Characteristics and environmental impact of non-point pollution of groundwater under the high-yield farmlands of North China—A case study from Huantai County,Shandong Province

Based on a case study of the typical highly yielding farmlands in Huantai County of North China,it is found that the polluted areas of non-point nitrate from farmlands develope unevenly.In a certain region, it is the flow of groundwater containing nitrate that differentiates the region into net-output and net-input zones,i.e.source zones and catchment zones.Groundwater pollution in the source zone is relatively stable but worsening in the catchment zones.The uniform spatial distribution of the polluted zones and the isolines of groundwater level strongly support an assumption that water flow decides the differential process of different polluted zones.The area of the polluted groundwater in the studying region accounts for about 56.57% of the total lands, among which 20.5% is more seriously contaminated with a nitrate concentration of 10mg/L.During a four years period,the nitrate concentration of groundwater increases by 27.2mg/L in the catchment zone, whereas the source zone keeps a little variation of 5.5～7.2mg/L. The nitrate-polluted shallow groundwater may cause the low-grade pollution of 5.8% and middle-grade pollution of 0.2% of the drinking water source, leading 38000 residents in health risk.In general,there is no inexorable correlation between the nitrate concentration of underlying groundwater and the farmland managements owing to not only the slow leaching but also the groundwater flowing.