Abstracts for presentations on the seminar “Carbon dynamics in terrestrial and aquatic
ecosystems: Effects of climate change” November 12-13, 2007.
Carbon sequestration in Swedish forest soils
Dan Berggren Kleja1, Magnus Svensson2, Per-Erik Jansson2 and Mats Olsson3
1
Department of Soil Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
2
Department of Land and Water Resources Engineering, Royal Institute of Technology, Stockholm, Sweden
3
Department of Forest Soils, Swedish University of Agricultural Sciences, Uppsala, Sweden
We present an integrated analysis of organic carbon (C) pools in soils and vegetation, withinecosystem fluxes and net ecosystem exchange (NEE) in three 40-year old Norway spruce stands
along a north-south climatic gradient in Sweden, measured 2001-2004. A process-orientated
ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for the
analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost
site (1.6 and 2.0-fold, respectively). Tree litter production (litterfall and root litter) was also highest
in the south, with about half coming from fine roots (< 1 mm) at all sites. However, when the litter
input from the forest floor vegetation was included, the difference in total litter input rate between
the sites almost disappeared (190-233 g C m-2 yr-1). We propose that a higher N deposition and N
availability in the south result in a slower turnover of soil organic matter than in the north. This
effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter
input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two
northern sites the corresponding figure was approx. 9%. The CoupModel accurately described
general C cycling behaviour in these ecosystems, reproducing the differences between north and
south. The simulated changes in SOC pools during the measurement period were small, ranging
from -8 g C m-2 yr-1 in the north to +9 g C m-2 yr-1 in the south. In contrast, NEE and tree growth
measurements at the northernmost site suggest that the soil lost about 90 g C m-2 yr-1.
References
Berggren Kleja D., Svensson M., Majdi,H., Jansson, P-E., Langvall, O., Bergkvist, B., Johansson,
M-B., Weslien, P., Lindroth, A & Ågren, G.I. 2007. Pools and fluxes of carbon in three Norway
spruce ecosystems along a climatic gradient in Sweden . Biogeochemistry (in press)
Svensson M., Jansson P.-E., Berggren Kleja D. 2007. Soil C sequestration in spruce forest
ecosystems along a Swedish transect based on current conditions. Biogeochemistry (in press)
Linking belowground Carbon with LiDAR
Terje Kristensen, Dep. of ecology and natural resource management (INA) Norwegian University
of Life Sciences (UMB).
Carbon stored belowground can be characterized by large heterogeneity, both in biochemical
attributes and spatial distribution. To understand the C dynamics in a forest ecosystem it is
necessary to disclose and quantify this heterogeneity. Until now it has been almost impossible to get
high definition information for large geographical areas, because conventional methology is too
expensive to bring forward the data needed. As there is an increased international interest in C
accounting in forest ecosystems, there is a need for efficient methods to estimate the above- as well
as the below-ground biomass components of the trees over large areas. LiDAR (Light Detection and
Ranging) enables us to draw a 3-dimensional picture of the structure of trees and ground. LiDAR
has proofed to be an accurate technology for precise estimation of aboveground biomass and C
stocks in boreal forests. Next step is to study the relationship between the aboveground biomass and
belowground C. The relationship between the biomass that can be derived from using LiDAR and
the amount of C in the soil might seem delicate, but new research results shows that the relationship
between the photosynthesis in the aboveground biomass and the biological activity in the soil
community is much more directly linked to each other than believed before. On behalf of this strong
connection and the fact that the respiration from the soil communities regulates the processing of
soil C, e.g. if the soil saves or releases C, is my hypothesis that LiDAR data could be used to
quantify the amount of C in forest soil.
Carbon sequestration in soil; the importance of Occam's razor in modelling and experiments
Lars Bakken, Dept. of Plant and Environmental Sciences, Norwegian University of Life Sciences
(UMB).
The carbon mineralization in soil is a very complex process, but can be modelled reasonably well
with simple first order decay models with some modifications to include the process of
"stabilization", i.e. transfer of fractions of the reactive compounds to stable pools.
