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Biogeochemistry of dissolved organic matter

Dissolved organic matter (DOM) in marine environments make out one of the largest C pools on the planet, harbouring an equal amount of C as all terrestrial biota or the atmospheric CO2. Freshwaters have been largely ignored in global C models, mainly due to the fact that they occupy only around a percent of the planet’s surface. However, recent research suggests that lakes and running waters are disproportionally active sites for C processing. Despite the significance of aquatic DOC to the global C cycle, major gaps in our understanding of what determines how DOC is transformed and preserved.

The import of terrestrial DOM is a dominant component of the C budget in freshwater systems, often larger than the in situ production of organic matter. An upward trend in the transport of terrestrial DOM to freshwaters and coastal areas has been observed. Though the mechanisms behind this increase are controversial, and has been ascribed to hydrological factors as well as temperature, changed land-use and increased pH in precipitation, it is bound to have a profound effect on the receiving ecosystems and biogeochemical cycles. We study causes and consequences of increasing amounts of terrestrially derived DOM in aquatic systems (Brownification).

IIn the aquatic system, the fate of the DOM is one of the following: it may flocculate and sediment, it may be remineralized through photooxidation, it may be transformed by bacteria to support production and respiration, or it may remain in the DOM pool. We study how the biogeochemical cycling of DOM in aquatic systems depend on different factors such as temperature, nutrient availability, the origin of the DOM (aquatic/terrestrial), the molecular structure of the bacterial communities. Thus the research overlaps the fields of biogeochemistry, microbiology, analytica chemistry and genetic structure/diversity of bacterial communities. Research is performed mainly in lakes and rivers in Sweden and in the Baltic Sea.

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