Wetlands and streams buffer the interactions among uplands and adjacent aquatic systems. Phosphorus (P) is often the key nutrient found to be limiting in both estuarine and freshwater ecosystems. As such, the ability of wetlands and streams to retain P is key to determining downstream water quality. This article reviews the processes and factors regulating P retention in streams and wetlands and evaluates selected methodologies used to estimate P retention in these systems. Phosphorus retention mechanisms reviewed include uptake and release by vegetation, periphyton and microorganisms; sorption and exchange reactions with soils and sediments; chemical precipitation in the water column; and sedimentation and entrainment. These mechanisms exemplify the combined biological, physical, and chemical nature of P retention in wetlands and streams. Methodologies used to estimate P retention include empirical input-output analysis and mass balances, and process kinetics applied at various scales, including micro- and mesocosms to full-scale systems. Although complex numerical models are available to estimate P retention and transport, a simple understanding of P retention at the process level is important, but the overall picture provided by mass balance and kinetic evaluations are often more useful in estimating long-term P retention.

Electrokinetically enhanced remediation is an innovative technology that has the potential to remediate hydrophobic organic compound (HOC) contamination in soils and groundwater. A surfactant/cosolvent is used to increase HOC desorption and solubilization, and an applied electric potential facilitates contaminant transport primarily by electroosmosis and/or electrophoresis. Electroosmotic flow generally improves soil–solution–contaminant interaction, especially in zones of high organic content and/or low hydraulic conductivity. The electrokinetically enhanced remediation process is fairly simple to implement and operate, but the fundamental reactions that govern the remediation method are complex. An adequate knowledge of the contaminant transport mechanisms and the physical, chemical, and electrochemical processes is essential in order to optimize system performance. This article reviews previous research efforts on HOC remediation and the use of in situ flushing and electrokinetics for organic contaminants. In addition, to gain a better understanding of the individual components and the complexities of the electrokinetically enhanced in situ flushing process, this article presents background information on HOCs and surfactants/cosolvents, as well as the basic parameters that affect the performance of in situ flushing and electrokinetic technologies. Since the success or failure of electrokinetic remediation for HOC pollutants in low permeability soils largely depends on electroosmotic advection and/or electrophoresis, the discussion concerning electrokinetics focuses on these contaminant transport mechanisms.