Why is Calcite a Strong Phosphorus Sink in Freshwater? Investigating the Adsorption Mechanism Using Batch Experiments and Surface Complexation Modeling
Calcium carbonate, Phosphates, Abiotic factors, Sediment dynamics, Nutrient
Digital Object Identifier (DOI)
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.
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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.