河口无机碳水样保存方法及CO2分压优化计算——以长江口为例
Optimization of estuarine inorganic carbon water sample storage technique and pCO2 calculation: A case study in the inner Changjiang (Yangtze River) Estuary
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摘要: 为了探索河口淡水端无机碳水样的保存方法，于2015年3月和7月在长江口淡水端及相邻的河海水混合区域，分别用涂敷特氟龙（Teflon）材料的250 mL具磨口塞玻璃瓶和60 mL硼硅酸盐螺口玻璃瓶采集无机碳水样，检验水样在长期储存过程中的稳定性.实验结果表明，用涂敷特氟龙的玻璃瓶保存河口淡水端无机碳水样在70 d内可维持稳定，溶解无机碳（DIC）和总碱度（TAlk）的均值变化大都少于10 μmol·kg-1.而用60 mL硼硅酸玻璃瓶保存的河口淡水端无机碳水样，其DIC浓度在20 d可下降20-92 μmol·kg-1，70 d平均下降速率可达0.9-2.6 μmol·kg-1·d-1.因此，对于河口淡水端的水样，若不能保证在一周内分析测定，就应该使用涂敷特氟龙的250 mL玻璃瓶作为保存容器.此外，利用长江口区域实测的DIC与TAlk计算的原位CO2分压结果与过去用水-气平衡法走航观测的结果接近，而用pH和DIC或用pH和TAlk数据计算得到的CO2分压则明显偏高.Abstract: During two field-sampling cruises in the inner Changjiang (Yangtze River) Estuary conducted in March and July 2015, we collected water samples using 250 mL Teflon-coated glass bottles (together with ground-glass stoppers) and 60 mL borosilicate glass vials for storage technique assessment. A loss rate of 0.9-2.6 μmol·kg-1·d-1 for the dissolved inorganic carbon (DIC) was observed for the samples stored in the borosilicate glass vials. However, carbonate system parameters in the Teflon-coated glass bottles were quite stable for a period of 70 days, with less than 10 μmol·kg-1 declined in DIC and total alkalinity (TAlk). The results suggest that the Teflon-coated glass bottle is suitable for the relatively long-term storage of freshwater carbonate samples. Our results also show that, partial pressure of CO2 (pCO2) calculated from DIC and TAlk has similar ranges and distributions to historical pCO2 data that measured with the air-water equilibrium method. However, the calculation based on pH together with either DIC or TAlk gives much higher pCO2 values than field-measured values in the inner Changjiang Estuary.
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