Salmon‐driven bed load transport and bed morphology in mountain streams

Abstract

Analyses of bed load transport data from four streams in British Columbia show that the activity of mass spawning salmon moved an average of almost half of the annual bed load yield. Spawning‐generated changes in bed surface topography persisted from August through May due to lack of floods during the winter season, defining the bed surface morphology for most of the year. Hence, salmon‐driven bed load transport can substantially influence total sediment transport rates, and alter typical alluvial reach morphology. The finding that mass‐spawning fish can dominate sediment transport in mountain drainage basins has fundamental implications for understanding controls on channel morphology and aquatic ecosystem dynamics, as well as stream responses to environmental change and designing river restoration programs for channels that have, or historically had large spawning runs.

Bed disturbance via foraging fish increases bedload transport during subsequent high flows and is controlled by fish size and species

“…Third, it is likely that foraging occurs where and whenever benthic feeding fish are present, albeit within seasonal constraints imposed by differences in food availability and metabolism, via water temperature. This suggests that foraging may have a persistent and spatially extensive impact on bed materials, perhaps extending the zoogeomorphic potential of fish across large portions of river networks and beyond the relatively more constrained impacts of lithophilic spawning (cf, Hassan et al, 2008).…”

“…With regard to fluvial systems, reviews by Statzner (2011), Rice et al (2012), and Albertson and Allen (2014) highlight the geomorphic capabilities of fish and macroinvertebrate fauna; but the number of studies is small and limited to a few species and impact mechanisms. The majority of research has focused on bed bioturbation during spawning by Salmonids (Field-Dodgson, 1987;Kondolf et al, 1993;Montgomery et al, 1996;Hassan et al, 2008), bed and bank bioturbation by crayfish (Statzner et al, 2003a;Zhang et al, 2004;Johnson et al, 2011;Harvey et al, 2014;Rice et al, 2014) and substrate consolidation through silk secretion by hydropsychid caddisflies (Cardinale et al, 2004;Johnson et al, 2009;. Rice et al (2012, their Figure 19.6) highlight a range of additional mechanisms by which fish and invertebrates might affect bed material conditions and thence sediment transport in gravel-bed rivers.…”

Recent advances and future directions in soils and sediments research

“…These flocs, which are larger and heavier than ambient suspended sediment, settle onto the channel bed, thereby enabling important marine-derived nutrients to be retained within the channel environment in headwater streams, as opposed to being flushed downstream. Similarly, Hassan et al (2008) have shown how spawning salmon are important in terms of bedload transport and in modifying the channel morphology through the construction of redds. Such work clearly shows how aquatic organisms regulate their environment so as to maintain optimum (physical and chemical) habitats.…”

The flocculation feedback loop: Delivery of marine derived nutrients in Pacific salmon streams.

“…Salmon play an important role in the ecology of their natal streams as demonstrated by investigations on the influence of redd creation on fine and coarse sediment movement (Kondolf, 2000;Hassan et al, 2008), streambed stability (Montgomery et al, 1996), and habitat maintenance (Poirier, 2004). The influence salmon have on the channel bed and the biota it supports is significant, prompting some researchers to refer to salmon as "ecosystem engineers" (Schindler et al, 2003).…”

“…Streambed excavation by the female salmon disturbs bed sediments, the finest of which (silts and clays) remain in suspension and flow downstream while the coarser sediments, such as sands and small gravels, settle out below the redd near the tailspill (Figure 2, Quinn, 2005). The quantity of streambed material moved during spawning can be substantial, rivaling spring freshet when spawning populations are high (Poirier, 2004;Hassan et al, 2008). …”