Eutrophication is a severe threat to the Baltic Sea ecosystem. During recent decades, eutrophication-associated problems - such as deep water oxygen deficiency, the spreading of dead bottom zones, increased frequency and intensity of cyanobacterial blooms - have been observed.
The ability to bind the molecular form of nitrogen (N2) that is abundant in air and seawater gives the cyanobacteria an advantage compared to other species when concentrations of nitrate and ammonia are low.
However, these processes are not fully understood and there is still a large uncertainty regarding the nitrogen input from nitrogen fixing cyanobacteria. Estimates in the literature of annual nitrogen input from nitrogen fixation to the Baltic Sea range from 20 106 kg N up to 800 106 kg N. The range is comparable to the total bioavailable nitrogen input from atmosphere and land to the Baltic Sea.
We will implement the new simplified version of the cyanobacteria life cycle model (see figure) into the existing 3D biogeochemical model RCO-SCOBI (Swedish Coastal and Ocean Biogeochemical model) and use available historical data to evaluate and improve the models.
New high-resolution atmospheric forcing and data assimilation will be used to improve the ocean model performance during 1979-2013.
We will perform reconstructions of cyanobacterial blooms of the period 1850-2006 and future climate scenarios extending from 2007-2100.
We will quantify the importance of anthropogenic activities during the past century and provide information about possible reference conditions as well as possible scenarios of future cyanobacteria blooms that may be used for defining actions and setting targets in policy making.
We will track the resting stages, follow the germination and map the spatial patterns of the two main stages of the life cycles of cyanobacteria in the model and investigate if the life cycle may regulate the locations where blooms are initiated.
We will perform cause and effect studies to elucidate the mechanisms causing high biomasses and large surface extensions of cyanobacteria blooms.
The results from the project, new findings and updates of the future climate scenario experiments will be discussed and disseminated to stakeholders, researchers and the public media. A new technique for an enhanced visualization of the project results will be used.
The work is done in collaboration with Professor Inga Hense (ACCOEM-Group).
Institute for Hydrobiology and Fisheries Science (IHF), Center for Earth System Research and Sustainability at University of Hamburg, Germany.
This project has received funding from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS).
Reference: Hense, I., and A. Beckmann, 2010, Ecological modeling, 221, 2330-2338.