-portal.org Biogeosciences Citation for the original published paper (version of record):

-portal.org Biogeosciences Citation for the original published paper (version of record):
http://www.diva-portal.org
This is the published version of a paper published in Biogeosciences.
Citation for the original published paper (version of record):
Bragee, P., Mazier, F., Nielsen, A., Rosén, P., Fredh, D. et al. (2015)
Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes.
Biogeosciences, 12(2): 307-322
http://dx.doi.org/10.5194/bg-12-307-2015
Access to the published version may require subscription.
N.B. When citing this work, cite the original published paper.
Permanent link to this version:
http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-100781
Biogeosciences, 12, 307–322, 2015
www.biogeosciences.net/12/307/2015/
doi:10.5194/bg-12-307-2015
© Author(s) 2015. CC Attribution 3.0 License.
Historical TOC concentration minima during peak sulfur deposition
in two Swedish lakes
P. Bragée1 , F. Mazier2 , A. B. Nielsen5,1,6 , P. Rosén3 , D. Fredh1 , A. Broström1,* , W. Granéli4 , and D. Hammarlund1
1 Quaternary
Sciences, Department of Geology, Lund University, Sweden
UMR5602, Jean Jaures University, Toulouse-Le Mirail, France
3 Department of Ecology and Environmental Science, Umeå University, Sweden
4 Department of Biology, Aquatic Ecology, Lund University, Sweden
5 Department of Physical Geography and Ecosystem Science, Lund University, Sweden
6 Department of Biology and Environmental Science, Linnæus University, Sweden
* now at: Swedish National Heritage Board, Contract Archaeology Service, Sweden
2 GEODE,
Correspondence to: P. Bragée ([email protected])
Received: 16 October 2013 – Published in Biogeosciences Discuss.: 19 December 2013
Revised: 20 November 2014 – Accepted: 25 November 2014 – Published: 19 January 2015
Abstract. Decadal-scale variations in total organic carbon
(TOC) concentration in lake water since AD 1200 in two
small lakes in southern Sweden were reconstructed based
on visible–near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts
of local land-use changes, regional variations in sulfur, and
nitrogen deposition and climate variations on the inferred
changes in TOC concentration, the same sediment records
were subjected to multi-proxy palaeolimnological analyses.
Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical
records provided information on catchment-scale environmental changes, and comparisons were made with available
records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD 1900, with additional variability coupled mainly to changes in forest cover
and agricultural land-use intensity. The last century showed
significant changes, and unusually low TOC concentrations
were inferred at AD 1930–1990, followed by a recent increase, largely consistent with monitoring data. Variations
in sulfur emissions, with an increase in the early 1900s to
a peak around AD 1980 and a subsequent decrease, were
identified as an important driver of these dynamics at both
sites, while processes related to the introduction of modern forestry and recent increases in precipitation and tem-
perature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD 1980 may therefore reflect a recovery
process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations
has reached pre-industrial levels, other forcing mechanisms
related to land management and climate change may become
the main drivers of TOC concentration changes in boreal lake
waters in the future.
1
Introduction
Several studies have demonstrated increases in dissolved organic carbon (DOC) concentrations and colour in surface waters across large parts of Europe and North America over
the last three decades (Stoddard et al., 2003; Hongve et al.,
2004; Evans et al., 2005; Worrall and Burt, 2007; Erlandsson
et al., 2008; Arvola et al., 2010). These trends have raised
concerns about drinking water quality, as contaminants and
toxic compounds may be associated with DOC (Ledesma et
al., 2012). This may lead to increased demands for chemical
pre-treatment in drinking water plants. Increased DOC export to surface waters may also have major consequences for
aquatic ecosystems (Karlsson et al., 2009) and recreational
values, as well as the role of lakes as carbon sources to the
atmosphere (Cole et al., 2007).
Published by Copernicus Publications on behalf of the European Geosciences Union.
308
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
A number of hypotheses have been put forward as explanations of the recent increase in DOC concentration. Several
studies have proposed a link to declining atmospheric acid
deposition (Evans et al., 2006; Vourenmaa et al., 2006; Monteith et al., 2007), while others have coupled enhanced leaching of DOC from soils to changes in climate (Freeman et al.,
2001; Hongve et al., 2004; Worrall and Burt, 2007; Haaland
et al., 2010) or nitrogen deposition (Findlay, 2005). Localscale land-use and land management practices have also been
demonstrated to influence DOC concentrations (Corell et al.,
2001; Mattsson et al., 2005; Armstrong et al., 2010; Yallop et
al., 2011). The lack of agreement on the mechanisms controlling DOC and colour variations in lake water during recent
decades may partly reflect that many studies have been performed on catchment areas with heterogeneous types of land
use, making it difficult to distinguish between co-existing
forcing factors. Moreover, most studies have been based on
monitoring data covering only a few decades, and have therefore failed to place the recent DOC trends in the perspective
of the pronounced dynamics of anthropogenic atmospheric
sulfur emissions that have occurred during the last century.
Correspondingly, long-term changes in vegetation, land use
and climate have also not been considered.
One way of gaining an increased understanding of this important environmental problem is to obtain long-term records
of past changes in total organic carbon (TOC) concentration in lake water by using inference models derived from
visible–near-infrared spectroscopy (VNIRS) of lake sediments (Rosén, 2005; Cunningham et al., 2011; Rosén et al.,
2011). Following methodological development, this palaeolimnological approach has recently gained increased attention as a trustworthy proxy for ambient variations in lakewater DOC concentrations, building on the fact that the dominant fraction (> 95 %) of TOC in Scandinavian lake waters consists of DOC, usually defined as organic matter not
retained by a filter of 0.45 µm in nominal pore size (Wetzel, 2001). The remaining fraction is particulate organic carbon (POC), which consists of larger organic compounds.
In boreal forested catchment areas, DOC is primarily allochthonous, originating from leaching of terrestrial soils.
Additional autochthonous DOC may be produced in lakes by
phytoplankton and aquatic macrophytes, although this part
commonly constitutes only a minor fraction of the DOC pool
in boreal lakes (Bade et al., 2007). The composition and
quantity of DOC may differ between sites depending on climate and catchment properties such as vegetation, hydrology and soil properties (e.g. Clark et al., 2010). Lake-water
DOC concentration and colour often show strong correlations (Pace and Cole, 2002; von Einem and Granéli, 2010)
and their mutual increases over recent decades have been
referred to as brownification (Granéli, 2012). Surface waters are variably coloured by humic substances, which are
formed by terrestrial humification during degradation of soil
organic matter and may comprise 50–75 % of the DOC pool
(McDonald et al., 2004). Humic substances absorb solar raBiogeosciences, 12, 307–322, 2015
diation, especially UV and short-wavelength visible radiation, and hence affect water temperature and aquatic primary productivity, with consequences for lake stratification
and ecosystem functioning (Snucins and Gunn, 2000; Diehl
et al., 2002; von Einem and Granéli, 2010). However, some
studies have reported clear discrepancies between DOC concentration and colour in lake water (Erlandsson et al., 2008;
Kritzberg and Ekström, 2012), indicating that the composition of DOC at the molecular level may be equally important
for changes in water colour.
Here we present a detailed multi-proxy study based on
well-dated sediment successions from two small nearby
lakes in southern Sweden spanning the last approximately
800 years. One of them (Åbodasjön) is oligotrophic mesohumic with a mosaic landscape in its catchment area and
with a long history of anthropogenic disturbance. The other
lake (Lindhultsgöl) is oligotrophic polyhumic with a catchment area dominated by forest and wetlands, and is historically less influenced by anthropogenic disturbance (Bragée
et al., 2013; Fredh et al., 2013). We applied a combination
of palaeolimnological methods to the sediment sequences,
including reconstruction of lake-water TOC concentration
based on VNIRS (Rosén, 2005), diatom analysis to determine water pH, and pollen analysis and the Landscape Reconstruction Algorithm approach for reconstruction of catchment land-cover change (Sugita, 2007a, b). The aim of this
study is to identify the major forcing mechanisms behind observed increases in TOC concentration in lakes of the upland area of southern Sweden during recent decades by comparing the impacts of changes in land use, sulfur and nitrogen deposition, and climate to long-term trends in lakewater TOC concentration since AD 1200. Particular focus is
placed on the effects of differences in catchment characteristics and the degree of land-use intensity between the two
study lakes. Ultimately, our findings may contribute to an
enhanced understanding of lake-water TOC dynamics generally, on timescales beyond monitoring series, and to prediction of the future development of lake-water quality in boreal
environments.
2
Study area and site descriptions
The two study lakes, Åbodasjön and Lindhultsgöl, are situated 6 km apart, about 30 km north-west of Växjö in the
province of Småland, southern Sweden (Fig. 1). The crystalline bedrock is dominated by granite and gneiss (Wikman, 2000) and covered by sandy till of various thicknesses and scattered peat deposits (Daniel, 2009). The area
is part of the boreo-nemoral zone characterized by mixed
coniferous and deciduous forest (Sjörs, 1963; Gustafsson,
1996). The climate is generally maritime with a mean annual temperature of 6.4 ◦ C (January 2.7 ◦ C, July 15.9 ◦ C)
and an annual precipitation of 651 mm (January 52 mm, July
75 mm), based on reference normals from Växjö for 1961–
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Table 1. Morphometric and hydrological characteristics of the two
study lakes, sampled in July 2007 (von Einem and Granéli, 2010).
309
N
a)
b)
Sweden
212
0.07
5
0.6
–
6.4
0.83
14.9
23.8
960
1993
Växjö
100 km
Åbodasjön
c)
Water
V
221
0.5
9
9.5
0.5
7.0
0.56
7.7
11.0
40
1984
V
Lindhultsgöl
V
Altitude (m)
Lake surface area (km2 )
Maximum depth (m)
Catchment area (km2 )
Residence time (yr)
pH
Alkalinity (mEq L−1 )
Chlorophyll a conc. (µg L−1 )
DOC conc. (mg L−1 )
Water colour (mg Pt L−1 )
Liming started
Åbodasjön
Open land
Lindhultsgöl
Wetland
Woodland
V
Road
Buildings
Catchment
area
1990 (Alexandersson et al., 1991). The lakes are situated
within the area of Sweden most significantly affected by increasing DOC concentrations since the 1990s (Löfgren et al.,
2003). Lake size was also taken into account at the selection
of study sites to enable reconstructions of local-scale land
use based on fossil pollen records. The lakes are situated in
the parish of Slätthög, established around AD 1000, and the
first local population data are available from AD 1571, revealing 301 inhabitants (Andersson Palm, 2000). During the
1700s the population started to increase rapidly and a population peak was reached in the end of the 1800s, followed by
a decrease in rural population due to industrialization.
