基于遥感的饮用水源地农业面源污染负荷估算

Assessment on agricultural non-point source pollution in a drinking water source using remote sensing images

近年来,农业面源污染(NPS)造成的水环境污染越来越严重、影响饮用水的安全,引起业内广泛关注。本文选取柴河饮用水源地二级保护区为研究对象,通过对当地居民进行问卷调查,提出一个新的机制性的方法来评估NPS的污染源(农业种植、畜禽养殖和农村生活)。利用动态平衡方程N污染=N流失+(1-α)N人+(1-β)N畜禽来分析TN、TP的动态变化和估算NPS总负荷。畜禽养殖和农村生活污染负荷评估采用排污系数法。此外,农业种植污染中施用化肥是一个重要的来源。利用遥感数据结合物候学理论,采用分类决策树法对作物进行分类并提取作物信息,确定作物类型。再建立归一化植被指数NDVI和不同作物产量之间的估产模型,施用肥料量可由此核算出来。结果表明,作物类型对遥感数据敏感,作物遥感估产模型的决定系数(R2)为0.91和0.64。由农业种植产生的TN和TP是最大的污染负荷,分别为205.9和61.61 t·a-1,这表明,农业种植是NPS的主要来源。研究成果有助于指导柴河饮用水源保护区的管理和降低下游水体受到污染的风险,达到恢复生态环境的成效。

Ever-increasing water environmental pollution, caused by non-point source （NPS） pollution, has seriously affected the safety of drinking water, which has drawn much more con- cern in recent years. Here, the secondary drinking water source protection of Chaihe Reservoir was selected. With a questionnaire survey, we proposed a new mechanistic method to assess the pollution sources of agricultural NPS pollution （e.g., agricultural planting, livestock farming and rural life） in this study. The dynamic equilibrium equation Np = NAp ＋ （ 1 -α ） NRF ＋ （ 1 -β） N1F, was used to analyze dynamic change of nitrogen and phosphorus and estimate the total load of NPS pollution. The livestock farming and rural life pollution loads were assessed by export coeffi- cient method. Additionally, the agricultural planting pollution load was mostly due to fertilizer ap- plication. Decision tree classification method was used to classify and extract the information of crop. The crop type was identified by land use, which was determined by remote sensing data and the theory of phenology. The amount of fertilizer application was calculated by crop-yield evalua- ting model, which was based on the relationship between NDVI and measured crop-yield. The re- suits showed that crop type was sensitive to remote sensing data. Both nitrogen and phosphorus pollution from agricultural planting contributed the maximum loads, being 205.9 and 61.61 t ·a^-1 , respectively, which indicated that agricultural planting was the main source of NPS load in the study area. Our results can help the management of this drinking water source protectionarea, decreasing in NPS loads into downstream water bodies and consequently restoring the eco- logical environment.