Are sediments in lakes and dams a sink or source for DOC?

Importance of the work and objectives: Increasing concentrations of dissolved organic carbon (DOC) in surface waters are observed worldwide in the northern hemisphere. This poses an increasing ecological threat as well as an... [ view full abstract ]

Importance of the work and objectives: Increasing concentrations of dissolved organic carbon (DOC) in surface waters are observed worldwide in the northern hemisphere. This poses an increasing ecological threat as well as an economic problem for drinking water reservoirs by higher water treatment costs to remove the DOC and the potential formation of toxic, carcinogenic disinfection by-products. Sediments could act either as a source or sink for several compounds depending on environmental conditions.
Methodologies: In this study we tested the sediment from two pre-dams of a drinking water reservoir for their exchange behavior of DOC by incubating sediment cores at different temperatures and redox conditions. The cores were taken from different sites of the pre-dams representing more riverine and lacustrine zones, respectively. Incubation was performed at in-situ conditions using climate chambers. Beside DOC, other solutes were analyzed in the overlying water.
Main results and conclusions: Only under oxic conditions and low temperatures the sediments acted as a sink for DOC. At higher temperatures and under anoxic conditions the sediment was a source for DOC. A strong positive correlation of the fluxes of DOC, iron and phosphorus was observed suggesting that adsorption of DOC on iron mineral surfaces was the major regulating mechanism. Temperature had also a significant effect on DOC release from the sediment by stimulating microbial processes. Higher temperatures as proposed for the future might then result in more reducing conditions in the hypolimnion of lakes and dams followed by enhanced benthic DOC release.