Åbodasjön (Table 1, Fig. 1) is an oligotrophic mesohumic
lake fed by two inlet streams, situated in the south and northeast, and with an outlet in the south-west. The village of
Åboda (40 residents in 2004) is situated west of the lake, and
the area around the lake margin is semi-open with mainly deciduous trees, grassland and cropland. The vegetation cover
within the catchment area is dominated by managed coniferous woodland, wetlands, and patches of grassland and cropland.
Lindhultsgöl (Table 1, Fig. 1) is an oligotrophic polyhumic lake with no visible inlet streams. At least two artificial ditches drain into the lake from nearby wetlands and
woodland, and there is an outlet consisting of an artificial
ditch in the south. The catchment area is covered by managed
coniferous forest and wetlands with shrubs and scattered pine
trees.
3
3.1
Methods
Fieldwork, subsampling and dating
0
1
2 Km
Figure 1. Location of study sites. (a) Map of Scandinavia and
southern Sweden. The study area is marked by a square, and the
closest city is Växjö. (b), (c) Maps of the studied lakes and the
present-day land cover in their surroundings.
ments and surface sediments were based on mineral magnetic
properties and X-ray fluorescence (XRF) measurements of
element compositions. The uppermost 1 m parts of the sequences were subsampled into 0.5 cm contiguous sections
for stratigraphic analyses. Age–depth models were based on
210 Pb dating along with 137 Cs, supplemented by radiocarbon dating of terrestrial plant remains and lead (Pb) pollution
concentration variations (Bragée et al., 2013).
3.2
Visible–near-infrared spectroscopy (VNIRS)
Past changes of TOC concentration in the lake waters were
reconstructed using a calibration model based on visible–
near-infrared spectroscopy (VNIRS) of surface sediments
from 140 Swedish lakes covering a TOC gradient from 0.7
to 24 mg L−1 (Cunningham et al., 2011). The inferred TOC
concentrations from Lindhultsgöl exceeded the range within
the calibration set, and an additional set of 160 Canadian
lakes with a DOC range of 0.6 to 39.6 mg L−1 was also used
(Rouillard et al., 2011). The model performance of the combined Swedish and Canadian calibration set is similar to the
Swedish calibration set with an R 2 value of 0.6 between
measured and predicted TOC concentration and a root-meansquared error of prediction (RMSEP) of 4.1 mg L−1 (10.5 %
of the gradient).
In early spring 2008 sequences of surface sediments were
obtained from Åbodasjön and Lindhultsgöl at water depths
of 8.6 and 5.2 m, respectively, using a gravity corer and a
1 m long Russian peat corer. Correlations between core segwww.biogeosciences.net/12/307/2015/
Biogeosciences, 12, 307–322, 2015
310
3.3
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Diatom analysis
Past changes in lake-water pH were reconstructed based on
diatom assemblages in the sediment records. Diatom samples were prepared following standard methods (Battarbee
et al., 2001). Following oxidization of freeze-dried sediment samples (0.01 g) with 15 % H2 O2 solution for 24 h,
30 % H2 O2 was added to digest organic matter using the
water-bath technique described by Renberg (1990). For some
samples HNO3 was added to digest the remaining organic
matter. To estimate diatom concentrations, known quantities of DVB (divinylbenzene) microspheres were added to
the digested and cleaned samples (Battarbee and Kneen,
1982; Wolfe, 1997). Samples of 0.2 mL of the mixtures were
evaporated onto cover slips and mounted onto microscope
slides using the Zrax mounting medium (refractive index
= ∼ 1.7+). At least 400 diatom valves per sample were
counted under a light microscope at 1000 × magnification,
using phase-contrast optics and identification keys (Krammer and Lange-Bertalot, 1986, 1988, 1991a, 1991b; LangeBertalot and Krammer 1989; Krammer , 1992). The diatom
counts were expressed as relative abundances of each taxon.
Diatoms were grouped into planktonic and benthic taxa for
calculation of planktonic / benthic (P / B) ratios, indicative
of light availability, as decreased light penetration reduces
benthic growth.
Changes in pH were inferred from sedimentary assemblages (Di-pH) using a transfer function set, the online combined pH training set in the European Diatom Database
(http://craticula.ncl.ac.uk/Eddi/jsp/). The calibration set for
the model consists of 627 lakes with a pH range of 4.3–8.4.
The diatom-inferred pH was based on locally weighted averaging and inverse deshrinking (Juggins and Birks, 2012).
The model performance of the transfer function applied to
Åbodasjön and Lindhultsgöl was assessed by leave-one-out
cross-validation, which showed an R 2 value of 0.8 and an
RMSEP of 0.4 pH units.
3.4
Carbon and nitrogen elemental analyses
The carbon–nitrogen (C / N) ratio of lake sediments gives
an indication of the source (terrestrial and aquatic) of organic matter (Meyers and Lallier-Vergès, 1999). Acid-treated
and freeze-dried sediment samples were analysed for sedimentary total organic carbon (TOCsediment ) and total nitrogen (TN) contents by combustion using a Costech ECS
4010 elemental analyser. The samples were pre-treated with
10 % HCl at 90 ◦ Cfor 5–7 min for removal of potential trace
amounts of CaCO3 . Elemental C / N ratios were converted to
atomic ratios by multiplication by 1.167.
3.5
Trace element concentrations and X-ray
fluorescence analysis (XRF)
Enhanced catchment erosion may be reflected by elevated
concentrations of lithogenic elements in the sediment profile (Engstrom and Wright, 1984). Concentrations of phosphorus (P), zirconium (Zr) and titanium (Ti) in the sediments were measured by X-ray fluorescence (XRF) analysis
(Boyle, 2000) followed by calculation of elemental Zr / Ti
ratios for estimation of mineral grain-size variations within
the lake sediments, as Zr is commonly associated with silt
particles and Ti often occurs in the fine silt and clay fractions (Koinig et al., 2003; Taboada et al., 2005). Freeze-dried
samples at 2–5 cm intervals of the sediment sequences were
measured, using an S2 Ranger XRF spectrometer for total
concentrations of 35 different major and trace elements. The
spectrometer was calibrated using certified reference materials. Mass attenuation correction was based on theoretical alpha coefficients, with calculations taking organic matter concentrations into account.
3.6
Pollen analysis and Landscape Reconstruction
Algorithm (LRA)
Changes in land use were quantified using LRA (Sugita,
2007a; b) based on pollen counts of dominant taxa in the
sediment records from the two study sites and an additional
lake (needed for the LRA calculation). A minimum of 1000
pollen grains of modelled arboreal and non-arboreal taxa
were counted for contiguous 0.5 cm samples (1–10 samples)
covering 20-year time spans.
The LRA allows the estimation of changes in the spatial
coverage of 26 target taxa at regional and local scales. The
pollen data, the LRA approach with its associated parameters, and the reconstructions of land use were described in
detail by Fredh et al. (2013, 2014) and Mazier et al. (2014).
In this paper, we focus on local land-use dynamics at 20year intervals since AD 1200 at a spatial scale (modelled
area) identified by Mazier et al. (2014) as a radius of 1740 m
around Åbodasjön and 1440 m around Lindhultsgöl. The inferred covers of individual taxa are grouped into five different categories of land use according to Mazier et al. (2014):
coniferous woodland, deciduous woodland, grassland, cropland and wetland. Although the LRA approach provides no
information on the spatial distribution of the types of land
use within the modelled areas – larger than the actual catchment areas – we assume that the changes in land use within
the modelled areas broadly reflect catchment-scale vegetation changes.
3.7
Multivariate analyses
To explore the impact of various potential driving forces on
the lake environment as reflected in the sediment record,
we carried out canonical ordinations. The palaeolimnological
Biogeosciences, 12, 307–322, 2015
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
parameters (VNIRS-inferred TOC concentration, sediment
TOCsed and TN, C / N ratio, sediment P content (ppm),
Zr / Ti ratio and diatom inferred pH) were used as response
variables. As potential forcing variables we used the polleninferred land-use categories (coniferous woodland, deciduous woodland, grassland, cropland and wetland) and in addition the cover of individual tree species (spruce and pine), total woodland cover (coniferous and deciduous), and the sum
of cropland and grassland.
For the entire period after AD 1200, 20-year time slices
were used for the analysis, using land cover as forcing. A
mean value for each sedimentary variable was calculated
over each 20-year time slice. A few time slices lacked measurements of P content and Zr / Ti ratio and were therefore
left out of the analysis. For Di-pH, the analytical resolution
was lower than 20 years (see Fig. 2), so linear interpolations
between the available estimates were used to calculate average values for each 20-year time slice. A separate analysis
was carried out for the period after AD 1880 including data
on atmospheric deposition of sulfur (S), ammonium (NH4 )
and nitrogen oxides (NOx ), and monitoring records of temperature and precipitation as potential forcing factors in addition to land cover. Annual climate data are available for the
region from AD 1860, and deposition data are available at 5year intervals from AD 1880. The temporal resolution of this
ordination analysis was determined by the resolution of the
inferred VNIRS-TOC reconstruction (see Fig. 3). Land cover
was considered constant for each 20-year interval. For the
other sediment parameters and for atmospheric deposition,
linear interpolation was used to derive an estimated value for
the year corresponding to each VNIRS-TOC sample. For the
climatic variables (annual mean temperature and total annual
precipitation), the value measured in the sample year and the
mean value for the 10 years up to and including the sample
year were both included in the analysis.
Ordinations were carried out using CANOCO v4.51. For
all analyses, preliminary detrended canonical correspondence analysis showed the response data set had a gradient length < 1 standard deviation units, implying that linear based ordination techniques such as redundance analysis
(RDA) were most suitable for these data sets (ter Braak and
Smilauer, 1998).
Land-cover percentages were square-root-transformed,
while the limnological parameters (which are measured in
different units) were centred and standardized. Time was
used as a co-variable to remove co-varying effects between,
for example, changes in land use and atmospheric deposition. Manual forward selection was used to explore the explanatory power of the different forcing variables, and Monte
Carlo tests with 999 unrestricted permutations were run to
check their statistical significance in order to select the best
explanatory variables for further analysis. The selected variables were checked for collinearity by inspecting their variance inflation factors, which were in all cases < 10, which
www.biogeosciences.net/12/307/2015/
311
indicates that the selected parameters are not too closely correlated (Oksanen, 2011).
