Characteristics of nitrate in major rivers and aquifers of the Sanjiang Plain, China

The characteristics of nitrate (NO3-) in major rivers and aquifers of the Sanjiang Plain, China were investigated by hydrogeochemical conditions, nitrogen isotope technique and CFCs trace. An overall understanding on the sources and fate of NO3- in the surface water and the groundwater was obtained. The NO3- concentrations in the surface water were low and no samples exceeds the WTO standards. However, 11.4% of the groundwater samples exceeded the WTO standards, indicating local NO3- pollution in rural areas. Redox condition analysis revealed that most of the surface water had oxic condition, while for the shallow groundwater (mean well depth smaller than 30 m), the redox condition began to change into anoxic zone, and the deep groundwater (mean well depth larger than 50 m) showed strong anoxic condition. The delta N-15-NO3 data indicated soil N and fertilizer contributed the major sources in the surface water, and NO3- in the groundwater mainly showed a manure origin. In the Songhua-Heilong River, dilution effect was dominating, while for the Wusuli River, it showed that mix with water contained excess of NO3- resulted in the NO3- concentration increased along the river. Additionally, the NO3- transportation in the groundwater was analyzed by groundwater ages derived from environmental tracer (CFCs) data. The relation between the groundwater ages and the NO3- concentrations showed that the young groundwater with the age less than 60 years had higher NO3- concentrations than the old groundwater over the age of 60 years because anthropogenic activities began to boom from 1950s in the Sanjiang Plain