Riverine Calcium End-Members Improve Coastal Saturation State Calculations and Reveal Regionally Variable Calcification Potential

Authors

Sean Thomas Beckwith, University of South FloridaFollow
Robert H. Byrne, University of South FloridaFollow
Pamela Hallock, University of South FloridaFollow

Document Type

Article

Publication Date

4-2019

Keywords

carbonate-rich groundwater, first-magnitude springs, ocean acidification, riverine calcium, seagrass, west florida coastal waters

Digital Object Identifier (DOI)

https://doi.org/10.3389/fmars.2019.00169

Abstract

Carbonate-rich groundwater discharged from springs, seeps, and spring-fed rivers on carbonate platforms creates environments of potential refuge for calcifying organisms in coastal waters by supplying higher [Ca²⁺] and [CO₃^2-] along with typically lower nutrient concentrations. The benefits associated with carbonate terrains are maximized in the presence of submerged aquatic vegetation (SAV), especially seagrasses. To improve the accuracy of carbonate saturation state (Ω) determinations, calculated values of [CO₃^2-] and Ksp^∗ were paired with [Ca²⁺] values determined using a model that incorporates directly measured riverine calcium end-members (model A). This model results in Ω values larger than those calculated by assuming that [Ca²⁺] is directly proportional to salinity (model B; e.g., using CO2SYS, CO2calc). As an example, for salinity (S) between 13.5 and 24, improvements in saturation states calculated as differences (ΔΩ) between model A and model B saturation states in the tidal mixing zone of the Weeki Wachee River (Florida, United States) ranged from 0.39 to 1.00 (aragonite) and 0.61–1.65 (calcite). Saturation state ratios (Ω_(A)/Ω_(B)) for coastal waters with enhanced [Ca²⁺] originating from carbonate-rich groundwater can be calculated from end-member calcium concentrations and salinity. Applied to several river systems in the conterminous United States, Ω_(A)/Ω_(B) values calculated at S = 20 lead to Ω_(A)/Ω_(B) ratios of 1.12 (Weeki Wachee), 1.09 (Anclote), 1.06 (Mississippi), and 1.03 (Columbia). These increases in saturation states can be used to identify potential calcification refugia for subsequent high resolution field studies that focus on, for example, the long-term viability of oyster communities and other calcifying organisms in brackish coastal waters.

Rights Information

This work is licensed under a Creative Commons Attribution 4.0 License.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Frontiers in Marine Science, v. 6, art. 169

Scholar Commons Citation

Beckwith, Sean Thomas; Byrne, Robert H.; and Hallock, Pamela, "Riverine Calcium End-Members Improve Coastal Saturation State Calculations and Reveal Regionally Variable Calcification Potential" (2019). Marine Science Faculty Publications. 892.
https://digitalcommons.usf.edu/msc_facpub/892