Abstract. The effects of ecological and human activities on nonpoint source (NPS) pollution are key issues for sustainable water resources management. In this study, the Improved Export Coefficient Model and the Revised Universal Soil Loss Equation were adopted to estimate the annual loads of NPS pollutants during the period from 1960 through 2003 in the upper reach of the Yangtze River (URYR). Ecological factors and human activities affecting NPS pollution were distinguished and their respective effects were assessed. Variations of the dominant cause (between ecological factors and human activities) were presented. Furthermore, the combined effect of them on NPS pollution were successfully revealed. The results showed that the annual loads raised from ecological factors of dissolved nitrogen (DN) and dissolved phosphorus (DP) were relatively steady from 1960 to 2003. But those of sediment, absorbed nitrogen (AN) and absorbed phosphorus (AP) decreased during that period. In terms of the annual loads caused by human activities, those of dissolved pollutants increased from 1960 to 2000 and then fell. Those of sediment as well as absorbed pollutants peaked in 1980 and then decreased. Simultaneously, the dominant cause of DN loads shifted from ecological factors to human activities after 1980 while DP loads were mainly contributed by human activities. However, sediment, dissolved pollutants were primarily exported by ecological factors. Finally, strategies for managing anthropogenic activities were proposed and their effects on NPS pollution reduction were also depicted quantitatively.

Nonpoint source pollution generated by agricultural production and city construction has been studied for decades, but very few researches have been conducted on the regional assessment of nonpoint source pollution in the acid rain regions, particularly relating to the control of pollutant in the drinking water source areas. In this study, an integrated framework was applied to estimate nitrogen and phosphorous load in a typical acid rain influenced reservoir, China. The method comprised three separate steps: (1) a watershed model-soil and water assessment tools-was used to estimate nitrogen and phosphorous load from the upper stream watershed; (2) collection of acid rain samples, together with a GIS-based calculation to estimate the atmospheric deposition flux; (3) introduction of a simple export coefficient method. The case study indicated atmospheric deposition accounted for 56.75 % of total nitrogen load during the year, with the highest level of deposition load taking place during the wet season. Maximum phosphorous (93.37 %) was linked to the upstream runoff, originating from the upper watershed. Further analysis by watershed model and export coefficient method indicated forest exported most total nitrogen (27.72 %) and total phosphorous (58.78 %) in the upstream watershed. Results indicated that in the region influenced by acid rain, the nitrogen management should encompass the management of land use practices and the control of acid rain in catchments feeding into drinking water storage areas. It could be inferred that NOX emissions might cause both globe warming and eutrophication in the drinking water sources. This paper could provide a basis for water quality management in such regions.

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