A large-scale biological control experiment to improve water quality in eutrophic Lake Taihu, China

Abstract

Lake eutrophication is one of the biggest environmental problems facing China. Since the mid-1990s, macrophyte restoration has been proposed and widely promoted as an affordable ecological solution. To assess the efficacy of this in-lake approach, an ecological engineering experiment was conducted in large, shallow, eutrophic Lake Taihu, China, from 2003 to 2006 that combined physical and biological clarifying measures targeted at improving water quality for the drinking water supply. An experimental area of 7 km2 was enclosed by a soft curtain to isolate it from the open lake and to block algal blooms. Inside this experimental area, around the intake of the waterworks, a 2 km2 inner enclosure was created with another soft curtain to promote the restoration of submersed and floating-leaf macrophytes intended to reduce nutrient loading inside the enclosure. Concrete pilings along the inner soft curtain protected it from wave action, and 945 bamboo rafts were deployed around the intake of the waterworks for wave control and floating macrophyte cultivation. Herbivorous fish and shellfish were introduced into the outer enclosure to reduce phytoplankton biomass. Monthly water quality monitoring before and after the clarifying measures suggested no significant difference in water clarity in the inner enclosure. The intended macrophyte-dominant system in the inner enclosure did not emerge during the experiment, which might be associated with high nutrient levels and low transparency. Following this experiment, eutrophic lake restoration in China has shifted to control of pollutant effluents entering lakes.