Simulation of Elbe warmingMesocosm experiment with 10,000 litres of river water

17 September 2024, by RTG2530

Researchers of the Research Training Group 2530 have developed a complex mesocosm experiment to simulate real environmental factors and predicted climate warming scenarios in the Elbe estuary, considering rising water temperatures.

Seven o'clock in the morning in Bunthaus, south of Hamburg – 10,000 litres of Elbe water flow through a long fire hose into ten 1,000-litre tanks with the help of a pump. PhD students Julia Golebiowska, Max Lambrecht, Sahed Ahmed Palash, Diana Nicole Puerto Rueda and other scientists of the RTG 2530 have spent several months thinking, testing, and planning the most effective methods for extracting and transporting these quantities of water for research purposes. Around three hours later, the lorry carrying the heavy tanks arrives at Große Elbstraße, where the experimental laboratory of the Institute of Marine Ecosystem and Fishery Science (IMF) is located. There, the water is carefully transferred from the central tanks to a total of nine so-called mesocosms over several hours using hydrostatic pressure created by the weight of the water. The mesocosms are placed in three climate chambers, in which the water temperatures are 21, 23 and 25 degrees Celsius, respectively. These temperatures are maintained over several weeks. The entire process is supported by engineers and technicians from the IMF.  

This mesocosm experiment aims to replicate real environmental factors and simulate anticipated global warming scenarios. "Measurements already show that the Elbe sometimes reaches water temperatures of 25 degrees for a few days during the summer months," reports doctoral student Max Lambrecht. However, little research has been conducted on how different temperatures affect the carbon cycle in the estuary. Estuaries like the Elbe estuary are dynamic ecosystems in which fresh and saltwater meet and create favourable conditions for the growth and diversity of plankton species. These play a key role in the production of oxygen (O₂) and the uptake and release of carbon dioxide (CO₂) and will be analysed in more detail as part of the research experiment.

Plankton species behave differently: plant phytoplankton species absorb CO₂ from the water with the help of light and release O₂, while animal zooplankton, such as small crustaceans or unicellular protozoa, release CO₂ through cellular respiration. Bacterioplankton, consisting of tiny bacteria, also release CO₂ through the decomposition of dead organic material. The researchers are therefore interested in finding out which plankton species thrive and dominate under which temperature conditions.

However, this is just one of the many research questions that will be investigated as part of the experiment. The mesocosms will also be used, among other things, to analyse why there is sometimes a lack of oxygen in the Elbe and what influence viruses have on life and the nutrient cycle in the estuary.