Upstream Population Gradient Drives Freshwater Salinization in the Occoquan Watershed

Abstract

Increased salinization of inland freshwater resources is present on a global scale, but is pro- gressing rapidly in the densely populated Mid-Atlantic United States. This phenomenon threatens aquatic health, ecosystem services and functionality, and can alter the percep- tion of potable drinking water. The Occoquan watershed, located in Northern Virginia has experienced rapid urbanization across recent decades and is now confronted with rising salinization. Various stakeholders in the area have focused efforts to quantify the drivers of salinization in order to take corrective action to preserve this resource. To aid these efforts, urbanization's relationship with in-stream salinity was analyzed, where its exerted influence was found to be dependent upon overland hydrologic flowpaths which connect urban areas to stream networks. The analysis was then broadened to Multiple Linear Regression models of urban and climatological drivers to statistically quantify each driver's relative influence on in-stream salinity. The models demonstrated that urbanization is the primary driver, where rainfall and roadway deicer application were also found to be significant. The model was then used to predict the magnitude of salinization in the Occoquan watershed to a time horizon of 2040 based on expected population growth as well as two anticipated climate scenarios. Finally, the analytical framework produced in this research was generated with scalability in mind, such that it can potentially be utilized as a watershed-scale screening tool accross the Mid-Atlantic, to inform proactive, regionally appropriate management decisions.