Experiments should be guided by such models to zoom in on critical factors governing the soil
organic carbon dynamics in soil. Occams razor should be "used" to avoid complication of the
models unless strongly supported by residuals. Examples are variable Q10 values for different
reactions and different humification coefficients for root- versus shoot-material, "priming" of
mineralization by soil tillage and input of fresh organic materials.
Global warming has fostered much headless and futile experimentation, and ditto interpretations.
Useful research schemes may involve mechanistic/molecular approaches to improve our
understanding of the stabilization experiment, but will not necessarily provide a basis for
improvement of predictive models.
Influence of climate change on growth and carbon sequestration potential of bioenergy crops
Susanne Eich-Greatorex, Dept. of Plant and Environm. Sciences, Norwegian University of Life
Sciences (UMB).
Bioenergy has a large potential for reducing use of fossil fuels both worldwide and in Norway. With
increasing temperatures due to climate change it is predicted that Northern Europe will increase its
importance for producing food and energy crops during the course of the 21st century. For Norway
with its limited area that is available for crop production, it will be important to know which energy
crops are the most productive in terms of yield per area while at the same time considering the
different potential of these crops with respect to C sequestration. The main objective of this project
therefore aims at developing a modelling tool to predict the consequences of climate change on the
yields and C sequestration potential of different energy crops in different climatic and geographical
regions of Norway. The energy crop systems include agricultural, traditional forest and shortrotation forest systems. The effects of climate change are to be evaluated based on sustainability
principles.
Existing data from field experiments in Norway, Sweden and Denmark will be collected in a
database on yield, carbon binding and soil characteristics of different land use systems for
calibration of the model. Due to the diversity of the crops to be simulated, several existing models
designed for different land use systems are being considered. A model originally designed for forest
systems will also be tried in an agricultural system or vice versa.
Climate change at the alpine treeline: Impacts of elevated CO2 and warming on carbon
cycling
Frank Hagedorn, Swiss Federal Institute of Forest, Snow and Landscape Research (WSL),
Zürcher Str. 111, CH-8903 Birmensdorf, Switzerland
The ongoing increase in atmospheric CO2 affects ecosystem functioning either directly through its
effects on photosynthesis or indirectly by climatic warming. At the Swiss alpine treeline, we are
assessing ecosystem responses to a seven-year free air CO2 enrichment experiment (FACE) and a
one-year experimental soil warming of 3°C. The added CO2 contains another 13C signature than
normal air, which allows to trace the new carbon through the plant and soil system and to gain
insight into carbon cycling at the treeline.
Our results show that CO2 enrichment stimulated photosynthetic CO2 uptake by pine and larch by
20 to 50% throughout the years. The growth response was, however, species and time dependent
with larch profiting initially (up to 35%) and pine and dwarf shrubs showing no response. Soil
respiration was about 30% greater at the higher CO2 level, suggesting that elevated CO2 increased C
cycling rates but not C storage which would be relevant for C sequestration. The 13C tracing
revealed that a large fraction was rapidly cycling through the plant and soil system: 70% of
assimilated carbon by plants was allocated to the belowground, from which more than 80% was
respired back to the atmosphere. Only 1-3% of the C allocated to the belowground was leached as
DOC from the organic layer, implying that DOC consists primarily of relative old C. Experimental
warming for one year affected C fluxes differently with soil respiration being most responsive, plant
growth showing a slight stimulation and DOC leaching not responding.
Effects of sheep grazing on levels of DOC and DON in soil and surface water in an alpine area
of Southern Norway
Vegard Martinsen, Department of Plant and Environmental Sciences, Norwegian University of
Life Sciences (UMB).
Much research has been done to determine effects of climate change and grazing on carbon and
nitrogen dynamics. Depending on site fertility, levels of grazing pressure and amplitude of climatic
changes, ecosystem impact may vary considerably. Increases in CO2 concentration leading to a
warmer climate may increase carbon sequestration (i.e. increased soil carbon stocks) if not
constrained by availability of nutrients or offset by increased decomposition. This may lead to
structural and functional changes in vegetation and thereby both directly and indirectly affecting
soil processes controlling carbon and nutrient availability. Herbivory is reported to affect productive
and unproductive ecosystems differently depending on grazing intensity, grazing frequency and
length of grazing season. These direct consequences of grazing activity may indirectly lead to
positive or negative feedback mechanisms controlling ecosystem structure and function.
