Macroinvertebrate community response to riparian canopy removal and salmon carcass addition in northern California coastal streams

Benthic macroinvertebrate community response to increased light and nutrient augmentation, via riparian canopy removal and salmon carcass addition, was evaluated in second order coastal streams of northern California. The study followed a split-plot experimental design in a total of six streams within the Klamath and Smith River catchments. Each stream consisted of two study reaches (100m) separated by a 250m buffer. Three randomly selected streams received carcass addition (whole-plot factor) and within each stream a study reach randomly received riparian hardwood removal (subplot factor), resulting in four replicated treatments (C- control, N- nutrient augmented, L- light augmented, L+N- light and nutrient augmented). Stream reaches were sampled once pre-manipulation and four times post-manipulation. Main effect results showed that while carcass addition had no effect on macroinvertebrate biomass, canopy removal led to moderately greater biomass (F(1,4)=5.33 p=0.0819), and all post-manipulation biomass was greater than pre-manipulation levels (F(4, 149)=5.14 p=0.0007). Pairwise comparisons of macroinvertebrate biomass treatment means, pre and post-manipulation, showed no difference within C and N treatments, and greater macroinvertebrate biomass in L (p=0.09) and L+N augmented treatments (p=0.0025).