秋季黄河pCO_2控制因素及水-气界面通量

Control factors of pCO_2 and CO_2 degassing fluxes from the Yellow River in autumn

根据2006年11月1-10日,秋季黄河平水期二氧化碳分压（pCO2）的现场实测数据及相关同步观测资料,对黄河表层水pCO2的分布及其影响因素进行了研究。结果表明：水体pCO2在80-166 Pa,平均值110 Pa,在世界主要河流中属中等偏下水平;空间分布存在较大的不均匀性,中游高于上游和下游。浮游植物的光合作用对pCO2有一定的影响但强度较弱,即使在叶绿素最高值3.58μg/L的包头站pCO2仍达到91 Pa。黄河水体有机物含量较低且继承了陆源有机物难降解的特性,干流和库区EpCO2/AOU的比值为0.14和0.20,远低于生物好氧呼吸作用控制水体pCO2的理论下限0.62,因此,生物好氧呼吸作用对水体pCO2的贡献不大。悬浮物（TSS）含量为3.77-1308mg/L,溶解无机碳（DIC）含量为3.03-4.14 mmol/L,普遍高于世界其它河流且最大值均出现在潼关站;同时水体pCO2与TSS、PIC、DIC含量具有极好的正相关性。因此黄河流域强烈的机械侵蚀和化学风化作用形成的碳酸盐体系是控制水体pCO2的主要因素。利用Wanninkhof提出的淡水水-气交换系数的通量模式估算,黄河水域水-气界面CO2交换速率约为0.229μmol/m^2.s,秋季可向大气释放CO214.5亿moL,相当于8 250 km^2草原或是112 km^2森林一年的固碳量。黄河CO2释放通量与渥太华河相近,但要远小于亚马逊河。

The partial pressure of CO2 （p CO2） in the water of the Yellow River was directly measured in November 2006, and the distribution and dynamics of p CO2 are discovered in the combination of the related parameters. The results indicate that the pCO2 in the surface water ranges between 80 and 166 Pa, with an average value of 110 Pa, and is lower than that in other important rivers in the world. Furthermore, the significant variations in the spatial p CO2 distribution, i. e, the p CO2 value in the middle part of the fiver is higher than upstream and downstream. Photosynthesis of phytoplankton has a slight effect on p CO2, even though Chla reaches the maximum 3.58 μg/L at Baotou station where the pCO2 value is still 91 Pa. Since the organic matter level in the Yellow River water is low and hard to degrade, the EpCO2/AOU value just varies from 0.14 to 0.20 in the mainstream and reservoir, lower than the theoretical value of 0. 62, which suggests that the biological aerobic respiration effect has little contribution to pCO2. The content of TSS and DIC in the Yellow River water varies from 3.77 to 1308.33 mg/L and from 3.03 to 4.14 mmol/L, respectively, both of which are generally higher than other rivers in the world, and the maximum appears at Tonggnan. Meanwhile the p CO2 has a positive relationships with TSS, PIC and DIC. So the main control factors of p CO2 are attributed to the carbonate system with high carbonate content induced by the strong mechanical erosion and chemical weathering in the Yellow River drainage area. Based on the model of Wanninkhof and the wind speed, the released CO2 from the Yellow River to atmosphere is estimated about 14.5 × 108 mol in autumn at the rate of 0.229 μmol/（m2·s）, which is equal to the CO2 absorption of 8250 km^2 grass or 112 km^2 forest. CO2 outgassing flux from the Yellow River is close to that of the Ottawa River and less than the Amazon River.