4
Results
Åbodasjön (Fig. 2): the inferred TOC reconstruction shows
maximum inferred values of 14 mg L−1 around AD 1250,
followed by a decrease to rather stable values at 9–10 mg L−1
after AD 1450. Around AD 1800 an increase was recorded,
reaching peak values at ca. 12 mg L−1 between AD 1860 and
1910, followed by a sudden decrease, reaching a sequence
minimum of ca. 7 mg L−1 in the 1980s. After AD 1990 an
increase to 9–10 mg L−1 was recorded.
The diatom-inferred pH varies between 6.2 and 6.7, with
a sample-specific standard error between 0.32 and 0.45.
(Fig. 2 and Supplement). Periods of slightly elevated pH
were recorded at AD 1350–1500 and AD 1700–1780, while
lower values were recorded at AD 1520–1670 and after
AD 1970. The diatom concentration increases to a peak
around AD 1400, followed by a decrease to relatively stable values and a second decrease after AD 1850. The planktonic diatom taxa vary between 40 and 70 % of the diatom
assemblage, and slightly elevated P / B ratios were recorded
at AD 1250–1500 and in the top sample.
Sediment total organic carbon content (TOCsed ) and TN
show slightly elevated values at AD 1250–1350, followed
by a slight transient decrease and a gradual increase after
AD 1450. In the 1800s TOCsed content stabilizes at maximum values. The C / N ratio increases in AD 1200 to ca.
1300, followed by a slight decrease and a continuous increase
from around AD 1450 to a sequence maximum at AD 1850–
1900. There is a shift towards substantially lower TOCsed
and TN content, and C / N ratios at ca. AD 1850 (TN) and
1900 (TOCsed and C / N). Thereafter, increasing trends in
both TOCsed and TN content is recorded from ca AD 1970
to the present, and C / N ratios after AD 1990.
P concentration decreases gradually from the beginning of
the sequence interrupted by a shift to higher values at ca.
AD 1440 and thereafter followed by continuously decreasing
concentrations. The onset of the 1900s is characterized by an
increase in P concentration peaking shortly after AD 1950.
The Zr / Ti ratio record shows a period of elevated values at
AD 1320–1450, followed by a temporary decease and continuously elevated values at AD 1600–1900. After around
AD 1950 a slight decrease was recorded.
The LRA-inferred woodland (coniferous and deciduous)
cover around Åbodasjön varies between 33 and 80 % since
AD 1200. The cover of grassland and cropland together is
40–50 % at AD 1240–1400, followed by a decrease to a
minimum of 15 % at AD 1520–1540, when deciduous and
coniferous woodland reaches a peak in cover. After around
AD 1540 grassland and cropland cover increases and reaches
maxima of ca. 60 and 12 %, respectively, between AD 1820
and 1900. During the 1900s coniferous woodland, dominated
Biogeosciences, 12, 307–322, 2015
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Åbodasjön
Year (AD)
312
2000
2000
1900
1900
1800
1800
1700
1700
1600
1600
1500
1500
1400
1400
1300
1300
1200
1200
Lindhultsgöl
Year (AD)
5
10
15
6
7 15 20 25 30 1
1.5
2 10 15 20 25 30 1000 1500 2000 0
0.05
0.1 0
0.5
1 0
1
3 0
2
10 20 30 0
20
40
60
80
100
2000
2000
1900
1900
1800
1800
1700
1700
1600
1600
1500
1500
1400
1400
1300
1300
1200
1200
10 15 20 25 5
6
VNIRS-inferred
TOC conc.
(mg L-1)
7 30 35 40 45 1
Di-pH
2
3 15 20 25 30 35 1000 1500 2000 0
C/N
ratio
TN
(%)
TOCsed
(%)
0.05
Zr/Ti
ratio
P
(ppm)
0.1 0
1 0 1 2 3 4 5 6 0
0.5
Diatom conc. P/B diatom
ratio
(valves g-1 dry
sediment x 109 )
Spruce
Pine
10 20 30 0
Population
(inhab. km-2)
Coniferous
woodland
20
40
60
80
100
Pollen-based land use
(%)
Deciduous woodland
Cropland
Grassland
Wetland
Year (AD)
Åbodasjön
Figure 2. Records of VNIRS-inferred lake-water total organic carbon (TOC) concentration, diatom-inferred pH (Di-pH) (horizontal error bars
represent ±1 SD), sediment total organic carbon (TOCsed ) and total nitrogen (TN) content, atomic carbon : nitrogen (C / N) ratio, elemental
phosphorus (P) content, elemental zirconium : titanium (Zr / Ti) ratio, diatom valve concentration, diatom planctonic : benthic (P / B) ratio,
documented population density, and pollen-based land use plotted against age from Åbodasjön (upper panel) and Lindhultsgöl (lower panel).
2000
2000
1950
1950
1900
1900
SO4-S
NH4-N
NOx-N
Year (AD)
Lindhultsgöl
5
10
15
0
1000
2000
500
600
700
800
5
6
7
0
20
40
60
80
100
2000
2000
1950
1950
1900
1900
SO4-S
NH4-N
NOx-N
10
15
20
VNIRS-inferred
TOC conc.
(mg L-1)
25
0
1000
2000
Atm. deposition
(mg m-2 yr-1)
500
600
700
Precipitation
(mm yr-1)
800
5
6
7
Temperature
(Cº)
Spruce
Pine
Coniferous
woodland
0
20
40
60
80
100
Pollen-based land use
(%)
Deciduous woodland
Cropland
Grassland
Wetland
Figure 3. Records of VNIRS-inferred lake-water total organic carbon (TOC) concentration and pollen-based land use since AD 1900 from
Åbodasjön and Lindhultsgöl plotted together with atmospheric sulfur (sulfate SO4 ) and nitrogen (ammonium (NH4 ) and nitrogen oxides
(NOx)) deposition (from the Swedish Environmental Research Institute MAGIC model) and climate data from Växjö (annual precipitation
and temperature expressed as 10-year running averages).
Biogeosciences, 12, 307–322, 2015
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
by spruce, increases from 10 to 30 %. Coniferous and deciduous woodland covers ca. 60 % of the lake catchment today.
RDA was used to describe the major gradients in the limnological data set and relate these patterns to the land-use
variables during the last 800 years. Total woodland cover was
identified as the most significant land-cover factor, explaining a statistically significant 13 %. Other land-cover variables
that were significant when analysed on their own were spruce
and cropland cover, each explaining 12 %; wetland and coniferous woodland, 10 %; and deciduous woodland, 6 %. When
total woodland cover was included in the RDA analysis, deciduous woodland cover could still explain an additional 6 %
of the variation, while no other land-cover parameters were
statistically significant at the P < 0.05 level, as most of the
variation they could explain was captured by the relationship
to total woodland cover.
The ordination results are presented as a so-called triplot
(Fig. 4a) showing the RDA scores for both the palaeolimnological response variables and the selected forcing variables,
as well as the trajectory of down-core sample scores over
time, along the first and second RDA axes. The figure indicates that the VNIRS-inferred TOC concentration along with
sediment TOCsed , C / N and Zr / Ti are all negatively related
with woodland cover, which is correlated with the first RDA
axis (r = 0.71). Deciduous tree cover is negatively correlated
with the second axis (r = −0.55), along with diatom-inferred
pH. Both seem to be negatively correlated with sediment TN.
For the period after AD 1880, five significant drivers were
retained on the basis of forward selection. NH4 deposition
was identified as the main driver and explained 21 % of the
variance, NOx deposition (additional 12 %), 10-year mean
annual precipitation (additional 3 %), sulfur deposition (additional 2 %) and 10-year mean annual temperature (additional
2 %). While some of the land-cover categories had significant
effects if analysed individually, such as deciduous tree cover
(18 %) and grassland cover (14 %), they were less important
than the depositional and climatic parameters, and did not
add significantly to the combined analysis. The RDA plot
(Fig. 4b) indicates that Di-pH is negatively correlated with
sediment TOCsed and VNIRS-inferred TOC, which are both
negatively related to NH4 - and S deposition and positively
related to precipitation.
Lindhultsgöl (Fig. 2): the VNIRS-inferred TOC concentration exhibits high and stable values (21–22 mg L−1 ) at
AD 1200–1500, followed by a small but sudden decrease
to values around 20 mg L−1 . After AD 1780 a gradual decrease was recorded, followed by a substantial decrease in
AD 1900 to minimum values (12 mg L−1 ) around AD 1930.
An increase was recorded at AD 1980, which was accentuated after AD 1990, and reached pre-1900 values in the surface sediments.
Diatom-inferred pH varies between 5.0 and 6.8, with
sample-specific standard errors between 0.31 and 0.47. The
highest value was recorded following an increase around
AD 1250 to above 6 between AD 1300 and 1450. The pewww.biogeosciences.net/12/307/2015/
313
riod between AD 1500 and 1800 shows rather stable values around 5.8. In the 1900s, pH decreases to a minimum
of 5.0 around AD 1960, followed by a slight increase until
AD 2008. The pH reconstruction for Lindhultsgöl was influenced by a few dominating diatom taxa. The high values inferred in the lower parts were associated with the high
abundance of the alkaliphilous (pH > 7) diatom taxon Aulacoseira ambigua (< 60 %), and the low pH in the 1900s was
affected by the dominant acidophilous (pH < 7) taxon Frustulia rhomboides (< 60 %). Inference models are always associated with uncertainties and diatoms may respond to other
variables than pH (Juggins, 2013). Therefore caution is necessary when interpreting the reconstructed pH data. The diatom concentration is high in the 1300s, followed by stable values until around AD 1850, when concentrations decrease. The planktonic diatom taxa vary between 15 and
85 % and the maximum in P / B ratio recorded in the 1300s
was followed by rather stable ratios with a slight increase in
the 1800s. Lowered P / B ratios were recorded after around
AD 1900.
Relatively stable values were recorded for TOCsed content
at ca. AD 1200–1700 and for C / N ratios at ca. AD 1200–
1550, followed by increasing values, peaking in the late
1800s. The total nitrogen (TN) content showed slightly decreasing values until AD 1900. At ca. AD 1900 significant
decreases in both TOCsed content and C / N ratio to minima
in the 1980s to 1990s together with a subsequent increase in
TN content to a coherent maxima in the 1980s were recorded.
This was followed by reversed trends and a coherent increase
after ca. AD 1990–2000 towards the top.
P concentration decreases gradually from the beginning
of the sequence interrupted by a shift to higher values in
the 1400s and thereafter followed by continuous decreasing
concentrations. The onset of AD 1900 is characterized by an
increase in P concentration peaking shortly after AD 1950.
The Zr / Ti ratio shows a peak around AD 1350, following a
gradual increase from ca. AD 1250. After a subsequent decrease, the Zr / Ti ratio increases around AD 1500 to rather
stable values in the AD 1800s, followed by a decrease after
AD 1930.
