|Abstract or Summary
- This research addressed the opportunity to obtain baseline data for both stream chemistry and soil resources for an intensively managed forest watershed, encompassed by the North and South Forks of Hinkle Creek Watershed Research and Demonstration Area Project near Sutherlin, Oregon. A solid representative database for both stream and soil nutrients in these forest watersheds will provide a model upon which to help gauge the effects of current and expected intensive forest management practices on industrial forest land. Eight original sampling points were described for water chemistry. In addition, samples were collected from three other locations directly below two clearcuts completed in 2001 that had subsequent intensive vegetation control measures in place. The total nutrient output in kg month [superscript -1] and kg ha [superscript -1] month [superscript -1] among the Hinkle Creek streams differed greatly due to discharge and watershed area, but their nutrient concentrations, with few exceptions, were closely related. All stream water N concentrations were low, except for some higher NO3-N concentrations for two partially treated watersheds, Clay and Beeby Creeks. DeMearsman Creek, a control, had an NO3-N + NO2-N concentration of 0.01mg L [superscript -1] in December, 2003. In contrast, a Beeby Creek tributary below a clearcut had a 1.75 mg L [superscript -1] concentration. The NO3-N concentrations increased substantially after urea fertilization of most of the Hinkle Creek basin in late October, 2004. Samples in January, 2005 showed a reversal of NO3-N + NO2-N concentrations between treatment vs. control watersheds (P < 0.02, T = 4.24). Partial clearcuts or completely forested basins both had similar nutrient concentration data, with the exception of N, especially NO3-N + NO2-N. Beeby Creek was significantly higher in NO3-N + NO2-N, with a two-sided inference (P < 0.0001, T = 6.2-6.5), than all of the other headwater streams. Clay Creek sampled above and below a clearcut showed no significant change (P = 0.272, T = 1.15). Hinkle Creek South Fork showed that the downstream effects of clearcutting, especially NO3-N + NO2-N output from smaller upstream tributaries, may transmit their effects to larger confluences downstream (P = 0.0001, T = 4.47).
Newly published soil surveys from the National Resource Conservation Service and Douglas County SCS were used to set up a methodology for sampling the representative Hinkle Creek soil resources. Eight main soil types were mapped, 27 representative soil pits were dug in accordance with the location of the mapped soils, and standard soil survey descriptions were created. Soil cores were taken from different depths (0-15, 15-30 and 30-60 cm). These data were used to estimate total soil C, N, P, and S resources, soil cation exchange capacity, and available base cations (Ca, Mg, K, and Na). Soil N was low, with the most prevalent soil series, (Orford Gravelly Loam) having 1010 kg ha [superscript -1] (S.E. 143) in the top 15 cm. Low stream N concentration may be correlated with the low soil N content, which may limit Hinkle Creek tree production.