雨季喀斯特小流域氮输出特征及其受降雨的影响

Characteristics of Nitrogen Export and the Effects of Rainfall during the Rainy Season in a Karst Small Catchment

以黔中典型喀斯特农业小流域后寨河流域为研究区域,探讨喀斯特小流域氮素输出形态特征及降雨对氮素输出的影响。通过对流域内落水洞、地表水和地下水水样各形态氮素的浓度进行监测,估算雨季氮素输出量,结合降雨量数据分析氮输出受降雨的影响。结果表明:(1)后寨河喀斯特小流域水体氮含量明显高于我国主要河流,流域地下水出口溶解性总氮(TDN)浓度均值为6.5mg/L;地表水出口TDN浓度均值为7.3mg/L。(2)氮素输出的主要形态为硝态氮(NO_3^--N),铵态氮(NH_4^+-N)、亚硝态氮(NO2--N)以及有机态氮(DON)输出占比极低。(3)流域内TDN,NO_3^--N,NH_4^+-N,NO2--N,DON雨季输出量估算值分别为55.13,52.12,0.40,0.01,2.61t。(4)持续性的多日降雨加速了水体氮素流失强度,流域上游水体硝态氮浓度在降雨事件发生后呈上升趋势,随着降雨事件的停止而呈下降趋势;流域总出口因降雨而产生的硝态氮浓度变化具有一定的滞后性。

In order to reveal the effects of rainfall on nitrogen export and the characteristics of nitrogen export in a Karst small catchment,this paper studied a typical small agricultural catchment in the Karst area,Houzhai catchment in Guizhou Province.This study monitored and tested concentrations of various forms of nitrogen in samples from sinkhole,surface water,and groundwater to estimate the annual flux of nitrogen during the rainy season,and investigated the effects of rainfall on nitrogen export with regional precipitation data.The results indicated that：（1）Nitrogen concentration in the Houzhai catchment was considerably higher than those in the large rivers in China：The average concentration of TDN was 6.5 mg/L in the groundwater system and 7.3mg/L in the surface water system.（2）The main nitrogen form was NO3^--N,with a small amount of NH4^＋-N,NO2^--N,and DON export in the Houzhai small catchment.（3）The estimated flux of the TDN,NO3^--N,NH4^＋-N,NO2—N,and DON output was 55.13,52.12,0.40,0.01,and 2.61 t,respectively,in the Houzhai catchment during the rainy season.（4）The continuous precipitation over a couple of days accelerated nitrogen loss in the Karst area.The NO3^--N concentration in the upstream increased after the beginning of rainfall events and decreased after the termination of precipitation.Moreover,there was an observable hysteresis between the change in NO3^--N concentration with the occurrence of rainfall at the outlet of the catchment.