The woodland (coniferous and deciduous) cover around
Lindhulsgöl varies between 44 and 70 % during the last 800
years. In contrast to Åbodasjön, wetlands cover more than
20 % during most of the period and decreases to less than
10 % after AD 1960. Grassland and cropland varies between
20 and 30 % at AD 1200–1580, followed by an increase to ca.
40 %. During the 1900s, coniferous woodland increases, and
this land-use category covers ca. 50 % of the lake catchment
today.
In the RDA analysis for the last 800 years, the forward
selection for this site showed that spruce cover, the main explanatory variable, explains 20 % of the variance. After its
inclusion in the RDA model, two other variables were found
significant – cropland and wetland covers, explaining 7 % respectively 4 % of additional variance.
Biogeosciences, 12, 307–322, 2015
a)
1.0
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
1.0
314
1610 1570
b)
1988
1993
Zr/Ti
1870
1985
TN
1710
2004
1530
1670
1990
1630
TOCsed
1830
1890 1290
1850
Zr/Ti
1350
1430
C/N 1770
1730
1790 1330
P conc. 1590
1946
1979
1892
1977
1896 1925 1966
1962
TOCsed
1911
1955
C/N 1906
1999
1951
2004 VNIRS-TOC1902
2002 1997
1919 1933
2005
2006
1938
Woodland
-1.0
1950
1250
1750 1910
1887
Di-pH
Temp. 10 y mean
1970
Deciduous
1.5
-1.0
1.0
-1.0
1390
c)
1881
TN
1650
1490
1390
1690 1930
Di-pH
1.0
Precip. 10 y mean 1970 P
-1.0
VNIRS-TOC
S-dep
NH4-dep
NOx-dep
1810
1.5
1981
d)
1989
1990
1770
1890
1810 Di-pH
1910 1410
Zr/Ti
1430
1885
1950
TN
1510
1970
1650
TOCsed 1290
1730
1590 1490
VNIRS-TOC
1470
C/N
1930
1790
1850
1710
1370 1610 1550
Wetland
P
Di-pH
TN
1916
1972
1902
1929
C/N
VNIRS-TOC
2006
2007
1948
TOCsed1937
Zr/Ti
P
1961
Cereals
-1.0
-1.0
1997
2000
Spruce
Cereals
-1.0
S-dep
NH4-dep
Deciduous
1.5
-1.0
1.5
Figure 4. Scores for samples (black circles), palaeolimnological parameters (blue arrows) and driving forces (green arrows) on the first and
second axes of the redundancy analyses for (a) Åbodasjön AD 1200–present, (b) Åbodasjön AD 1880–present, (c) Lindhultsgöl AD 1200–
present and (d) Lindhultsgöl AD 1880–present. Sample ages represent the midpoint of each 20-year time slice.
A triplot showing the first and second RDA axes (Fig. 4c)
indicates that TOCsed , C / N and to a lesser extent VNIRSinferred TOC concentration seem to be positively related to
wetland cover, and negatively with spruce cover along the
first axis. Sediment TN is positively correlated with spruce
cover, while along the second axis sediment P content is correlated with cereal cover.
For the period after AD 1880, the RDA analysis indicates
that cereal cover was the most important driver, alone explaining 28 % of the variation in the palaeolimnological data.
The stepwise forward selection showed that three further
variables could contribute significantly to the explanatory
power of the model, i.e. S deposition (which could explain
an additional 10 % of the variation if included together with
cereal cover), NH4 deposition (5 %) and deciduous tree cover
(3 %). Ten-year mean precipitation has a small significant effect on its own, explaining 14 %, but is not significant once
crop cover was included. No other climate parameter seems
to have an effect at Lindhultsgöl, being overshadowed by the
stronger effect of land use change at this site. The RDA plot
(Fig. 4d) indicates that, like at Åbodasjön, VNIRS-inferred
TOC concentration is negatively related to NH4 - and S deposition. But at this site, TOC and Di-pH seem to be positively related. The sediment TN and P content at this site
Biogeosciences, 12, 307–322, 2015
are positively related to cereal cover and the atmospheric N
deposition.
5
5.1
Discussion
Impacts of land-use changes prior to AD 1900
In Åbodasjön, the highest lake-water TOC concentration was
inferred at the beginning of the record, around AD 1200, and
decreased during the following century, while human impact
increased (Fig. 2). From AD 1260 the pollen record indicates
an agricultural expansion with increased extent of croplands,
meadows and pastures in the catchment (Fig. 2; Fredh et al.,
2014). This expansion probably resulted in increased erosion
and input of coarse lithogenic material, as indicated by elevated Zr / Ti ratios in the sediments. Also, elevated pH and
diatom concentration suggest that more base cations and nutrients were released from the catchment, thereby reflecting
cultural alkalinization (Renberg, 1990; Rosén et al., 2011).
However, despite increased erosion, TOC concentration decreased in the lake water during the 1200s, which may be
explained by decreased woodland cover, which lowered the
terrestrial biomass production, from where a large portion of
the TOC in lake water originates (Rosén et al., 2011).
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
At Lindhultsgöl, increasing anthropogenic impact was
recorded during the 1200s from enhanced Zr / Ti ratios
(Fig. 2) and increased charcoal concentrations (Fredh et al.,
2014), reflecting increased erosion and land clearance by fire,
respectively. During this time, the pH increased from 5.6 to
6.6, which was most likely caused by release of bases and nutrients from burning and grazing in the landscape (Renberg et
al., 1993; Boyle, 2007). Moreover, the diatom concentration
peaked, indicating temporarily enhanced aquatic productivity (cf. Rosén et al., 2011). However, the sediment record
shows only a slight increase of open land, mainly grassland
and cropland, around the lake. The persistently high TOC
concentrations in the lake were probably related to the large
proportion of wetlands within the catchment, as also indicated by the RDA results. High proportions of wetland are
often associated with substantial supplies of DOC to nearby
lakes (Rasmussen et al., 1989; Kortelainen, 1993; Xenopoulos et al., 2003; Mattsson et al., 2007). The lack of response
in lake-water TOC concentration to catchment disturbance
at Lindhultsgöl during the period of increased anthropogenic
impact and potential alkalinization may be related to the unchanged proportion of open land, indicative of stable biomass
production with a continuously high supply of DOC to the
lake.
From ca. AD 1350 there was a reduction of humaninduced catchment disturbance at Åbodasjön, as indicated by
a decline in cropland and grassland cover (Fig. 2), and coniferous woodland, in particular spruce, increased substantially
around AD 1400. This agricultural regression was followed
by decreasing catchment erosion and stabilization of TOC
concentrations in the lake water, an event that may be related to the Black Death pandemic, which struck Sweden in
AD 1350. This was followed by several outbreaks throughout the 1400s, and as much as 60–70 % of the farms in the
region were abandoned (Lagerås, 2007; Myrdal, 2012). At
ca. AD 1450 there was a shift to lower lake-water TOC concentrations, accompanied by decreasing Zr / Ti ratio and diatom concentration. At Lindhultsgöl the regression led to decreases in catchment erosion, inferred pH and diatom concentration from ca. AD 1400 in response to increased cover
of coniferous woodland.
From ca. AD 1450 to 1800 TOC concentrations in Åbodasjön were relatively stable, with only minor variations, despite major changes in land use. Following the increase at
ca. AD 1350, coniferous woodland reached maximum cover
of ca. 50 % around AD 1550, followed by a decrease related
to the onset of a second agricultural expansion in the region
(Lagerås, 2007). The pollen records from both lakes showed
a gradual increase in cropland, meadows and pasture, more
pronounced at Åbodasjön, together with enhanced erosion as
reflected by increasing C / N and Zr / Ti ratios.
A substantial increase in lake-water TOC concentration
was inferred at Åbodasjön from ca. AD 1800, peaking at
AD 1860–1900, simultaneously with a substantial increase in
population density (Fig. 2). The increase in rural population
www.biogeosciences.net/12/307/2015/
315
led to increased demands for land for crop cultivation, meadows and grazing, and areas previously regarded as less suitable for agriculture were cleared and drained (Myrdal, 1997).
The pollen record shows a dominance of open-land taxa,
and the open-land cover, predominantly grassland, reached
a maximum of ca. 60 %. The RDA plot (Fig. 4a) also reflects that both total and deciduous woodland cover reached
minimum values around this time. These changes were accompanied by maximum C / N ratios and TOCsed values, reflecting an elevated input of terrestrial organic matter to the
lake. From ca. AD 1700 improvements of the agrarian management in Sweden enhanced food productivity through a
number of reforms, such as land divisions, crop rotation, irrigation, marling and better management of manure and urine
(Emanuelsson, 2009). The introduction of agriculture in lake
catchments, even at low proportions, is commonly associated
with elevated DOC export and lake-water DOC concentrations (Correll et al., 2001; McTiernan et al., 2001; Mattsson et al., 2005). In contrast to the decrease in the inferred
TOC concentrations in response to the early agricultural expansion, the new agricultural management in the 1800s improved organic productivity through the application of manure and fertilizers, leading to increased leaching of DOC
to the lake water (cf. McTiernan et al., 2001). These agricultural reforms, in combination with the general increase in
land-use pressure, may hence explain the substantial increase
in the inferred TOC concentration at Åbodasjön.
At Lindhultsgöl broadly similar trends in C / N ratio and
TOCsed from the late 1700s to ca. AD 1900 as compared to
Åbodasjön suggest increased land-use pressure and disturbance within the lake catchment. Coniferous woodland decreased, especially after AD 1800 and was partly replaced
by deciduous woodland, indicating increased logging and expanding semi-open grazing areas. However, the high proportion of wetlands made the catchment less suitable for crop
cultivation and resulted in a strikingly different development
as compared to Åbodasjön. In the more marginal, forestdominated area around Lindhultsgöl the increase in anthropogenic impact resulted in an increase in pH and a corresponding decrease in TOC concentration in the lake around
AD 1800, probably reflecting decreased catchment biomass
in a gradually more open woodland.
5.2
Forcing mechanisms during the last century
Around AD 1900 pronounced decreases in TOC concentrations were recorded in both of the study lakes (Figs. 2, 3).
At Åbodasjön the decrease was slightly more gradual, reaching minimum values in the 1980s, while the inferred values at Lindhultsgöl declined rapidly to a sequence minimum
around AD 1940 (Fig. 3). At AD 1980–1990 increasing
trends were initiated at both lakes. These inferred variations
in TOC concentration during the last century are in general
inversely correlated with historically documented trends in
sulfur deposition regionally in southern Sweden (Fig. 3), and
Biogeosciences, 12, 307–322, 2015
Liming
Ditching
Modern forestry
Agrarian intensity
TOC conc.
