Characteristics of spatial distributions for nitrate and traceability of pollution in shallow groundwater of the Qingshui River Basin, China

ABSTRACT To investigate the primary reasons for the increase in nitrate concentrations in shallow groundwater within the water source unit of small watersheds in northern China, the Qingshui River watershed was selected as a representative case study. This study employed water chemistry and stable isotope analyses to draw conclusions. The groundwater chemistry in the study area was characterized by the HCO3– + CO32– − Ca2+ + Mg2+ type. At the onset of the cultivation period in May, the composition of groundwater substances is largely controlled by the dissolution of rock, while the impacts of fecal sewage and agricultural fertilizers remain minimal. However, by June, the nitrate concentration in the groundwater of the study area had doubled compared to that in May. The nitrate concentration in the western part of the study area exhibited an exponential increase, which was primarily attributed to nitrogen transport in the soil. Cropland emerged as the land use type exerting the most significant influence within the 500 and 1,000 m of buffer zones. Consequently, the composition of groundwater in the source area is primarily regulated by natural factors; however, with seasonal changes, increasingly frequent farming, and other anthropogenic activities, there has been an abnormal rise in nitrate levels.