基于SWAT模型的汾河灌区非点源污染负荷评估

Evaluation of non-point source pollution load in Fenhe Irrigation District based on SWAT model

近年来,由于集约化种植、畜禽养殖及农村生活污水排放等,大部分灌区出现严重的农业非点源污染,了解灌区内非点源污染程度及其产输出特征,对于保证灌区的可持续发展显得越加重要。以山西汾河灌区为研究区域,利用灌区出口义棠水文站1997—2006年水量、2004—2006年总氮TN和总磷TP实测数据,基于SWAT模型构建了汾河灌区非点源污染分布式模型。探讨了灌区农业非点源污染负荷(主要是TN和TP)的时间分布规律,识别了非点源污染关键区,并分析了各类污染源的贡献率。结果表明:灌区TN、TP流失大多发生在汛期(7—9月),二者在汛期的流失量分别占全年负荷量的58.5%和76.0%;灌区自上而下,氮、磷污染有逐渐加重的趋势,灌区硝态氮浓度均小于10mg/L,可溶性磷关键区(可溶性磷浓度大于50μg/L)主要分布在汾河太原段、汾西和三坝灌区;土壤固有养分流失、种植施肥、农村生活和畜禽养殖污水排放产生的TN负荷分别占灌区总量的47.1%、24.3%、13.0%和15.6%,产生的TP负荷分别占58.7%,12.1%、7.6%和21.6%。

There are very serious non-point source pollution problems in irrigation districts of China due to intensive crop planting and fertilizer application. It is of importance to quantify the non-point source pollu- tion and understand its characteristics in such areas. The Soil and Water Assessment Tool （SWAT） has been proved to be capable and effective in simulating water, sediment, and chemical loadings in watershed scale. In this study, SWAT （version 2009） was evaluated using ten years of measured flow data and three years of measured Total Nitrogen/Phosphorus （TN/TP） data in the Fenhe irrigation district in Shanxi prov- ince of North China. For the water cycle, the model was calibrated during the period of 1997--2001 and validated during the period of 2002--2006, and for the Total Nitrogen/Total Phosphorus （TN/TP） loads,it was calibrated in 2004--2005 and validated in 2006, respectively. Based on the calibrated SWAT model, time distribution of pollution loadings were analyzed, the key source areas were identified and the pollution loading contributions from different sources were also discussed. The results show that TN/TP losses mostly occurred in the rainy season （July to September）, and the amount of the TN and TP loss in the flood sea- son accounted 58.5% and 76.0% of the total annual load, respectively; the nitrogen and phosphorus loss in- creased gradually from north to south, and the nitrate concentration was below 10mg/L, while the key source areas of soluble phosphorus with concentration of soluble phosphorus greater than 50p^g/L were near Taiyuan and within Fenxi and Sanba irrigation areas; TN loss from soil nutrients, fertilizer, rural life and livestock accounted for 47.1%, 24.3%, 13.0% and 15.6% of the total TN load while the percentage of TP was 58.7%, 12.1%, 7.6% and 21.6%, respectively.