PHOSPHOROUS AND SEDIMENT FLUXES ANALYSIS IN AQUIA CREEK BASIN, VIRGINIA, USA

Aquatic systems are negatively affected by excess input of phosphorus bound to sediments generated by landscape surficial erosion and in-channel stream erosion. Excess phosphorus can lead to diverse problems such as toxic algal blooms, loss of oxygen, and reductions in biodiversity. This study examines stream water phosphorous levels in the basin of Aquia Creek, a 3^rd order tributary of the Potomac River (U.S.A). Sediment traps, bank erosion pins, analysis of LIDAR data and historic orthorectified aerial images, and the Revised Universal Soil Loss Equation (RUSLE), coupled with a sediment delivery ratio (SDR) were used in analyzing watershed rill and inter-rill sediment fluxes from the basin as well as internally generated stream bank sediments. Water samples continue to be taken at six different locations bi-weekly, including one auto sampler location. The preliminary results of stream water total P ranges from 0.054 to 95.012 ppm, with elevated levels occurring during the autumn and spring seasons. RUSLE results estimate total surficial soil losses of 55,082 Mg yr^-1 with a total flux of 9,041.4 Mg yr^-1. The model sensitivity analysis shows that slope and anthropogenic land alterations determine soil erosion variability in the basin, with the highest per hectare losses generated in deciduous forests with slopes between 23.6 and 63.4°. Deciduous forests comprise 57% of the basin, and generate an estimated 24,462.2 Mg yr^-1 of soil. Cultivated land yielded the second largest losses with 11,424.2 Mg yr^-1 being lost annually. The ongoing sediment trap measurements will be used in verifying the accuracy of RUSLE in soil loss analysis. The preliminary results of bank erosion pin measurements show that rates vary from 1.2 to 38.76 cm yr^-1, with the highest values incurred along reaches draining urban areas. Stream bank soils total P content ranged from 2 to16 µg g^-1. Bank erosion rates and phosphorous concentrations will be used to determine P fluxes from cut banks within the basin. Preliminary 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.