Influence of hydrogeological and geochemical parameters on N2O in the groundwater in the irrigation area of lower reaches of Yellow River

The plains of the lower reaches of rivers are important areas for food production. In the groundwater of irrigated agricultural areas of these regions, the N2O concentration was generally observed to be higher than that of the water-gas equilibrium. Due to the complexity and uncertainty of the aquifers, the mechanisms by which groundwater N2O are affected by groundwater hydrogeology and geochemistry remain unexplored. In this study, 41 groundwater samples were collected from three zones of the irrigation area of the lower reaches of Yellow River (i.e., piedmont plain, coastal plain, and central plain), and the hydrogeological parameters of these three areas were characterized. The results showed significant differences of the N2O concentration in the groundwater of the three zones of the lower reaches of Yellow River plain, which was 14.1 +/- 13.1 mu g/L, 1.84 +/- 1.48 mu g/L, and 36.5 +/- 40.5 mu g/L for the piedmont plain, central plain, and coastal plain, respectively. The differences were attributed to different groundwater N input and hydrogeological parameters in the three zones. The infiltration coefficient of precipitation was found to be the most important hydrogeological parameter affecting groundwater N2O. This study also evaluated the indirect N2O emission factor in the irrigation area of the lower reaches of Yellow River. The N2O emissions induced by groundwater exploitation in the irrigation area of the lower reaches of Yellow River were found to be 1.87 g hm-2 year-1. These findings provide a foundation to develop strategies to reduce N2O production and emissions in the agricultural area of the lower reaches of rivers.