Characteristics of nitrogen wet deposition and flux with runoff during the spring freeze-thaw period in permafrost region watershed of Da Hinggan Mountains, Northeast China

Abstract

Nitrogen (N) transport is an important component of a watershed's nutrient cycle, which has significant impacts on global nitrogen cycle. In this study, we measured precipitation and daily stream N concentrations during the spring freeze-thaw period (April 9-June 30, 2021) in a small forest watershed (Laoyeling) in the permafrost region of Da Hinggan Mountains to calculate wet N deposition and stream N flux. The results showed the wet deposition fluxes of ammonium, nitrate, and total N were 695.88, 448.72 and 1947.35 g·hm-2, respectively, while the stream N fluxes were 86.37, 186.87 and 1160.78 g·hm-2, respectively over the whole study period. Precipitation was the main influencing factor of wet N deposition. During the freeze-thaw cycle period (April 9 to 28), the stream N flux was dominated by runoff and was affected by soil temperature through its influence on runoff. During the melting period (April 29 to June 30), it was affected by both runoff and runoff N concentration. The stream total N flux accounted for 59.6% of wet deposition during the study period, which indicated that the watershed had a strong N fixation potential. These findings would have important implications for understanding the impact of climate change on N cycling in permafrost watersheds.