The role of cyanobacteria for the mercury emission by the Baltic Sea

• Applicant: Dr. Joachim Kuß
• Subject Area: Oceanography
• Term: from 2011 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 184037700

During research campaigns with R/V Elisabeth Mann Borgese in summer 2011, as a pilot study, and with R/V Meteor in summer 2012 (M87/4) samples were collected and measurements have been done to determine the causes of the summer mercury emission maximum of the Baltic Sea. The important research campaign for the project with R/V Meteor was delayed from summer 2011 to summer 2012. Thus sample analyses and data syntheses will go on beyond the scheduled end of the project (March 2013). The studies also showed that additional culture experiments would be necessary to improve the understanding of the processes. Hence a proposal for a one year extension of the project is made after reporting the preliminary results.Up to now the investigations show that the transformation of ionic mercury to elemental mercury is mainly biogenic (about 65%). That was shown by on-board incubation experiments. Also the spatial distribution of the elemental mercury concentration showed a good correlation with the dominant cyanobacteria species Aphanizomenon and Nodularia (Summer 2011). To investigate different cyanobacteria species with regard to its mercury reduction capability additional culture experiments are proposed for the third year. The existence of the MerA gen in Cyanobacteria from the Baltic Sea was shown by microbiological methods. However, the mechanism in phototrophic cyanobacteria seems different in comparison to the well described reduction in heterotrophic bacteria. The MerA gen in Nodularia sp. showed a deviating base sequence and another gen glutaredoxin is essential to induce the mercury reduction.In the proposed third year the focus will be on a comprehensive elaboration and synthesis of the data of the M87/4 cruise. Results will be presented on the International Conference on Mercury as a Global Pollutant in Edinburgh and on the Baltic Sea Science Congress in Klaipeda. Moreover some additional incubation experiments will be done to study the meaning of temperature, turbulence and nutrient availability on the development of specific cyanobacteria and thus the production of elemental mercury.

• DFG Programme: Research Grants