PHOSPHOROUS AND SEDIMENT FLUX ANALYSIS IN AQUIA CREEK A SUB-WATERSHED OF THE CHESAPEAKE BAY BASIN, VIRGINIA, USA

Aquatic systems are negatively affected by excess input of phosphorus bound to sediments generated by surficial and in-channel erosion and the release of P from wetland and floodplain soils. This study examines stream water and wetland soils phosphorous levels in the basin of Aquia Creek, a 3^rd order tributary of the Potomac River (U.S.A). Bank erosion pins, analysis of LIDAR data and historic aerial images, along with the Revised Universal Soil Loss Equation (RUSLE) coupled with a sediment delivery ratio (SDR) were used in analyzing rill and inter-rill sediment fluxes as well as internally generated stream bank sediments. Soil core properties including pH, soil organic matter (SOM), cation exchange capacity (CEC), and sorption sites including Fe, Al, Ca, Mg, and Mn were analyzed to understand the physiochemical conditions that trigger release of P into the creek from its wetlands. Water samples were taken at six different locations bi-weekly and total P ranged from 0.05 to 95.88 ng g^-1, with elevated levels occurring during the autumn and spring seasons. RUSLE results estimate total surficial erosion losses of 55,082 Mg yr^-1 with a total flux of 9,041.4 Mg yr^-1. Bank erosion pin measurements show that rates vary from 1.2 to 75.7 cm yr^-1, with the highest values incurred along downstream reaches draining urban areas. Stream bank soils total P content ranged from 2 to 16 µg g^-1. The preliminary result from 40 soil cores along 9 transects perpendicular to the stream flow in two wetland sites shows that percent SOM and CEC were higher in the downstream site (30.8 ± 11% and 16.8 ± 4.3 cmol/kg, respectively) compared to upstream site (2.56 ± 2.1% and 7.35 ± 1.3 cmol/kg). Soil total P was also greater in the downstream site with an average concentration of 17.9 ± 7.2 µg g^-1 compared to 6.36 ± 4.3 µg g^-1 upstream. The data suggests that acceleration of runoff due to urbanization and subsequent increases in internal erosion rates may significantly contribute to elevated phosphorus concentrations in Aquia Creek. Completion of this study will provide insight into the relationship between P supplied from surficial and in-channel erosion and P sorption-desorption dynamics in the wetland soils in a system affected by both urbanization and sea level rise.