N2 and N2O production and emission variation during the flood period of Poyang Lake (China)

Abstract

Lakes are globally important sites to alleviate nitrogen (N) concentrations through gaseous N production and emission, and hydro-geomorphological characteristics can influence the spatial variation, patterns, and efficiency of N removal in lakes. In this study, gaseous N removal via dinitrogen (N2) and nitrous oxide (N2O) production and emission in different hydro-geomorphological areas of Poyang Lake, China, were investigated through direct measurement of excess dissolved N2 and N2O (ΔN2 and ΔN2O) using the N2:Ar ratio method and headspace equilibrium technique, respectively. The highest value of ΔN2 (75.2 ± 31.0 μmol N2 L−1) was observed in the open lake, while the lowest ΔN2 (47.2 ± 14.9 μmol N2 L−1) occurred in the south estuarine delta (p < 0.05). However, the distribution of ΔN2O was opposite to that of ΔN2 with the highest ΔN2O being observed in the south estuarine delta (5.1 ± 5.0 nmol N2O L−1). Gaseous N2 removal fraction (the ΔN2 proportion among the sum of dissolved inorganic nitrogen (DIN) concentration and ΔN2) varied from 36% in the south estuarine delta to 48% in the open lake, while N2O yield (the ΔN2O proportion among the sum of ΔN2 and ΔN2O) varied from 0.04‰ in the open lake to 0.10‰ in the south estuarine delta. Correlation analyses showed that NO3− was the main factor controlling N2O yield. This study confirmed that N removal fractions and patterns vary with different hydro-geomorphological areas.