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AnoxPOP: Anoxic sediments as a source of persistent organic pollutants: the role of organic carbon and iron reduction

01.12.2015 - 30.11.2016
Project manager:
Dr. Simone Peter
DFG - Deutsche Forschungsgemeinschaft

Pollution of the Baltic Sea is of great environmental concern and there is a need to understand processes of transport and transformation of persistent organic pollutants (POPs) in this environment. Sediments constitute a significant reservoir for POPs but can also act as a source of these chemicals to the water column. POPs strongly interact with organic carbon, both the solid and dissolved phase. In sediments organic carbon is one of the most efficient sorbent for POPs and in the dissolved phase, POPs can be transported along with dissolved organic carbon (DOC). Therefore, processes that are regulating organic carbon dynamics in the sediments might be a key to better explain the fate of POPs. Conventionally, anoxic sediments are perceived as zones of high organic carbon burial. However, iron-bound organic carbon can be mobilized under anoxic conditions during reductive iron dissolution and diffuse from the sediment pore water into the water column. Due to the high association of POPs with organic carbon, it is likely that concomitant with organic carbon also POPs are released from the sediment to pore water and consecutively co-diffuse with DOC into the water column. Thus, pollutant fate and dynamics are tightly related to change in oxygen regime in aquatic systems. The relevance of this process in aquatic systems, especially in the Baltic Sea where an increase in anoxia has been reported, is currently not known. We hypothesize that the change in oxygen concentration in sediments will affect the partitioning of POPs between solid and dissolved phase. Specifically, at anoxic conditions, POPs that are associated with iron-bound organic carbon will be remobilized into pore water from where the compounds can diffuse into the water column. For this study we will investigate the effect of oxygen depletion on POPs and DOC dynamics in sediments of the Gotland Deep in the Baltic Sea. The Gotland deep is usually anoxic over several years. But currently, an intrusion of oxygen-rich salt water exposes anoxic sediment layers to oxygen. This phenomenon opens great opportunities to study the effect of changing oxygen conditions on the fate of organic pollutants. In this project, several campaigns are planned to sample sediment and the water column at the Gotland Deep for DOC, iron and POPs concentrations, covering the time during oxic conditions and when anoxic conditions will be re-established. Additionally, fluxes of POPs and DOC from anoxic sediments will be quantified by incubation experiments under different oxygen conditions. The results will contribute (i) to understand the complex interactions of POPs and organic carbon and (ii) to quantify the remobilization of POPs under changing environmental conditions.