The importance of the relationship between scale and process in understanding long-term DOC dynamics

Science of The Total Environment

Gustafsson

Bringmark

2010

This is an author produced version of a paper published in Science of The Total Environment. This paper has been peer-reviewed and is proofcorrected, but does not include the journal pagination.Citation for the published paper: Löfgren, S., Gustafsson, J. P., Bringmark, L. (2010) Recently, a hypothesis was presented on how various spatial and temporal factors affect 4 the DOC dynamics. It was concluded that declining sulphur deposition and thereby 5 increased DOC solubility, is the most important driver for the long-term DOC 6 concentration trends in surface waters. If this recovery hypothesis is correct, the DOC 7 levels should increase both in the soil solution as well as in the surrounding surface 8 waters as soil pH rises and the ionic strength decline due to the reduced input of SO 4 2-9 ions. In this project a geochemical model was set up to calculate the net humic charge and 10 DOC solubility trends in soils during the period 1996-2007 at two integrated monitoring 11 sites in southern Sweden, showing clear signs of acidification recovery. The Stockholm 12Humic Model was used to investigate whether the observed DOC solubility is related to 13 the humic charge and to examine how pH and ionic strength influence it. Soil water data 14 from recharge and discharge areas, covering both podzols and riparian soils, were used. 15The model exercise showed that the increased net charge following the pH increase was 16 in many cases counteracted by a decreased ionic strength, which acted to decrease the net 17 charge and hence the DOC solubility. Thus, the recovery from acidification does not 18 necessarily have to generate increasing DOC trends in soil solution. Depending on 19 changes in pH, ionic strength and soil Al pools, the trends might be positive, negative or 20 indifferent. Due to the high hydraulic connectivity with the streams, the explanations to 21 the DOC-trends in surface waters should be searched for in discharge areas and 22 peatlands. 23 24 25

supporting

confidence: 75%

Decreasing DOC trends in soil solution along the hillslopes at two IM sites in southern Sweden — Geochemical modeling of organic matter solubility during acidification recovery

Science of The Total Environment

Gustafsson

Bringmark

2010

“…Several authors have suggested that the observed increase in concentrations of dissolved organic carbon (DOC) in surface waters in Europe, Canada, and the US is due to the mobilization and transport of soil organic carbon (SOC) resulting from the reduction in acid deposition, primarily S (Clark et al 2010;Evans et al 2005;Monteith et al 2007), i.e., it is an anthropogenic acidification recovery response rather than a climate change response. However, based on soil water data from southern Sweden, the postulated causal link between recovery from anthropogenic acidification and increases in surface water DOC has been challenged (Löfgren et al 2010b;Löfgren and Zetterberg 2011).…”

Section: Introductionmentioning

confidence: 99%

Recovery of Soil Water, Groundwater, and Streamwater From Acidification at the Swedish Integrated Monitoring Catchments

Aastrup

Bringmark

et al. 2011

AMBIO

Recovery from anthropogenic acidification in streams and lakes is well documented across the northern hemisphere. In this study, we use 1996-2009 data from the four Swedish Integrated Monitoring catchments to evaluate how the declining sulfur deposition has affected sulfate, pH, acid neutralizing capacity, ionic strength, aluminum, and dissolved organic carbon in soil water, groundwater and runoff. Differences in recovery rates between catchments, between recharge and discharge areas and between soil water and groundwater are assessed. At the IM sites, atmospheric deposition is the main human impact. The chemical trends were weakly correlated to the sulfur deposition decline. Other factors, such as marine influence and catchment features, seem to be as important. Except for pH and DOC, soil water and groundwater showed similar trends. Discharge areas acted as buffers, dampening the trends in streamwater. Further monitoring and modeling of these hydraulically active sites should be encouraged.

“…However, over-reliance on simple models and purely statistical criteria may lead to overly simplistic views of the environment. If nothing else, it can be argued that more than 30 years of research into surface water DOC, and its links to acidification, acidity, climate and hydrology (Krug and Frink 1983;Laudon et al 1999;Erlandsson et al 2008Erlandsson et al , 2010Lepistö et al 2008;Clark et al 2010;Haaland et al 2010;Haei et al 2010;Löfgren et al 2010b;Löfgren and Zetterberg 2011), has shown that numerous factors influence or covary with surface water DOC. So, we must conclude that, on the basis of our current understanding, reality is over-determined but that models can be a useful tool for environmental hypothesis testing and understanding.…”

Section: Discussionmentioning

confidence: 99%

“…A number of hypotheses have been proposed to explain these trends, including climate change (Lepistö et al 2008), declining acid deposition (Monteith et al 2007;de Wit et al 2007;Clark et al 2010) and changes in flow and rates of sulfate (SO 4 2-) deposition (Erlandsson et al 2008). Moldan et al (2011) have also recently demonstrated that rates of chloride (Cl -) deposition significantly affect surface water [DOC].…”

Section: Introductionmentioning

confidence: 99%

Simulating Dissolved Organic Carbon Dynamics at the Swedish Integrated Monitoring Sites with the Integrated Catchments Model for Carbon, INCA-C

Bishop

Köhler

et al. 2011

AMBIO