Ecosystem response to a salmon disturbance regime: Implications for downstream nutrient fluxes in aquatic systems

Abstract

Recent work in salmon spawning streams has shown that sediment resuspended during nest construction flocculates with salmon organic matter to form suspended composite particles characterized by increased size and settling velocities. In a river system, these flocs have the potential to interact with benthic biofilms, suggesting a mechanism for the incorporation of organic matter into aquatic food webs. Using the Horsefly River spawning channel in central British Columbia, the spatial scale of biofilm floc trapping was evaluated for a salmon disturbance regime, which consists of the active digging of redds, spawning, and carcass decay. We stocked two sequential enclosures in the spawning channel with sockeye salmon (Oncorhynchus nerka) and established one upstream control enclosure. Biofilms were sampled for chlorophyll a, trapped sediment, and marine isotope tracers (d 15 N and d 13 C). In the active-spawn period, biofilm abundance was reduced due to spawning disturbance, with isotope values indicating low utilization of marine-derived nutrients (MDNs). During the post-spawn period, downstream biofilm abundance exceeded pre-spawn values, indicating a near-field nutrient pulse with isotope values reflecting biofilm utilization of MDNs. At the same time, an increase in biofilm trapping efficiency occurred in concert with a significant increase in the in situ particle size of suspended sediment, suggesting that flocs were a temporary storage site of MDNs. The retention of MDNs over short spatial scales acts to retard the flushing of MDNs to downstream rearing lakes. The magnitude of these processes has ecological implications on the downstream lake's productivity, thereby influencing the success of future salmon stocks.

Nutrient additions to mitigate for loss of Pacific salmon: consequences for stream biofilm and nutrient dynamics

“…However, export of nutrients and organic matter driven by this disturbance may lead to increased delivery of salmon nutrients to downstream river reaches (Albers and Petticrew 2012), rearing lakes (Moore et al 2007), and estuaries (Cak et al 2008), and in some cases, these exported nutrients have been linked to increased biofilm standing crop in these downstream ecosystems (Albers and Petticrew 2012). Therefore, the effects of salmon spawning may be more appropriately viewed at the scale of stream segments or watersheds, rather than reaches.…”

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

“…Literature Review substantial quantities of marine-derived nutrients (MDN) to the nutrient-poor freshwater systems in which they spawn (Naiman et al 2002). This annual event provides an important source of nutrients and energy to enhance fish and aquatic productivity, as well as terrestrial wildlife and plant species (Bilby et al 1996, Willson et al 1998, Helfield & Naiman 2001, Albers & Petticrew 2012.…”

“…In interior British Columbia, this annual pulse of salmon nutrients occurs in the fall (Albers & Petticrew 2012), providing a significant nutrient subsidy to enhance stream productivity (Cedarholm et al 1999, Gende et al 2002, Naiman et al 2002, Schindler et al 2003, Janetski et al 2009). 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.…”

“…The macroinvertebrate community is relatively simple, with dozens, as opposed to hundreds, of specific taxa, including some FFGs that are represented by only one species or family. The present study, in conjunction with studies from Albers (2010) and Albers & Petticrew (2012, present a useful baseline understanding of the biogeochemical nutrient dynamics that occur because of salmon spawn. From this simplified framework, strong food web models can be developed and interpreted with the intention of discovering critical linkages that elucidate the resilience of salmon populations.…”

It's sedimentary, my dear Watson : implications of watershed processes on the sediment fingerprinting approach

“…Much of the literature focuses on the infiltration of sand-sized particles into the gravel matrix (e.g., Wooster et al 2008;Grams and Wilcock 2014) and less on the infiltration of fine-grained sediment (< 63 μm) as this material is often considered to move though a river system unimpeded (i.e., wash load). However, fine-grained sediment storage within the gravel bed is an important consideration as it can reduce hyporheic exchange, compromise invertebrate and fish habitat, and act as a legacy source of sediment-associated nutrients and contaminants (Rehg et al 2005;Rex and Petticrew 2008;Albers and Petticrew 2012).…”