An assessment of HgII to preserve carbonate system parameters in organic‐rich estuarine waters

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Abstract This work assesses the effectiveness of sample preservation techniques for measurements of pHT (total scale), total dissolved inorganic carbon (CT), and total alkalinity (AT) in organic‐rich estuarine waters as well as the internal consistency of measurements and calculations (e.g., AT, pHT, and CT) in these waters. Using mercuric chloride (HgCl2)‐treated and untreated water samples, measurements of these carbonate system parameters were examined over a period of 3 months. Respiration of dissolved organic matter in untreated samples created large discrepancies in CT concentrations (~37 μmol kg−1 increase, p < 0.0001), while CT was effectively constant in treated samples (3095.0 ± 1.14 μmol kg−1). AT changes were observed for both treated and untreated samples, with HgCl2‐treated samples showing the greatest variation (~ 26 μmol kg−1 decrease, p < 0.001). In response to changing AT/CT ratios, pHT changes occurred in both treated and untreated samples but were relatively small in treated samples. Results in organic‐rich estuarine waters that reflect the in situ carbonate system characteristics of the samples at the time of collection can be improved when samples obtained for CT and AT analysis are collected and stored separately. Accurate analyses of CT can be obtained by filtration and preservation with HgCl2. Accuracy of AT analyses can be improved by filtration and storage without adding HgCl2. The quality of pHT measurements can be improved by prompt analysis in the field and, if this cannot be accomplished, then samples can be preserved with HgCl2 and measured in the laboratory within 1 week.

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