(mg L-1)
14
Catchment-scale Regional
forcing
forcing
vvv
Liming
Ditching
Modern forestry
Agrarian intensity
Sulfur dep.
Precipitation
Temperature
v v v v
Sulfur dep.
Precipitation
Temperature
Åbodasjön
Åbodasjön
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Catchmen -scale Regional
forcing
forcing
316
12
10
8
6
22
16
Lindhultsgöl
18
TOC conc.
(mg L-1)
20
1200
1300
1400
1500
1600
1700
1800
1900
Agrarian intensity
Modern forestry
Ditching
Liming
Catchment-scale
forcing
12
Agrarian intensity
Modern forestry
Ditching
Liming
v v v
Catchment-scale
forcing
Lindhultsgöl
14
2000
Year (AD)
Figure 5. Records of VNIRS-inferred lake-water total organic carbon (TOC) concentration from Åbodasjön (upper graph) and Lindhultsgöl
(lower graph) in the perspective of possible regional and catchment-scale forcings of TOC changes. Regional forcings include sulfur deposition, precipitation and temperature (Fig. 3). Local forcings include site-specific liming history, regional trends in ditching (Hånell, 2009)
and changes in land use inferred from pollen data (Fig. 2) and historical accounts (agrarian intensity and modern forestry). Horizontal lines
represent periods of activity, thick lines represent periods of increase or high intensity, and dashed lines represent periods of decrease or low
intensity. Arrows indicate ongoing processes. The star marks a major drainage effort undertaken at the inlet of Åbodasjön in AD 1922. The
vertical dashed lines represent AD 1900. Note the different scale for the period AD 1900–2010.
the RDA data also indicate that sulfur deposition is among
the significant drivers of limnological changes in both lakes
since AD 1880. Sulphur deposition started to increase at the
onset of industrialization at the end of the 1800s, which led to
acidification of soils and surface waters across large parts of
Europe (Rohde et al., 1995). Thereafter, sulfur deposition increased significantly in the 1940s, peaking at AD 1980–1995
(Schöpp et al., 2003), followed during recent decades by progressively decreasing deposition and widespread recovery
from acidification through decreasing sulfate concentrations
in lakes and streams throughout Europe and North America
(Evans et al., 2001, Skjelkvåle et al., 2003). The timing of
this recovery is largely consistent with the increasing TOC
concentrations in our two study lakes (Fig. 3) as well as with
a study of TOC trends in Swedish rivers (Erlandsson et al.,
2010). The deposition of nitrogen oxides, which also contribute to acidification, also showed a dramatic increase during the 1900s, with deposition peaking slightly later than for
sulfur deposition, around AD 1990 (Fig. 3). In addition to
contributing to acidification, deposition of nitrogen, both in
the form of nitrogen oxides and ammonia, may contribute to
eutrophication, and therefore can have an impact on limnic
ecosystems. It has also been suggested that the response of
soil microbial activity to nitrogen deposition may affect the
export of humic matter to freshwaters (Findlay, 2005). Our
analysis indicates that nitrogen deposition was among the
Biogeosciences, 12, 307–322, 2015
most significant drivers of change in the palaeolimnological
record over the last century together with sulfur deposition.
Increases in lake-water DOC concentration have been
linked to increased solubility of soil organic matter in response to declining acid deposition (Evans et al., 2006; Monteith et al., 2007), and, conversely, elevated sulfur deposition usually results in reduced transport of soil organic matter. In our lakes, declining VNIRS-inferred TOC concentrations were accompanied by decreasing C / N ratios, which
suggests a reduction of terrestrial organic matter deposition with increased acid deposition. Decreasing values of inferred pH from the late 1800s to minimum values around
AD 1960 at Lindhultsgöl also provide evidence of the acidification history. Although the diatom-based pH reconstruction
indicates continued acidification until the 1960s, the minimum in VNIRS-inferred TOC concentration was reached already around AD 1940, a few decades before sulfur deposition peaked. This may be explained by the high proportion of wetlands in the catchment of Lindhultsgöl. Evans et
al. (2012) showed that already acidic soils may exhibit limited responses to enhanced acid deposition as DOC leaching
stabilizes at a certain pH, below which no further decrease in
DOC concentration occurs.
Despite the general negative correlation between sulfur deposition and inferred TOC concentration at our study sites,
major changes in land use during the last century may also
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
have had important effects on DOC export to the lakes. The
onset of industrialization in the late 1800s led to urbanization
and the documented decrease in rural population. Traditional
types of land use were abandoned, in particular meadows and
pastures, which were typically converted into spruce plantations and cultivated fields (Antonsson and Jansson, 2011).
This development is clearly reflected in our pollen records as
concomitant decreases in grassland and increases in coniferous woodland cover in the 1900s (Fig. 3). This land-use
change is most pronounced at Lindhultsgöl, where grassland,
cropland and wetland cover are reduced at the expense of
woodland, and the RDA indicates a significant effect of especially the cereal cover reduction at this site. A significant
reduction of the supply of terrestrial organic matter, as indicated by decreasing C / N ratios at both lakes, may be partly
explained by the increase in sulfur deposition, which suppressed leaching of soil organic matter. However, reduced
catchment erosion may also have been a direct effect of stabilization of previously disturbed soils following the rural
population decrease and woodland succession. At the transition to commercial forestry and crop cultivation around
AD 1900, new management practices with possible effects
on lake-water TOC concentration, such as ditching, drainage
and clear-cut harvesting, were introduced. However, ditching and drainage of forests and crop cultivations may involve complex responses of surface-water DOC concentrations, as some studies report increases (Ecke, 2008), while
others provide evidence of decreases (Åström et al., 2001;
McTiernan et al., 2001). In Sweden, ditching and drainage
operations started in the late 1800s, with substantial increases
from AD 1900 to the 1930s (Hånell et al., 2009). A major
artificial deepening of the inlet stream at Åbodasjön in the
early 1920s resulted in enhanced export of lithogenic material from the adjacent croplands for a few decades (Bragée
et al., 2013). The interruption of decreasing TOC concentrations in the lake at ca. AD 1920–1960 (Fig. 3) was possibly reinforced by increased supply of soil-derived DOC
through enhanced export from the inlet surroundings. Crop
cultivation along the inlet was abandoned in the 1950s, which
led to decreased supply of lithogenic material (Bragée et al.,
2013) and an accelerated decrease in TOC concentration in
the lake. Previous studies have attributed variations in the release of DOC to surface waters to changing forestry practices, and clear cutting can significantly affect stream-water
DOC levels in boreal forests (Lepistö et al., 2008; Laudon
et al., 2009). Considering the increased areal distribution of
woodland and forestry activities within the catchments during the last century, this may constitute a potential source
of increased DOC supply. Given the increase in the extent
of clear cuts between AD 1946 and 2005, from 1 to 20 % of
the modelled land-use area at Åbodasjön and from 0 to 13 %
at Lindhultsgöl (Mazier et al., 2014), this process may have
contributed to the elevated TOC concentrations in the lakes
in the 1990s. However, ditching and clear-cutting probably
result in only temporary increases in the supply of DOC, afwww.biogeosciences.net/12/307/2015/
317
fecting at least the following growth season (Laudon et al.,
2009) and may therefore be difficult to distinguish in palaeolimnological records.
The increase in VNIRS-inferred TOC concentration at
both lakes around AD 1990 is most likely linked to the recovery from acidification. The low sample resolution in the uppermost parts of the diatom records precludes detailed evaluation of recent changes in pH in response to decreased sulfur deposition, although the slight increase in the uppermost
part of the record from Lindhultsgöl indicates a recent recovery. However, pH is not a straightforward measure of recovery from acidification (Skjelkvåle et al., 2003; SanClements
et al., 2012), and the inconsistent responses in our records
may be explained by the contemporary increase in lake-water
TOC concentration as organic acids usually have an acidifying effect (Evans et al., 2001). Soil conditions are important
for the solubility of organic matter, and the high proportion of
coniferous woodland at both lakes and wetlands at Lindhultsgöl, typically associated with organic-rich soils, may have induced increased leaching of DOC in response to decreasing
sulfur deposition during recent decades (Evans et al., 2012).
Site-specific catchment soil properties may therefore be important for explaining the observed increases in TOC concentration in our study lakes after AD 1990 compared to other
lakes in the region that show unchanged or even decreasing trends in DOC concentration (von Einem and Granéli,
2010). In addition, wetland areas in the catchments of both
lakes have been treated by liming on a yearly basis to mitigate acidification, starting in AD 1984 at Åbodasjön and in
AD 1993 at Lindhultsgöl, which may have contributed to the
effects of declining sulfur deposition by accelerated leaching
of DOC to the lakes (cf. Hindar et al., 1996).
In addition to changes in sulfur deposition and land management practices, climate may affect DOC concentration
of lake waters through a variety of processes, including
temperature-driven soil organic productivity and decomposition as well as precipitation-driven water table fluctuations
and transport of organic carbon from terrestrial soils (e.g.
Sobek et al., 2007). Increases in precipitation and temperature have been brought forward as potential causes of observed increases in DOC concentration in lake waters during the last three decades in several studies (Freeman et al.,
2001; Hongve et al., 2004; Sarkkola et al., 2009). Future climate predictions for northern Europe include higher seasonal
amounts and intensity of precipitation, as well as increasing
mean annual air temperatures (Alcamo et al., 2002), which
may result in continued increases in DOC export to lake waters (Larsen et al., 2010). Available meteorological data from
Växjö (Fig. 1), reaching back to AD 1860, show an increase
in annual precipitation from ca. AD 1980 and an increase in
mean annual temperature from ca. AD 1990 (Fig. 3). Hence,
climate change may have contributed to the observed and reconstructed increases in lake-water TOC concentration over
recent decades, and the RDA data indicate that, at least at
Åbodasjön, both precipitation and temperature have had an
Biogeosciences, 12, 307–322, 2015
318
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
impact on the lake over the last century, while these effects
seem to be less important at Lindhultsgöl. A possible explanation may be the larger catchment of Åbodasjön, making it
more sensitive to changes in run-off, erosion and transport
of terrestrial organic matter. The large proportion of wetland around Lindhultsgöl may also have a dampening effect on increased precipitation. At Lindhultsgöl, changes in
land use have played a more important role at the centennial
timescale. Changes in sulfur deposition during the last century have been a main driver for limnological change at both
sites, despite their different land use and catchment characteristics (Figs. 3, 4), which supports the interpretation that
this is a key factor behind the regional changes observed in
lake-water TOC concentrations. This demonstrates the importance of applying a long-term perspective on lake-water
DOC dynamics in order to differentiate between causal relationships.