In the last decades a woody encroachment has been observed in mountainous areas in Norway. This
has been attributed to combined effects of changes in land use and climate. Studies have shown
positive correlations between amount of DOC in surface water and factors such as soil carbon
stocks, which is highly affected by vegetation cover. It has been reported increased levels of nitrate
draining highly grazed areas, indicating nitrogen saturation or changed hydrological pathways (e.g.
reduced infiltration rate and increased surface runoff). Little has been done to determine effects of
changes in land use patterns in Norway.
Even though we are starting to understand some of the biogeochemical changes caused by changes
in climate and land use, there is still a lack of knowledge regarding integrated effects in high
latitude ecosystems. Few studies have looked at the combined effect of changes in these
environmental drivers. The aim of this talk is to present the site and methodology that will be used
determining impacts on above ground and below ground processes controlling levels of carbon and
nitrogen as affected by different grazing pressures of sheep and altitudinal differences in
temperature and moisture. Hypothesis will be presented and discussed.
Carbon Pool and Potential Carbon Sequestration of the Land use Types in Central Rift valley
of S. Ethiopia
Ambachev D Wele, Dept. of Plant and Environmental Sciences, Norwegian University of Life
Sciences (UMB).
Global warming caused by the build-up of greenhouse gases (GHGs) is threatening mankind. The
major causes for the efflux of these gases are fossil fuel combustion, deforestation, and land use
changes around the world. Poor land cover, overgrazing and mismanagement of agricultural lands
are strongly correlated with the loss of soil organic matter, C pool and many essential nutrients for
plant growth. Decrease in plant productivity may lead to reduction in soil C sequestration and
increase in net emission of GHGs. Occurrence of these processes in an environment of limited
resources and in areas where introduction of sustainable technologies and practices are not
propitious, resource degradation and the vicious cycle of poverty is exacerbated. In Ethiopia, the
forest cover is reduced from 16% in the early 1950s to 2.8 % in the 1990s resulting in rural poverty
and underdevelopment. The Rift Valley is characterized with diverse climatic conditions, vegetation
cover and agricultural land use systems. Clearing of woodlands and overgrazing are rampant.
Reduction in soil productivity and desertification are the main threats to natural resources. The C
sequestration potential of the vegetation and other land use systems in the study area has not yet
been assessed. Therefore, this study aims at investigating the effect of vegetation management and
land uses on C sequestration to restore degraded soils in the central Rift Valley of southern
Ethiopia.
Carbon dynamics in mires - in perspective of a changing climate
Mats Nilsson, Department of Forest Ecology and Management, SLU, Umeå, Sweden.
Since the last deglaciation mires in the northern hemisphere has accumulated organic carbon and
emitted methane to the atmosphere. Based on extensive data from peat cores the global estimate of
the Holocene apparent carbon accumulation rate centre around 15-30 g C m-2 yr-1. More detailed
studies of peat cores from the more recent Holocene time period (~ 500 – 2000 BP) though indicate
a decline in apparent C-accumulation. Some data on the contemporary land-atmosphere exchange
of CO2 (NEE) as well as theories on both mire development and their response to a changing
climate has also resulted in that the current role of mires as a net carbon sink has been questioned.
A rigorous evaluation of the contemporary mire C-balance requires that all significant C-fluxes
are considered. The net ecosystem carbon balance (NECB), including all C-fluxes, of mires is
dominated by three flux components: the land-atmosphere exchange of 1) CO2 (NEE), and 2)
methane, and 3) the runoff export of carbon. Data on the annual C-flux for each flux component are
relatively frequent. However, data based on full year measurements are still limited. Even more
important is that simultaneous full year measurements of all significant flux components from the
same mire are even more restricted.
