THE GEOCHEMISTRY OF NATURAL WATERS

1. 1 THE GEOCHEMISTRY OF NATURAL WATERS THE CARBONATE SYSTEM CHAPTER 3 - Kehew (2001) Alkalinity

2. 2 LEARNING OBJECTIVES Understand sources of CO2 in natural waters. Define and understand alkalinity. Learn to calculate the solubility of carbonate minerals such as calcite. Understand the common-ion effect. Become familiar with the concept of incongruent dissolution. Apply these concepts to some case studies. In this lecture we will pick up where we left off in Lecture 3, and continue with Chapter 3 in Kehew (2001). First we will consider sources of CO2, other than atmospheric, in natural waters. We will then define the concept of alkalinity and attempt to understand its relevance. The bulk of this lecture is devoted to understanding solubility equilibria of carbonate minerals, such as calcite. This includes being able to calculate the solubility of carbonates under specified conditions of pCO2 and pH, considering the common-ion effect and its relevance to natural waters, and familiarizing ourselves with the concept of incongruent dissolution. With these tools under your belt, you are then directed to the latter half of Chapter 3 in Kehew (2001), where he applies these concepts in a discussion of some interesting case studies. Because Kehew (2001) does a very good job describing these case studies, and we have limited time together, I will not be reviewing the case studies in class. However, I direct you to the Lecture 4 page on the course web site for some study questions to help guide your reading in the text. In this lecture we will pick up where we left off in Lecture 3, and continue with Chapter 3 in Kehew (2001). First we will consider sources of CO2, other than atmospheric, in natural waters. We will then define the concept of alkalinity and attempt to understand its relevance. The bulk of this lecture is devoted to understanding solubility equilibria of carbonate minerals, such as calcite. This includes being able to calculate the solubility of carbonates under specified conditions of pCO2 and pH, considering the common-ion effect and its relevance to natural waters, and familiarizing ourselves with the concept of incongruent dissolution. With these tools under your belt, you are then directed to the latter half of Chapter 3 in Kehew (2001), where he applies these concepts in a discussion of some interesting case studies. Because Kehew (2001) does a very good job describing these case studies, and we have limited time together, I will not be reviewing the case studies in class. However, I direct you to the Lecture 4 page on the course web site for some study questions to help guide your reading in the text.

3. 3 BRIEF REVIEW We saw in Lecture 3 that pH, pCO2 and bicarbonate ion concentrations are all interrelated. Rearrangement of the equations we have worked with previously yields: Thus, if we measure pH and bicarbonate ion concentration, we can calculate pCO2.