Differential response of blue-green algal groups to phosphorus load reduction in a large shallow lake: Balaton, Hungary

Padisák, Judit and Istvánovics, Vera (1997) Differential response of blue-green algal groups to phosphorus load reduction in a large shallow lake: Balaton, Hungary. In: SIL Congress in Sao Paulo 1995, 1995, Sao Paulo.

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Abstract

Lake Balaton is the largest shallow lake in Central Europe. The elongated lake (length 77,9 km; average width: 7,2 km) has a surface area of 593 km(2), and has a mean depth of 3,14 m (maximum: 11m). The theoretical retention time is 3-8 years. The catchment area of the lake is 5182 km(2), the Zala River itself drains an area of 2622 km(2). As a result of the increased phosphorous load, the originally mesotrophic lake underwent rapid eutrophication in the 1960s-1970s (Herodek 1984). Between 1975 and 1981, the total P load was estimated as 2,47 g m(-2) year(-1) in the western part of the lake, and 0,31 g m(-2) year(-1) in the eastern part (Somlyódy and Jolánkai 1986). As a consequence of the morphometric and loading conditions, a sharp trophic gradient has developed in the lake. In the early 1980s, a large-scale eutrophication management program was started (Istvánovics et al. in press). So far, the program has resulted in about 30% reduction of the biologically available P (BAP) load of the lake. This load reduction was expected to reduce slightly the phytoplankton development in the lake (Herodek 1984). This paper describes phytoplankton changes between 1989 and 1994 in two basins of the lake (siófok Basin and Keszthely Basin) that are different in their trophic status. Special attention will be paid to Cylindrospermopsis raciborskii, a bloom-forming subtropical blue-green alga.

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