Original paper

Changes in water clarity during fish manipulation and post-manipulation periods in a shallow eutrophic lake

Tátrai, István Mátyás; György, Á gnes I. Havasi

Abstract

A food web manipulation experiment was conducted in the small, shallow, eutrophic Lake Major, part of the Kis-Balaton Water Protection System (KBWPS) wetland area. Several factors affected the development of turbid water during the fish manipulation period (FMP) in 2000-2001 versus clear water during the post manipulation period (PMP) in 2002 and 2005-2006. A > 40 % percentage macrophyte cover was the most important factor to differentiate between the years with diverse water quality. However, the concentrations of soluble reactive phosphorus (SRP) did not change significantly between the periods. Lake Major exhibited maximum fish species richness (12 species) during PMP, when richness was twice as high as during FMP. There was a clear succession of macrophyte taxa, mostly related to the natural variability in fish. Initially, the macrophyte community was dominated by Najadosum marini, but after fish removal and restocking of piscivores, Ceratophyllum demersi became dominant. This study showed that there is a high potential for restoration of species-rich submerged macrophyte stands even in a hypertrophic lake having been for more than two decades in a turbid state. Water of Lake Major, as the whole KBWPS wetland area, had not previously been in such a good ecological condition since its establishment in 1986. However, it cannot be concluded from this study whether the new trophic state created by fish manipulation is sustainable for longer period.

Keywords

fish manipulationmacrophyte coverchlorophyll-alphaphytoplankton structurefish cpueshallow lake