AUTUMN CHEMISTRY OF OREGON COAST RANGE STREAMS

During an autumn runoff event we sampled 48 streams with predominantly forested watersheds and igneous bedrock in the Oregon Coast Range. Th e streams had acid neutralizing capacities (ANC) > 90 mu eq/L and pH > 6.4. Streamwater Na+, Ca2+, and Mg2+ concentrations were greater than KC concentrations. Anion concentrations generally followed the order of Cl- > NO3- > SO42-. Chloride and Na+ concentrations were highest in samples collated in streams near the Pacific Ocean and decreased mark edly as distance from the coast increased. Sea salt exerted no discern ible influence on stream water acid-base status during the sampling pe riod. Nitrate concentrations in the study streams were remarkably vari able, ranging from below detection to 172 mu eq/L. We hypothesize that forest vegetation is the primary control of spatial variability of th e NO3- concentrations in Oregon Coast Range streams. We believe that s ymbiotic N fixation by red alder in pure or mixed stands is the primar y source of N to forested watersheds in the Oregon Coast Range.