Isotopic Evidence for Enrichment of Salmon-Derived Nutrients in Vegetation, Soil, and Insects in Riparian Zones in Coastal British Columbia
Thomas E. Reimchen, Deanna D. Mathewson, Morgan D. Hocking, Jonathan Moran, and David Harris
Abstract.—Anadromous fishes such as salmonids link marine and terrestrial ecosystems in coastal watersheds of western North America. We examine here the extent of isotopic enrichment of salmon-derived nutrients in soil, vegetation, and terrestrial insects among six watersheds from coastal British Columbia that differ in the density of salmon. Results demonstrate a direct relationship between the salmon spawning density and 15N enrichment in humus soil, in riparian vegetation (Tsuga heterophylla, Vaccinium parvifolium, Rubus spectabilis), and in riparian insects including herbivorous and carnivorous Carabidae (Pterostichus, Scaphinotus, Zacotus). The results suggest broad cycling of salmon-derived nutrients into multiple trophic levels of terrestrial ecosystems. We also describe for the first time the detection of salmon-derived nitrogen in wood samples extracted from oldgrowth riparian conifers. This result suggests new opportunities for assessing relative nutrient transfer and salmon abundance in past centuries.