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| Water and nutrient losses on runoff plots in the mountainousarea at western Beijing |
| Lu Bingjun, Wang Zhiqiang |
| Beijing Normal University, State Key Laboratory of Earth Surface Processes and Resource Ecology, School of Geography, 100875, Beijing, China |
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Abstract Many studies on the nonpoint pollution in Beijing area have been conducted in the last couple of decades, and the nutrient losses by rainfall erosion on farmland once were considered as the major source of nonpoint pollution in Beijing area. Nevertheless, thanks to intensified soil and water conservation measures, the ecosystems in Beijing are being recovered, and the types of land use are also changing from monotonous land use dominated by farmland to multiple land use types. This change of landuse has made it urgent to identify source areas of nonpoint pollution to establish more effective measures of nonpoint pollution control. This study analyzed the sediment yield (SD), runoff, total phosphorus (TP) and total nitrogen (TN) losses based on the data collected at the 21 runoff plots located in the mountainous area of western Beijing in 9 years from 2005 2013. Some of the plots were mainly composed of natural grasses with varying vegetation coverage, some were in the process of various soil and water conservation practices,and the rest were fallow croplands. The results showed that 1) there were significant correlations among the values of sediment yield (SD), runoff, TP loss and TN loss. 2) The SD, runoff, TP and TN losses decreased exponentially with the increase of grass vegetation coverage. 3) Natural grass (NG), plante dgrass (PG), stone terrace /vegetable (ST), tree disk /planted tree (TD) can significantly decrease the SD, runoff, TP and TN losses. The average ratios of SD, runoff, TP and TN losses of the four plots with conservation measures to those of the fallow plots were 0.02, 0.21, 0.15 and 0.32, respectively. Amongthe conservation strategies, the PG was the most efficient one, with the NG and TD followed. Although crops were the least effective in controlling SD, runoff, TP and TN losses compared to other measures, they still reduced SD, runoff, TP and TN losses by 77%, 34%, 36% and 39%, respectively compared to fallow plots. The results of this study showed clearly that above mentioned conservation measures can largely reduce SD, runoff, TP and TN losses; however, their efficiency in controlling TN loss was less than that for SD, partly due to some forms of nitrogen are dissolved in the runoff. Considering that the runoff controlling efficiency of those conservation practices was less than SD, the nitrogen loss may remain as an environmental problem that needs further assessment, and more control practices should be taken even combining with the existing soil and water conservation measures.
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Received: 12 February 2015
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