Response of Phytoplankton to Nutrient Limitation in the Ecological Restoration of a Subtropical Shallow Lake

Lake restoration, achieved through a combination of biomanipulation and the recovery of submerged macrophytes, can effectively reduce nutrient concentrations, thereby suppressing phytoplankton biomass. Nevertheless, there is limited knowledge regarding the impact of nutrient limitation in phytoplankton biomass on lake restoration efforts. We compared the changes in nutrient levels and phytoplankton biomass (measured by chlorophyll a, Chl a) between restored and unrestored areas of a subtropical shallow Lake Yiai. Furthermore, we assessed the nutrient limitation patterns in these two areas through field nutrient addition experiments conducted during the summer. Monitoring results indicated that mean concentrations of Chl a and nutrients were significantly lower (t-test p < 0.0001) in the restored area compared to the unrestored area. In the nutrient addition experiment, phytoplankton biomass was nitrogen-limited in the unrestored part, whereas it was co-limited by both nitrogen and phosphorus in the restored area. These findings suggest that nutrient limitation may serve as a crucial mechanism in sustaining low phytoplankton biomass following the restoration of shallow lakes, particularly during the summer season, with the recovery of submerged macrophytes.