The Stream Inlet to a Shallow Bay of a Drinking Water Reservoir, a ‘Hot‐Spot’ forMicrocystisBlooms Initiation

Stream inlets into shallow bays of reservoirs and lakes may be ‘hot‐spots’ for toxic cyanobacterial bloom initiation. These ‘hot‐spots’ may be connected with the permanent inflow of high nutrient concentrations from the catchment, optimal physical conditions (wind protected areas) that occur in shallow areas and/or ineffective top‐down control. Four sampling sites along a transect from stream to reservoir in a shallow bay of Sulejow Reservoir (Poland) were studied to test the above hypothesis, comprising a transition zone between lotic and pelagic habitats. Investigations showed that stream inlet into shallow bay acted as incubator forMicrocystisblooms. The nutrient level, especially phosphorus, was identified as the major cause of cyanobacterial bloom growth. The increase ofMicrocystisbiomass strongly correlated with increasing microcystin concentrations, however, a relationship with microcystin content was not observed. Toxicity of bloom demonstrated seasonal variability, reaching its maximum at the initial phase of bloom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)