Change and Prediction of Water Purification Function in the South Bank of Hangzhou Bay in the Past 20 Years

Abstract

The investigation of regional water purification functionality and its influencing factors holds significant pragmatic implications in understanding the potential of regional water purification, guiding context-specific regional comprehensive planning schemes, and environmental conservation measures. The study site, situated along the southern coast of Hangzhou Bay, represents a prototypical region characterized by intricate land-sea interactions that bear substantial economic and ecological functions. By assimilating a meticulously collected topographical and land-use dataset, in conjunction with site-specific meteorological records, the water purification model embedded within the integrated valuation of ecosystem services and trade-offs (InVEST) framework was employed to scrutinize the spatiotemporal dynamics of nitrogen (N) and phosphorus (P) loads, discharges, and removals within the southern coast of Hangzhou Bay. The prime objective of this study was to unravel the differentials in water purification functionality under diverse developmental scenarios. The investigation unearthed distinct temporal discrepancies in N and P discharges and removals over two temporal dimensions. Relative to the benchmark year 2000, the total N load experienced a reduction of 276.72 t, whereas the N discharge and removals decreased by 140.86 and 137.86 t, respectively, in the year 2020. In contrast, the total P load observed an increase of 93.65 t, accompanied by a surge in P discharge and removals by 28.91 and 64.74 t, respectively. Spatially, the distribution pattern of N and P discharges exhibited a general inclination of elevated values in the northern region and subdued values in the southern region, with certain pockets in the southern region exhibiting pronounced peaks, intimately associated with land-use typologies. Simulation analyses conducted under distinct scenarios unveiled that under the natural development priority scenario, the N and P discharges within the study area amounted to 1 682.36 and 115.50 t, respectively. Conversely, under the scenario emphasizing economic development, the regional N and P discharges showed an approximate escalation of 83.02% and 79.93%, correspondingly. In contrast, under the scenario emphasizing environmental conservation, the regional N and P discharges exhibited a notable decline of approximately 79.96% and 56.44%, respectively. Hence, the scenario prioritizing the amalgamation of environmental conservation and development effectively reduced the N and P discharges within the region, bolstering the water purification functionality. The results derived from this study furnish a solid theoretical foundation for effectuating region-specific planning schemes fostering coordinated economic and ecological advancement within the study area.