Stream Nutrient Retention in Three Northeastern Oklahoma Agricultural Catchments

Stream nutrient retention was examined in three adjacent agricultural catchments (Cherokee Creek, Cloud Creek,and Dry Creek) in the Ozark Plateau. Retention efficiency was measured using shortterm nutrient and tracer injections toestimate nutrient uptake length (Sw ) during summer 1999 and winter 2000. A onedimensional transport model was used toestimate dispersion, transient storage size, and exchange. Soluble reactive P (SRP) and NO3 N concentrations were leastin the stream with the lowest proportion of pasture in the upland (Dry Creek), whereas concentrations and land use weresimilar in Cherokee Creek and Cloud Creek. Water column SRP concentrations were similar between seasons in all streams,but NO3 N concentrations varied significantly. Injected NO3 N was not significantly retained in these systems, probablybecause the streams were saturated by ambient NO3 N concentrations (greater than 0.1 mg L 1 ). Phosphorus was retainedduring summer injections (Sw ranged from 200900 m), but Sw regressions were not significant in winter. Variation incatchment land use was not a major determinant in P retention during summer, but stream hydrology, such as discharge andtransient storage, was a regulating factor. Therefore, land use changes that alter stream hydrology may have a greater impacton P retention in these streams.