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| Characteristics and simulation of nitrogen and phosphorus in complex watersheds:A case study in the Yuntaishan River Basin in Nanjing City, China |
| Received:July 22, 2020 |
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| KeyWord:complex watershed;nitrogen and phosphorus pollution;temporal and spatial distribution;non-point source pollution load simulation;output characteristics |
| Author Name | Affiliation | E-mail | | REN Zhi-hui | School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China | | | ZHAO Chun-fa | Water Affairs Bureau of Jiangning District, Nanjing City, Nainjing 211100, China | | | WANG Qing-qing | School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China | | | XU Yun-yun | School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China | | | GUO Jia-xun | School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China | | | WANG La-chun | School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China | wang6312@263.net.cn |
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| Abstract: |
| To quantitatively evaluate the impact of nitrogen and phosphorus from non-point source pollution on the water environment of a complex watershed, the Yuntaishan River Basin in Nanjing City was considered a case study. A rainfall-runoff hydrological model and nonpoint source pollution load model was constructed in combination with in-situ observations. The temporal and spatial characteristics of the total nitrogen(TN)and total phosphorus(TP)concentration in Yuntaishan River were analyzed, as well as the inflow characteristics of TN non-point source pollution on different underlying surfaces of the basin. The monitoring results showed that the average concentration of TN was 5.1 mg·L-1, exceeding the Grade Ⅳ water quality standards. The average concentration of TP was 0.14 mg·L-1, and only the tributary of Yangshan River exceeded the Grade Ⅳ water quality standard. The overall TN concentration in the downstream region was higher than that in the upstream region, and higher in the dry season than in the rainy season. The spatial change in TP concentration was not obvious, with a slow downward trend throughout the year. The hydrological model and non-point source pollution load model had a good simulation effect on TN. The simulation results showed that the annual TN output in the basin was 581.1 t, mainly from farmland runoff and rural living pollution sources. Shengli River and the main stream areas were the key sources of TN pollutants. The annual amount of TN pollutant in the Yuntaishan River basin was 187.8 t, accounting for 32% of non-point source production. Land use and urbanization affected the amount of nitrogen pollutant in the rivers in different areas, showing significant spatial differences. To achieve the target water quality, TN needs to be reduced by 137.3 t·a-1 in the watershed, and farmland runoff/rural pollution needs to be controlled. This study showed that in the absence of hydrological data, the combination of in-situ observations and model construction could achieve the quantitative estimation of non-point source pollutant load in a watershed. |
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