The relationship between land use and nutrient concentrations in central Arkansas: identifying potential nonpoint-sources of pollution in the Lake Conway – Point remove watershed Danielle Braund1, Greg Phillips2, Randy Easley3, Sally Entrekin1,4 University of Central Arkansas1, GBMc & Associates2, Central Arkansas Water3, Virginia Tech4 Background • Agricultural practices and urbanization cause runoff and subsequent nonpoint-source pollution in aquatic systems.ạ ã Increases in nutrient concentrations can alter water characteristics that can impact biotic communities ² • The Lake Conway – Point Remove (LCPR) watershed in central Arkansas has been identified as a top contributor of nitrogen and phosphorus to the Gulf of Mexico, ranking in the top 150 watersheds in the Mississippi River Basin (Figure 1) ³ • The sources of nonpoint-source pollution within the watershed are currently unknown • The LCPR watershed land use contains a mix of forested, agricultural, and developed areas (Figure 1) • Our objective is to identify sub-watersheds contributing nonpoint-source pollution to the Arkansas River and to pinpoint what anthropogenic practices are causing nutrient inputs • Subwatersheds accumulate drainage from headwater streams, which can account for 80% of total stream length and, subsequently, nutrient runoff Results Conclusion / Future Directions Table Land use compositions of the ten study streams in the LCPR watershed were calculated using data from the National Land Cover Dataset from 2011 • Baseflow TN and TP concentrations increased with increases in both percent development (Figure 2a) and agriculture (Figure 2b) • Baseflow nutrient loads (TN and TP) were greater in streams WC-1, CC-1, TB-1, and GC-1 • Urban development increases aqueous nutrients from stormwater discharge and agriculture increases nutrients form fertilizer runoff in both row crop and pasture • We plan to compile contemporary data collected on this project with historic watershed data to create a watershed management plan (WMP) We also plan to included: LCPR study streams Land use category SD-1 LC-1 WC-1 WPR-1 CC-1 TB-1 EPR-1 GC-1 EPR-2 WPR-2 Agriculture 1.7 2.8 8.8 15.0 33.8 35.9 36.0 50.8 71.0 112.7 Development 17.2 9.5 11.9 6.2 7.1 24.5 6.1 8.8 10.9 21.1 Forest 1.6 0.5 12.4 156.7 99.3 39.6 89.9 49.7 155.9 405.2 Other 0.3 0.2 1.8 12.1 11.7 8.5 14.8 7.0 19.5 33.3 • Alkaline phosphatase activity which describes nutrient limitation b a • Equilibrium phosphorus concentrations (EPC) which describe sorption patterns of excess phosphorus and predicts theoretical sources or sinks for phosphorus • Storm sampling data to further expand our model compare nutrient loads with other studies to determine if loads are elevated Figure The LCPR watershed in central Arkansas contains a mix of forested, agricultural, and developed areas The cities of Conway, Morrilton, and Russellville are located within the LCPR watershed Total Nitrogen Annual Loads Total Phosphorus Annual Loads By identifying anthropogenic practices that are increasing nonpoint-source pollution in small sub-watersheds, nutrient concentrations and the consequent accumulated annual loads from headwater streams can be reduced b 10 Annual load per squar kilometer [ (mg / yr) / km² ] • Study Sites- Ten streams were selected in major sub-basins in the LCPR watershed The watersheds ranged in area size and land use composition • Land use- National Land Cover Dataset 2011 was used to: • quantify % landcover (Table 1) • area of landcover (km²) • Nutrients- Grab samples taken at baseflow were filtered in field and processed in at the AWRC lab for: • Total nitrogen (TN), ammonium, nitrate-nitrite • Total phosphorus (TP), soluble reactive phosphorus (SRP) • Data Analysis- Nutrient concentrations and land use composition were analyzed using multiple linear regression models in R Annual load per square kilometer [ (mg / yr) / km² ] Methods a 10 Calculate baseflow annual nutrient loads for the LCPR study streams Final goal to create a watershed management plan for the LCPR watershed • Figure Baseflow nutrient concentrations in the LCPR watershed related to percent land cover using NLCD 2011 2a Nutrients containing nitrogen (ammonium, nitrate-nitrate, and TN) increased in concentration with increases in developed land cover (R²=0.84, F5,39=43.99, p More % agriculture ACKNOWLEDGEMENTS USGS 104B grant #2016AR387B Figure Annual baseflow nutrient loads for TN (a) and TP (b) per square mile of catchment within the LCPR watershed study steams 3a Total nitrogen loads were greater in Whig Creek (WC-1), Cypress Creek (CC-1), lower reach of the east fork of Point Remove Creek (EPR-2), and Galla Creek (GC-1) 3b Total phosphorus loads were greater in Whig Creek (WC-1), Cypress Creek (CC-1), Galla Creek (GC-1), and Tupelo Bayou (TB-1) University of Central Arkansas, GBMc & Associates, Arkansas Water Resource Center, Lake Conway – Point Remove Watershed Alliance Lab and field assistance: Anastasia Mogilevski, Brian Staley, Rostollan, and Rebecca Relic Jennifer Main, Mason