Impact of land use patterns and agricultural practices on water quality in the Calapooia River Basin of western Oregon

摘要: Agricultural practices, including tillage, fertilization, and residue management, can affect surface runoff, soil erosion, nutrient cycling. These processes, in turn, may adversely (1) quality of aquatic resources as habitat for amphibians, fish, invertebrates, (2) costs treating ground water to meet drinking standards, (3) large-scale biogeochemistry. This study characterized the sources nitrogen (N) (total, nitrate (NO 3 − ), ammonium (NH 4 + dissolved organic N) sediment active within 40 subbasins Calapooia River Basin western Oregon monthly samples over three cropping years. The included both independent nested drainages, with wide ranges tree cover, agricultural slopes, soils. Sediment N form concentra- tions were tested against weather practice variables. Subbasin land use ranged from 96% forest 100% agriculture. Average slopes varied 1.3% 18.9%, 0.5 43 mg L -1 (ppm) total maxima 29 249 suspended maxima. Total during winter was positively related percentage landcover seven common crops (nongrass seed summer annuals, established perennial ryegrass (Lolium perenne L.), tall fescue (Schedonorus phoenix {Scop.} Holub), orchardgrass (Dactylis glomerata clover (Trifolium spp.), newly planted stands clover) negatively cover by trees one crop, Italian (annual) multiflorum). Results NO highly simi- lar. concentrations most strongly rainfall totals periods 14 days prior sampling, smaller effects disturbance. Fourier analysis time identified four prominent groups subbasins: those low, medium, high impacts (up 2, 8, 21 , respectively) a strong cyclical signal peaking December (4) very impact ) weak series signal. Preponderance streams draining agriculturally dominated ion, implying mineralization that had been incorporated plant tissue following its initial application spring urea-based fertilizer. Since is driven seasonal temperature patterns, changes agronomic practices designed reduce prompt runoff fertilizer are unlikely achieve more than ~24% reduction export streams.