Dissolved CO₂ concentration calculated from historical or in situ alkalinity and pH measurements according to carbonate equilibria is widely applied in freshwater CO₂ studies yet there is long concern on systematic errors associated with the calculation. Correction of the CO₂ calculation errors is however hampered by a lack of correct understandings of error sources and magnitudes. Here through reviewing literature quantification of the effect, we point out pH measured by commercial glass electrodes is not reliable and biased unidirectionally toward lower values by −0.14 ± 0.20 on average. This effect, together with high organic alkalinity, is responsible for unreliable CO₂ calculations in low ionic strength freshwaters. Relying on a series of interdependencies between freshwater properties, the analysis further proposes a roadmap for correction of the errors. The method, when testing against a dataset of direct CO₂ measurements, is proved effective at reducing CO₂ calculation errors. The analysis represents a significant progress in freshwater CO₂ studies based on carbonate equilibria and future applications of the method are advised to apply the corrections to freshwaters of <1000 μeq L⁻¹ in total alkalinity.

中文翻译：

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从低离子强度淡水中的有机碱度和pH测量误差评估CO2计算误差

根据碳酸盐平衡根据历史或原位碱度和pH测量值计算得出的溶解CO ₂浓度已广泛用于淡水CO ₂研究中，但长期以来人们一直担心与计算有关的系统误差。然而，由于缺乏对误差源和幅度的正确理解，阻碍了对CO ₂计算误差的校正。在这里，通过回顾文献对效果的量化，我们指出由商用玻璃电极测量的pH值是不可靠的，并且平均会单向偏向较低值-0.14±0.20。这种效应与高有机碱度一起导致了不可靠的CO ₂低离子强度淡水的计算。依靠淡水属性之间的一系列相互依存关系，该分析进一步提出了纠正错误的路线图。当针对直接CO ₂测量数据集进行测试时，该方法被证明可有效减少CO ₂计算误差。分析表示在淡水CO一个显著进展₂基于碳酸盐平衡，并且该方法的未来的应用的研究建议更正适用于<1000的淡水 μ当量大号^-1在总碱度。