Effects of Forest Fertilization with Urea on Major Biological Components of Small Cascade Streams, Oregon

摘要

During April, 1976, 1.9 x 10 ha of second growth Douglas fir, located in the Willamette National Forest of Oregon, were fertilized with 224 kg urea-N/ha. Unfertilized buffer strips of 60 and 90m were maintained along all second and third order streams, respectively. Sharp increases in urea concentrations (maximum of 12 mg/l) during the fertilization phase were due to the unintentional, direct application to the streams. Immediately following fertilization all nitrogen species returned to near background levels. The second year following fertilization only NO3-NO2 appeared to be slightly elevated due to fertilization. Two-month fish bioassays using Salmo gairdneri showed no mortalities which could be attributed to by-products or contaminants of urea. Algal assays using Selenastrum capricornutum, and chlorophyll a and ATP-biomass of periphyton from glass slide samplers showed low supporting capacity and generally no significant increase in biomass resulting from fertilization.