The effects of salmon carcasses on soil nitrogen pools in a riparian forest of southeastern Alaska

Long-term studies in Alaska have demonstrated that bears may capture and carry to the riparian forest a large number of salmon that return to spawn in small freshwater streams. Most of the carcasses are partially consumed, resulting in a large amount of salmon nutrients in the form of biomass deposited on the forest floor. Using an experimental approach, we examined how these carcasses may influence the spatial and temporal dynamics of soil C and N in a riparian forest in southeastern Alaska. At their peak, ammonium (NH4+-N) concentrations in soil 10 cm from carcasses were as much as several orders of magnitude greater than soils in adjacent control plots without carcasses and remained elevated until the onset of winter. Nitrate (NO3–-N) and δ15N concentrations also increased coincident with maximum NH4+-N concentrations. However, soil N concentrations were only moderately elevated 20 cm from carcasses and closely resembled background concentrations at 30 cm. These results suggest that salmon carcasses, via bear foraging activities, can dramatically influence soil N pools, although the impacts appear to be highly localized and largely dependent on the spatial distribution of carcasses in the riparian forest.