Satellite measurements of cyanobacterial bloom frequency in the Baltic Sea: interannual and spatial variability

Abstract

Owing to the potentially harmful character of nitrogen-fixing filamentous cyanobacterial blooms in the Baltic Sea, a capacity to predict their occurrence is of interest. We quantified the surface accumulations of cyanobacteria, mainly Nodularia spumigena, using ocean colour satellite data. The spatial and temporal frequency of the accumulations was mapped with an automated detection algorithm, using their high reflectance in the 670 or 555 nm bands. Coastal Zone Color Scanner (CZCS) data were used for a first period (1979 to 1984), and combined SeaWiFS and MODIS-Aqua data for a second period (1998 to 2006). The frequency of cyanobacterial accumulations (FCA) for each 1 km 2 pixel was calculated as the ratio of scenes with detected cyanobacteria to the number of valid cloud-free scenes in July-August. FCA varied greatly among years and the basins of the Baltic Sea. Mean FCA was 39% higher in the second period, but the increase was not statistically significant. The mean FCA for the whole Baltic was positively correlated with the residual phosphate (RP) concentration after the spring bloom in May-June. RP was a useful predictor of FCA in the coming summer, but could not predict the spatial pattern of the bloom. This was better explained by prevailing winds, with high FCA in the southwestern Baltic after northerly winds in July. It seems that, at the time of writing, useful FCA predictions can be made after the spring bloom, but only for the whole Baltic.

Multidecadal time series of satellite-detected accumulations of cyanobacteria in the Baltic Sea

“…An analysis of the environmental conditions explaining the interannual patterns in FCA (cf. Kahru et al, 2007) is planned for the future. Future work should also compare this FCA data set with the more advanced multi-and hyperspectral methods like the maximum peak height (Matthews et al, 2012).…”

“…The methods applied to ocean color sensors such as Sea- WiFS, MODISA, MODIST and VIIRS as well as the early CZCS were essentially the same as described in Kahru et al (2007). After the 2009 reprocessing, the standard NASA ocean color output is expressed as remote sensing reflectance (Rrs) instead of the formerly used normalized water-leaving radiance (nLw).…”

Satellite Monitoring of the Ocean Climate Parameters. Part 2

“…Анализ временной изменчивости интенсивности цветения цианобактерий в Балтий-ском море на основе данных сенсоров CZCS (1979CZCS ( -1984, Sea WiFS и MODIS (1998-2006 гг. ) был проведён в работах (Kahru et al, 2007;Kahru, Elmgren, 2014).…”

Environmental Impacts—Marine Biogeochemistry

“…However, in the Baltic Proper, the Gulf of Finland, and to some extent also in the Gulf of Riga and the Bothnian Sea (Wasmund et al 2011), new production also takes place because N-fixing cyanobacteria blooms occur during summer. The magnitude of these blooms has been explained by excess inorganic dissolved phosphorus (eDIP), which due to the low N:P ratio in the winter nutrient pool still exists after the spring bloom NO 3 depletion (Janssen et al 2004;Kahru et al 2007;Lips and Lips 2008;Lilover and Stips 2008;Eilola et al 2009). However, eDIP is already exhausted before the summer cyanobacteria bloom starts.…”