Study on diurnal variation of CO2 flux from reservoir and the influencing factors of partial pressure of CO2 in melting and non-melting seasons

Abstract

以位于黄土高原北洛河流域的南沟水库为研究对象,采用Li-850静态箱法,于融冰期(3月)、非融冰期(5月)对水体CO2分压(p(CO2))和水-气界面CO2逸出(F(CO2))分别进行了5d40次昼夜监测,同时测定了各种水体理化指标,着重对比了水体p(CO2)在两个时期间的差异和两时期内的昼夜变化特征,系统分析了水体p(CO2)的影响因素.结果表明;融冰期p(CO2)((324.8±59.4) Pa)比非融冰期((124.9+14.1) Pa)高出近3倍,差异性显著(p＜0.05),但两个时期内昼夜p(CO2)值并无显著性差异(p＞0.05);水体p(CO2)与水温、pH、叶绿素(Chla)、溶解氧(DO)呈显著负相关,与溶解无机碳(DIC)、溶解有机碳(DOC)呈显著正相关,水体P(CO2)受流域碳酸盐体系和水温影响最大,相关系数分别达0.92和-0.91,光合呼吸作用的影响其次;研究区小水库F(CO2)范围为101～1589 g·m-2·a-1,是大气持续碳“源”,其平均排放量与个别温带、亚热带小型水库接近,但低于热带水库. By using the floating chamber and headspace equilibrium methods along with a Licor-850 gas analyzer, this paper investigates the partial pressure of carbon dioxide(p(CO2)) and CO2 emission flux(F(CO2)) across water-air interface in the Nangou Reservoir, located in the upper reach of the Beiluo River on the Loess Plateau. A monitoring of CO2 evasion at 3 h intervals for 5 days (in total 40 measurement) were conducted in March 2019 (melting season) and May 2019 (non-melting season) respectively. Moreover, the accompanying physicochemical parameters were also measured to explore the seasonal variation of surface water p(CO2) and its influencing factors. The results indicated that the mean p(CO2) in the melting season ((324.8±59.4) Pa) was nearly three times higher than that in the non-melting season ((124.9±14.1) Pa). However, the p(CO2) exhibited no significant difference between day and night within each season (p>0.05). In addition, we found that the surface water p(CO2) presented an extremely significant negative correlation with water temperature, pH, Chla and dissolved oxygen (DO) while an extremely positive correlation with dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The CO2 emission flux ranged from 101 to 1589 g·m-2·a-1, indicating that it is a carbon source for the atmosphere. The CO2 emission flux of the Nangou Reservoir is at the intermediate level of CO2 emission from small reservoirs in temperate and subtropical climates, but significantly lower than that from tropical reservoirs.