How does the Elbe affect the German Bight?

Joint press release: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Helmholtz-Zentrum Hereon and GEOMAR Helmholtz Centre for Ocean Research in Kiel

The campaign, part of the research initiative MOSES (Modular Observation Solutions for Earth Systems), began in the Czech Republic in June and will end in the German Bight in mid-September. This first part in the freshwater Elbe was organized from the UFZ. From 23 to 25 August, the Helmholtz-Zentrum Hereon’s research ship Ludwig Prandtl was underway between Geesthacht and Cuxhaven for this purpose. From 28 August to 15 September, three coastal research ships from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), GEOMAR Helmholtz Centre for Ocean Research in Kiel, and the Helmholtz-Zentrum Hereon will engage in successive scientific cruises in the southern North Sea between Büsum, Helgoland and Cuxhaven.

The carefully planned cruises on the Elbe and the North Sea are intended to track a predefined “water package” that has been subjected to analysis since late June in a (freshwater) segment of the Elbe during its journey to the saline coastal area and ultimately to the North Sea. In this regard the Elbe estuary, i.e., that part of the river that is affected by the tide and which extends from Geesthacht to Cuxhaven, plays a unique part. Estuaries essentially serve as massive filters between rivers and oceans: Here, organic substances are degraded, transformed, or accumulate in the sediment; given the effects of the tide, the water’s residence time here is much longer than in the river itself.

Once it reaches the North Sea, the “water package” from the estuary will be tracked using transponders, which will drift along with it and transmit their positions at regular intervals. The participating research ships will constantly monitor their signals, allowing them to collect water samples at the transponders’ locations and take detailed readings on the concentrations of various components. Three “swarms” of three to four transponders each will be deployed in the Elbe outflow near Cuxhaven. The transponders will follow the freshwater coming from the Elbe, which at first will chiefly stay in the surface layer of the coastal water before increasingly mixing with the North Sea water, both horizontally and vertically. The ships will track the transponder swarms, which will also gradually disperse horizontally, allowing the researchers to analyse the route and gradual dissolution of the “water package” from the Elbe in the estuary and the North Sea. By doing so, they hope to successfully track changes in the package and its mixing with North Sea water in the coastal area, and to analyse in detail the fate of its dissolved and particulate components.

Since it remains unclear how water from the Elbe behaves in the North Sea, the research ships can’t follow a previously charted route; they’ll have to constantly check the transponders’ current position. To do so, they will rely e.g. on new measuring instruments developed as part of the Helmholtz project MOSES, which can record and visualise temporally highly resolved data in real-time. One example: a fully equipped MOSES laboratory container with special-purpose sensors and which, once prepared, can be transferred from ship to ship. The container will first be brought on board Hereon’s Ludwig Prandtl in Cuxhaven. After a week of transponder tracking, it will be transferred to GEOMAR’s Littorina and, after another week, to the AWI research ship Mya. This system ensures that, although different vessels are involved, the same sensors are used, yielding data that is uniform and intercomparable.

At the same time, each of the three ships and institutes will have its own “speciality”. The AWI’s focus will be on precisely measuring and analysing the distribution of the greenhouse gases methane and CO₂ and their atmospheric levels. GEOMAR will concentrate on the transport of pollutants from the Elbe to the German Bight, applying an innovative system to gather water samples for a range of pollutants including TNT and mercury. Hereon will contribute its expertise on microplastic sampling, heavy metals, dissolved carbon, and nutrient loads, while the UFZ, which was responsible for the first phase of the project on the Elbe, will analyse additional water and sediment samples.

Taken together, the institutes’ efforts and expertise will make a valuable contribution to the years of environmental observations made on the Elbe and in the German Bight in connection with MOSES, and to a new German Marine Research Alliance (DAM) project dubbed “ElbeXtreme”, which, from 2024, will investigate the effects of extreme events on Germany’s coastal system.