Characteristics and traceability analysis of nitrate pollution in the Yellow River Delta, China

Abstract

The Yellow River Delta is one of the regions with the highest nitrogen application rate in China. Because of the high-intensity development and utilization of the Yellow River Delta, a large number of nitrate inorganic nitrogen pollutants have been transported offshore through rivers, which poses a threat to the ecological environment security of the region. The distribution characteristics of nitrate pollution, the source and transport characteristics of nitrate in surface water are unclear. In this study, we collected soil and surface water samples, determined stable isotopes of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3 and δ18O-NO3), and used the Isosource model to quantitatively analyze the distribution characteristics of soil nitrate-nitrogen and source characteristics of surface water nitrate. The results showed that: (1) The average content of NO3 --N in cultivated soil was 3.99 times higher than that in non-cultivated soil, in which cornfield > cotton field > soybean field > paddy field; (2) The nitrate flux of surface water increased from upstream to downstream, which was positively correlated with basin area; (3) In the middle and upper reaches of the study area, the surface water is mainly replenished from the Yellow River water and groundwater, while the lower reaches are affected by seawater intrusion; (4) The primary source of nitrate in the study area was dominated by human activities of agricultural production and residents’ lives, with a total contribution of 60.8%. This study will provide a scientific basis for the treatment of nitrate pollution in coastal areas.