PRECIPITATION CHEMISTRY ALONG AN INLAND TRANSECT ON THE OLYMPIC PENINSULA, WASHINGTON

The objective of this study was to examine oceanic influences, seasonal variation, and effect of distance from the ocean on the chemistry of bulk precipitation falling on the Pacific coast of Washington State. Bulk precipitation was collected at Sites 4, 13, 24, and 31 km inland from the Pacific Ocean. Mean electrical conductivity of precipitation ranged from 0.47 to 1.02 mS m(-1) and mean pH ranged from 5.3 to 5.6. Annual precipitation increased from 2780 mm at 4 km to approximately 3500 mm at 13 km from the coast and remained constant through 31 km Inland. Precipitation was highest in the late fall and winter months and lowest during the summer. Rates of ion deposition had a similar seasonal pattern to that of precipitation. Concentrations of Cl, SO4, Mg, Na, and excess Ca (Ca in excess of expected sea salt levels) were highest nearest to the coast and were reflected in higher electrical conductivity in precipitation falling closest to the coast. Much of the change in precipitation chemistry occurred between 4 and 13 km from the coast. This corresponds to the change in precipitation and suggests that the changes in chemistry are dilution effects due to increased rainfall. Annual deposition of Na, K, Mg, Ca, excess Ca, NO3, and Cl were lower at the collection site farthest from the ocean. Sulfate deposition remained relatively unchanged with increased distance from the ocean; however, excess SO4 (SO4 in excess of expected sea salt levels) deposition increased and deposition of SO4 from sea salt (total minus excess) decreased with increasing distance from the ocean.