Detection of nitrate sources in urban groundwater by isotopic and chemical indicators, Hangzhou City, China

The sources of nitrate in the shallow groundwater at urban area, Hangzhou City, China were investigated using chemical and isotopic techniques. Groundwater electric conductivity was high in the study area and ranged from 369-1,544 μS/cm. Most of the groundwater was weakly alkaline and the groundwater chemistry was seriously influenced by land use in the city. There was a high frequency of groundwater (43% of total) with nitrate above World Heath Organization's standards of 10 mg NO^sub 3^/L. The different land-use areas had different nitrate concentrations (0.04-34.41 mgN/L) and δ^sup 15^N^sub NO3^ values (7.8~35.5[per thousand]). Domestic wastewater was the major nitrate source of shallow groundwater in the urban area, and the point source (septic tank) still existed in residential settings. At agricultural settings manure was the major NO^sub 3^ sources. High δ^sup 15^N^sub NO3^value (>20[per thousand]) and temporal variations of the δ^sup 15^N^sub NO3^ value suggested that in residential areas it probably resulted from denitrification.[PUBLICATION ABSTRACT]