Pollution footprint and its application in regional water pollution pressure assessment: a case study of Huzhou City in the upstream of Taihu Lake Watershed

After nearly twenty years of development, ecological footprint has become one of the most widely applied methods for sustainable development assessment. The ecological footprint is, however, unable to evaluate the impacts of human activities on natural ecosystems in an all-round way. The authors indicated that the failure of the conventional ecological footprint in providing a comprehensive measurement on human impacts lies in that the assumption of the exclusive land function has prevented the non-bioproductive commodities and services from being considered. To overcome the limitations in conventional ecological footprint theories, the authors suggested that the multi-functionality of land be acknowledged and the ecological footprint be built on multiple ecosystem services. The authors then proposed the concept of pollution footprint and elaborated its model construction and calculation methods. The pollution footprint, an ecological footprint based on pollution absorption, is a typical ecosystem services-based ecological footprint. It should be noted that the pollution footprint is not a simple replacement of energy footprint in the conventional ecological footprint; it is able to account for most pollutants incurred by human activities and to be further clarified in terms of different classes or types of pollutants. Given that organic matter, nitrogen and phosphorus are the main pollutants in Taihu Lake Watershed, the authors constructed organic, nitrogen and phosphorus pollutant footprint models and then utilized them to evaluate water pollution pressure of Huzhou City in the upstream of the watershed. Results showed that (1) pollution footprint of Huzhou City in 2007 was 39948.73 hm super(2), of which the eastern plain river-net areas accounted for a larger part than the western mountainous and hilly areas; (2) phosphorus and nitrogen pollutant footprints were larger than organic pollutant footprint in most counties and even towns of Huzhou City, which indicated that surplus phosphorus and nitrogen released by human activities there needed more water areas to assimilate than that organic pollutants required; (3) pollution capacity of Huzhou city in 2007 was 20896.00 hm super(2), leaving 19052.73 hm super(2) as pollution deficit, which implied that the amount of pollutants discharged by human activities there went far beyond the assimilation ability of local water body; (4) pollution pressure index of Huzhou City in 2007 was 1.91, revealing that the ci