5.3
Recent brownification and future implications
Our reconstructions indicate that TOC concentrations in the
lakes were generally high during the past eight centuries,
reaching similar or higher concentrations than those observed during recent decades. Commonly, there is a correlation between water colour (usually measured as absorbance
at ca. 420–436 nm or using the platinum scale) and DOC concentration in lake waters. However, colour is strongly influenced by the composition of DOC, and a recent study has
demonstrated that declining acidification in southern Sweden has led to increased leaching from soils of mobile, hydrophobic and aromatic DOC that contains relatively large
and strongly coloured molecular compounds (Ekström et al.,
2011). Moreover, iron has a strong influence on water colour,
and elevated iron concentrations have been observed with the
recent brownification in the UK (Neal et al., 2008) as well
as in Sweden (Huser et al., 2011; Kritzberg and Ekström,
2012). Therefore, the VNIRS-inferred changes in TOC concentration in our two study lakes may not necessarily reflect
changes in colour, although monitoring data from Åbodasjön
indicate that this was indeed the case during recent decades
(County Administrative Board of Kronoberg, unpublished
data), consistent with increases in water colour observed in
several other lakes in the study region. This is supported by
high abundances of the diatom Aulacoseira tenella (> 20 %)
in surface sediments from Åbodasjön, a species often associated with high DOC concentrations and strongly coloured
lake waters (Huttunen and Turkia, 1994).
In contrast, the elevated TOC concentrations recorded in
Åbodasjön during the late 1800s were most likely not associated with a corresponding increase in water colour, as indicated by unchanged diatom planktonic : benthic (P / B) ratios. Benthic and planktonic diatom communities are likely
to respond to changes in the input of terrestrial organic matter through associated effects on the transparency of the water column, as the benthic community is primarily limited
Biogeosciences, 12, 307–322, 2015
by light in nutrient-poor lakes (Rosén et al., 2009; Karlsson
et al., 2009). At this site, the pronounced increase in agricultural intensity in the late 1800s probably resulted in enhanced
export of DOC compounds with relatively low molecular
weights, which are typically associated with agriculture (cf.
Cronan et al., 1999; Dalzell et al., 2011). A dominance of
this type of DOC would not result in any significant increase
in water colour as DOC derived from agricultural areas is
in general structurally less complex and less coloured than
DOC from forest soils (Wilson and Xenopoulos, 2009).
The early agricultural expansion in the 1200s resulted in
a change in the diatom community towards elevated P / B
ratios and a dominance of planktonic taxa typically favoured
by high pH (Fig. 2). Hence, this diatom response to increased
nutrient transport to the lake was most likely associated with
early land use and not with any major increase in water
colour caused by increased input of terrestrial organic carbon.
At Lindhultsgöl, minimum P / B ratios were recorded during the period of maximum sulfur emissions at AD 1950–
1990, which indicates a decrease in water colour associated
with the corresponding minima in inferred lake-water TOC
concentration and pH.
Based on our results we can conclude that the increases in
TOC concentration and water colour in our study lakes during the past three decades have been driven mainly by declining atmospheric sulfur deposition. This suggests a recovery
from the phase of maximum sulfur emissions, which resulted
in exceptionally low TOC concentrations in the lakes at ca.
AD 1930–90. The RDA data obtained from the palaeolimnological records over the period since AD 1880 also indicate
a recovery. At both sites, the temporal development of the
RDA scores during this period (Fig. 4b and d) show that the
youngest samples fall near the oldest, indicating a return to
pre-industrial conditions, following a time of highly anomalous conditions. At Åbodasjön, there was first a period of
low inferred lake-water TOC concentration and high pH in
the 1930s–1960s, followed by decreasing pH but high Zr / Ti
ratios (perhaps indicating enhanced erosion) in the 1980s and
early 1990s, and then increasing lake-water TOC concentration and low Zr / Ti ratios towards the present. At Lindhultsgöl, the temporal development of the RDA scores also illustrates a partial recovery with similar scores, especially on the
first axis, for young and old samples, while the period 1930–
1980 was characterized by high first axis scores, associated
with sedimentary indicators of low pH and VNIRS-inferred
TOC concentration, while the driving forces were characterized by high sulfur and nitrogen deposition values and relatively high cereal cover in the catchment.
Our long-term records demonstrate that the TOC concentrations of the study lakes were strongly influenced by
changes in agricultural practices, general land-use pressure,
and associated variations in forest cover during the last 800
years (Fig. 5). The historical differences in the extent of
agricultural activity at the sites establish that site-specific
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
catchment characteristics and land-use dynamics are of great
importance for lake-water DOC variations. The recently initiated increase in TOC concentration in the lakes may continue in the near future depending on the quantity of organic
carbon stored in catchment soils due to suppression of DOC
leaching during the acidification episode. However, the recovery of lake-water TOC concentrations has now reached
levels that are comparable to the situation before the onset of
20th century acidification, which may lead to a levelling-off
of the increasing trend. Given the reduction of atmospheric
sulfur emissions during recent decades, it is likely that previously suppressed or masked effects of changes in land management and climate during the last century will become progressively more important drivers of lake-water DOC concentrations in the future.
The Supplement related to this article is available online
at doi:10.5194/bg-12-307-2015-supplement.
Acknowledgements. This work was funded by the Swedish
Research Council Formas (grant to W. Granéli). The authors are
grateful to Shinya Sugita for input on the quantitative vegetation
reconstructions, and Sofia Holmgren, Linda Randsalu-Wendrup
and Christian Bigler for helpful support with diatom preparation
and categorization. We are very grateful to all members of the
NordForsk network LANDCLIM (coordinated by M. J. Gaillard,
Linnaeus University, Sweden) for useful and inspiring discussions
during the numerous workshops (2009–2011). We acknowledge
the Swedish Meteorological Institute (SMHI) for precipitation
and temperature data, and the Swedish Environmental Research
Institute and MAGIC for sulfur and nitrogen deposition data.
Constructive comments by the reviewers improved the final
presentation.
Edited by: C. P. Slomp
References
Alcamo, J., Mayerhofer, P., Guardans, R., van Harmelen, T., van
Minnen, J., Onigkeit, J., Posch, M., and de Vries, B.: An integrated assessment of regional air pollution and climate change in
Europe: findings of the AIR-CLIM Project, Environ. Sci. Policy,
5, 257–272, 2002.
Alexandersson, H., Karlström, C., and Larsson-McCann, S.: Temperature and precipitation in Sweden, 1961–90, Reference normals, SMHI report 81, SMHI, Norrköping, 1991.
Andersson Palm, L.: Folkmängden i Sveriges socknar och kommuner 1571–1997, Books-on-Demand, Göteborg, 385 pp., 2000.
Antonsson, H. and Jansson, U. (Eds.): Agriculture and forestry in
Sweden since 1900, The Royal Swedish Academy of Agriculture
and Forestry, Stockholm, pp. 512, 2011.
Armstrong, A., Holden, J., Kay, P., Francis, B., Foulger, M., Gledhill, S., McDonald, A. T., and Walker, A.: The impact of peatland
www.biogeosciences.net/12/307/2015/
319
drain-blocking on dissolved organic carbon loss and discolouration of water; results from a national survey, J. Hydrol., 381, 112–
120, 2010.
Arvola, L., Rask, M., Ruuhijärvi, J., Tulonen, T., Vuorenmaa, J.,
Ruoho-Airola, T., and Tulonen, J.: Long-term patterns in pH and
colour in small acidic boreal lakes of varying hydrological and
landscape settings, Biogeochemistry, 101, 269–279, 2010.
Åström, M., Aaltonen, E.-K., and Koivusaari, J.: Effect of ditching
operations on stream-water chemistry in a boreal forested catchment, Sci. Total Environ., 279, 117–129, 2001.
Bade, D. L., Carpenter, S. R., Cole, J. J., Pace, M. L., Kritzberg,
E., Van de Bogert, M. C., Cory, R. M., and McKnight, D. M.:
Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions, Biogeochemistry,
84, 115,-129, 2007.
Battarbee, R. W. and Kneen, M. J.: The use of electronically
counted microspheres in absolute diatom analysis, Limnol.
Oceanogr. 27, 184–188, 1982.
Battarbee, R. W., Jones, V. J., Flower, R. J., Cameron, N. G., Bennion, H., Carvalho, L., and Juggins, S.: Diatoms, in: Tracking environmental change using lake sediments, Volume 3: terrestrial,
algal and siliceous indicators, edited by: Smol, J. P., Birks, H.
J. B., and Last, W. M., Kluwer Academic, Dortrecht, 155–202,
2001.
Boyle, J. F.: Rapid elemental analysis of sediment samples by isotope source XRF, J. Paleolimnol., 23, 213–221, 2000.
Boyle, J. F.: Loss of apatite caused irreversible early-Holocene lake
acidification, The Holocene, 17, 543–547, 2007.
Bragée, P., Choudhary, P., Routh, J. Boyle, J. F., and Hammarlund,
D.: Lake ecosystem responses to catchment disturbance and airborne pollution: an 800-year perspective in southern Sweden, J.
Paleolimnol., 50, 545–560, 2013.
Clark, J. M., Bottrell, S. H., Evans, C. D., Monteith, D. T., Bartlett,
R., Rose, R., Newton, R. J., and Chapman, P. J.: The importance
of the relationship between scale and process in understanding
long-term DOC dynamics, Sci. Total Environ., 408, 2768–2775,
2010.
Cole, J. J., Prairie, Y. T., Caraco, N. F., McDowell, W. H., Tranvik,
L. J., Striegl, R. G., Duarte, C. M., Kortelainen, P., Downing J.
A., Middelburg, J. J., and Melack, J.: Plumbing the global carbon
cycle: integrating inland waters into the terrestrial carbon budget,
Ecosystems, 10, 172–185, 2007.
Correll, D. L., Jordan, T. E., and Weller, D. E.: Effects of precipitation, air temperature, and land use on organic carbon discharges
from Rhode River watersheds, Water Air Soil Poll., 128, 139–
159, 2001.
Cronan, C. S., Piampiano, J. T., and Patterson, H. H.: Influence of
Land Use and Hydrology on Exports of Carbon and Nitrogen in
a Maine River Basin, J. Environ. Qual., 28, 953–961, 1999.
Cunningham, L., Bishop, K., Mettävainio, E., and Rosén, P.: Paleoecological evidence of major declines in total organic carbon
concentrations since the nineteenth century in four nemoboreal
lakes, J. Paleolimnol., 45, 507–518, 2011.
Dalzell, B. J., King, J. Y., Mulla, D. J., Finlay, J. C., and Sands, G.
