Response Characteristics of Phytoplankton Communities in Plateau Shallow Lakes to Enclosure-Based Ecological Restoration

In this study, an in situ ecological restoration experiment was conducted using methods such as enclosure wave suppression, sediment exposure, and plant cultivation to investigate the effects of different restoration strategies on water quality, submerged plants, and phytoplankton communities. The results indicated that combining plant cultivation with enclosure wave suppression effectively restored the submerged plant. Wave suppression alone supported natural plant recovery but with significantly lower coverage and biomass than artificial planting. Water quality improvement was most notable in the closed enclosure + sediment exposure + plant cultivation (closed enclosure + sediment exposure restoration experiment, CS) group compared to the permeable enclosure + plant cultivation (open enclosure restoration experiment, OE) and closed enclosure wave suppression (closed enclosure restoration experiment, CE) groups. The OE group exhibited the highest phytoplankton species richness (204 species), followed by the CS (187 species) and CE groups (170 species). However, the phytoplankton cell density was highest in the CE group (0.75–6.61×106 cells/L), moderate in the OE group (0.26–1.96×106 cells/L), and lowest in the CS group (0.08–0.47×106 cells/L), highlighting the superior water ecological improvement achieved by the CS measures. Non-metric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM) identified distinct algal community structures across restoration strategies, with the OE group displaying the highest variability. Redundancy analysis (RDA) revealed that the phytoplankton communities in the CE group were influenced by water temperature (WT), ammonium nitrogen (NH+4-N), nitrate nitrogen (NO-3-N), and dissolved oxygen (DO), whereas those in the OE group were mainly affected by WT and NO-3-N. In the CS group, the key factors included WT, chemical oxygen demand (CODMn), NH+4-N, and pH. This study highlights the ecological benefits of different restoration measures and could provide valuable insights into lake ecological restoration.