Award: OCE-1658377

Project Outcomes Report

Award Title: Collaborative Research: Organic Alkalinity: Impacts of the [OTHER] Alkalinity on Estuary and Coastal Ocean Chemistry

Principal Investigator: Christopher Hunt

Award Number: 1658377

In 2017, the University of New Hampshire and the University of South Florida received a collaborative award entitled “Organic Alkalinity: Impacts of the [OTHER] Alkalinity on Estuary and Coastal Ocean Chemistry.”  Measurements of total alkalinity, through titrations with strong acid, provide valuable information about the acids and bases present in natural waters.  This project examined how the presence of organic molecules in natural waters affects the titration of total alkalinity. We made several analytical advances during this project, which should lead to improved organic alkalinity measurements in future studies. We also compared both the seasonality and distributions with salinity of organic alkalinity in two estuaries with differing total alkalinity source waters. Additionally, we examined how these organic measurement effects may lead to problems in using total alkalinity measurements for the study of the inorganic carbon and acid-base systems in estuary environments.

Analytical development: a standard method for quantifying and characterizing organic alkalinity does not exist, although a few publications have described similar approaches. This study compared measurements of the same sample using multiple methods, with results showing consistent differences. The differences indicate that the measured organic alkalinity concentrations are sensitive to the analytical method chosen and the acid-base characteristics of the organic compounds in solution. This comparison of methods, together with other analytical improvements developed in this project, should guide the methodology of future organic alkalinity studies.

Contrasting estuarine systems: The substantial concentrations of organic alkalinity in each estuary were sometimes not conservative with salinity, and were typically associated with very low pH. The portion of total alkalinity contributed by organics was typically higher in the Pleasant estuary (up to 78%) than the St. John estuary (up to 10%). Both estuaries had a higher proportion of organic alkalinity than the adjacent coastal ocean (less than 0.4%). The Pleasant estuary also showed seasonal differences in organic alkalinity (and dissolved organic carbon), while the St. John estuary did not.

Improvements in estuary pH estimates: We performed titrations to characterize the acid-base characteristics of the organic compounds in our estuary samples.  These characteristics, together with our measurements of total organic alkalinity concentration, were used to improve estimates of estuary pH from other common measurements (pCO₂, dissolved inorganic carbon, and total alkalinity).  Estimated pH improved with the inclusion of organic alkalinity information, when compared to actual measurements of estuary pH.  However, a persistent pH offset remained in both estuaries.

Summary: Over its extended study period this project provided a new comparison of methodologies for measuring organic alkalinity and highlighted the disagreement between two published methods.  Estuary samples collected during the fieldwork component of this project showed distinct differences in seasonal organic alkalinity distributions and concentrations, but little difference in the acid-base characteristics of the organic charge groups.  Application of the organic alkalinity results from this study resulted in improved retrievals of pH from inorganic carbon system modeling; however, the pH retrievals still showed a pH overestimate at mid- and low salinities.  This consistent underestimate indicates that the effect of organic alkalinity on the acid-base system in these estuaries is still not completely characterized and further study is needed.

 

Last Modified: 01/17/2024
Modified by: Christopher Hunt