We tested the hypothesis that concentrations of mercury species (Hg) and nutrients (NH , NO , P, and dissolved ϩ Ϫ 4 3 organic carbon) in abiotic and biotic components would be altered by the decomposition of salmon carcasses in streams. We investigated a tributary stream of Lake Ontario receiving spawning runs of Chinook salmon (Oncorhyncus tshawytscha) for 2 yr with contrasting bear activity. Stations with high carcass densities had significantly higher levels of aqueous total Hg, methylmercury (MeHg), particulate Hg, and nutrients than did stations with lower carcass densities. Hg levels in aquatic and terrestrial invertebrates feeding on carcasses increased by up to 25-fold. In 2001, a bear removed most carcasses at the downstream station, and aqueous Hg and nutrient concentrations were significantly lower than during the preceding year, when no bear was active at that station. A preliminary budget for this stream shows that (1) salmon carcasses can be an important source of Hg and nutrients to aquatic and terrestrial food webs, and (2) terrestrial invertebrates and vertebrates can be important water-to-land vectors of Hg.

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This study quantified the unique variation in stream fish and habitat and a land use disturbance index (LDI) at a variety of spatial scales: catchment, eight riparian polygons that varied in width and length (e.g. 50 m to all upstream reaches), upstream polygons of 1.6 and 3.2 km and the residual upland area of each site watershed not accounted for by each polygon. The analyses confirmed a hockey stick‐shaped relationship between the fish community and the LDI, with sensitive species only present below an LDI of 11. The largest variation for most metrics was explained by the largest polygons, suggesting that local riparian conditions were not as important predictors of stream condition. LDI in upland areas, where zero‐order streams occur, was also an important predictor of fish biomass and taxa richness. Contrary to expected, additive models with both catchment and riparian corridors provided minimal increases in predictive power, and no improvement in model performance occurred when data sets were stratified into sites below the LDI threshold. Finally, there was considerable covariation in the template and stressor predictor variables that made it difficult to quantify the unique variation in biological and physical responses accounted for by land use. That the 1600‐m proximal polygon provided the best predictor of the fish community and temperature is supportive of there being some proximal effects of land use. Overall, our findings suggest that stream management must consider processes that occur in the entire upstream catchment and the entire riparian corridor, including the headwaters for success. Copyright © 2012 John Wiley & Sons, Ltd.