Heather Rogers, Dr. Brian Benham , Dr. Karen Kline

1. Effects of Converting Agricultural and Forested Land Uses to Urban Land Uses on Surface Water Nutrient Loads Heather Rogers, Dr. Brian Benham, Dr. Karen Kline Introduction Methods Research Questions: Using mathematical relationships, the Hydrological Simulation Program-FORTRAN (HSPF) uses watershed characteristics and meteorological data to simulate pollutant fate and transport. An HSPF model was developed and calibrated for Opequon Creek to simulate nutrient loads in response to land use changes. Hourly loads of total nitrogen and phosphorus were simulated for a 5 year period. Average annual N and P loads for existing conditions (no land use change) served as a baseline to which results for land use conversions were compared. Two land use conversion scenarios were evaluated: Scenario1: Agricultural (ag) land use was converted to urban land use in 25% increments. Forested land use was unchanged. Nutrient load sources associated with ag land use (septic systems and cattle) were reduced in 25% increments as ag land use was converted to urban land use. Scenario 2: Forested land use was converted to urban land use in 25% increments. Ag land use was unchanged. Resulting loads from each land use change were calculated as a percent (%) change from baseline conditions. 1) Does it make a difference in nutrient loading at the watershed outlet if development consumes agricultural or forested land? • Acre for acre, deforestation results in similar N and P load increases at the outlet in both watersheds. • The conversion of agricultural to urban land use results in decreases in N and increases in P at both watershed outlets. • From a nutrient loading perspective, the conversion of agricultural land use to urban land use appears to be the better alternative. 2) Assuming development will continue in the Opequon Creek watershed, is it better to focus new development in an already urbanized watershed (Abrams Creek) or a more agricultural watershed (Upper Opequon Creek)? • From a nutrient loading perspective, N and P loads at the watershed outlet will be minimized if new development is focused in agricultural areas. The Chesapeake Bay is the largest estuary in North America. Estuaries are the source of over 75% of commercial seafood in the U.S.* According to the Chesapeake Bay Foundation, excess nutrients (nitrogen and phosphorus) are the leading cause of the Bay’s rapid deterioration over the last two decades. Nutrients support the growth of algal blooms, which deplete dissolved oxygen in the water as they decompose, as well as reducing sunlight penetration limiting photosynthesis of aquatic plants. Non-point nutrient loads, which are largely a function of land use and management, are a critical source of pollution to the Bay. To protect the Bay from further degradation, non-point source nutrient pollution must be better understood and controlled. The fate and movement of nutrients within a watershed can be simulated using computer-based water quality models. This research focused on assessing the impact of land use changes on nutrient loads at the watershed outlet of two tributary watersheds to the Chesapeake Bay. Results Hypothesis • Urbanization, regardless of the land use conversion, will increase nutrient loads at the watershed outlet. • Agricultural to urban land use conversion in both watersheds resulted in decreases in N loads. • However, P is the most crucial with respect to water quality impairment, and it increased with both land use conversion scenarios in both watersheds. blog.ratestogo.com dolphin.upenn.edu Aerial photograph of Chesapeake Bay including the Bay Bridge Map showing Chesapeake Bay • N inputs on ag land use in Abrams creek are less than Upper Opequon, producing smaller decreases in simulated N loads when ag land use is converted to urban land use. • N loading on forested land use was the same for both watersheds, producing similar increases in simulated N loads at watershed outlets when converting from forested land use to urban land use. Study Watershed Two subwatersheds of the Opequon Creek watershed – Abrams Creek and Upper Opequon Creek– were used for this study. Opequon Creek drains into the Potomac River, which drains into the Chesapeake Bay. Abrams Creek is mostly urban, whereas Upper Opequon Creek is mostly rural. For this research, more specific types of land uses were aggregated into 3 broad types: agricultural, forested, and urban. Future Research • Further examination of the conversion of the specific land use types (e.g. cropland, pasture, low density and high density residential) that were aggregated to form the ‘agricultural‘ and ‘urban’ land use categories is needed to draw more specific conclusions and make more specific recommendations with respect to targeting development in the Opequon Creek watershed. pubs.ext.vt.edu tmdl.bse.vt.edu • Acknowledgements • Virginia Polytechnic Institute and State University • Biological Systems Engineering • Multicultural Academic Opportunities Program (MAOP) • *http://www.estuaries.gov/estuaries101/About/Default.aspx?ID=245 • P inputs on ag land use in Abrams Creek are less than Upper Opequon, producing larger increases in simulated P loads when ag land use is converted to urban land use. • P loading on forested land use was the same for both watersheds, producing similar increases in simulated P loads at watershed outlets when converting from forested land use to urban land use. Opequon Creek Watershed Land Use Location of Opequon Creek Watershed