Temporal-Spatial Evolution of Groundwater Nitrogen Pollution Over Seven Years in a Highly Urbanized City in the Southern China.

Understanding the temporospatial variation in nitrogen pollution in groundwater and the associated controlling factors is important to establish management practices that ensure sustainable use of groundwater. In this study, we analyzed inorganic nitrogen content (nitrate, nitrite, and ammonium) in 1164 groundwater samples from shallow, middle-deep, and deep aquifers in Zhanjiang, a highly urbanized city in the southern China. Our data span a range of 7 years from 2005 to 2011. Results show that shallow aquifers had been heavily contaminated by nitrate and ammonium. Temporal patterns show that N contamination levels remained high and relatively stable over time in urban areas. This stability and high concentration is hypothesized as a result of uncontrolled, illicit sewer discharges from nearby business facilities. Groundwater in urban land and farmland displays systematic differences in geochemical characteristics. Collectively, our findings demonstrate the importance of continuously monitoring groundwater quality and strictly regulating sewage discharges in Zhanjiang.