Spatial distribution characteristics of nitrate in shallow groundwater of the agricultural area of the North China Plain

Nitrate contamination of groundwater in the North China Plain had attracted much attention. However, the characteristics and degree of nitrate contamination of groundwater on large scale were not uniform due to the effect of different factors such as landscape type, land-use, soil structure, and aquifer hydrogeology. This paper comprehensively summarized some studies on the status of nitrate pollution in groundwater in the North China Plain. It also included our results on nitrate concentration in shallow groundwater in agricultural areas in the North China Plain in recent years. It was found that nitrate pollution in shallow groundwater existed in three typical landscape types, including headwater area (hilly areas of Taihang Mountain), piedmont plain and lowland plain. The headwater area had different land-use and good soil and aquifer permeability and therefore required much attention in terms of controlling nitrogen input. There was also the need for researches on how climate change affected hydrological process and nitrogen transport in the region. The piedmont plain had high agricultural production, with deep groundwater depth and thick saturated zone. Relatively high nitrate concentration in the piedmont plain was not only related to point source, wastewater leakage and wastewater irrigation, but also to over application of fertilizer in the farmland. The impact of over application of fertilizer on groundwater, the flow path and the potential threat on shallow groundwater quality were very important for future researches. The leaching rate of nitrate was lowered due to the fine sediment of soil in the lowland area. However, groundwater was at high risk of nitrate contamination because of the shallow groundwater depth. There was therefore the need for correct assessment of potential risks of nitrate pollution of groundwater based on surface water, soil and groundwater interactions.