Reference ion method: A simple and fast method for quantitatively identifying the source of nitrate and denitrification rate in groundwater

Abstract

The effective control and management of nitrate (NO3−) pollution requires the identification of the sources of NO3− pollution in groundwater and quantification of their contribution rates. In this study, the molar concentration ratio of NO3−/Cl− (n(NO3−)/n(Cl−)) and the molar concentration of Cl− (n(Cl−)) (reference ion method; RIM) was first used to identify the NO3− sources and estimate their contribution rates in groundwater. The relationship between the Cl− concentration and NO3− concentration (reference ion method; RIM) was used to judge whether denitrification had occurred and to estimate the denitrification rate in groundwater. It was proved that homology analysis was the prerequisite for applying the RIM. The main NO3− sources included chemical fertilizers (CF), sewage/manure (M&S) and soil nitrogen (SN). The contribution rate of CF in the vegetable planting area (upstream regions) (69.12%) was significantly higher than that in the grain planting area (midstream regions and downstream regions) (14.29% and 14.29%). The difference in the contribution rates of NO3− in the grain planting area was greater than that in the vegetable planting area. The results indicated that denitrification rate in the grain planting area was higher than that in the vegetable planting area, while the temporal variations in the denitrification rate in the vegetable planting area were consistent with in the grain planting area. The RIM offers a useful and simple way to quantify the contribution rates of NO3− sources and denitrification rates in groundwater.