Aquatic Nutrient Cycles

Research Topics

The effects of anthropogenic activities on the nitrogen cycle are numerous, and can be detected both in the atmosphere and in water, in estuaries, rivers, and the coastal zone in Europe and worldwide.

The combined use of state-of-the-art isotope techniques, nutrient determination and measurement of dissolved gas (such as nitrogen or nitrous oxide) in water samples allows the assessment of different processes in the nitrogen cycle. Ultimately, different nitrogen sources and processes that may alleviate the effect of excess nutrient inputs shall be quantified.

Atmospheric deposition of nitrate and ammonium can contribute significantly to nitrogen inputs into ecosystems. To unravel its input pathways and emission trends of nitrogen deposition, we investigate temporal and spatial changes in wet and dry deposition and its isotope signature. A focus of research in this context is the growing contribution of ship emissions to NOx emission and deposition, a topic that we investigate jointly with the department “Chemistry Transport Modelling”.

Riverine nutrient loads derive mostly from agriculture and urban waste water. These nutrient loads are modified in estuaries, where the residence time of water masses is higher: Nitrate can be denitrifed in sediments, produced by nitrification, or assimilated by phytoplankton. All these processes leave an imprint on the isotope signature of dissolved nitrogen. In various rivers and coastal regions, we quantify these processes by isotope measurements in water samples and particles that we take during seasonal cruises and, in the Elbe River, by regular water sampling near the weir Geesthacht.

Nitrous oxide, N2O, is a potent greenhouse gas that can be emitted from water bodies and sediments, where it can be produced during nitrification or denitrification. Within the framework of a joint project with the UFZ Magdeburg, we measure the production of N2O in regions that are exposed to different levels of anthropogenic pressure, like pristine vs. eutrophic rivers or the Wadden Sea. Beside N2O concentration, a new focus of research is the isotope and isotopomer composition of N2O, which depends largely on its formation pathway and also allows the detection of N2O consumption.