基于AnnAGNPS模型的三峡库区秭归县非点源污染输出评价

Assessment of non-point source pollution export from Zigui county in the Three Gorges Reservoir area using the AnnAGNPS model

非点源(NPS)污染已成为全球关注的环境问题。由于NPS特点、实验手段和监测数据的局限,其研究多采用数学模型进行时间和空间模拟。模型模拟提供了一种成本低效率高的手段来评定区域非点源污染。选择连续农业非点源污染AnnAGNPS(Annualized AGricultural Non-Point Source)模型,构建该模型数据库,模拟秭归县黑沟、兰陵溪、杉木溪等3条典型流域和县域径流、泥沙和营养物质的输出。结果表明:AnnAGNPS模型对3条典型流域的径流模拟能力高于对泥沙和养分的模拟,径流模拟误差均在可接受范围之内,说明模型中采用的径流预测(SCS曲线)法对研究区的地理气候条件是适用的;对3条典型流域泥沙输出模拟误差较高,对氮磷等养分输出模拟的误差最高,通过调整RUSLE和HUSLE等子模型的输入参数来减小泥沙模拟误差;对小型降雨径流事件,模型泥沙、养分模拟误差有偏大趋势,对较大降雨径流事件,模型泥沙和养分模拟误差有偏小趋势;2006年秭归县县域模型模拟的地表径流量为363 mm,泥沙输出为19.6 t/hm2,总氮输出为122 kg/hm2,总磷输出为28 kg/hm2,有机碳输出为581 kg/hm2,模拟结果与相关文献研究和政府统计数据较为相符;AnnAGNPS模型对NPS污染物输出模拟具有一定的不确定性,但作为一个较好的高级农业流域管理工具,该模型可以在三峡库区地理气候条件下使用。

Non-point source（NPS） pollution has become a global environmental issue and a widely discussed form of environmental degradation in recent years.Because of the nature of NPS and the limitations of assessing it through experiments and field measurements,its management is highly dependent on spatial simulation modeling which helps deal with the spatial uncertainty associated with NPS pollution.In the last three decades,several computer simulation models have been developed to provide a better understanding of hydrological systems,sediment transport and associated pollutant loading.Annualized AGricultural Non-Point Source（AnnAGNPS） is a continuous simulation,watershed-scale model intended to be used as a tool to evaluate NPS pollution.In the Three Gorges Reservoir area,non-point source pollution studies are still in their infancy.Although soil erosion has been a major problem in this area,erosion studies are very much limited to using the universal soil loss equation（USLE）.The objectives of this study were to prepare a database for the simulation of runoff and non-point source pollution using the AnnAGNPS model,and to assess the applicability and predictive capability of the model as a long-term monitoring tool in Zigui county.The model was calibrated and validated using observed stream flow and sediment load data from the Heigou,Lanlingxi and Shamuxi watersheds in Zigui county.The calibrated model was then used to simulate runoff,sediment yield and nutrient export from the county.Digital elevation models were generated from digitized topographical data.Based on critical source area and minimum source channel length specifications,Zigui county was divided into 1966 cells and 986 channel reaches.Results showed that the model predicted the runoff volume of the three typical watersheds within an acceptable range.This indicates that the SCS curve number method used in the AnnAGNPS model is suitable for runoff volume prediction.Sediment yield predictions for the three typical watersheds were only moderately accurate but the predictions were improved by amending the input parameters for both the RUSLE and HUSLE sub-models.In general,the model performed well in simulating runoff compared to sediment and nutrient loadings.For smaller events,the model generally over-predicted sediment and nitrogen loadings,while under-predicting for larger events.The prediction for total phosphorus showed obvious uncertainties.The model predicted the export from Zigui county in 2006 of 363 mm of runoff,19.6 t/hm2 of sediment yield,122 kg/hm2 of total nitrogen,28 kg/hm2 of total phosphorus,and 581 kg/hm2 of total organic carbon.The simulation results were in accordance with related studies and government statistics.As a watershed management tool,AnnAGNPS can be used to formulate different management strategies for soil and water conservation in hilly parts of the Three Gorges Reservoir area with mixed types of land use and steep slopes.