Why is calcite a strong phosphorus sink in freshwater? Investigating the adsorption mechanism using batch experiments and surface complexation modeling

Details

• Journal Title:
  Chemosphere
• Personal Author:
  Flower, Hilary ; Rains, Mark ; Taşcı, Yasemin ; Zhang, Jia-Zhong ; Trout, Kenneth ; Lewis, David ; Das, Arundhati ; Dalton, Robert
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; AOML (Atlantic Oceanographic and Meteorological Laboratory)
• Description:
  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.
• Keywords:
  Freshwater Phosphates
• Source:
  Chemosphere, 286: 131596
• DOI:
  https://doi.org/10.1016/j.chemosphere.2021.131596
• Document Type:
  Journal Article
• Rights Information:
  Accepted Manuscript
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:cba5ee021b794fb217f8581593b51f7af7b1b54319eb7b7fcb467932d96816b6
• Download URL:
  https://repository.library.noaa.gov/view/noaa/45178/noaa_45178_DS1.pdf
• File Type:
  [PDF - 4.11 MB ]