Factors limiting algal growth in eutrophic Chaohu Lake, China

Abstract

Enclosure experiments, combined with regular monitoring of limnological parameters, were undertaken to investigate factors limiting algal growth in Chaohu Lake, China, where Microcystis was the dominant algal species. Nutrient concentrations in the lake water were high with an annual average total phosphorus concentration of 0.142 mg/l, soluble reactive phosphorus (SRP) concentration of 0.026 mg/l and total nitrogen concentration of 1.63 mg/l. The lake water contained a large quantity of suspended mineral particles and had high turbidity. Light intensity was significantly reduced at 1.0 m below the water surface and net primary productivity was negative at levels deeper than 1.0 m. Algal growth did not increase with elevated phosphorus concentrations above a critical (threshold) level. The threshold concentration of SRP for maximum algal growth in the lake was estimated as 0.019 mg/l, which was lower than the actual SRP concentration commonly recorded in the lake. The data suggested that it was not nutrients but light which limited algal growth in the lake during most of the summer and autumn. A large-scale reduction in the nutrient loads would be required to bring the lake to a phosphorus-limiting state as the first step towards a comprehensive eutrophication control strategy.