Transfer of Nutrients from Spawning Salmon to Riparian Vegetation in Western Washington

Abstract

The extent to which nutrients from Pacific salmon are transported to riparian areas may be influenced by differences in spawning behavior among species. Chum salmon Oncorhynchus keta, pink salmon O. gorbuscha, and sockeye salmon O. nerka typically spawn in dense aggregations, while species like steelhead O. mykiss and coho salmon O. kisutch spawn at lower densities. The contribution of nutrients to riparian vegetation was compared at two watersheds in western Washington, Griffin Creek (used by coho salmon) and Kennedy Creek (used by chum salmon). Salmonberry Rubus spectabilis foliage was collected at the channel edge above and below barriers to spawning salmon and at 20, 50, and 100 m upslope from the stream and analyzed for nitrogen stable isotope ratio (δ15N, an indicator of salmon‐derived nitrogen), total nitrogen (N), and phosphorus (P) content. Cover, plant density, and the species richness of shrub and understory vegetation were compared between sites with and without salmon. The δ15N values in salmonberry leaves were higher at sites with salmon than at corresponding distances from the channel at sites without salmon at Kennedy Creek but not Griffin Creek. Salmonberry foliage adjacent to salmon spawning reaches possessed significantly higher levels of total N and P in both watersheds. Nitrogen content was positively associated with δ15N values at the Kennedy Creek sites but not at the Griffin Creek sites. At Kennedy Creek, shrub species diversity and understory plant density and species diversity were higher at sites with salmon than at sites without salmon. These results suggest that areas bordering streams utilized by high‐density‐spawning species like chum salmon receive a substantial nutrient contribution from the fish and that this subsidy influences the vegetation. We did not see clear evidence for a similar nutrient contribution from coho salmon.

Seasonal persistence of marine‐derived nutrients in south‐central Alaskan salmon streams

“…MDN is transferred to the riparian environment by hyporheic processes, flooding, and terrestrial scavengers (Cederholm et al 1989, Ben-David et al 1998, Hilderbrand et al 1999, O'Keefe and Edwards 2002), where it enriches riparian soils (Bartz andNaiman 2005, Drake et al 2005). Riparian vegetation can derive a substantial proportion of nitrogen from this pool (Bilby et al 2003, Reimchen et al 2003, which may lead to enhanced growth rates Naiman 2001, 2002; but see Kirchhoff 2003 and.…”

Macroinvertebrate community dynamics: strong negative response to salmon redd construction and weak response to salmon-derived nutrient uptake

“…spawn and die (Kline et al 1990, Larkin and Slaney 1997, Cederholm et al 1999, Bilby et al 2003. These marine-derived nutrients stimulate primary production and increase freshwater productivity and the growth and survival of stream-dwelling salmonids (Wipfli et al 2003).…”

The delivery, seasonal storage, and trophic transfer of marine-derived nutrients within a stream-riparian ecotone

“…However, certain types of organisms may have a better advantage to benefit from MDN because of their trophic role, the local ecology, and the timing of salmon spawn (Hicks et al 2005, Lessard et al 2009, Wipfli & Baxter 2010, Rinella et al 2012. Additionally, nutrient pulses are carried through aquatic systems more quickly than terrestrial, so location within or proximity to a stream may affect nutrient assimilation and retention (Ben-David et al 1998, Bilby et al 2003, Nowlin et al 2008.…”

“…C are incorporated into terrestrial vegetation adjacent to salmon spawning streams (Bilby et al 1996, Ben-David et al 1998, Bilby et al 2003, Reimchen et al 2003, Hocking & Reimchem 2009). On…”

“…Despite an apparent contrast in run timing and plant growth, biological uptake of MDN can occur quickly and be stored within riparian soil and plants (Drake et al 2006) and stream organisms (Bilby et al 1996 ). There are still questions, however, especially in regard to the environmental factors that limit uptake and persistence of MDN in individual species and in the riparian forest as a whole (Drake et al 2011, Devries 2012, Rinella et al 2013 (Bilby et al 1996, Ben-David et al 1998, Reimchen et al 2002, Bilby et al 2003). …”