Effect of submerged macrophyte restoration on improving aquatic ecosystem in a subtropical, shallow lake

Submerged macrophyte restoration was used to combat with lake eutrophication and improve water quality in a subtropical, shallow lake. A consistent investigation for three years about macrophyte, phytoplankton, zooplankton and water quality has been conducted to explore the effect of macrophyte restoration on improving aquatic ecosystem. The results showed that macrophyte biomass and coverage after the restoration were as high as 821 g/m2 and 55%, respectively, and the dominant species were Ceratophyllum demersum, Myriophyllum verticillatum and Potamogeton crispus. Moreover, chemical oxygen demand (COD), total nitrogen (TN), total suspended solids (TSS) and nitrate nitrogen (NN) significantly decreased yearly, but the changes in total phosphorus (TP) and ammonia nitrogen (AN) were not significant during the investigation. Phytoplankton density and biomass significantly decreased, and the dominant species changed from blue-green algae to green algae. Zooplankton density and biomass, however, significantly increased yearly, and the small-sized dominant species (such as, Keratella cochlearis, Polyarthra trigla, etc.) were gradually replaced by the large-sized species (such as, Asplanchna priodonala, Alona guttata, etc.) during the restoration. In addition, macrophyte was negatively correlated with nutrients, but positively correlated with zooplankton. Phytoplankton was also positively related with TN. These correlations showed that restored macrophytes could decrease nutrition loading in water body, inhibit phytoplankton growth to decrease the risk of algae blooms, and support more large-sized zooplankton to strengthen the top-down control of phytoplankton. Therefore, our results showed that macrophyte restoration is a very potential and effective method to combat with the eutrophication and develop water quality in the eutrophic subtropical lakes, and deserves more attentions in future subtropical/tropical lake managements.