Estimates of the contemporary annual NEE based on continuous Eddy-Covariance
measurements exist from about ten sites in the northern hemisphere. The estimated annual NEE
constitute in all cases a net uptake ranging between ≈ 20 - 80g CO2-C m-2 yr-1. This annual net
uptake of CO2-C from the atmosphere is though counterbalanced by loss through methane emission
and water runoff export of C. The emission of methane range from about zero in “dry” ombrogenic
mires (bog) to > 30 g CH4-C m-2 yr-1 from more “wet” minerogenic mires (fen). The runoff-C is
comprised by total organic carbon (TOC) > dissolved inorganic carbon (DIC) + dissolved CO2 >>
CH4. The annual export of the major component TOC from mires varies between ~ 5 g – 25 C m-2
yr-1.
The relative importance of each of the C-flux components though varies most substantially
depending on mire type and climatic regions. Also the climatic drivers for each C-flux component
are most different. The effect of a changing climate on the mire net ecosystem carbon balance
(NECB) might therefore be quite different depending on mire type and climatic region. Published
data on multi year measurements of all flux components exists, to my knowledge, only from two
mires, one ombrotrophic mire (bog) in southern Canada and one minerogenic mire (fen) in northern
Sweden. Both mires constituted net carbon sinks, comparable in size to the long term average.
Exploring CH4 fluxes in a stratified boreal landscape
P. Dörsch1, H. Lange2, C. Auterives3 and L. Bakken1
1
Dept. of Plant and Environmental Sciences, Norwegian University of Life Sciences (UMB).
Norwegian Institute of Forest and Landscape
3
Department of Biology, University for Oslo
2
A significant part of the boreal landmass is covered by poorly drained soils which act as long-term
sinks for atmospheric carbon and net source for methane (CH4). It is unknown how changes in
climate will affect the balance between organic matter storage and CH4 source strength; hydroclimatic changes affect both C sequestration through changes in productivity and decomposition
and CH4 emission through changes in substrate quality and hydrological status. To advance our
understanding of boreal responses to future climate change, we need to study emergent
biogeochemical patterns in complex landscapes and to delineate the mechanisms that drive such
changes at multiple scales.
Small-scale variability of CH4 emission rates was studied by chamber methods (0.07 – 1 m2)
in a highly stratified mountainous landscape within the Langtjern watershed in Buskerud county,
Southern Norway (60o22’ N 9o39’E, 510-750 m, 3oC, 850 mm). The watershed is characterized by
mostly unproductive, old-growth Scots pine forest interspersed with peatlands covering ca. 30% of
the area. Deep peat (> 3 m) is encountered in depressions, floodplains and in riparian zones.
Shallower peat (< 1m) is found on gentle sloping food hills connecting the deeper peatlands along
hydrological drainage networks. Typical peatland types are forested swamps with heath-dominated
transition zones, Sphagnum-Carex lawns and hummocky fens. The latter are characterized by
microtope complexes consisting of hummocks, hollows, strings and pools.
We report ongoing attempts to characterize spatio-temporal CH4 emission patterns in this
landscape and outline synoptic approaches based on ‘emerging technologies’ such as ground
penetrating radar, remote imagery and molecular biology, to develop proxies for biogeochemical
settings in general and CH4 fluxes in particular. The overall goal of this approach is to improve
quantification of gas exchange between biosphere and atmosphere in complex landscapes.
Complex or Interactive? New Perspectives in Ecological Modelling
Michael Hauhs, Ecological Modelling University of Bayreuth.
Modelling offers two perspectives at environmental systems and ecosystems. The first one
originated from Newtonian physics and is based on the theory of dynamic systems. Its central
physical notion is that of state. This first approach is widespread among environmental modellers
and is sometimes even identified with the scientific method as such. The second (new) approach has
recently been derived within computer science. Its central notions are behaviour and interaction,
which can be implemented with today’s computers. The notion of interactive computation extends
the physical notion of functions into the realm of decision making, e.g. in a growing organism.
Difficulties and limits of ecological modelling have often been described as resulting from the high
complexity of these systems. Such an interpretation can now be challenged with the view, that
principle limits may be linked with the interactive nature of Life rather than with its complexity.
The alternate perspectives will be illustrated in an example from hydrology.
