大兴安岭多年冻土区流域春季冻融期氮湿沉降与水体氮输出特征

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

氮(N)的输移过程是流域养分循环的重要组成部分,对全球氮循环有着极为重要的影响。本研究以大兴安岭多年冻土区典型小流域——老爷岭流域为对象,在2021年春季冻融期(4月9日—6月30日)对其降雨和逐日径流氮浓度进行观测,计算了氮湿沉降和径流氮输出通量。结果表明:在春季冻融期,流域铵态氮、硝态氮和全氮湿沉降通量分别为695.88、448.72和1947.35 g·hm^(-2);径流氮输出通量分别为86.37、186.87、1160.78 g·hm^(-2);降雨量为氮湿沉降的主要影响因素;冻融循环期(4月9—28日)径流量是河流氮输出通量的主导因素,土层温度主要作用于径流量进而影响氮输出通量;融化期(4月29日—6月30日)氮输出通量受到径流量和径流氮浓度的共同影响;研究期内流域径流全氮输出通量占湿沉降的59.6%,流域具有较强的固氮潜力。研究结果对理解气候变化对多年冻土区流域氮循环的影响有重要意义。

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.