窟野河水-气界面CO_(2)交换通量变化特征及其影响因素分析

Variations of CO_(2) exchange in the Kuye River basin and its influencing factors

近年来内陆水体CO_(2)释放受到广泛关注,为揭示黄土高原地区内陆水体CO_(2)的释放特征,于2018年7月和10月及2019年3月和6月利用LI-7000 CO_(2)分析仪对窟野河及代表性水库开展了高频次的水体CO_(2)分压(pCO_(2))和水-气界面CO_(2)交换通量(FCO_(2))观测,并分析其时空变化规律。结果表明:窟野河水体pCO_(2)和FCO_(2)(分别为996μatm和94.5 mmol·m^(-2)·d^(-1))均高于水库(分别为752μatm和10.3 mmol·m^(-2)·d^(-1))。FCO_(2)季节性差异明显:对于河流而言,表现为秋季最高(165.7 mmol·m^(-2)·d^(-1)),春季最低(42.9 mmol·m^(-2)·d^(-1));对于水库而言,变化趋势则完全相反,表现为春季最高(16.6 mmol·m^(-2)·d^(-1)),秋季最低(-5.4 mmol·m^(-2)·d^(-1))。生物地球化学活性更强的支流FCO_(2)(107.4 mmol·m^(-2)·d^(-1))高出干流(66.5 mmol·m^(-2)·d^(-1))约50%;同时,位于中下游黄土丘陵区的水库FCO_(2)(16.4 mmol·m^(-2)·d^(-1))显著高于位于上游呼鄂丘陵区的水库FCO_(2)(1.2 mmol·m^(-2)·d^(-1))。整体来看,流域水体pCO_(2)受碳酸盐体系影响最大,有机碳分解作用次之;流速是控制水-气界面气体交换速率的关键因素。在年尺度上,窟野河的河流与水库水体均为大气持续碳源。窟野河平均CO_(2)释放量与我国长江及国外温带河流相近,但低于黄河中游的其他支流。

This study aimed to examine the riverine CO_(2) emissions on the Loess Plateau.The river water CO_(2) partial pressure(pCO_(2))and CO_(2) outgassing across the water-air interface(FCO_(2))in the Kuye River basin,situated in the northern Loess Plateau,was holistically investigated in July and October 2018 and March and June 2019 using a LI-7000 CO_(2) analyzer.Both pCO_(2) and FCO_(2) were higher in rivers(996μatm and 94.5 mmol·m^(-2)·d^(-1),respectively)than in reservoirs(752μatm and 10.3 mmol·m^(-2)·d^(-1),respectively).Meanwhile,the FCO_(2) exhibited pronounced seasonal variations.For the river waters,the highest FCO_(2) of 165.7 mmol·m^(-2)·d^(-1) occurred in autumn,and the lowest FCO_(2) of 42.9 mmol·m^(-2)·d^(-1) occurred in spring.For the reservoir waters,the opposite was observed with the highest FCO_(2) of 16.6 mmol·m^(-2)·d^(-1) occurring in spring and the lowest FCO_(2) of −5.4 mmol·m^(-2)·d^(-1) occurring in autumn.Spatially,the FCO_(2) in the tributary rivers(107.4 mmol·m^(-2)·d^(-1))with a stronger biogeochemical activity was significantly higher than that in the Kuye mainstream(66.5 mmol·m^(-2)·d^(-1))by 50%.While for reservoirs,the FCO_(2) of the reservoir waters(1.2 mmol·m^(-2)·d^(-1))in the upper sandy hilly area was lower than that in the middle and lower loess hilly area(16.4 mmol·m^(-2)·d^(-1)).In summary,the pCO_(2) was mostly affected by the carbonate system,followed by dissolved organic carbon.Additionally,flow velocity had a substantial impact on the gas transfer velocity(k),whereas there was no significant correlation between k and wind speed.On an annual scale,both rivers and reservoirs were strong carbon sources for the atmosphere,and their average effluxes were close to that of the Yangtze River while substantially lower than that of the other tributaries in the middle Yellow River Basin.