Modeling Soil Organic Carbon Stocks and Changes in a Nepalese Watershed
B. M. Shrestha1, S. Williams2, M. Easter2, K. Paustian2, B. R. Singh1*
1
Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, PO
Box 5003, 1432 ÅS, Norway
2
The Natural Resources Ecology Laboratory, Colorado State University, Fort Collins, CO 805231499, USA
* Corresponding author:
Email: balram.singh@umb.no, Phone +47 6496 5564, Fax +47 6496 5601
Land use, land use change and forestry activities play an important role in determining whether the
soil is a sink or source of atmospheric carbon dioxide (CO2). Effect of Land use change on climate
change in many developing countries is receiving greater attention. We studied changes in soil
organic carbon (SOC) pool over 100 years (1950 – 2050) under managed forest (DS), rain fed
upland (Bari) and irrigated low land (Khet) of Pokhare Khola, a mid-hill watershed of Nepal, by
using Century C model. The modelled temporal blocks of 1950-1970, 1971-1990 and 1991-2004
were based on the history of land use changes in the study area and the projection was done for the
period 2005-2050. The model was calibrated and parameterized on the basis of biophysical and
weather data of the watershed. Field work was done in September/October 2004. Historic carbon
pool data was calculated following IPCC guideline for year 1976 and 1989. The Century C model
performed well in its representation of the effect on SOC of various land management systems in
Pokhare Khola watershed. Model results underscored the human impacts on the system. There was
dramatic loss of SOC due to the removal of tree biomass in the first temporal block (1950-1970).
However, it has been shown that partial recovery of lost SOC is possible through better forest
management, especially if erosion is abated. In the cultivated land we found better recovery by
addition of farm yard manure and fertilizer. In all the land use systems, the SOC recovery was
lower under climate change scenario than under prevailing climate.
Key words: Century C model, Climate Change, Land Use Change, Mountain Watershed, Nepal,
SOC pool
Growth in situ of Lobaria spp, area measurements with digital photography.
Per Larsson, Dept. of Ecology and Natural Resource Management, Norwegian University of Life
Sciences.
The growth of Lobaria pulmonaria and L. scrobiculata is quantified in situ on small twigs of Picea
abies in boreal rain forests in Nord-Trøndelag, middle Norway. Area growth of individual juvenile
thalli will be monitored throughout a two years period by means of repeated digital photography. In
addition, the first appearance and enlargement of surface areas devoted for vegetative reproduction
propagules will be recorded. Size-dependent growth curves and onset of reproductive stage allow as
assessment of the generation time under natural conditions. A similar study of the in situ growth of
L. pulmonaria on trunks of Populus tremula is conducted in southeast Norway and will be
compared with the study on twigs in Nord-Trøndelag. Methodology and some data for the first
recording interval will be presented.
Carbon, climate change, and why sulphur and nitrogen make things more complicated
Chris Evans, Centre Ecology Hydrology, Bangor, UK.
Peatlands and other organic-rich soils contain large stores of carbon. Much recent work has
suggested that soils in northern temperate and boreal ecosystems may be highly sensitive to climate
change, either reducing their current role as a carbon sink, or converting them into a carbon source.
This would represent a positive climate change feedback, with potentially severe consequences. In
the UK, long-term data showing increases in surface water dissolved organic carbon (DOC)
concentrations, and apparent decreases in soil C stocks, have been taken as evidence that these
positive climate-change feedbacks are already occurring. This presentation will review this
evidence, taking into account some of the other anthropogenic factors influencing carbon cycling in
the UK and in other industrialised areas of the world. It is argued that perturbations to other
biogeochemical cycles, notably sulphur and nitrogen, may be having a significant impact on carbon
cycling, that changes in these cycles may help to explain observed trends. The influence of these
other pollutants needs to be taken fully into account if environmental change in terrestrial and
aquatic ecosystems is to be correctly attributed, climate change impacts accurately predicted, and
appropriate policies applied to protect these ecosystems in future.
Precipitation experiments using small catchments in a montane heathland area in Southern
Norway
Haaland S.1*, Austnes K.1, Kaste Ø.2, Mulder J.1, Riise G.1, Semb Vestgarden L.1, Stuanes A.1
1
Norwegian University of Life Sciences, Department of Plant- and Environmental Sciences, P.O.