R.: Influence of subsurface drainage on quantity and composition
of dissolved organic matter export from agricultural landscapes,
J. Geophys. Res., 116, G02023, doi:10.1029/2010JG001540,
2011.
Biogeosciences, 12, 307–322, 2015
320
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Daniel, E.: Beskrivning till jordartskartan 5E Växjö NV, K 168
Sveriges Geologiska Undersökning (SGU), 77 pp., 2009.
Diehl, S., Berger, S., Ptacnik, R., and Wild, A.: Phytoplankton,
light, and nutrients in a gradient of mixing depths: field experiments, Ecology, 83, 399–411, 2002.
Ecke, F.: Drainage ditching at the catchment scale affects water
quality and macrophyte occurrence in Swedish lakes, Freshwater
Biol., 54, 119–126, 2008.
Ekström, S. M., Kritzberg, E. S., Kleja, D. B., Larsson, N., Nilsson,
P. A., Graneli, W., and Bergkvist, B.: Effect of acid deposition
on quantity and quality of dissolved organic matter in soil–water,
Environ. Sci. Technol., 45, 4733–4739, 2011.
Emanuelsson, U. (Ed.): The rural landscapes of Europe: how man
has shaped European nature, Swedish Research Council Formas,
Stockholm, Sweden, pp. 384, 2009.
Engstrom D. R. and Wright H. E. J.: Chemical stratigraphy of lake
sediments as a record of environmental change, in: Lake Sediments and Environmental History, edited by: Haworth E. Y. and
Lund J. W. G., Leicester University Press, Bath, 11–68, 1984.
Erlandsson, M., Buffam, I., Fölster, J., Laudon, H., Temnerud, J.,
Weyhenmeyer, G. A., and Bishop, K.: Thirty-five years of synchrony in the organic matter concentrations of Swedish rivers explained by variation in flow and sulphate, Global Change Biol.,
14, 1191–1198, 2008.
Erlandsson, M., Cory, N., Köhler, S., and Bishop, K.: Direct and
indirect effects of increasing dissolved organic carbon levels on
pH in lakes recovering from acidification, J. Geophys. Res., 115,
G03004, doi:10.1029/2009JG001082, 2010.
Evans, C. D., Cullen, J. M., Alewell, C., Kopácek, J., Marchetto, A.,
Moldan, F., Prechtel, A., Rogora, M., Vesely, J., and Wright, R.:
Recovery from acidification in European surface waters, Hydrol.
Earth Syst. Sc., 5, 283–298, 2001.
Evans, C. D., Monteith, D. T., and Cooper, D. M.: Long-term
increases in surface water dissolved organic carbon: Observations, possible causes and environmental impacts, Environ. Pollut., 137, 55–71, 2005.
Evans, C. D., Chapman, P. J., Clark, J. M., Monteith, D. T., and
Cresser, M. S.: Alternative explanations for rising dissolved organic carbon export from organic soils, Glob. Change Biol., 12,
2044–2053, 2006.
Evans, C. D., Jones, T. G., Burden, A., Ostle, N., Zieliński, P.,
Cooper, M. D., Peacock, M., Clark, J. M., Oulehle, F., Cooper,
D., and Freeman, C.: Acidity controls on dissolved organic carbon mobility in organic soils, Glob. Change Biol., 18, 3317–
3331, 2012.
Findlay, S. E.: Increased carbon transport in the Hudson River: unexpected consequence of nitrogen deposition?, Front. Ecol. Environ., 3, 133–137, 2005.
Fredh, D., Broström, A., Rundgren, M., Lagerås, P., Mazier, F., and
Zillén, L.: The impact of land-use change on floristic diversity
at regional scale in southern Sweden 600 BC–AD 2008, Biogeosciences, 10, 3159–3173, doi:10.5194/bg-10-3159-2013, 2013.
Fredh, D., Mazier, F., Bragée, P., Lagerås, P., Rundgren M., Hammarlund, D., and Broström, A.: The effect of local land-use on
floristic diversity during the past 1000 years in southern Sweden,
The Holocene, submitted, 2014.
Freeman, C., Evans, C. D., Monteith, D. T., Reynolds, B., and Fenner, N.: Export of organic carbon from peat soils, Nature, 412,
785, 2001.
Biogeosciences, 12, 307–322, 2015
Granéli, W.: Brownification of Lakes, in:. Encyclopedia of Lakes
and Reservoirs, edited by: Bengtsson, L., Herschy, R. W., and
Fairbridge, R. W., Springer Science, New York, 117–119, 2012.
Gustafsson, L.: Geographical classifications of plants and animals,
in:, National Atlas of Sweden, Geography of plants and animals,
edited by: Gustafsson, L. and Ahlén, I., SNA publishing, Stockholm, 25–28, 1996.
Haaland, S., Hongve, D., Laudon, H., Riise, G., and Vogt, R. D.:
Quantifying the drivers of the increasing colored organic matter
in boreal surface waters, Environ. Sci. Technol., 44, 2975–2980,
2010.
Hånell, B.: Möjlighet till höjning av skogsproduktionen i Sverige
genom dikesrensning, dikning och gödsling av torvmarker, in:
Skogsskötsel för ökad tillväxt, edited by: Fahlvik, N., Johansson, U., and Nilsson, U., Faktaunderlag till MINT-utredningen,
SLU, Rapport, Bilaga 4, 1–28, 2009.
Hindar, A., Kroglund, F., Lydersen, E., Skiple, A., and Høgberget,
R.: Liming of wetlands in the acidified Lake Røynelandsvatn
catchment in southern Norway: effects on stream water chemistry, Can. J. Fish. Aquat. Sci., 53, 985–993, 1996.
Hongve, D., Riise, G., and Kristiansen, J.: Increased colour and organic acid concentrations in Norwegian forest lakes and drinking
water – a result of increased precipitation?, Aquat. Sci. 66, 231–
238, 2004.
Huser, B. J., Köhler, S. J., Wilander, A., Johansson, K., and Fölster,
J.: Temporal and spatial trends for trace metals in streams and
rivers across Sweden (1996–2009), Biogeosciences, 8, 1813–
1823, doi:10.5194/bg-8-1813-2011, 2011.
Huttunen, P. and Turkia J.: Diatoms as indicators of alkalinity and
TOC in lakes: Estimation of optima and tolerances by weighted
averaging, in: Proceedings of the 11th International Diatom Symposium, San Francisco, U.S.A., 12–17 August 1990, Memoirs of
the California Academy of Sciences, No 17, edited by: Kociolek
J. P., 649–658, 1994.
Juggins, S.: Quantitative reconstructions in palaeolimnology: new
paradigm or sick science?, Quaternary Sci. Rev., 64, 20–32,
2013.
Juggins, S. and Birks, H.J.B.: Quantitative environmental reconstructions from biological data, in: Tracking environmental
change using lake sediments, Volume 5: data handling and numerical techniques, edited by: Birks, H. J. B„ Lotter, A. F., Juggins, S., and Smol, J. P., Springer, Dordrecht, 431–494, 2012.
Karlsson, J., Bystrom, P., Ask, J., Ask, P., Persson, L., and Jansson,
M.: Light limitation of nutrient-poor lake ecosystems, Nature,
460, 506–509, 2009.
Koinig, K. A., Shotyk, W., Lotter, A. F., Ohlendorf, C., and Sturm,
M.: 9000 years of geochemical evolution of lithogenic major and
trace elements in the sediment of an alpine lake–the role of climate, vegetation, and land-use history, J. Paleolimnol., 30, 307–
320, 2003.
Kortelainen, P.: Content of total organic carbon in Finnish lakes and
its relationship to catchment characteristics, Can. J. Fish. Aquat.
Sci., 50, 1477–1483, 1993.
Krammer, K.: Pinnularia: Eine Monographie der Europäischen
Taxa, Bibliotheca Diatomologica, Vol. 26, Cramer J. Gebrüder
Borntraeger Verlag, Berlin/Stuttgart, pp. 353, 1992.
Krammer, K. and Lange-Bertalot, H.: Bacillariophyceae, 1. Naviculaceae, in: Süsswasserflora von Mitteleuropa, Vol. 2, edited by:
www.biogeosciences.net/12/307/2015/
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
Ettl, H., Gärtner, G., Gerloff, J., Heynig, H., and Mollenhauer D.,
Gustav Fischer Verlag, Stuttgart, pp. 876, 1986.
Krammer, K. and Lange-Bertalot, H.: Bacillariophyceae, 2. Bacillariaceae, in: Süsswasserflora von Mitteleuropa, Vol. 2, edited by:
Ettl, H., Gärtner, G., Gerloff, J., Heynig, H., and Mollenhauer D.,
Gustav Fischer Verlag, Stuttgart, pp. 596, 1988.
Krammer, K. and Lange-Bertalot, H.: Bacillariophyceae, 3. Centrales, Fragilariaceae, Eunotiaceae, in: Süsswasserflora von Mitteleuropa, Vol. 2, edited by: Ettl, H., Gärtner, G., Gerloff, J.,
Heynig, H., and Mollenhauer D. (Eds.), Gustav Fischer Verlag,
Stuttgart, pp. 576, 1991a.
Krammer, K. and Lange-Bertalot, H.: Bacillariophyceae, 4.
Achnanthaceae, Kritische Ergänzungen zu Navicula (Lineolatae)
und Gomphonema, in: Süsswasserflora von Mitteleuropa, Vol. 2,
edited by: Ettl, H., Gärtner, G., Gerloff, J., Heynig, H., and Mollenhauer D., Gustav Fischer Verlag, Stuttgart, pp. 437, 1991b.
Kritzberg, E. S. and Ekström, S. M.: Increasing iron concentrations in surface waters – a factor behind brownification?, Biogeosciences, 9, 1465–1478, doi:10.5194/bg-9-1465-2012, 2012.
Lagerås, P.: The ecology of expansion and abandonment-Medieval
and post-medieval land-use and settlement dynamics in a landscape perspective, National Heritage Board, Stockholm, pp. 256,
2007.
Lange-Bertalot, H. and Krammer, K.: Achnanthes, eine Monographie der Gattung: mit Definition der Gattung Cocconeis und
Nachträgen zu den Naviculaceae, Bibliotheca Diatomologica,
Vol. 18, Cramer J. Gebrüder Borntraeger Verlag, Berlin/Stuttgart,
pp. 393, 1989.
Larsen, S., Andersen, T. O. M., and Hessen, D. O.: Climate change
predicted to cause severe increase of organic carbon in lakes,
Global Change Biol., 17, 1186–1192, 2010.
