Biogeochemistry of the Baltic Sea in a Changing Climate: From Catchment to Open Sea

Project description

The major aim of this project is to establish a biogeochemical study of the Baltic from the catchment to the open sea to investigate how inorganic and organic matter released from terrestrial systems is transformed as it passes through the fluvial system before being released into coastal waters. Study sites along very different catchment types (peat, forest and agricultural dominated) have been selected. The effects of this matter on the biological activity, composition of the microbial network and biomass in the receiving estuarine and coastal waters will be investigated.

The fate of riverine dissolved organic matter (DOM) has long been regarded as poorly constrained, being subject to many variables, such as its reactivity with the surface of mineral and biogenic particles, sunlight, and, ultimately, micro-organisms. The interaction of DOM with particle surfaces (sorption, flocculation) has been found important in terms of the physical-chemical properties of particles and the regulation of solid-liquid phase speciation of specific components of the DOM pool (e.g., humic material) but not so for its net transit through estuaries. The terrestrial DOM that enters aquatic ecosystems can be oxidized to inorganic nutrients (remineralization) by biotic respiration and, abiotically, by photo-oxidation. There is growing evidence for rapid microbial processing (respiration) of young terrestrial organic material within the river and estuary, resulting in oxidation of dissolved organic carbon (DOC) and outgassing of the resulting CO2 to the atmosphere. In this respect, the residual, and commonly measured older DOC transported downstream and exported to the coastal ocean is often resistant to further biological attack (refractory) in the river channel and is potentially recycled over long time scales in coastal waters. Where the microbial processing of exported terrestrial DOC further ashore in the coastal zone is comparatively slower, export of significant amounts to the open ocean can occur. The evidence for the dynamics of dissolved organic nitrogen (DON) in freshwater, estuarine, and coastal systems has only recently begun to emerge, suggesting extremely variable bioavailability (2 to 80%) depending on DON source (anthropogenic, wetland, autochthonous plankton-derived DON), ecosystem (marine versus freshwater microbes), and season.

More information

Leading Researcher Riitta Autio  Finnish Environment Institute SYKE, Phone: +358 50 520 3305, E-mail:

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Published 2013-04-22 at 14:55, updated 2013-04-22 at 14:53