Long-Term Effects of Ecological Factors on Nonpoint Source Pollution in the Upper Reach of the Yangtze River

Abstract

Nowadays, nonpoint source pollution has been a dominant cause of water quality deterioration and eutrophication. For large basins, long-term effects of ecological factors on nonpoint source pollution are significant and have gained worldwide attention. Yangtze River is the largest river in China, and water environment protection of its upper reach is crucial to maintain the whole river health and the Three Gorges Project successful operation. The objective of this study is to reveal the effects of ecological factors on nonpoint source pollution in the upper reach of the Yangtze River during the period from 1960 through 2003 by the Improved Export Coefficient Model and the Nutrient Losses Empirical Model. The results indicated that during those decades the effects of ecological factors on dissolved pollutants were constant whereas those on sediment as well as absorbed pollutants changed slightly and decreased obviously after 2000. Comparing to anthropogenic factors, ecological ones had a dominant influence on sediment and absorbed pollutants. As for load intensities, long-term effects of ecological factors on dissolved pollutants hadn't changed much, while those on sediment as well as absorbed pollutants was increasingly significant and then reached an ultimate in 1980. Atmospheric deposition, grassland as well as forest were important sources of dissolved nitrogen export, nevertheless, grassland and forest were the main export areas of dissolved phosphorus, sediment as well as absorbed pollutants. The study would facilitate the source identification and nonpoint source pollution control in the upper reach of the Yangtze River to improve water quality.

Long-Term Effects of Anthropogenic Factors on Nonpoint Source Pollution in the Upper Reaches of the Yangtze River

“…It was further shown that the loss of sediment and adsorbed pollutants was related to soil erosion and pollutant characteristics. These results are consistent with previous studies [2,22], indicating that anthropogenic factors were main sources of dissolved pollutants, and ecological factors were main sources of sediment and adsorbed pollutants.…”

“…It was further shown that the loss of sediment and adsorbed pollutants was related to soil erosion and pollutant characteristics. These results are consistent with previous studies [2,22], indicating that In terms of DN, the annual loads caused by rural life, livestock breeding, land use and atmospheric deposition all showed an upward trend from 1960 to 2000, and declined by 2003. The contribution rate of rural life to the total pollution load decreased, and the contribution rate of livestock breeding did not change significantly.…”

“…where L is loss of nutrients (kg); α is precipitation impact factor; β is terrain impact factor; E i is the export coefficient for the nutrient source i (kg/ca·yr or kg/km 2 ·yr); A i is area of the watershed occupied by land use type i (km 2 ), or number of livestock type i, or that of rural people; I i is the input of nutrients to source i (kg); and p is the input of nutrients from atmospheric deposition (kg). Moreover, the calculation methods of precipitation impact factor α and terrain impact factor β have been presented in previous articles [2]. Next, this study determined the value of α t through regression analysis and related formulas.…”

“…Both anthropogenic factors and ecological factors have a major impact on NPS pollution. Ecological factors bring pollutants into water sources through rainfall [2], soil loss and transport of nutrients such as nitrogen and phosphorus pollutants [3]. Anthropogenic factors mainly take into account the sediment particles; nitrogen, phosphorus, and other nutrients; pesticides and other harmful substances [4]; livestock breeding wastewater [5]; and urban living garbage.…”

“…According to previous studies, although ecological factors have had a certain impact on non-point source pollution, anthropogenic factors [12] have had more serious effects. Anthropogenic factors such as agricultural land use and rural life have increased the content of pollutants in soils and atmosphere, have affected change climatic characteristics, topography, soil structure and vegetation areas, and have destroyed ecosystems on land [2]. Therefore, many scholars have studied the non-point source pollution in the Yangtze River Basin.…”