Eutrophication Assessment Revealed by the Distribution of Chlorophyll-a in the South China Sea

Abstract

Highlights: What are the main findings? Chlorophyll-a in the South China Sea shows strong seasonal and spatial variability. Ordinary Kriging reconstruction of chlorophyll-a provides the most accurate basis for eutrophication risk assessment. What is the implication of the main finding? Spatio-temporal chlorophyll-a patterns provide key insights into marine ecosystem health. Long-term satellite-derived chlorophyll-a supports reliable monitoring of eutrophication dynamics. Chlorophyll-a is a key indicator characterizing the health of marine ecosystems. This study aimed to assess eutrophication risk by investigating the spatio-temporal evolution of chlorophyll-a in the South China Sea (SCS). Based on MODIS-Aqua remote sensing data from 2003 to 2024, five spatial interpolation methods were compared, and Ordinary Kriging was selected as the optimal method (r = 0.96) for reconstructing the chlorophyll-a distribution. The findings indicate that chlorophyll-a is higher in winter and autumn than in summer and spring, with significant enrichment observed near coastal areas. Concentrations decrease with increasing distance from the shore. The Mekong River estuary consistently exhibits high values, while the concentration in the SCS Basin remains persistently low. Furthermore, the spatial extent where chlorophyll concentrations exceed the bloom threshold was evaluated to highlight potential eutrophication risk. These results provide a scientific basis for understanding the response mechanism of the SCS ecosystem to climate change and have important implications for regional marine environmental management and ecological conservation.