Agricultural chemicals and heavy metals in upland soils and valley alluviums of the little Washita River Basin

ABSTRACT: Because of concern about agricultural chemicals and heavy metals accumulating in valley alluvium within a large, dominantly agricultural river basin, about 54,000 hectares (133,000 acres) in southwestern Oklahoma, alluvial cross-section deposits were sampled and compared to associated upland soil materials. Parameters measured included plant nutrients (N, P, K), soil reaction (pH), pesticides (organochlorides, organophosphates, and phenoxys), heavy metals (As, Cd, Pb, Th, and U), particle-size distribution, and fallout Cs-137 (to estimate sediment deposition). Plant nutrient contents, except for K, tended to be lower in the alluvial deposits than in the soils. Differences in pH were minor. No problems with pesticide residues were evident. The low and/or uniform heavy metal contents indicated no lingering, deleterious impact from mining or industrial activities. Particle size and Cs-137 data indicated a preferential sorting and deposition of sediment materials, with the fines moving farther downstream. Generally, results indicated a decreasing removal of plant nutrients and other chemicals from the upland soils during a recent 5-year period with improved soil conservation practices.