Box 5003, NO-1432 Ås, Norway
2
Norwegian Institute for Water Research, Televeien 3, NO-4879 Grimstad, Norway
Projected changes in climate in Southern Norway include increases in summer and autumn
precipitation. This may affect the production and leaching of dissolved organic matter (DOM) from
soils. Effects of experimentally added extra precipitation (10 mm week-1) to small headwater
catchments in a montane heathland landscape in southern Norway (59°0´N, 550 – 600 m a.s.l.) on
concentrations and fluxes of total organic carbon (TOC) and total organic nitrogen (TON) in runoff
were assessed. Experimental manipulation was done during the growing season of three years (2004
– 2006). Episodic changes in TOC and TON concentrations occurred, but in general extra
precipitation did not have a significant effect on the average TOC and TON concentrations in
runoff. Hence, fluxes of TOC and TON increased almost proportionally with water fluxes. This
suggests that a store of accumulated TOC and TON in catchment soils buffers the concentration of
DOM in runoff. Pronounced droughts did not occur during the 3-year ecosystem manipulation
period. Effects of relatively short drought episodes on TOC and TON fluxes in runoff from the
reference catchments at Storgama are small.
Linking surface water NO3 and TOC; results from a N addition field experiment.
Anne Merete Smelhus SJØENG 1
Dag Olav HESSEN 2
Brit Lisa SKJELKVÅLE 1
Søren Larsen 2
Berit Kaasa 2
(annemerete.sjoeng@niva.no)
(d.o.hessen@bio.uio.no)
(brit.skjelkvaale@niva.no)
(soren.larsen@bio.uio.no)
(berit.kaasa@bio.uio.no)
1. Norwegian Institute for Water Research, P.O. 173 Kjelsås, N-0411 Oslo, Norway
2. The University for Oslo, Section of Marine Biology and Limnology, Department of Biology,
P.O. Box. 1064, Blindern, N-0316 Oslo, Norway
Recent studies have shown an inverse relationship between dissolved organic carbon (DOC) and
nitrate in surface water (see fig 1, Skjelkvåle et al., 1998), and a causal relationship between DOC
and nitrate has been suggested (Goodale et al., 2005). In previous field manipulation experiments
chronic N addition to (the NITREX project, Moldan et al., 2006 In press) or N removal from (the
RAIN project, Wright et al., 1993) atmospheric deposition of these catchments did not cause any
changes in DOC leaching from the catchment soil to surface water, thus the causal link in soils does
not seem to be supported by empirical evidence. To test whether the observed inverse relationship
between DOC and nitrate in surface water is due to processes within the water column, a field
manipulation experiment was conducted in small humic lakes from June to November 2005. We
hypothesized that N addition to humic lakes with low nutrient (e.g. nitrogen and phosphorus)
content would stimulate bacterial production, hence resulting in an increased bacterial consumption
of DOC and burn-off to CO2. If this actually would occur, we would expect a stabilization of the
DOC concentrations during fall, rather than an increase as normally is observed in these lakes. Two
small humic lakes were manipulated; one by adding nitrogen (NaNO3) and the other by adding
nitrogen (NaNO3) + phosphorus (NaH2PO4). Three other humic lakes in the same area (<1 km
apart) were chosen as controls. The lakes were sampled daily the first week after manipulation, then
approximately weekly for about nine weeks. Results indicate that primary production (measured as
chlorophyll a) increased more than the bacterial consumption of DOC, particularly in the N+P
added lake.
250
Hardangervidda
Femundsmarka
NO3 µg N/l
200
Rondane
150
100
Figure 1 Relationship between
TOC and NO3- concentrations
in mountain lakes (Skjelkvåle et
al., 1998)
50
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
TOC mg C/l
References
Goodale, C.L., Aber, J.D., Vitousek, P.M. & McDowell, W.H. 2005. Ecosystems 8: 334-337. Moldan, F., Kjønaas, J.O., Stuanes, A. & Wright, R.F.
2006. Environmental Pollution xx: 1-11.Skjelkvåle, B. L. & Henriksen, A. 1998. NIVA report LNO 3895-98, 48pp. In Norwegian.
