Research project Can climate change, input of nutrients or a combination of both explain the development of hypoxia in the Baltic Sea and other coastal waters with limited water exchange? This project will provide advice to water managing authorities how to reduce the occurrence of oxygen free waters.
To manage our water bodies properly a better understanding of processes and factors influencing oxygen consumption is required. Current scientific literature emphasizes a surprisingly weak relationship between respiration and primary production and suggest co-regulation of oxygen consumption by both temperature and supply of organic matter. Therefore, climate factors (e.g., temperature, salinity, pH) including discharge of riverine organic matter may all explain observed changes in oxygen status, rather than only contemporary eutrophication.
This project challenges the current view that contemporary primary production is the main cause of hypoxia, including the concept of base line respiration. We also hypothesize a remarkably stronger temperature dependence of respiration than presently recognized, with potential influence on global ocean CO2 emissions. A new experimental approach to estimate Q10-values (i.e., temperature sensitivity), and its interactive dependence on season (i.e. ambient temperature) and level of dissolved organic carbon (DOC) will be investigated. A new optical technology using Optode-sensors to measure oxygen consumption is applied, facilitating field studies and resolution of experimental data.
Important objectives are estimating the role of riverine DOC driven respiration, influence of DOC quality, salinity, pH, and photolysis. A wide range of values to analyse is generated by sampling the Baltic gradient, tropical and polar biotopes. By using the production minima in the field during winter the importance of rDOC for driving respiration and its control will be investigated. The control of respiration by riverine DOC and its interaction with temperature will further be determined in mesocosm experiments using winter sea water and concentrated DOC from river water.