Abstract
Shanghai, as one of the megacities and economic centers of China, is facing critical water quality challenges. This study analyzed the impact of urbanization on the water quality in Shanghai, from 2007 to 2015, using remote sensing (RS) and geographic information system (GIS) techniques. Five measurements of water quality were employed: total discharged wastewater volume, general water quality levels, dissolved oxygen (DO), permanganate, and ammonia nitrogen. The impacts of urban land-use changes on water quality were examined. An urban index was extracted from satellite image classification and was used to quantify the anthropogenic activities. In the watershed level, unit watersheds were delineated from topography and stream segments. Results showed that the primary contributors of water quality degradation in Shanghai were DO and ammonia nitrogen. Both indicators expressed clear seasonal patterns that can be explained by agricultural activities and urbanization processes in Shanghai during the study period. Water quality was also regulated through water use policies. For example, the degraded water quality in suburban outskirts and improved water quality was achieved through the enforced wastewater discharge regulations in central Shanghai. Analytical findings provide spatially explicit information for governmental management on protecting water resources and controlling wastewater emissions, thus, improving the quality of living environments in this ever-growing megacity.
Highlights
Water is the most vital living prerequisite for mankind
Applying an approach developed by Li et al [14] to address water quality problems, this study explored long-term water sampling records within the study period of 2007–2015 using two satellite images to investigate the spatial-temporal variation of water quality and its relationships with land-use changes in the urban watershed of Shanghai
The study area covers the city of Shanghai, which is composed of 16 urban districts, 210 suburban townships, and rural villages with a total area of 6341 km2 (Figure 1)
Summary
Water is the most vital living prerequisite for mankind. China has been pressured by an enormous population, limited water resources [1,2], and water contamination issues [3,4]. The extensive use of pesticides and fertilizers is of grave concern for ground and surface water contamination with biological chemicals [28,36] These influential factors in Shanghai urban ecosystems have not been thoroughly investigated and merit further study. Applying an approach developed by Li et al [14] to address water quality problems, this study explored long-term water sampling records within the study period of 2007–2015 using two satellite images to investigate the spatial-temporal variation of water quality and its relationships with land-use changes in the urban watershed of Shanghai
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