Spectrophotometric Determinations of Carbonic Acid Dissociation Constants for Estuarine Conditions

人类健康和福祉在许多方面与我们的河口和沿海沃茨的健康息息相关。然而令人惊讶的是，我们对这些重要沃茨的某些方面的了解比我们对更遥远的深海沃茨的了解要少。该项目将使用最先进的分光光度法（即基于光和颜色的方法）来促进我们对这些沃茨的基本和不断变化的化学性质的理解，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性质。我们将使用的新工具是最近表征的pH指示剂-根据海水的酸度改变海水颜色的化学物质。这些经过特别挑选的纯净指示剂可用于测量pH值，具有无与伦比的精度和准确度。我们将在实验室实验中使用指示剂来确定二氧化碳系统的关键参数（称为“K2”的解离常数）如何根据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了解得越多，我们就能更好地理解和预测碳在自然沃茨中的移动和循环。这些测量不仅将扩大我们对K2的理解，还将扩大我们对许多其他海水特征的理解，这些特征可以从K2计算出来。最终，这项工作将有助于解释和预测与人类健康和沿海经济有关的许多海洋过程，如海洋酸化（由于大气中二氧化碳增加而导致海洋pH值下降）和碳酸钙溶解（由此导致的贝壳物质溶解）。因此，研究结果将为海洋酸化如何影响作为具有重要经济意义的海洋动物/渔业和人类食物的各种有壳生物的新视角奠定基础。这项工作的结果也将有助于改进湖泊、河流、地下孔隙沃茨和生理流体中二氧化碳动力学的模型。 至于更广泛的影响，这项工作将有助于PI继续通过对研究生，本科生和高中生的培训将他在这一重要主题上的知识传授给下一代。 该项目将支持一名研究生和一名本科生，并帮助两名少数民族博士生目前的研究项目。 最后，PI计划继续参与旨在让少数民族学生参与科学的博士课程。在海水中，两个碳酸解离常数（K1和K2）描述了溶液pH值与溶解的碳酸根离子、碳酸氢根离子和溶解的二氧化碳的相对浓度之间的关系。这些CO2系统常数在广泛的环境条件下的准确表征一直是一个非常抢手的目标超过50年，因为这些条款的知识是必不可少的定量解释和预测的地球化学循环的碳在所有天然水系统。CO2系统计算的准确性对K2的不确定性特别敏感，K2是描述碳酸氢根离子解离产生氢离子和碳酸根离子的平衡常数。本研究项目旨在使用分光光度法pH测量（单独）来表征这一重要常数。在这项工作中使用的纯化pH指示剂提供了无与伦比的精度和准确度的海水pH测量。使用选择的指标，其属性最近已被表征在淡水到海水的盐度和温度范围内，我们将确定K2在类似的范围内，以提高在河口和沿海海洋沃茨的CO2系统计算的准确性。由此产生的洞察平衡特性将有助于解释和预测的pH值缓冲水系统中，提供了一个更好的理解碳酸钙的溶解度行为，并导致改进模型的CO2-系统的行为在淡水湖泊，河流，土壤和沉积物孔隙沃茨，和生理流体。该项目的长期效益将扩展到评估海洋酸化对作为重要经济海洋生物食物的含碳酸盐生物生命周期的影响。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

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.