University of British Columbia Vancouver, British Columbia, Canada
Every autumn, migratory pacific salmon (Oncorhynchus spp.) return to their native streams to spawn and die. In coming home, they carry with them a lifetime’s accumulation of nutrients stored in their flesh; this high-protein, high-fat material represents an ecosystem subsidy of marine-derived nutrients (MDN) from the ocean to riparian zones. Here, I examine the effects of returning salmon on riparian soils in Heiltsuk traditional territory, near the community of Bella Bella on the Central Coast of British Columbia, Canada. My main objectives were to: 1) quantify how salmon affect forest soil chemistry; and 2) quantify how salmon affect soil fungal communities. To answer these questions, I examined 22 chemical measures and used next-generation environmental sequencing to quantify soil fungal communities. My experimental methodology used two observational approaches: the first examined watersheds along a natural gradient of salmon density, and the second used sites where waterfalls block salmon migration, allowing for within-watershed comparisons above and below these barriers.
I found that salmon affected soil chemistry, with impacts on concentrations of nitrogenous compounds, exchangeable cations, phosphorus, and metals, as well as differences in pH. Using next-generation environmental sequencing, I found salmon inputs impact fungal relative abundance, soil fungal β- and α- diversity, but did not affect phylogenetic dispersion. In general, symbiotrophic fungi were affected by salmon inputs more than saprotrophs. These results show that salmon are important in structuring riparian soil chemistry and microbial ecology, and support the hypothesis that fungi play an important role in salmon nutrient processing and retention by soil communities.