Determination of hydrogen ion concentration in softwater lakes using carbon dioxide equilibria |
| |
| Authors: | Andrew L Herczeg Raymond H Hesslein |
| |
| Institution: | 1. Department of Geological Sciences and Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York 10964 U.S.A.;2. Department of Fisheries and Oceans, Freshwater Institute, Winnipeg, Manitoba R3T 2N6, Canada |
| |
| Abstract: | A strategy for determining the hydrogen ion content of fresh waters is proposed that involves total dissolved inorganic carbon (DIC or σCO2) and CO2 partial pressure (PCO2) measurements rather than pH electrode measurements. This recommendation derives from discrepancies between pH and carbon dioxide equilibria measurements made on several softwater lakes at the Experimental Lakes Area, northwestern Ontario. The pH calculated from DIC, PCO2, and the first dissociation constant of carbonic acid (K1) data was consistently higher than that directly measured with a pH electrode. Similarly, calculation of PCO2 of surface waters from pH, DIC, and K1 data gave values up to twice that of atmospheric saturation despite repeated equilibrations with atmospheric PCO2. Laboratory experiments demonstrated that the high dissolved organic carbon content of these waters appears to alter the electrode response yielding pH values lower than the true values. Furthermore, the uptake of protons by weak organic acid anions appear to be the cause of the measured difference between total (Gran) and carbonate (DIC — dissolved CO2) alkalinity. Therefore bicarbonate ion concentration must be calculated from the difference between the total dissolved inorganic carbon content and uncharged dissolved CO2 content. These procedures should provide more accurate and consistent results in the pH trend in surface waters and hence yield a solid baseline against which the effects of acid precipitation can be assessed. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
