Dissertation/Thesis Abstract

Modeled Affinity Constants for Phosphorus Adsorption and Desorption due to Saltwater Intrusion
by Taşcı, Yasemin, M.S., University of South Florida, 2019, 82; 13810857
Abstract (Summary)

It is important to understand the processes that regulate phosphorus (P) fluxes to coastal environments, because P is an important nutrient in coastal ecosystems. Phosphorus adsorbs to the surface of minerals in sediment and bedrock, and an influx of seawater can cause some of that P to desorb, raising the P concentration of ambient water. Although seawater-induced P desorption is thought to be an important source of P to coastal environments, the chemical reactions that underlie it have not been established. Previous work provides some relevant surface reactions and associated affinity constants between various aqueous P species and the surface of calcite and in dilute calcium carbonate-P solutions. However, these reactions with their respective affinity constants from the literature fail to predict the behavior of P with calcite in seawater. In this study, we conducted a series of batch experiments involving both adsorption and desorption of P in seawater, freshwater, dilute seawater, and mixtures of seawater and freshwater. We used these results in the geochemical model PHREEQC and the parameter estimation model PEST to optimize the affinity constants for the existing surface reactions. We found that after making minor adjustments to the affinity constants, the existing surface complexation models of calcite surface reactions from the published literature are sufficient to explain seawater-induced P desorption. Specifically, our results suggest that CaPO4 and either CaHPO40 or HPO42– may be important species in the P adsorption/desorption reactions in freshwater-seawater mixing.

Indexing (document details)
Advisor: Rains, Mark, Flower, Hilary
Commitee: Trout, Kenneth
School: University of South Florida
Department: Geology
School Location: United States -- Florida
Source: MAI 58/06M(E), Masters Abstracts International
Subjects: Geology, Geological engineering, Chemistry
Keywords: Limestone, PEST, PHREEQC, Phosphorus, Sea level rise, Surface complexation
Publication Number: 13810857
ISBN: 978-1-392-22831-9
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