水库水体二氧化碳分压研究进展

天然水体中存在同化二氧化碳(CO2)的光合作用,也存在释放CO2的微生物呼吸过程。地球表层水体与大气之间的CO2交换构成全球碳循环的一个重要环节。水-气之间CO2交换的方向和通量主要受大气圈和水体表层CO2分压(pCO2)的制约。水体pCO2值可以通过对近水面气体成分变化过程的现场仪器检测或者根据测定的水体化学参数运用经验公式计算求得。迄今对陆地水体,尤其河流筑坝形成的"蓄水河流"(下称水库)水体CO2动态研究中,由于水域及其近表层大气成分的时空多变,一般采用水化学参数计算方法求得水体的pCO2值。全球约70.97%的水库表层水体pCO2高于大气pCO2。全球尺度上水库表层水体pCO2自热带向寒温带逐渐递减;单个水库水体的pCO2一般呈现"出库>入库>库中"、pCO2随深度而增加的变化规律。水库表层水体pCO2的时间变化一般表现为"冬季>夏季、消融期>冰冻期、黑夜>白天"。水库水体的pCO2是其水化学平衡的结果,受水温、水体pH、水生生物活动以及外来水体的混合等多种因素影响,变化较为复杂。为精确量化水库水-气界面CO2交换通量,水文学、湖沼学、生态学和地球化学等领域的学者有必要合作,共同努力进行水库流域尺度的实地观测,完善水体溶解无机碳计算模型,深入探讨水库水体碳动力学机制,为全球碳循环研究和气候变化预测提供可靠的基础数据。

A REVIEW OF CARBON DIOXIDE PARTIAL PRESSURE OF WATER BODIES IN RESERVOIRS

Photosynthesis of assimilated carbon dioxide (CO2) and microbial respiration processes simultaneously occur within the natural waters. CO2 exchange between water bodies and the atmosphere constitutes a major part of the global carbon cycle. The CO2 current direction and flux between water column and atmosphere are mainly controlled by CO2 partial pressure (pCO2) between the atmosphere and the surface water bodies. The pCO2 values of water bodies can be obtained by on-site instrumental detection on the basis of gas composition change near the water surface layer or by empirical calculation in terms of measuring hydro-chemical parameters. Up to now, with regard to CO2 dynamics in inland waters, especially in reservoir water bodies formed by damming, the calculation method of hydro-chemical parameters is generally conducted to calculate the pCO2 values due to the complex spatiotemporal variability of atmospheric composition near water surface layer. It is reported that about 70.97% of pCO2 values in the global reservoirs are higher than the atmospheric pCO2. On the global scale, the surface water pCO2 in the reservoir shows a gradual decline from tropical zone to boreal zone;for a single reservoir, the pCO2 generally presents a variation pattern of "outlet of the reservoir > inlet of the reservoir > in the reservoir", and the pCO2 rises with increasing depth. The pCO2 temporal variation trend in the reservoirs surface water is generally winter > summer, snow melting period > freezing period, and night > day. The pCO2 of the reservoir water is the result of chemical elements equilibrium which varies in a complicated pattern, and is influenced by many factors, such as water temperature, water pH, aquatic biological activities and the mixing of exotic water. In order to accurately quantify the exchanged CO2 flux at the water-air interface, it is necessary for hydrologists, limnologists, ecologists and geochemists to cooperation to conduct field observations at reservoir watershed scale, to improve the calculation model of dissolved inorganic carbon in water, to explore the carbon dynamics mechanism of the reservoir water bodies, and to provide reliable data for studying global carbon cycle and predicting climate change.