How does the River Elbe affect the German Bight?

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

The campaign, part of the MOSES (Modular Observation Solutions for Earth Systems) research initiative, started in the Czech Republic in June and will end in the German Bight in mid-September. The first part in the freshwater Elbe River was organised by the UFZ. From 23 to 25 August, the research ship Ludwig Prandtl of the Helmholtz Centre Hereon was underway between Geesthacht and Cuxhaven. From 28 August to 15 September, three coastal research vessels of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), GEOMAR Helmholtz Centre for Ocean Research Kiel, and the Helmholtz Centre Hereon will carry out 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 designed to follow a pre-defined "water package", which has been analysed since the end of June in a (freshwater) section of the Elbe on its way to the saline coastal area and finally to the North Sea. The Elbe estuary, i.e. the tidal part of the river from Geesthacht to Cuxhaven, plays a unique role. Estuaries essentially act as massive filters between rivers and oceans: Here, organic substances are broken down, transformed or accumulated in the sediment; due to the effects of the tides, the residence time of the water here is much longer than in the river itself.

Once it reaches the North Sea, the "water package" from the estuary will be tracked by transponders that will drift with it and transmit their positions at regular intervals. Participating research ships will constantly monitor their signals, allowing them to take water samples at the transponders' locations and make detailed measurements of the concentrations of various components. Three "swarms" of three to four transponders each will be deployed in the Elbe estuary near Cuxhaven. The transponders will follow the fresh water coming out of the Elbe, which will initially remain mainly in the surface layer of the coastal water, before mixing increasingly with the North Sea water, both horizontally and vertically. The ships will follow the swarms of transponders, which will also gradually disperse horizontally, allowing the researchers to analyse the route and gradual dissipation of the "water package" from the Elbe in the estuary and the North Sea. By doing so, they hope to successfully track how the package changes and mixes 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 the water from the Elbe behaves in the North Sea, the research vessels cannot follow a pre-planned route; they'll have to constantly check the current position of the transponders. To do this, they will rely on new measuring instruments developed as part of the Helmholtz project MOSES, which can record and visualise high-resolution data in real time. One example is a fully equipped MOSES laboratory container with special sensors, which can be transferred from ship to ship once it has been prepared. The container is first 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 vessel Mya. This system ensures that, although different ships are involved, the same sensors are used to provide consistent and comparable data.

At the same time, each of the three ships and institutes will have its own "speciality". The AWI will focus on the precise measurement and analysis of the distribution and atmospheric concentrations of the greenhouse gases methane and CO2. GEOMAR will focus on the transport of pollutants from the Elbe into the German Bight, using an innovative system to collect water samples for a range of pollutants, including TNT and mercury. Hereon will contribute its expertise in sampling microplastics, 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 years of environmental observations in the Elbe and German Bight in the context of MOSES, and to a new project of the German Marine Research Alliance (DAM) called "ElbeXtreme", which will investigate the effects of extreme events on the German coastal system from 2024.

Background: MOSES

MOSES stands for "Modular Observation Solutions for Earth Systems". In this initiative, coordinated by the Helmholtz Centre for Environmental Research - UFZ, nine research centres of the Helmholtz Association have jointly developed mobile and modular observation systems. This allows them to study the effects of temporally and spatially limited dynamic events, such as extreme precipitation and runoff events or droughts, on the long-term development of Earth and environmental systems. MOSES has been in regular operation since 2022.