College of Geography and Tourism, Chongqing Normal University, Chongqing 401331, China.
College of Resources and Environment, Southwest University, Chongqing 400716, China.
Environ Sci Process Impacts. 2015 Nov;17(11):1976-89. doi: 10.1039/c5em00380f.
Nonpoint source pollution is one of the primary causes of eutrophication of water bodies. The concentrations and loads of dissolved pollutants have a direct bearing on the environmental quality of receiving water bodies. Based on the Johnes export coefficient model, a pollutant production coefficient was established by introducing the topographical index and measurements of annual rainfall. A pollutant interception coefficient was constructed by considering the width and slope of present vegetation. These two coefficients were then used as the weighting factors to modify the existing export coefficients of various land uses. A modified export coefficient model was created to estimate the dissolved nitrogen and phosphorus loads in different land uses in the Three Gorges Reservoir Region (TGRR) in 1990, 1995, 2000, 2005, and 2010. The results show that the new land use export coefficient was established by the modification of the production pollution coefficient and interception pollution coefficient. This modification changed the single numerical structure of the original land use export coefficient and takes into consideration temporal and spatial differentiation features. The modified export coefficient retained the change structure of the original single land use export coefficient, and also demonstrated that the land use export coefficient was not only impacted by the change of land use itself, but was also influenced by other objective conditions, such as the characteristics of the underlying surface, amount of rainfall, and the overall presence of vegetation. In the five analyzed years, the simulation values of the dissolved nitrogen and phosphorus loads in paddy fields increased after applying the modification in calculation. The dissolved nitrogen and phosphorus loads in dry land comprised the largest proportions of the TGRR's totals. After modification, the dry land values showed an initial increase and then a decrease over time, but the increments were much smaller than those of the paddy field. The dissolved nitrogen and phosphorus loads in the woodland and meadow decreased after modification. The dissolved nitrogen and phosphorus loads in the building lot were the lowest but showed an increase with the progression of time. These results demonstrate that the modified export coefficient model significantly improves the accuracy of dissolved pollutant load simulation for different land uses in the TGRR, especially the accuracy of dissolved nitrogen load simulation.
非点源污染是水体富营养化的主要原因之一。溶解态污染物的浓度和负荷直接关系到受纳水体的环境质量。本文基于 Johnes 输出系数模型，引入地形指数和年降雨量实测数据，建立了污染物产生系数；考虑到现有植被的宽度和坡度，构建了污染物截留系数。然后，将这两个系数作为加权因子，对各种土地利用类型的现有输出系数进行修正，建立了改进的输出系数模型，以估算三峡库区 1990 年、1995 年、2000 年、2005 年和 2010 年不同土地利用类型的溶解态氮磷负荷。结果表明，新的土地利用输出系数是通过修正产污系数和截留系数得到的。这种修正改变了原有土地利用输出系数的单一数值结构，考虑了时空分异特征。改进后的输出系数保留了原有单一土地利用输出系数的变化结构，同时也表明土地利用输出系数不仅受土地利用变化本身的影响，还受到下垫面特征、降雨量和植被整体状况等其他客观条件的影响。在分析的 5 个年份中，计算中应用修正后，稻田的溶解态氮磷负荷模拟值增加。旱地的溶解态氮磷负荷占三峡库区总量的最大比例。修正后，旱地的值随时间呈先增加后减少的趋势，但增量远小于稻田。林地和草地的溶解态氮磷负荷修正后减少。建设用地的溶解氮磷负荷最低，但随着时间的推移呈增加趋势。这些结果表明，改进的输出系数模型显著提高了三峡库区不同土地利用类型溶解污染物负荷模拟的准确性，特别是溶解氮负荷模拟的准确性。
