LITERATURE STUDY ON HARMFUL BLUE-GREEN ALGAL BLOOMS and DATABASE OF MOST COMMON BLOOM FORMING BLUE-GREEN ALGAE IN EUROPE
Cyanobacterial blooms are a common problem occurring in Europe and in other parts of the world. Their occurrences can be both the symptom and the indicator of water eutrophication. Cyanobacteria are highly opportunistic organisms. The effects of cyanobacterial blooms include high biomass concentration, biodiversity decline, and high oxygen deficits that influence the entire limnic ecosystem.
Bloom occurrences on lakes are correlated, to a considerable degree, with weather conditions and consequently with climate conditions in a given area. In the case of Northern Europe, cyanobacterial blooms are observed mostly during the summer season.
Bloom is defined as a profuse growth of one or more phytoplankton species. The consequences of cyanobacterial blooms are:
– decreased oxygen concentration,
– decreased biodiversity,
– negative effects on water taste and odour,
– decreased recreational value of lakes,
– presence of cyanobacterial toxins in water.
The mechanism of bloom occurrences is very complex. Factors such as weather conditions, physiography of the lake floor, shape of a lake and its shorelines, and also water physico-chemical conditions are known to affect bloom formation. However, not all processes linked to cyanobacterial blooms have been identified and the investigation on the factors causing blooms is still incomplete. So far, only a number of factors that stimulate the development of cyanobacterial blooms and conditions sustaining it have been identified.
Eutrophication, defined as nutrient enrichment of water, especially in nitrogen and phosphorus, results in accelerated growth of algae and higher plant species resulting in disturbances of biological relationships in aquatic ecosystem and deterioration of water quality. Some causes of the increased level of nutrients, i.e. eutrophication, are:
– changes in lake catchment development,
– logging and burning of forests,
– expanding arable lands,
– use of fertilizers,
– conversion from animal husbandry to extensive livestock farming,
– releasing effluents from catchment area directly into water reservoirs.
The negative changes in aquatic ecosystems caused by eutrophication processes manifest themselves in lower concentrations of dissolved oxygen, reduction of water clarity and massive algal and cyanobacterial blooms. The latter pose particular problem because of their toxicity. Many species of Cyanoprocaryota float on water surface forming mats that can release unpleasant or toxic substances into the water. In case that such severe blooms are blown by winds into bays or along shorelines, they create an additional threat as the rapid decomposition of blooms may deplete the water of oxygen and produce high concentrations of ammonia, occasionally resulting in massive mortalities of fish and other aquatic organisms. Eutrophication also leads to restructuring of species composition within lakes.