Tracking phycocyanin dynamics in East Lake using Landsat-8 and generalized additive models: impact of COVID-19 and conservation efforts.

The COVID-19 pandemic led to temporary environmental improvements, including changes in urban lake ecosystems. This study investigated spatiotemporal variations in phycocyanin concentrations in East Lake, Wuhan, from March to September (2018-2022), using generalized additive model (GAM) with Landsat-8 imagery to assess changes before, during, and after the lockdown. The GAM model exhibited strong predictive accuracy (R2 = 0.967, RMSE = 1.637 μg/L) for phycocyanin estimation, particularly with lake-specific site data. Results revealed significant phycocyanin reductions in 2020, particularly in TL, SG, and GZ lakes, concurrent with reduced human activity during the lockdown. However, phycocyanin levels rebounded post-lockdown, with variations across sub-lakes, indicating that temporary reductions in human activity alone were insufficient for sustained water quality improvement. Further analysis showed that long-term conservation strategies played a decisive role in the continued water quality improvements observed in 2022. Key interventions included increasing aquatic vegetation cover (from 0.9% in 2017 to 3.3% in 2019), implementing wastewater regulations, dredging lake sediments, and improving runoff management. These efforts contributed to reduced nutrient accumulation and greater ecosystem stability, reinforcing the importance of proactive watershed management over short-term activity restrictions. This study highlights the interplay between human activity, remote sensing-based water quality monitoring, and policy-driven conservation strategies. The findings provide a framework for sustainable lake management and offer valuable insights for future ecological monitoring and policy-making.