Estimation And Analysis Of Total Suspended Solid Yields From The Mica Creek Experimental Watershed, Idaho

Abstract

Transport and concentration of Total Suspended Solids (TSS) in forested streams play an important role in ecosystem health, affecting the health of fish populations and playing a role in nutrient delivery to floodplains. Despite a long history of studying TSS yields, estimates of TSS yields remain uncertain. Multiple methods have been commonly used to estimate time-aggregated TSS yields from water samples. This study investigated the effects of contemporary timber harvest practices on TSS yields as well as the robustness of conclusions to different methods of TSS yield calculation. TSS yields were calculated using linear interpolation, flow-weighted averaging, and statistical regression. The study utilized a paired-watershed design, with 6 years of calibration data between the control watershed and 2 treatment watersheds. One watershed was clearcut across 50% of its area and allowed to recover for the remaining 12 years of the study period. The other treatment watershed had 50% of basal area removed across 50% of it's total area. After the thinning treatment, the watershed was allowed to recover for 9 years before being clearcut across 46% of the area which was originally thinned. The watershed was then allowed to recover for the remaining 3 years of the study. Harvest impacts on TSS yield varied between treatment watershed and season, with the most significant changes occurring during spring (March through June). Furthermore, the different methods of TSS yield estimation provided different conclusions about TSS yield trends as well as total yields, with statistical regression providing the most consistently defensible estimates.