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| Linking Watershed Nutrient Loads and Riverine Export to Reservoir Eutrophication: The Case of Shanzai Reservoir, Fujian Province |
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| KeyWord:reservoir watershed; nutrients pollution; eutrophication; N∶P ratio; Shanzai Reservoir |
| Author Name | Affiliation | | CHEN Neng-wang | College of the Environment and Ecology/Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University | | WU Yin-qi | College of the Environment and Ecology/Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University | | ZHANG Yu-zhen | Fujian Provincial Academy of Environmental Science | | SU Yu-ping | Environmental Science and Engineering College of Fujian Normal University | | ZHAN Xuan-can | Environmental Science and Engineering College of Fujian Normal University | | MO Xiu-juan | Fujian Provincial Environmental Monitoring Center |
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| Abstract: |
| A quantitative analysis of watershed nitrogen（N） and phosphorus（P） loads, riverine export and other inputs to reservoir was conducted for Shanzai reservoir in Fujian Province. Spatial variation of N and P pollution and major components were interpreted at town and sub-watershed scale using GIS techniques, and the critical source area（CSA） was indentified. The linkage between reservoir water quality and watershed nutrients loading and riverine export fluxes was examined. Results revealed that total N and P loads per unit area of the Shanzai watershed were 13.4 kg N·hm-2·a-1 and 0.82 kg P·hm-2·a-1, respectively. Domestic sewage and fertilizer runoff accounted for 64% of total N load, and livestock waste and domestic sewage shared 90% of total P load. Total N and P loads to the Shanzai reservoir were 3248 t N·a-1 and 192 t P·a-1, 62% and 89% of which were through riverine transport and the remainder mostly from sediment release. Less than 2% of inputs were from non-point sources in the surrounding area. Town-level N and P loads per unit area ranged from 3.54~20.0 kg N·hm-2 and 0.38~2.50 kg P·hm-2, respectively. Two towns（Rixi and Huokou） adjacent to the reservoir were identified as CSA of fertilizer runoff and livestock waste, while human sewage dominated the nutrient load（42%~84% of total） in other towns in the upstream area. Huangdidong subwatershed was the most polluted catchment（19.4 kg N·hm-2; 1.95 kg P·hm-2）, followed by the lower reaches of Huokou River and Rixisubwatershed. The high value of total N concentration was observed near the dam head and Rixi inlet, whereas high total P concentration was found in channel from Huokuo inlet to Xiaocang. The spatial variation of the nutrients level in the reservoir was highly associated with watershed nutrient loads, riverine export and sediment-water exchange, indicating that riverine input is the decisive factor contributing to eutrophication of the reservoir. The average N∶P ratio of the nutrient load was calculated as 16 for the whole watershed, which combined with the TN∶TP ratio of 15~20 observed in reservoir surface water suggested that the reservoir ecosystem was weakly limited by P and tended to stimulate algal bloom. To mitigate eutrophication, reduction of both N and P pollution should be considered in those CSAs, with a priority given to P pollution from livestock and phosphate fertilizer loss. |
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