Total alkalinity (A_T) is an important parameter in the study of aquatic biogeochemical cycles, chemical speciation modeling, and many other important fundamental and anthropogenic (e.g., industrial) processes. We know little about its short‐term variability, however, because studies are based on traditional bottle sampling typically with coarse temporal resolution. In this work, an autonomous A_T sensor, named the Submersible Autonomous Moored Instrument for Alkalinity (SAMI‐alk), was tested for freshwater applications. A comprehensive evaluation was conducted in the laboratory using freshwater standards. The results demonstrated excellent precision and accuracy (± 0.1%–0.4%) over the A_T range from 800 to 3000 μmol L⁻¹. The system had no drift over an 8 d test and also demonstrated limited sensitivity to variations in temperature and ionic strength. Three SAMI‐alks were deployed for 23 d in the Clark Fork River, Montana, with a suite of other sensors. Compared to discrete samples, in situ accuracy for the three instruments were within 10–20 μmol L⁻¹ (0.3–0.6%), indicating good performance considering the challenges of in situ measurements in a high sediment, high biofouling riverine environment with large and rapid changes in temperature. These data reveal the complex A_T dynamics that are typically missed by coarse sampling. We observed A_T diel cycles as large as 60–80 μmol L⁻¹, as well as a rapid change caused by a runoff event. Significant errors in inorganic carbon system modeling result if these short‐term variations are not considered. This study demonstrates both the feasibility of the technology and importance of high‐resolution A_T measurements.

中文翻译：

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自主测量淡水碱度

总碱度（A _T）是研究水生生物地球化学循环，化学形态建模以及许多其他重要的基本和人为（例如工业）过程的重要参数。但是，我们对其短期可变性知之甚少，因为研究是基于传统的瓶采样，通常具有粗糙的时间分辨率。在这项工作中，针对淡水应用测试了一种自动A _T传感器，即潜水式碱度自动系泊仪器（SAMI-alk）。在实验室中使用淡水标准进行了全面评估。结果表明，在800至3000μmol L ^-1的A _T范围内，其 精度和准确度均极佳（±0.1％–0.4％）。该系统在8天的测试中没有漂移，并且还显示出对温度和离子强度变化的敏感性有限。在蒙大拿州的克拉克福克河上部署了三个SAMI-alk，共23天，并配备了其他传感器。相比离散样本，原位精度为三个文书内10-20  μ摩尔大号^-1（0.3-0.6％），这表明良好的性能考虑在高的沉积物在原位测量的挑战与大的，高生物污染河流环境以及温度的快速变化。这些数据揭示了通常被粗略采样遗漏的复杂的A _T动态。我们观察到_Ť昼夜周期一样大60-80  μ摩尔大号^-1，以及由径流事件引起的快速变化。如果不考虑这些短期变化，则会导致无机碳系统建模中的重大错误。这项研究证明了该技术的可行性以及高分辨率A _T测量的重要性。