Wright, R.F., Lotse, E. & Semb, A. 1993. Canadian Journal of Fisheries and Aquatic Sciences 50: 258-268.
Climate change and eutrophication process in lakes
Aleksandra Romarheim, Dept. of Plant and Environmental Sciences, Norwegian University of
Life Sciences (UMB).
Enrichment of nutrients (eutrophication) in freshwater ecosystems enhances the primary production
which seriously might affect the biogeochemical cycling of several elements. Oxygen depletion and
changes in biodiversity with frequent blooms of blue green bacteria are consequences that might
occur. Many shallow temperate lakes, such as the eutrophic lake Årungen, show a delay in the
recovery process although several countermeasures have been made to reduce the external loading
of nutrients, such as improved agricultural practices, treated sewage systems, construction of
wetlands and other abatement strategies that reduce loss of phosphorus transported with eroded
particles from the catchment. Lately, lots of attention has been given to climate changes and its
impact on lake ecosystems. Increased precipitation and warming can change the seasonal
availability of nutrients and thus the seasonality of the lake phytoplankton.
Drivers of long-term DOC trends in surface waters: climate or deposition?
Heleen de Wit, Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, N-0349 Oslo, Norway
heleen.de.wit@niva.no, +47 9543 4360
Lake and stream water in glaciated landscapes across substantial areas of North America and northern and
central Europe has become enriched in dissolved organic carbon (DOC) over the past two decades.
Hypotheses about underlying causes include climate-change driven changes in temperature and precipitation
and changes in acid deposition. Time series of DOC are analysed using step-wise regression to test various
hypotheses on controls of DOC trends. First, an assessment of time series from over 500 acidificationsensitive sites in North America and northern Europe shows that the tendency for DOC increases in most
regions between 1990 and 2004 can be explained by changes in the acid anion concentration of atmospheric
deposition. DOC concentrations have increased proportionally with the decline both in anthropogenic
sulphur, and, in some regions, seasalt deposition. This analysis is based on statistical correlation of annual
mean element concentrations. Second, an analysis of time series of weekly DOC in 3 acid-sensitive
catchments in Norway shows that seasonal variation in DOC is primarily climatically controlled, while acid
deposition explains the long term increase in DOC. Increased humic charge and reduced ionic strength –
both increasing organic matter solubility – are proposed as mechanistic explanation for the statistical relation
between reduced acid deposition and increased DOC. Further reduction of atmospheric deposition will be
limited suggesting that future increases in DOC will level off. In coast-near areas, DOC is likely to be
impacted by seasalt deposition that fluctuates with the North Atlantic Oscillation index (NAOi). GCMs
predict a higher frequency of positive NAOi under climate change, possibly correlated with more seasalt
deposition.
Causes for the increasing trends in DOC and colour
Rolf D. Vogt; Dept. of Chemistry, University of Oslo.
The concentration of dissolved natural organic matter (DOM) and water colour of lakes and streams
in Europe and North America, which have been suffering from acid rain, have showed an
unprecedented increase during the last two decades. Several hypotheses to explain this increase
have been put forward. This presentation argues that the strong decrease in aluminium
concentrations, due to reduced acid deposition, has acted as a strong governing factor for the
increased amount of aquatic DOM and specially colour in surface waters in Norway. Aluminium is
a powerful precipitator and flocculent of DOM, particularly its more coloured hydrophobic fraction.
This conceptual hypothesis is empirically substantiated by a multivariate statistical analysis of
monitoring data on surface water chemistry in water courses that have been to varying degree
exposed to acid rain in Norway and the UK. Inorganic labile aluminium (Al_i ) and total organic
carbon (TOC) show strong opposite scores along the first two principal components (PC) in
principal component analysis (PCA) at the 4 most acidified of the 10 monitored water courses in
Norway. In addition strong negative correlations were found along either the first or second PC at 5
of the other sites. The same relationships were found in sites in the UK where there has been a
significant reduction in Al_i concentrations. Hydrology (discharge) and temperature (daily
deviation from norm) were not found to have any significant explanatory value in the Norwegian
high order water courses at a long term scale.