Why is Calcite a Strong Phosphorus Sink in Freshwater? Investigating the Adsorption Mechanism Using Batch Experiments and Surface Complexation Modeling

Authors

Hilary Flower, Eckerd College
Mark Rains, University of South FloridaFollow
Yasemin Taşcı, University of South Florida
Jia-Zhong Zhang, Ocean Chemistry and Ecosystems Division, Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL, 33149, United States
Kenneth Trout, University of South Florida
David Lewis, University of South FloridaFollow
Arundhati Das, University of South Florida
Robert Dalton, University of South Florida

Document Type

Article

Publication Date

2022

Keywords

Calcium carbonate, Phosphates, Abiotic factors, Sediment dynamics, Nutrient

Digital Object Identifier (DOI)

https://doi.org/10.1016/j.chemosphere.2021.131596

Abstract

One of the primary drivers of Phosphorus (P) limitation in aquatic systems is P adsorption to sediments. Sediments adsorb more P in freshwater compared to other natural solutions, but the mechanism driving this difference is poorly understood. To provide insights into the mechanism, we conducted batch experiments of P adsorption to calcite in freshwater and seawater, and used computer software to develop complexation models. Our simulations revealed three main reasons that, combining together, may explain the greater P adsorption to calcite in freshwater vs. seawater. First, aqueous speciation of P makes a difference. The ion pair CaPO₄⁻ is much more abundant in freshwater; although seawater has more Ca²⁺ ions, MgHPO₄⁰ and NaHPO₄⁰ are more thermodynamically favored. Second, the adsorbing species of P make a difference. The ion pair CaPO₄⁻ (the preferred adsorbate in freshwater) is able to access adsorption sites that are not available to HPO₄²⁻ (the preferred adsorbate in seawater), thereby raising the maximum concentration of P that can adsorb to the calcite surface in freshwater. Third, water chemistry affects the competition among ions for surface sites. Other ions (including P) compete more effectively against CO₃²⁻ when immersed in freshwater vs. seawater, even when the concentration of HCO₃⁻/CO₃²⁻ is higher in freshwater vs. seawater. In addition, we found that under oligotrophic conditions, P adsorption is driven by the higher energy adsorption sites, and by the lower energy sites in eutrophic conditions. This study is the first to model P adsorption mechanisms to calcite in freshwater and seawater.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Chemosphere, v. 286, issue Part 1, art. 131596

Scholar Commons Citation

Flower, Hilary; Rains, Mark; Taşcı, Yasemin; Zhang, Jia-Zhong; Trout, Kenneth; Lewis, David; Das, Arundhati; and Dalton, Robert, "Why is Calcite a Strong Phosphorus Sink in Freshwater? Investigating the Adsorption Mechanism Using Batch Experiments and Surface Complexation Modeling" (2022). School of Geosciences Faculty and Staff Publications. 2328.
https://digitalcommons.usf.edu/geo_facpub/2328