Cycling of Matter
We investigate if and how the turnover of organic matter and important trace metals, such as manganese (Mn) and Molybdenum (Mo), in the water column and the surface sediments of the Wadden Sea, are influenced by events like phytoplankton blooms. We hypothesize that at the break down of phytoplankton blooms, aggregation events are triggered by microbial activities and that during still water periods at high and low tide the abundance of bacteria on suspended aggregates increases. This will lead to sub- and anoxic microzones in the aggregates and a partial reduction of Mn(IV) to dissolved Mn(II), which is released into the water column. At the same time Mo is fixed in the aggregates and scavenged from the dissolved phase. A fraction of the aggregates sinks out and settles at the sediment surface. The subsequent microbial mineralization of the aggregates leads to the release<s style="text-line-through: double"> </s>of Mn and Mo and their retarded reintroduction into the water column. This hypothesis will be investigated by intense field studies experimentally in rolling tank systems under controlled conditions and by modelling approaches.