BIOGEOCHEMISTRY OF AN OLD-GROWTH FORESTED WATERSHED, OLYMPIC NATIONAL-PARK, WASHINGTON

The biogeochemistry of a coastal old-growth forested watershed in Olym pic National Park, Washington, was examined. Objectives were to determ ine: (1) concentrations of major cations and anions and dissolved orga nic C (DOC) in precipitation, throughfall, stemflow, soil solution and the stream; (2) nutrient input/output budgets; and (3) nutrient reten tion mechanisms in the watershed. Stemflow was more acidic (pH 4.0-4.5 ) than throughfall (pH 5.1) and precipitation (pH 5.3). Organic acids were important contributors to acidity in throughfall and stemflow and tree species influenced pH. Soil solution pH averaged 6.2 at 40 cm de pth. Stream pH was higher (7.6). Sodium (54.0 mu eq L(-1)) and Cl (57. 6 mu eq L(-1)) were the dominant ions in precipitation, reflecting the close proximity to the ocean. Throughfall and stemflow were generally enriched in cations, especially K. Cation concentrations in soil solu tions were generally less than those in stemflow. Ion concentrations i ncreased in the stream. Dominant ions were Ca (759.7 mu eq L(-1)), Na (174.4 mu eq L(-1)), HCO3 (592.0 mu eq L(-1)), and SO4 (331.5 mu eq L( -1)) with seasonal peaks in the fall. Bedrock weathering strongly infl uenced stream chemistry. Highest average NO3 concentrations were in th e stream (5.2 mu eq L(-1)) with seasonal peaks in the fall and lowest concentrations in the growing season. Nitrogen losses were similar to inputs; annual inputs were 4.8 kg/ha (not including fixation) and stre am losses were 7.1 kg/ha. Despite the age and successional status of t he forest, plant uptake is an important N retention mechanism in this watershed.