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

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.

Integrating Mental and Physical Health Services Using a Socio-Emotional Trauma Lens.

This article provides a synthesis of the lessons learned from the Pediatric Integrated Care Collaborative (PICC), a SAMHSA-funded project that is part of the National Child Traumatic Stress Network. The high prevalence of trauma exposure in childhood and shortage of mental health services has informed efforts to integrate mental and behavioral health services in pediatric primary care. This article outlines strategies to integrate care following the six goals of the PICC change framework: create a trauma/mental health informed office; involve families in program development; collaborate and coordinate with mental health services; promote resilience and prevent mental health problems through a particular focus on trauma-related risks; assess trauma-related somatic and mental health issues; and address trauma-related somatic and mental heath issues. We conclude with a summary of key strategies that any practice or practitioner could employ to begin or continue the process of integration.