Phase-Specific Water-Quality Responses to Enhancement Harvesting and Filter-Feeding Fish Stocking: A Dense Sentinel-2 Time-Series Assessment

Enhancement harvesting and filter-feeding fish stocking are increasingly applied in shallow eutrophic lakes, but their water-quality effects are difficult to evaluate because management signals overlap with seasonal and hydrometeorological variability. We analyzed dense Sentinel-2 observations of Taibo Lake during 2019–2026 using three management stages, phase-specific event windows, and matched forbidden-fishing controls. Regressions adjusted for antecedent precipitation and month used 25 scenes from the 2024 and 2025 events. Chlorophyll-related proxies were descriptively lower during enhancement harvesting than in the 2019 reference year, with no consistent advantage over forbidden fishing. The contrast with 2019 remains confounded by year-specific environmental conditions. Integrated optical and turbidity-related indicators showed no uniform directional change, and representative September scenes revealed substantial within-lake heterogeneity. Event-window comparisons showed no consistent immediate directional response to harvesting or stocking. Exploratory models suggested higher post-stocking normalized difference chlorophyll index (NDCI) values and high-NDCI ratios; only NDCI remained nominally significant after Bonferroni adjustment (adjusted p = 0.036 versus 0.204). Limited event replication and unmodeled temporal dependence precluded confirmatory inference. These findings support phase-specific water-quality monitoring with seasonally matched baselines and continued observation through the post-stocking period to inform adaptive enhancement-fishery management.