From River to Sea: Improving Carbon System Measurement Methods for use in Rivers, Estuaries, and Oceans
Doctor of Philosophy (Ph.D.)
Degree Granting Department
Robert Byrne, Ph.D.
Timothy Conway, Ph.D.
Chuanmin Hu, Ph.D.
Lisa Robbins, Ph.D.
Kimberly Yates, Ph.D.
spectrophotometric pH, spectrophotometric total alkalinity, carbonate alkalinity, thymol blue, bromocresol purple, freshwater, estuaries
Over the last 30 years, spectrophotometric methodologies have been developed, with increasing rigor, to accurately measure all four carbon system parameters: total alkalinity (AT), total carbon (CT), partial pressure of CO2 (pCO2), and pH. Spectrophotometric measurements of carbon system parameters rely on quantitative characterizations of the response of sulfonephthalein indicator dyes (e.g., meta-cresol purple (mCP), thymol blue (TB), and bromocresol purple (BCP)) to changing solution pH, as well the response of indicator physical-chemical characteristics to key environmental variables (salinity (SP), temperature (T), and pressure). Until recently, the physical-chemical properties of pH indicator dyes had only been determined over the range of SP encountered in the open-ocean (20 ≤ SP ≤ 40), impeding the application of spectrophotometric methods for investigation of carbon system behavior in estuaries and fresh waters. As a second major impediment to the quantitative application of pH indicators, it became recognized that the use of sulfonephthalein pH indicators can be compromised by the presence of light-absorbing impurities. This dissertation describes efforts to add two sulfonephthalein indicators to the limited list of pH indicators that are (a) free of impurities and (b) calibrated over a river to sea range of salinities (0 ≤ SP ≤ 40).
TB is a sulfonephthalein indicator with a pH-indicating range best suited for spectrophotometric pH assessments in mildly alkaline waters and is the indicator of choice for waters that have a pH somewhat above the optimal indicating range of mCP. Chapter two of this dissertation provides a method to obtain pure TB using flash chromatography and algorithms that describe the SP and T dependence of the physical-chemical properties of purified TB. BCP is a sulfonephthalein indicator with a pH-indicating range appropriate for spectrophotometric pH assessments in mildly acidic waters (e.g., alpine lakes or waters impacted by acid-mine drainage). The low indicating range of BCP makes it especially suitable for spectrophotometric AT measurements in titrated water samples. Chapter three of this dissertation provides a method for obtaining pure BCP, and algorithms that describe the SP and T dependence of the physical-chemical properties of purified BCP. The characterizations of purified TB and BCP were obtained by pairing absorbance measurements of each of these indicators with absorbance measurements obtained with mCP, which has been purified and well-characterized over the SP and T range encountered from river to sea (i.e., 0 ≤ SP ≤ 40, 278.15 ≤ T ≤ 308.15 K; Muller and Rehder (2018); Douglas and Byrne (2017b)). This method produces pH algorithms for TB and BCP that are directly linked to the molecular properties of mCP. Therefore, if mCP algorithms are improved in the future, the algorithms of TB and BCP can also be revised and improved.
The characterizations of TB and BCP presented in chapters two and three of this dissertation enable spectrophotometric assessments of aqueous environmental systems over a wide range of conditions. However, CO2 system characterizations of low salinity environments still present challenges, both logistical (e.g., portability of instrumentation) and methodological (e.g., total alkalinity measurements). Chapter four of this dissertation describes application of the BCP characterizations in chapter three to improve carbon system analysis of fresh waters. A novel spectrophotometric method is presented to determine individual alkalinity components (total alkalinity (AT), carbonate alkalinity (AC), and non-carbonate alkalinity (ANC)) of fresh water. These characterizations, along with measured pH, allow determinations of total dissolved inorganic carbon (CT). To demonstrate the efficacy and portability of this method, the carbon system of the Snake River, in southern Idaho, was investigated. Using the novel spectrophotometric method presented in chapter four, direct characterizations of the pH and AC of Snake River samples produced useful characterization of changes in river chemistry in response to seasonal changes in river flow.
Scholar Commons Citation
Hudson-Heck, Ellie, "From River to Sea: Improving Carbon System Measurement Methods for use in Rivers, Estuaries, and Oceans" (2021). USF Tampa Graduate Theses and Dissertations.