The horizon of hope for L. Vesijaervi, southern Finland: 30 years of water quality and phytoplankton studies

摘要

Water quality in L. Vesijaervi and especially in Enon-selkae has recovered substantially since the beginning of the 1980s, particularly since biomanipulation started in the late 1980s. Noxious cyanobacterial blooms, which were perhaps the greatest obstacle to recreational use of the lake, disappeared in a stepwise fashion: in 1984-1985, cyanobacterial biomass dropped and dominance shifted from Planktothrix agardhii to Aphanizomenon flos-aquae, and in 1989-1990 blooming species of cyanobacteria disappeared for over a decade. Collapse of the cyanobacterial blooms in the early 1990s was most likely driven by biomanipulation-induced changes in the recycling rates of the remaining nutrients. A burst of cyanobacteria in August 2002 was caused by the increased external loading and the hypolimnetic anoxia with food web interactions. However, it did not prevail.