The removal of Cyanobacteria blooms in the Baltic Sea

Blooms of cyanobacteria are a major concern during the summer period in the Baltic Sea Proper. The nitrogen-fixing Nodularia spumigena forms massive toxic blooms in the surface layers with a concentration of biomass in the uppermost one metre water layer. This pilot study describes the construction and test of a Nodularia collecting device during the summer of 2006. The field study was performed at the Askö Laboratories in the archipelago of Stockholm/Trosa, Sweden. Oil booms were modified in that way that the skirt of the oil boom was replaced with water permeable forming fabrics that are used in the pulp and paper industry. The collecting device was tested in the field but not during an intensive Nodularia bloom, since they were absent during the study period. The results show that the modified oil booms work and behave in a functional way when towed in the sea. Calculations showed that the collecting device used in this study has a theoretical capacity of cleaning 11 hectares (0.11 Km2) of sea surface per hour, which could be compared, with the 6600 Km2 of the Baltic Sea that was covered by Nodularia blooms during the summer of 2005. The intention is to proceed with the test of the collecting device in intensive Nodularia blooms during the summer of 2007 and 2008. Finally future possibilities of Nodularia harvesting are discussed and an idea of constructing a floating harvesting station is presented.

Funding:
The Project is financed by Stiftelse för teknisk vetenskaplig forskning till minne av J. Gust. Richert

Contact:
Ass. Professor Fredrik Gröndahl, fredrik@kth.se