0,224 0,090

K -0,184 0,432 -0,213 -0,296

92

Appendix G. Reagents, instruments and other equipment

G-1: Chemicals

Nitric acid (HNO3), 65%, pro analysis was used in the experimental work

G-2: Gases

The argon gas (99.99%) used in ICP-OES was from AgA,Oslo; Norway

G-3: Water qualities

The following types of water were used:

Type 1 water,resistance >18.0 MΩ cm (at 25

0

C), Millipore Elix-5/Milli-Q purification system

(Millipore, Billerica,Ma USA)

Type 2 water resistance > 1.0 MΩ cm (at 25

0

C), Millipore Elix-10 (Millipore, Billerica, MA

USA)

G-4: Standard reference materials

Certified Reference Material BCR

®

- 277R (IRRM)

Certified Reference Material BCR

®

- 280R (IRRM)

G-5: Standard stock solutions

Multi-element standard solutions used to make inter-calibration and calibration solutions are listed in appendix B

G-6: Instruments and other equipment

∙ A field pH meter was used for determination of pH in the field

∙ An EcoScan CON 5 Conductivity Handheld Meter was used for the determination of

conductivity and temperature of water in the field.

∙ A Dionex IC was used for the determination of main anions in selected water samples.

∙ A Varista Varian ICP-AES with radial view plasma and a V –Groove Nebulizer and

CCD simultaneous detector was used for the determination of selected metals in the

water samples.

∙ A DIONEX 2000 IC with IonPac® AS18 analytical columns with ASRS-Ultra auto-

suppressor was used for the determination of anions.

93

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