河口二氧化碳水-气交换研究进展

Research Advance in Air-Water CO_2 Exchange of Estuaries

河口区是联系大气圈、岩石圈、水圈和生物圈的重要枢纽。厘清河口区碳的行为机理，特别是二氧化碳（CO，）在水-气界面的交换过程，有助于提高对近海碳源汇格局的认识。通过总结河口CO2水-气交换的国内外最新进展，得出如下结论：①不同河口水体二氧化碳分压（pCO2）空间分布存在一般模式，但pCO2具体季节变化存在差异；②全球河口区面积虽小，但其CO2的水-气释放通量高达0．25×10^15～0．50×10^15gC／a，约有1／3的河流碳经过河口过程被释放到大气中；③有机质的呼吸降解、外源CO2的横向传递、水体内部矿物沉淀以及水流的紊动构成了河口水体CO2向大气释放的主要驱动过程。目前，气体传输速率南和全球河口面积估算的不确定性依旧很大，已有的河口样本还不能充分代表不同类型的河口系统来支撑全球河口CO2水-气界面交换通量的精确估算。

Estuary holds a key position in linking the four geo-spheres, i. e. , atmosphere, lithosphere, hydro- sphere and biosphere. Figuring out the transfer mechanisms of cstuarine carbon, especially the exchange of CO2 at the air-water interface is conducive to understanding the carbon pattern in coastal oceans. To date, many fruitful studies have been conducted on the control mechanism towards the partial pressure of C02（pCO2 ） in different estuarine areas around the world. By a thorough research on the latest studies of estuarine CO2 exchange with the atmos- phere, it is concluded as follows： （1）A common pattern is found on the spatial distribution ofpCO2 in different estuarine areas. However, the concrete seasonal change of pCO2 shows great differences, and the conesponding control factors also vary considerably. （2）Estuaries are believed to be large sources of CO2 to the atmosphere. It is estimated that the global estuarine CO2 degassing fluxes, although the global surface area of estuaries is small, are up to 0.25×10^15～0.50×10^15gC/a; and about 1/3 of riverine carbon is released into the atmosphere during the estuarine transit. （3）Degradation of organic matter, lateral transfer of marsh-derived CO2 , mineral deposits in water and tur- bulence in the liquid phase are the main factors that are responsible for the emission of estuarine CO2. At present, this estimate of estuarine CO2 exchange with the atmosphere is based on limited spatial data, therefore problems such as the limitation in the depth and scope of studies still exist. There are also varieties of uncertainties in the es- timation of gas transfer velocity and the whole areas of global estuaries, all of them make it difficult to reach an accurate evaluation of CO2 fluxes at the air-water interface. It is difficult to predict the future trend of the CO2 exchange at the air-water interlace due to the complexities of the driving forees and feedback mechanisms in estuarine carbon cycle and the intense anthropogenie disturbance. Investigating the mechanism of pCO2 in estuarine areas, improving the accuracy of evaluation of CO2 fluxes and comparing studies of different estuaries would be new scopes in the future researches on the exchange of CO2 at the air-water interface in estuaries.