Aarhus University Seal / Aarhus Universitets segl

Dissolved organic matter - from soil to sea

Sources and processing of dissolved organic matter - from soil to sea

Introduction

Dissolved organic carbon, dissolved organic nitrogen and dissolved organic phosphorus (together called dissolved organic matter or DOM) control the carbon cycle in aquatic ecosystems and modulate related biogeochemical cycles.  Moreover, DOM has recently been recognized as an important and highly active part of the global carbon cycle (Battin et al. 2008). In a anthropogenic landscape like in Denmark, arable farming soils are a major source of DOM, however its composition and amount is different from natural sources, which is likely to alter the functions of DOM in this and other aquatic ecosystems (Graeber et al. 2012).  Both farming practice, eutrophication abatement measures like e.g. constructed wetlands, and the ecology of freshwater systems are likely to influence the DOM composition, characteristics and fate of DOM. However, the origin of DOM in arable soils and its fate in the aquatic ecosystems are still poorly understood. To investigate this topic, the project couples approaches from soil, freshwater and marine sciences to assess sources and fate of DOM from arable farming and reference sites.

Description of the project

The project consists of three work packages (WP’s) (Fig. 1):  the analysis of DOM sources in soils (WP1, Søren Munch Kristiansen, Geoscience and Daniel Graeber, Bioscience), the assessment of DOM processing in streams and rivers (WP2, Brian Kronvang and Daniel Graeber, Bioscience), as well as in estuaries (WP3, Stiig Markager and Daniel Graeber, Bioscience).  The concentration, load and composition of DOM will be analyzed in all WP’s using the same methodology (spectroscopic methods, elemental analysis of carbon, nitrogen and phosphorus and size-exclusion chromatography) at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany. Furthermore, additional co-variables to assess the source of the water in WP1 will be analyzed in the Department of Geoscience. In WP1, DOM amount and composition in agricultural subsoils, groundwater and riparian topsoils will be analyzed within two small catchments. Furthermore, the DOM in subsurface tile drains and the stream itself will be measured. In WP2, the uptake of this terrestrial DOM will be followed through the stream and river network and ultimately traced into the estuary. Finally, the processing of DOM reaching the estuary will be analyzed in WP3 in a detailed sampling. The final outcome will be related to existing catchment and estuary model results for revealing the impact of DOM on the nutrient cycle and ecological conditions.

References

Battin, T.; Kaplan, L.; Findlay, S.; Hopkinson, C.; Marti, E.; Packman, A.; Newbold, J. & Sabater, F. Biophysical controls on organic carbon fluxes in fluvial networks. Nature Geoscience, 2008, 1, 95-100

Graeber, D.; Gelbrecht, J.; Pusch, M.; Anlanger, C. & von Schiller, D. Agriculture has changed the amount and composition of dissolved organic matter in Central European headwater streams. Science of the Total Environment, Elsevier, 2012, 438, 435-446

Fig. 1

Contact