Spectrophotometric Determinations of Carbonic Acid Dissociation Constants for Estuarine Conditions

人类的健康和福祉在许多方面都与我们的河口和沿海海域的健康有关。然而，令人惊讶的是，我们对这些重要水域的某些方面的了解，比我们对深海更遥远的水域的了解要少。这个项目将使用最先进的分光光度方法(即基于光和颜色的方法)来促进我们对这些水域的基本和不断变化的化学物质的了解，并最终了解这些变化对海洋生物的影响。这项研究的重点将是了解海水中二氧化碳的化学组成。我们将使用的新工具是最近表征的pH指示器--根据海水的酸度改变海水颜色的化学物质。这些经过特别挑选、提纯的指示器可用于以无与伦比的精密度和准确度测量pH值。我们将在实验室实验中使用这些指示剂来确定二氧化碳系统的一个关键参数(称为“K2”的离解常数)如何随水的温度和盐度而变化。50多年来，表征K2一直是海洋化学家的目标。我们对K2的了解越多，我们就越能更好地理解和预测碳如何在自然水域中移动和循环。这些测量不仅将扩大我们对K2的理解，而且还将扩大我们对可以从K2计算出的许多其他海水特性的了解。归根结底，这项工作将有助于解释和预测许多与人类健康和沿海经济有关的海洋过程，例如海洋酸化(大气中二氧化碳增加导致海洋pH值降低)和碳酸钙溶解(贝壳物质的溶解)。因此，研究结果将为研究海洋酸化如何影响各种贝类生物奠定基础，这些贝类生物是经济上重要的海洋动物/渔业和人类的食物。这项工作的结果还将有助于改进湖泊、河流、地下孔隙水和生理流体中二氧化碳动力学的模型。至于更广泛的影响，这项工作将帮助PI通过对研究生、本科生和高中生的培训，继续将他在这个重要主题上的知识传授给下一代。该项目将资助一名研究生和一名本科生，并帮助目前两名少数民族博士生的研究项目。最后，PI计划继续参与博士桥项目，旨在让少数族裔学生参与到科学中来。在海水中，两个碳酸离解常数(K1和K2)描述了溶液pH与溶解的碳酸盐离子、碳酸氢根离子和溶解的二氧化碳的相对浓度之间的关系。50多年来，在广泛的环境条件下准确表征这些二氧化碳体系常数一直是一个非常受欢迎的目标，因为这些术语的知识对于定量解释和预测所有天然水体系中碳的生物地球化学循环至关重要。二氧化碳体系计算的准确性对K2的不确定性特别敏感，K2是描述碳酸氢根离子解离生成氢离子和碳酸盐离子的平衡常数。本研究项目旨在(仅)使用分光光度pH测量来表征这一重要的常量。这项工作中使用的净化pH指示器提供了无与伦比的精确度和准确度的海水pH测量。使用最近在淡水到海水的盐度和温度范围内表征其性质的选定指标，我们将在类似范围内确定K2，以便提高河口和沿海海域二氧化碳系统计算的准确性。由此得到的对平衡特性的认识将有助于解释和预测水体系中的pH缓冲，提供对碳酸钙溶解行为的更好的理解，并导致对淡水湖泊、河流、土壤和沉积物孔隙水以及生理流体中CO2系统行为的改进模型。该项目的长期利益将延伸到评估海洋酸化对碳酸盐有机体生命周期的影响，碳酸盐有机体是经济上重要的海洋生物的食物。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Human health and well-being are linked in many ways to the health of our estuaries and coastal ocean waters. Yet surprisingly, we know less about some aspects of these important waters than we do the more distant waters of the deep ocean. This project will use state-of-the-art spectrophotometric methods (that is, light- and color-based methods) to advance our understanding of the fundamental and ever-changing chemistry of these waters and, eventually, the effects of these changes on marine life. The focus of this study will be to understand the chemistry of carbon dioxide in seawater. The new tools we will use are recently characterized pH indicators — chemicals that change color in seawater depending on the acidity of that water. These specially selected, purified indicators can be used to measure pH with unsurpassed precision and accuracy. We will use the indicators in laboratory experiments to determine how a critical parameter of the carbon dioxide system (a dissociation constant known as “K2”) changes depending on the temperature and salinity of the water. Characterizing K2 has been a goal of marine chemists for more than 50 years. The better we know K2, the better we can understand and predict how carbon moves through and cycles within natural waters. These measurements will expand our understanding of not only K2 but also the many other seawater characteristics that can be calculated from K2. Ultimately, this work will facilitate the interpretation and prediction of many ocean processes relevant to human health and coastal economies, such as ocean acidification (the lowering of ocean pH due to increasing carbon dioxide in the atmosphere) and calcium carbonate dissolution (the resulting dissolution of seashell material). The results will thus lay the groundwork for new perspectives on how ocean acidification affects the various shelled organisms that serve as food for economically important marine animals/fisheries and for people. The results of this work will also help to improve models of carbon dioxide dynamics in lakes, rivers, underground pore waters, and physiological fluids. As regards broader impacts, this work will help the PI continue to transfer his knowledge on this important topic to the next generation via his training of graduate, undergraduate, and high school students. This project would support one graduate and one undergraduate student, as well as help the current research projects of two minority doctoral students. Lastly, the PI plans to continue his involvement in the Bridge to the Doctoral Program aimed at getting minority students involved in the sciences.In seawater, two carbonic acid dissociation constants (K1 and K2) describe the relationship between solution pH and the relative concentrations of dissolved carbonate ions, bicarbonate ions, and dissolved carbon dioxide. Accurate characterization of these CO2-system constants over broad ranges of environmental conditions has been a much sought-after goal for more than 50 years because knowledge of these terms is essential for quantitatively interpreting and predicting the biogeochemical cycling of carbon in all natural aqueous systems. The accuracy of CO2-system calculations is especially sensitive to uncertainties in K2, the equilibrium constant that describes the dissociation of bicarbonate ions to produce hydrogen ions and carbonate ions. This research project is designed to use spectrophotometric pH measurements (solely) to characterize this important constant. The purified pH indicators to be used in this work provide seawater pH measurements of unsurpassed precision and accuracy. Using select indicators whose properties have recently been characterized over freshwater-to-seawater ranges of salinity and temperature, we will determine K2 over similar ranges so as to improve the accuracy of CO2-system calculations in estuaries and coastal ocean waters. The resulting insight into equilibrium characteristics will facilitate interpretations and predictions of pH buffering in aqueous systems, provide an improved understanding of calcium carbonate solubility behavior, and lead to improved models of CO2-system behavior in freshwater lakes, rivers, soil and sediment pore waters, and physiological fluids. The longer-term benefits of this project will extend to assessments of the influence of ocean acidification on the life cycles of carbonate-bearing organisms that serve as food for economically important marine organisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.