| 摘要: |
| 海水Ca2+浓度是计算碳酸钙饱和度的重要参数之一，通常由海水钙盐比值计算得出，但该方法在受多种因素影响的近海海域可能不适用。本研究开展了EGTA自动电位滴定法对不同盐度海水Ca2+浓度测定精度和准确度的研究，探究“盐效应”对Ca2+浓度测定可能存在的影响，并比较了近海养殖区海水实测Ca2+浓度与通过钙盐比估算值的差异。研究表明：①EGTA自动电位滴定法测定不同盐度海水Ca2+浓度精度较高，在各个盐度条件下，5次平行测定的标准偏差为0.001~0.006 mmol/kg，精度均优于0.1%；②在盐度20.00~34.62范围内，Ca2+的实测值与通过钙盐比值计算所得的相对误差为-0.043%~0.023%，准确度在± 0.05%内；③不同盐度海水样品Ca2+浓度的实测值与理论值基本吻合，电位滴定法测定Ca2+浓度不存在“盐效应”问题；④受陆源输入过程的影响，近海（烟台牟平养殖区）表层及底层海水Ca2+的实测值比按钙盐比值的计算值分别高出0.360 mmol/kg和0.333 mmol/kg，表明利用钙盐比值估算法不适用于近海海水中Ca2+浓度，通过实测Ca2+浓度计算近海海水碳酸钙饱和度可以更准确评估近海酸化的程度。 |
| 关键词: 海洋化学 近海海水 海洋酸化 钙盐比 钙离子 电位滴定法 |
| DOI：10.3969/J.ISSN.2095-4972.20220402001 |
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| 基金项目:国家重点研发计划“全球变化及应对专项”(2020YFA0608304); 广东省基础与应用基础研究基金（2021B1515120080）；山东大学青年学者未来计划（2018WLJH43） |
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| Precision of EGTA titration on seawater Ca2+ concentration and the necessity for actual measurement in offshore waters |
| ZHANG Zhe,BIAN Haizhen,REN Hongwei,HU Yubin |
| (Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China) |
| Abstract: |
| Seawater Ca2+concentration is one of the important parameters for calculating calcium carbonate saturation, which is usually derived from seawater calcium-salinity ratio, but this may not be applicable in offshore waters because of influences of many factors. In this study, the accuracy and precision of Ca2+concentration determined by automatic potentiometric titration at different salinities were investigated and the potential influence of the “salt effect” was evaluated. The difference between the measured Ca2+ concentration and the estimated value by seawater calcium-salinity ratio in the offshore mariculture area was compared. The results showed that: (1) the precision of Ca2+concentration determined by automatic potentiometric titration was high at different salinities, with the standard deviations of five replicate determinations ranging from 0.001 to 0.006 mmol/kg, which were better than 0.1 %. (2) In the salinity range of 20.00-34.62, the relative errors between the measured and calculated values based on the calcium-salinity ratio of Ca2+ were -0.043 %-0.023 %, which were within ± 0.05 %. (3) The measured and calculated values of Ca2+concentration in seawater samples at different salinities agreed with each other, indicating that there was no “salt effect”. (4) The measured values of surface and bottom seawater Ca2+ concentration in Muping Marine Ranching were higher than the calculated ones i.e. 0.360 mmol/kg and 0.333 mmol/kg, respectively, which might result from the impact of riverine input. Therefore, calculating the calcium carbonate saturation of offshore seawater by measured Ca2+ concentration can more accurately assess the extent of offshore acidification. |
| Key words: marine chemistry coastal seawater ocean acidification calcium-salinity ratio calcium ion potentiometric titration |
