Quantitative detecting of cyanobacteria during blooms conditions

Tiit Kutser, Liisa Metsamaa
Estonian Marine Institute, Mäealuse 10a, Tallinn 12618, Estonia.
Tiit.Kutser@sea.ee

Niklas Strömbeck
Department of Limnology, University of Uppsala, Norbyvägen 20, Uppsala 75236, Sweden

ABSTRACT

Intense cyanobacterial blooms in a water body may impact recreation, ecosystem integrity, and human and animal health. Effective tools are needed to monitor cyanobacterial blooms in coastal and inland waters. This is especially important in the case of the Baltic Sea where cyanobacterial blooms may cover area more than 100 000 km². Remote sensing can potentially provide the tool for detecting and monitoring cyanobacterial blooms if we can separate blooms of other algae from cyanobacterial blooms based on their optical signatures. We studied the influence of optical properties of 14 different algal species (including 7 cyanobacteria species) on just above the water surface reflectance spectra using a bio-optical model. The modelling was carried out mimicking optical properties of CDOM rich coastal waters and open Baltic Sea waters. Concentration of chlorophyll-a varied between 1 and 300 mg m^-3 in both cases. The modelling results show that cyanobacteria can be separated from other algae species in the open Baltic Sea waters based on the phycocyanin absorption feature near 630 nm and increased reflectance at 640-650 nm. However, the chlorophyll concentration has to be at least 7-8 mg m^-3 that is corresponding to relatively intensive bloom. Strong absorption of light by CDOM in coastal waters near CDOM-rich river estuaries prevents recognising of cyanobacterial blooms based on their reflectance spectra as the CDOM absorption masks phycocyanin absorption feature.

Last Update: 2005-03-16