Influence of partial harvesting on stream temperatures, chemistry, and turbidity in forests on the western Olympic Peninsula, Washington

Stream temperatures, chemistry and turbidity were monitored in two partiall y harvested (7-33%) watersheds, Rock and Tower creeks, and an uncut old-gro wth watershed, West Twin Creek in the Hoh River Valley on the Olympic Penin sula, Washington. Douglas-fir (Pseudotsuga menziesii (Mirb.) France) was re planted in the harvested areas and red alder (Alnus rubra Bong.), a nitroge n fixer, dominated the riparian areas in the sampling sites on Rock and Tow er creeks. We collected grab stream water samples monthly, from May 1996 to June 1998 and analyzed them for pH, electrical conductivity, total N and P , and major cations and anions. Stream temperatures were monitored continuo usly and turbidity was monitored monthly from May 1997 to June 1998. Partia l harvesting had little influence on stream temperature, chemistry and turb idity 11-15 years after harvesting. Stream temperatures were more seasonall y variable in the harvested streams compared to the unharvested old-growth site with an average summertime maximum elevated by 3.5 degrees C. Maximum stream temperatures did not exceed 16 degrees C in any stream and therefore salmonid species are not likely to be affected. There were significant dif ferences in concentrations of some cations, anions and EC between the old-g rowth and the partially harvested watershed streams, but in most cases conc entrations were actually higher in the unharvested watershed. Nitrate conce ntrations and stream turbidity were not significantly higher in the harvest ed watersheds.