Ecosystem stability and water quality improvement in a eutrophic shallow lake via long-term integrated biomanipulation in Southeast China

Biomanipulation is one of the most promising measures in ecological restoration and used to mitigate eutrophication in water bodies. Current biomanipulation methods, such as traditional biomanipulation (based on large-size zooplankton) and non-traditional biomanipulation (based on filter-feeding fish), are often carried out independently and focus on algae control. Integrated biomanipulation, including traditional and non-traditional biomanipulation, was implemented in Longhu Lake, a drinking water source, to successfully control cyanobacterial blooms and improve water quality for 20 years. In order to study the mechanism of algae control and the ecosystem stability, we analysed the effects of integrated biomanipulation and single-biomanipulation on the phytoplankton community and the ecosystem via model simulation. The results revealed that compared with the other single-biomanipulation scenarios of 'filter-feeding fish biomanipulation', 'omnivorous fish biomanipulation', 'piscivore biomanipulation', and 'without biomanipulation', integrated biomanipulation combined the advantages of traditional and non-traditional biomanipulation. In this case, cyanobacteria biomass (4.5 ton/km(2)) was kept at a low level, although the biomass of small phytoplankton was high. The slope of trophic-levels spectrum was low (18.54%), and the biomass distribution of the community was balanced (less 'up-and-down'). The energy flow transfer efficiency of food web was as high as 14.1% and the ratio of grazing food chain and detrital food chain was close to 1:1. The ascendency was better than other scenarios. These data indicated that the ecosystem after integrated manipulation was more stable and mature than that other single-biomanipulation. Moreover, integrated biomanipulation could substantially increase fishery income. Integrated biomanipulation can therefore be used to meet the requirements of sustainable development, especially in tropical and subtropical eutrophic lakes used as drinking water source.