MODELING EFFECTS OF PREDICTED INCREASED IMPERVIOUS SURFACES ON PHOSPHORUS FLUXES USING THE SOIL AND WATER ASSESSMENT TOOL IN AQUIA CREEK WATERSHED, VIRGINIA, USA

Phosphorus (P), originating from point and nonpoint sources within watersheds, is one of the leading limiting nutrients in fresh waterbodies, contributing to the process of eutrophication and damaging the health and functionality of aquatic systems. The simulation P flux variations using temporal land-use projections comprehensively throughout a watershed, reveals how long-term landuse change patterns influence P, and can assist with landuse planning and lasting conservation efforts. This study achieved a multi-year landuse simulation of Aquia Creek, a 26600 hectare subwatershed of the lower Chesapeake Bay, using the Soil and Water Assessment Tool (SWAT). The SWAT database, constructed via soil properties, climate, elevation, point source additives, water flow and landuse inputs, was used to construct a model of P loading from the Aquia Creek watershed. This model was calibrated/validated using field site data from 2010-2013/2014-2016 respectively with validation results yielding a 0.6 Nash-Sutcliffe coefficient. The landuse transformation prediction database for the year 2030 was aggregated using an artificial neutral network approach and inputs such as population growth projections, proximity to transportation and infrastructure, and hotspots of impervious surface development. The results indicated that a 15 percent increase in impervious surface area resulted in an average increase in stream P concentrations by 0.032 mg/L, demonstrating a relationship between impervious landuse change and P flux. The increase in impervious surface area lowered rates of soil retention of P and increased the resuspension rates of legacy P from erodible coastal plain depositions. These findings enhance understandings of the temporal variations that affect P and can assist in planning future development goals to diminish the effects of local pollution.