ABSTRACT
IntroductionWith the rapid growth of China’s economy, more and more nutrients such as nitrogen (N) and phosphorous (P) are utilized through human economic and consumption activities. Consequently, huge wastewater-containing nutrients are discharged into the water environment and have caused more and more serious eutrophication (Carpenter et al., 1998; Chen et al., 2008). Eutrophication is a process by which lakes becomes increasingly rich in plant biomass as a result of the enhanced input of plant nutrients mainly N and P (Golterman et al., 1991). It has been shown to negatively affect water-use for fisheries, recreation, industry, agriculture, and drinking (Carpenter et al., 1998). Eutrophication has also become
one of the most important factors in the delay in Chinese economic growth, while at the same time actually pushing China away from its desired sustainable development goals (Liu & Qiu, 2007). In order to mitigate eutrophication, the Chinese government has promoted a range of actions, including new policies and technologies (SEPA, 2002). These have made great progress and improved the environmental quality. While focused only on natural factors, such as lake sediment, sludge, and algae, influencing water quality, these new policies lack systematic and comprehensive analysis of the human activities, which primarily cause eutrophication (Huang et al., 2008; Matsuoka et al., 1986). Eutrophication has become increasingly serious in China, particularly in recent years (Li, 2006; Li et al., 2004; Zhang & Liu, 2007; Zhao et al., 2010). For many lakes, excessive P, rather than N, is usually the limiting nutrient for growth of aquatic plants and thus the primary cause of eutrophication (Carpenter et al., 1998; Drolc & Koncan, 2002). Meanwhile, as eutrophication mainly originates from human activities, such as the application of fertilizer and manure to crops, increased soil erosion and runoff from fields, feeding animals, and the discharge of urban and industrial wastes (Bennet et al., 1999; Deunert et al., 2003; Drolc and Koncan, 2002; Schroder et al., 2004; Smil, 2000), reducing the impacts of these sources on surrounding water is critical to alleviating eutrophication of lakes around. For mitigating eutrophication, it is important to understand the driving forces of P loss to water in the socioeconomic system first. Therefore, tracing and identification of the anthropogenic P pathways or flows throughout socioeconomic ecosystem is necessary for eutrophication mitigation based on the concept of life cycle nutrient management (Kennedy et al., 2007). In order to identify and trace the sources of P loads into water environment, we launched a longtime research program to quantify the pathways of anthropogenic P and N flows in Taihu and Chaohu watershed. We conducted an analysis of anthropogenic P in Chaohu watershed in 2008 (Li et al., 2010; Yuan et al., 2011a; 2011b; 2011c), as a pilot, through which we concluded that the largest three contributors to P losses into surface water environment in the socioeconomic system are crop farming, large-scale breeding, and rural consumption. However, the question is how to identify and analyze the factors that cause the present situation of anthropogenic P loss.