Laudon, H., Hedtjärn, J., Schelker, J., Bishop, K., Sørensen, R.,
and Ågren, A.: Response of Dissolved Organic Carbon following Forest Harvesting in a Boreal Forest, AMBIO, 38, 381–386,
2009.
Ledesma, J. L. J., Köhler, S. J., and Futter, M. N.: Long-term dynamics of dissolved organic carbon: Implications for drinking
water supply, Sci. Total Environ., 432, 1–11, 2012.
Lepistö, A., Kortelainen, P., and Mattsson, T.: Increased organic C
and N leaching in a northern boreal river basin in Finland, Global
Biogeochem. Cy., 22, GB3029, doi:10.1029/2007GB003175,
2008.
Löfgren, S., Forsius, M., and Andersen, T.: The color of water – climate induced water color increase in Nordic lakes and streams
due to humus, Nordic council of Ministers brochure, Copenhagen, pp. 12, 2003.
Mattsson, T., Kortelainen, P., and Räike, A.: Export of DOM from
boreal catchments: impacts of land use cover and climate, Biogeochemistry, 76, 373–394, 2005.
Mattsson, T., Kortelainen, P., Lepistö, A., and Räike, A.. Organic
and minerogenic acidity in Finnish rivers in relation to land use
and deposition, Sci. Total Environ., 383, 183–192, 2007.
Mazier, F., Broström, P., Bragée, P., Fredh, D., Stenberg, L., Thiere,
G., Sugita, S., and Hammarlund, D.: Two hundred years of landuse change in South Swedish Uplands: comparison of historical
map-based estimates with pollen-based reconstruction using the
Landscape Reconstruction Algorithm, Rev. Palaeobot. Palyno.,
in press, 2014.
www.biogeosciences.net/12/307/2015/
321
McDonald, S., Bishop, A. G., Prenzler, P. D., and Robards, K.: Analytical chemistry of freshwater humic substances, Anal. Chim.
Ac., 527, 105–124, 2004.
McTiernan, K. B., Jarvis, S. C., Scholefield, D., and Hayes, M. H.
B.: Dissolved organic carbon losses from grazed grasslands under different management regimes, Water Res., 35, 2565–2569,
2001.
Meyers, P. A. and Lallier-Verges, E.: Lacustrine sedimentary organic matter records of Late Quaternary paleoclimates, J. Paleolimnol., 21, 345–372, 1999.
Monteith, D. T., Stoddard, J. L., Evans, C. D., De Wit, H. A., Forsius, M., Hogasen, T., Wilander, A., Skjelkvale, B. L., Jeffries,
D. S., Vuorenmaa, J., Keller, B., Kopacek, J., and Vesely, J.:
Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry, Nature, 450, 537–540, 2007.
Myrdal, J.: En agrarhistorisk syntes, in: Agrarhistoria, edited by:
Larsson, B. M. P., Morell, M., and Myrdal, J., LTs Förlag, Stockholm, 302–322, 1997.
Myrdal, J.: Scandinavia, in: Agrarian change and crisis in Europe,
1200–1500, edited by: Kitsikopoulos, H., Routledge, New York,
204–249, 2012.
Neal, C., Lofts, S., Evans, C. D., Reynolds, B., Tipping, E., and
Neal, M.: Increasing iron concentrations in UK upland waters,
Aquat. Geochem., 14, 263–288, 2008.
Oksanen, J.: Multivariate analysis of ecological communities in R:
vegan tutorial, R package version 1.7., 2011.
Pace, M. L. and Cole, J. J.: Synchronous variation of dissolved organic carbon and color in lakes, Limnol. Oceanogr., 47, 333–342,
2002.
Rasmussen, J. B., Godbout, L., and Schallenberg, M: The humic
content of lake water and its relationship to watershed and lake
morphometry, Limnol. Oceanogr., 34, 1336–1343, 1989.
Renberg, I.: A procedure for preparing large sets of diatom slides
from sediment cores., J. Paleolimnol., 4, 87–90, 1990.
Renberg, I., Korsman, T., and Birks, H. J. B.: Prehistoric increases
in the pH of acid-sensitive Swedish lakes caused by land-use
changes, Nature, 362, 824–827, 1993.
Rohde, H., Grennfelt, P., Wisniewski, J., Ågren, C., Bengtsson, G.,
Johansson, K., Kauppi, P., Kucera, V., Rasmussen, l., Rosseland,
B., Schotte, l., and Selldén, G.: Acid Reign 95 – Conference
Summary Statement, Water Air Soil Pollut., 85, 1–14, 1995.
Rosén, P.: Total organic carbon (TOC) of lake water during the
Holocene inferred from lake sediments and near-infrared spectroscopy (NIRS) in eight lakes from northern Sweden, Biogeochemistry, 76, 503–516, 2005.
Rosén, P., Cunningham, L., Vonk, J., and Karlsson, J.: Effects of
climate on organic carbon and the ratio of planktonic to benthic
primary producers in a subarctic lake during the past 45 years,
Limnol. Oceanogr., 54, 1723–1732, 2009.
Rosén, P., Bindler, R., Korsman, T., Mighall, T., and Bishop, K.:
The complementary power of pH and lake-water organic carbon reconstructions for discerning the influences on surface waters across decadal to millennial time scales, Biogeosciences, 8,
2717–2727, doi:10.5194/bg-8-2717-2011, 2011.
Rouillard, A., Rosén, P., Douglas, M. S., Pienitz, R., and Smol, J. P.:
A model for inferring dissolved organic carbon (DOC) in lakewater from visible-near-infrared spectroscopy (VNIRS) measures in
lake sediment, J. Paleolimnol., 46, 187–202, 2011.
Biogeosciences, 12, 307–322, 2015
322
P. Bragée et al.: Historical TOC concentration minima during peak sulfur deposition
SanClements, M. D., Oelsner, G. P., McKnight, D. M., Stoddard,
J. L., and Nelson, S. J.: New insights into the source of decadal
increases of dissolved organic matter in acid-sensitive lakes of
the Northeastern United States, Environ. Sci. Technol., 46, 3212–
3219, 2012.
Sarkkola, S., Koivusalo, H., Laurén, A., Kortelainen, P., Mattsson,
T., Palviainen, M., Piirainen, S., Starr, M., and Finér, L: Trends in
hydrometeorological conditions and stream water organic carbon
in boreal forested catchments, Sci. Environ., 408, 92–101, 2009.
Schöpp, W., Posch, M., Mylona, S., and Johansson, M.: Long-term
development of acid deposition (1880–2030) in sensitive freshwater regions in Europe, Hydrol. Earth Syst. Sci., 7, 436–446,
2003,
http://www.hydrol-earth-syst-sci.net/7/436/2003/.
Sjörs, H.: Amphi-Atlantic zonation, Nemoral to Arctic, in: North
Atlantic biota and their history, edited by: Löve, A. and Löve,
D., Pergamon Press, Oxford, 109–125, 1963.
Skjelkvåle, B. L., Evans, C., Larssen, T., Hindar, A., and Raddum,
G. G.: Recovery from acidification in European surface waters:
A view to the future, AMBIO, 32, 170–175, 2003.
Snucins, E. and Gunn, J.: Interannual variation in the thermal structure of clear and colored lakes, Limnol. Oceanogr., 45, 1639–
1646, 2000.
Sobek, S., Tranvik, L. J., Prairie, Y. T., Kortelainen, P., and Cole,
J. J.: Patterns and regulation of dissolved organic carbon: An
analysis of 7500 widely distributed lakes, Limnol. Oceanogr., 52,
1208–1219, 2007.
Stoddard, J. L., Kahl, J. S., Deviney, F. A., DeWalle, D. R., Driscoll,
C. T., Herlihy, A. T., Kellogg, J. H., Murdoch, P. S., Webb, J. R.,
and Webster, K. E.: Response of surface water chemistry to the
Clean Air Act Amendments of 1990, Report EPA 620/R-03/001,
US Environmental Protection Agency, North Carolina, 2003.
Sugita, S.: Theory of quantitative reconstruction of vegetation I:
pollen from large sites REVEALS regional vegetation composition, The Holocene, 17, 229–241, 2007a.
Biogeosciences, 12, 307–322, 2015
Sugita, S.: Theory of quantitative reconstruction of vegetation II: all
you need is LOVE, The Holocene, 17, 243–257, 2007b.
Taboada, T., Cortizas, A. M., García, C., and García-Rodeja, E.:
Particle-size fractionation of titanium and zirconium during
weathering and pedogenesis of granitic rocks in NW Spain, Geoderma, 131, 218–236, 2005.
Ter Braak, C. J. F. and Smilauer, P.: CANOCO reference manual and User’s guide to CANOCO for Windows – Softward for
Canonica Community Ordination (version 4), Centra for Biometry, Wageningen, pp. 351, 1998.
von Einem, J. and Granéli, W.: Effects of fetch and dissolved organic carbon on epilimnion depth and light climate in small forest lakes in southern Sweden, Limnol. Oceanogr., 55, 920–930,
2010.
Vuorenmaa, J., Martin, F., and Jaakko, M.: Increasing trends of total
organic carbon concentrations in small forest lakes in Finland
from 1987 to 2003, Sci. Total Environ., 365, 47–65, 2006.
Wetzel, R.: Limnology, 3 edition: Lake and River Ecosystems, Academic Press, San Diego, pp. 1006, 2001.
Wikman, H.: Beskrivning till berggrundskartorna 5E Växjö NO och
NV, Af 201 and 216, Sveriges Geologiska Undersökning (SGU),
108 pp., 2000.
Wilson, H. F. and Xenopoulos, M. A.: Effects of agricultural land
use on the composition of fluvial dissolved organic matter, Nat.
Geosci., 2, 37–41, 2009.
Wolfe, A. P.: On diatom concentrations in lake sediments: results
from an inter-laboratory comparison and other tests performed
on a uniform sample, J. Paleolimnol., 18, 261–268, 1997.
Worrall, F. and Burt, T. P.: Trends in DOC concentration in Great
Britain, J. Hydrol., 346, 81–92, 2007.
Xenopoulos, M. A., Lodge, D. M., Frentress, J., Kreps, T. A.,
Bridgham, S. D., Grossman, E., and Jackson, C. J.: Regional
comparisons of watershed determinants of dissolved organic carbon in temperate lakes from the Upper Great Lakes region and
selected regions globally, Limnol. Oceanogr., 48, 2321–2334,
2003.
Yallop, A. R., Clutterbuck, B., and Thacker, J.: Increases in humic
dissolved organic carbon export from upland peat catchments:
the role of temperature, declining sulphur deposition and changes
in land management, Clim. Res., 45, 43–56, 2011.
www.biogeosciences.net/12/307/2015/
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement