Research PaperCombined effects of submerged macrophytes and aquatic animals on the restoration of a eutrophic water body-A case study of Gonghu Bay, Lake Taihu

- Mesocosm and field experiment was conducted to clarify the combined effects of submerged macrophytes and aquatic animals on the restoration of eutrophic water bodies.
- Silver carp (Hypophthalmichthys molitrix) may deteriorate water quality, whereas triangle sail mussels (Hyriopsis cumingii) could promote the establishment of a clear-water state.
- Suggestions about practical ecological engineering were proposed.

Submerged macrophytes and filter-feeding aquatic animals have been widely used in ecological engineering to control eutrophic pollution. However, the use of filter-feeding aquatic animals to control eutrophic water bodies remains debatable. As such, more work is needed to understand the combined effects of submerged macrophytes and aquatic animals on the restoration of eutrophic water bodies. In this study, we first conducted a mesocosm experiment to evaluate the combined effects of submerged macrophytes and aquatic animals on water body restoration, and then applied these results in the field. We found that silver carp (Hypophthalmichthys molitrix) deteriorated water quality by increasing nutrient and total suspended solid concentrations, and decreased the biomass of submerged macrophytes. However, triangle sail mussels (Hyriopsis cumingii) promoted the establishment of a clear-water state by grazing on phytoplankton and detritus, and stimulating submerged macrophyte growth. In practical ecological engineering, we suggest that silver carp can be used at low density (20 g/m3) as a biomanipulation tool, despite their potential to deteriorate water quality. Furthermore, stocking mussels in nets at a biomass of 150 g/m3 can be effectively used to restore eutrophicated water bodies. Finally, Hydrilla verticillata and Potamogeton malaianus, in combination with filter-feeding aquatic animals, are suitable submerged macrophyte species for the restoration of eutrophicated lakes.