Effects of Diversity, Coverage and Biomass of Submerged Macrophytes on Nutrient Concentrations, Water Clarity and Phytoplankton Biomass in Two Restored Shallow Lakes

Yiming Gao,Yaohui Hu,Baohua Guan,Zhaoxia Wang,Pingping Liu,Yu Zhao,Zhengwen Liu,Wei Zhen,Jinlei Yu,Chunyu Yin

doi:10.3390/w12051425

Abstract

Transplantation of submerged macrophytes to restore shallow lakes has been used as an effective measure to maintain a clear water state. Water quality is highly correlated with submerged macrophytes community, however, the relationships between water quality and the diversity, coverage and biomass of submerged macrophytes are, so far, not yet well studied. We analyzed the correlations of nutrient concentrations, water clarity and phytoplankton biomass with the metrics of submerged macrophytes community in two Chinese restored shallow subtropical lakes, Lake Wuli (Wuli-E, 5 ha) and Lake Qinhu (Qin-E, 8 ha). A similar biomass of submerged macrophytes was transplanted into each lake, while both the species richness and coverage of macrophytes in Qin-E were lower than Wuli-E. After a 1–2-year restoration, the diversity almost had no change, but the biomass density and coverage decreased in Wuli-E. As for Qin-E, the coverage of submerged macrophytes increased but biomass density and diversity decreased. The dominance of canopy-forming submerged macrophyte species Myriophyllum spicatum was observed in Qin-E and less meadow-forming biomass and species was observed than that in Wuli-E. Moreover, it was also observed that Wuli-E had a better water quality than that of Qin-E after transplantation. Path analysis results showed that macrophyte coverage and the diversity related to meadow-forming species (e.g., Vallisneria spinulosa) had strong effects on enhancing clarity and reducing nutrient concentrations. But the high biomass density accompanied by the canopy-forming species like M. spicatum was unfavorable for controlling nutrients. Our results provide important insight into the different roles that macrophyte diversity, biomass and coverage play in improving water clarity and controlling nutrient concentrations. This new knowledge will be instrumental in implementing more effective lake restoration, especially using macrophyte transplantation as a restoration tool in warm shallow lakes.

Highlights

Recovery of submerged macrophytes has been considered as an effective measure in restoration of shallow eutrophic lakes
Our results showed that the biomass density, diversity index (Shannon–Wiener index) and coverage of the macrophyte community decreased in both restoration areas from summer to winter and increased again in the following year
Forming macrophytes and the decline of meadow-forming species, almost all the macrophytes found in Qin-E the year after restoration were canopy-formers, the exception being a few floating-leaved macrophytes that appeared in summer (Figure 2d)

Summary

Introduction

Recovery of submerged macrophytes has been considered as an effective measure in restoration of shallow eutrophic lakes. Transplantation of submerged macrophytes to the eutrophic lakes may favor the quick recovery of macrophyte diversity [4,7,11], especially in lakes with rich sediments and lack of propagules which will limit the natural recovery of submerged macrophytes that may occur, even if water quality and light conditions are improved [12] In these lakes and the restoration goal including the re-introduction of those species typically dominating in nutrient-poor lakes, transplantation is often deemed relevant after sediment removal and fish community manipulation [4,7,11,13,14]

Methods

Results

Conclusion