长江口淡水端淡、盐水混合表层pCO_2的急剧变化及其影响机制

Rapid Variation of pCO_2 and Its Influencing Factors at the Initial Mixing Stage of Freshwater and Saltwater in the Changjiang River Estuary

根据2004年5月长江口淡水端淡、盐水混合初期表层水二氧化碳分压,（pCO2）的实测数据，结合水文、化学和生物等要素的同步观测资料，对pC02的变化及其影响因素进行了研究。研究结果表明：在长江口淡水端盐度0～15的淡、盐水混合初期，表层水pC02由3500μatm左右大幅度下降至约1000μatm。生源要素的补充使生物活动的急剧增加是pCO2以对数形式大幅度降低的主要原因，这一性质显著体现的拐点为（S〈0．6，50〈浊度〈110）这一范围。同时由于生物活动和物理混合作用的分别控制，使得长江口淡水端淡、盐水混合初期表层水碱度与盐度呈二次抛物线关系。拐点处的盐度约为0．6。

Carbon dioxide partial pressure （pCO2） of the surface water at the initial mixing stage of freshwater and saltwater was measured on the freshwater side in the Changjiang River Estuary in May, 2005. The variation of pCO2 and its influencing factors were studied by using the measured data of surface pCO2, Taking into consideration synchronously observed data of hydrological, chemical and biological factors. The results showed that surface pCO2 at the initial mixing stage of freshwater and saltwater fell sharply from about 3 500μatm to 1 000μatm approximately on the freshwater side where the salinity ranged 0-15 in the Changjiang River Estuary. The rapid increase of biologic activity due to the supply of biogenic elements led to the decline of pCO2 in logarithm from. This character remarkably presented itself at an inflection point with salinity 0.6 and turbidity 110. Because of the respective control of biologic activity and physically mixing effect, surface alkalinity and salinity show a second-degree parabolic relationship, with the inflection point salinity being 0.6 approximately.