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| Spatial distribution and release risk of phosphorus in the sediment of agricultural ditch systems in the Chaihe River basin |
| Received:March 30, 2025 |
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| KeyWord:sedimentary phosphorus;phosphorus speciation;phosphorus loss risk;non-point source pollution;Chaihe River basin |
| Author Name | Affiliation | E-mail | | CAO Qianru | Institute of International Rivers and Eco-Security of Yunnan University, Kunming 650500, China | | | LUO Jiayi | School of Ecology and Environment, Yunnan University and Yunnan Provincial Key Laboratory of Highland Mountain Ecology and Degraded Environment Restoration, Kunming 650500, China | | | NONG Xinyi | Institute of International Rivers and Eco-Security of Yunnan University, Kunming 650500, China | | | ZHOU Wenlong | Institute of International Rivers and Eco-Security of Yunnan University, Kunming 650500, China | | | WU Xiaoni | School of Agriculture and Life Sciences, Kunming University, Kunming 650214, China | wuxiaoxiaoni@163.com | | FU Denggao | School of Ecology and Environment, Yunnan University and Yunnan Provincial Key Laboratory of Highland Mountain Ecology and Degraded Environment Restoration, Kunming 650500, China
International Joint Research Center for Ecological Restoration and Watershed Management of Plateau Lakes in Yunnan Province, Kunming 650500, China | dgfu@ynu.edu.cn |
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| Abstract: |
| The Chai River basin is a major contributor of agricultural phosphorus inputs to Dianchi Lake, and its ditch-stream network serves as a critical pathway for phosphorus migration. To elucidate the spatial heterogeneity and source-sink functions of sediment phosphorus during dynamic transport and to quantify the patterns of phosphorus accumulation and migration at different positions from farmland to river channels, this study established 11 representative sampling sites along the runoff pathway in the Chai River basin during the rainy season(August)of 2021. These sites encompassed greenhouse farmland/ditches, open-field farmland/ditches, secondary ditches, and river channels. Total phosphorus(TP), Olsen-P, and inorganic phosphorus fractions(Fe-P, Al-P, Ca-P, and O-P)in sediments were determined using conventional sequential extraction methods. The phosphorus activation coefficient(PAC)and risk assessment index(R) were employed to evaluate phosphorus release risk, and the source-sink functions were identified through spatial analysis. The results showed that soil phosphorus levels differed markedly between cultivation types: TP(4.8 g·kg-1)and Olsen-P(483.20 mg·kg-1)in greenhouse farmland soils were significantly higher than those in open-field farmland soils(TP 3.6 g·kg-1, Olsen-P 322.14 mg·kg-1). However, the corresponding ditch sediments in greenhouse areas had lower TP(2.5 g·kg-1)and Olsen-P(191.75 mg·kg-1)than those in open-field ditches(TP 4.7 g·kg-1, Olsen-P 545.51 mg·kg-1), indicating that greenhouse covering helps reduce the amount of phosphorus carried by runoff. Along the transport pathway(from site S1 farmland to S9 wetland), sediment TP and Olsen-P exhibited an initial increase followed by a decrease, with peak values observed in the upper river reaches(S5-S7: TP 4.0 g·kg-1, Olsen-P 471.70 mg·kg-1). Inorganic phosphorus accounted for 55%-86% of TP, and in river sediments Ca-P constituted as much as 62%-74%; the risk index R ranged from 0.35 to 1.03, suggesting a relatively high release risk. The phosphorus activation coefficient and risk assessment revealed that the farmland source areas(especially ditches in open-field cultivation zones)and the river sediments in the upper agricultural reaches of the Chai River functioned as the main“sources”of phosphorus loss, whereas the river sediments near the wetland displayed a potential “sink”function. In conclusion, greenhouse cultivation indirectly reduced phosphorus accumulation in ditches by curtailing runoff, whereas open-field farmland ditches became high-risk phosphorus“sources”due to particulate phosphorus inputs. Different landscape types along the transport pathway resulted in a spatial differentiation of sediment phosphorus characterized by an initial rise and subsequent decline. It is recommended that agricultural non-point source pollution control prioritize the interception of particulate phosphorus from open-field farmlands, optimize phosphorus fertilizer application rates in greenhouse areas, and expand wetland ecological barriers to strengthen their “sink”function. |
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