Abstract:

[Objective] This study aims to reveal the spatial distribution characteristics and loss patterns of soil nitrogen (N) and phosphorus (P) in the Danjiangkou Reservoir area, identify high-risk zones of N and P loss, and evaluate the mitigation effect of the Grain for Green Program on N and P loss. [Methods] Based on the 1꞉250000-scale soil geochemical survey comprising 5251 topsoil sampling points in the reservoir area, Kriging interpolation and ArcGIS spatial mapping were employed to characterize the spatial distribution patterns of soil N and P. A comprehensive risk assessment method for N and P loss was developed using the Soil and Water Assessment Tool (SWAT) model by integrating source intensity, transport risk, and receptor sensitivity, and the spatiotemporal characteristics of N and P loss loads were simulated. Three Grain for Green scenarios, with afforestation proportions of 10%, 30%, and 50%, were established to evaluate their mitigation effects on N and P loss. [Results] The distribution of soil N and P showed a “high in the south and low in the north” pattern, with high-value areas located in the southern mountainous forest regions and low-value areas concentrated in the northern and central agricultural hilly and valley areas. High N/P loss-load zones were mainly located in the northern and central agricultural areas, whereas high-sensitivity zones showed the opposite spatial pattern. The loss loads exhibited significant seasonal variation, with losses during the flood season (May-October) accounting for 80.4% and 82.8% of the annual N and P losses, respectively. The Grain for Green Program significantly reduced N and P loss; when the afforestation proportion reached 50%, the loss loads of total nitrogen (TN) and total phosphorus (TP) decreased by 70.32% and 71.87%, respectively. [Conclusions] Rainfall is the primary driving force of soil N and P loss, whereas land use and agricultural fertilization are the key anthropogenic factors. The Grain for Green Program can reduce the risk of N and P loss by decreasing surface runoff and soil erosion, and these findings provide a scientific basis for nonpoint-source pollution control and ecological management in the reservoir area.

Key words: geochemical survey, soil, SWAT model, nitrogen and phosphorus loss, Danjiangkou Reservoir area

摘要：

【目的】揭示丹江口库区土壤氮磷的空间分布特征与流失规律，识别氮磷流失高风险区，评估退耕还林对氮磷流失的削减效应。【方法】依托库区1꞉25万土壤地球化学调查（5251个表层样点），采用克里金插值与ArcGIS空间制图揭示土壤氮磷空间分布格局；基于SWAT模型，综合考虑源强、迁移风险和受体敏感性，构建氮磷流失综合风险评估方法，模拟其流失负荷的时空特征；设置10%、30%和50%等3组退耕还林情景，评估其对氮磷流失的削减效果。【结果】土壤氮磷分布呈“南高北低”格局，高值区位于南部山地林区，低值区集中在北部和中部农耕丘陵及河谷区。氮磷流失高负荷区与高敏感区分布格局相反，主要位于北部和中部农耕区。流失负荷季节变化显著，汛期（5－10月）氮磷流失量分别占全年的80.4%和82.8%。退耕还林可显著削减氮磷流失，退耕比例达50%时，总氮和总磷流失负荷分别削减70.32%和71.87%。【结论】降雨是土壤氮磷流失的主要驱动力，土地利用和农业施肥是关键人为因素。退耕还林通过减少地表径流和土壤侵蚀可降低氮磷流失风险，研究结果为库区面源污染防控和生态管理提供了科学依据。

关键词: 地球化学, 土壤, SWAT模型, 氮磷流失, 丹江口库区