Enclosure experiments on and lacustrine practice for eliminatingMicrocystis bloom

Abstract

Microcystis bloom, one of the most objectionable characteristics of eutrophication in tropical and subtropical waters, occurred in Donghu Lake (East Lake) of Wuhan every summer from the 1970s up to 1984, but from 1985 up to now failed to occur there. The cause of its disappearance remained in obscurity until recently.In situ enclosure experiments in the lake for three years showed that the stocking of the filter-feeding silver carp (Hypophthalmichthys molitrix) and big-head carp (Aristichthys nobilis) played a decisive role in eliminatingMicrocystis bloom from the lake; but that recurrence of the bloom is possible under certain conditions. This paper presents the details and the results of enclosure experiments. The authors' analysis of fish biomass data obtained by echo-sounding and the fishery production of the lake over the years, revealed that the recurrence ofMicrocystis bloom can be prevented so long as the combined biomass of silve carp and big-head carp remains at or exceeds 50 g per cubic meter of lakewater, as was the case in the lake's 1985 fish yield of 1015 t.