Coastal areas are amongst the most valuable of the world’s ecosystems, but are continuously polluted by high anthropogenic nutrient inputs from traffic, agriculture and sewage. This leads to an accumulation of nutrients (eutrophication), which is visible in e.g. enhanced algal blooms and declining oxygen concentrations in bottom waters.
The sensitivity towards these enhanced inputs, however, depends both on input pathways and on the actual nutrient loads: Atmospheric deposition reaches the coastal ocean directly, whereas terrestrial inputs are microbiologically turned over in rivers and estuaries, which can potentially remove large portions of surplus nutrients before they reach the coastal ocean. On the flipside, this turnover can also bring historical nutrient loads from the sediments back into the water column, again promoting eutrophication. Whether internal sources or sinks of nutrients are more important is hard to predict in regions as dynamic as the coastal ocean – this makes it a worthwhile goal to investigate the influence of sedimentary and water column nutrient turnover on nutrient budgets.
In the working group “Isotopes”, we trace the input pathways and turnover processes of different nitrogenous substances using their stable isotope signature. We aim to evaluate the relevance of different nutrient sources for rivers and the coastal ocean. Measuring changes in these isotope signatures both in natural environments and laboratory experiments, we want to investigate whether a surplus in nutrient inputs is increseased or remediated by natural turnover processes in the coastal ocean.