Stream food web response to a salmon carcass analogue addition in two central Idaho, U.S.A. streams

Abstract

OnlineOpen: This article is available free online at www.blackwell-synergy.com SUMMARY 1. Pacific salmon and steelhead once contributed large amounts of marine-derived carbon, nitrogen and phosphorus to freshwater ecosystems in the Pacific Northwest of the United States of America (California, Oregon, Washington and Idaho). Declines in historically abundant anadromous salmonid populations represent a significant loss of returning nutrients across a large spatial scale. Recently, a manufactured salmon carcass analogue was developed and tested as a safe and effective method of delivering nutrients to freshwater and linked riparian ecosystems where marine-derived nutrients have been reduced or eliminated. 2. We compared four streams: two reference and two treatment streams using salmon carcass analogue(s) (SCA) as a treatment. Response variables measured included: surface streamwater chemistry; nutrient limitation status; carbon and nitrogen stable isotopes; periphyton chlorophyll a and ash-free dry mass (AFDM); macroinvertebrate density and biomass; and leaf litter decomposition rates. Within each stream, upstream reference and downstream treatment reaches were sampled 1 year before, during, and 1 year after the addition of SCA. 3. Periphyton chlorophyll a and AFDM and macroinvertebrate biomass were significantly higher in stream reaches treated with SCA. Enriched stable isotope (d 15 N) signatures were observed in periphyton and macroinvertebrate samples collected from treatment reaches in both treatment streams, indicating trophic transfer from SCA to consumers. Densities of Ephemerellidae, Elmidae and Brachycentridae were significantly higher in treatment reaches. Macroinvertebrate community composition and structure, as measured by taxonomic richness and diversity, did not appear to respond significantly to SCA treatment. Leaf breakdown rates were variable among treatment streams: significantly higher in one stream treatment reach but not the other. Salmon carcass analogue treatments had no detectable effect on measured water chemistry variables. 4. Our results suggest that SCA addition successfully increased periphyton and macroinvertebrate biomass with no detectable response in streamwater nutrient concentrations. Correspondingly, no change in nutrient limitation status was detected based on dissolved inorganic nitrogen to soluble reactive phosphorus ratios (DIN/SRP) and nutrient-diffusing substrata experiments. Salmon carcass analogues appear to increase freshwater productivity. 5. Salmon carcass analogues represent a pathogen-free nutrient enhancement tool that mimics natural trophic transfer pathways, can be manufactured using recycled fish

Water quality, chlorophyll, and periphyton responses to nutrient addition in the Kootenai River, Idaho

“…N and P additions in aquatic systems can increase periphyton biomass, chlorophyll accrual rate, and the abundance and biomass of plankton and invertebrate communities (Kohler et al 2008, Kohler andTaki 2010). Investigators also have reported significant increases in salmon production following nutrient addition in nutrient-depleted lakes and streams in British Columbia, Idaho, and Alaska (Johnson et al 1990, Stockner 2003.…”

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

“…Condition, production, and lipid concentrations of stream-resident cutthroat trout (Oncorhynchus clarki) and production and lipid content of young-of-theyear coho salmon (Oncorhynchus kisutch) increased in natural and artificial stream channels following SCA treatment . Kohler et al (2008) demonstrated a positive stream foodweb response to SCA additions. The responses included elevated periphyton chlorophyll a and ash-free dry mass (AFDM), macroinvertebrate density and biomass, periphyton and macroinvertebrate stable isotope (d 15 N) values, and increased leaf decomposition rates in a stream reach containing SCA.…”

“…Kohler et al (2008) demonstrated gross stream foodweb responses to SCA treatment, but ecologically meaningful effects on macroinvertebrate assemblages might have gone undetected. Macroinvertebrate communities represent a potentially important vector of marine-derived nutrients to aquatic and terrestrial consumers and warrant closer examination.…”

“…Our study is a follow-up to the study by Kohler et al (2008) and focuses on the macroinvertebrate community response to SCA treatment in 2 central Idaho streams. We examined macroinvertebrate community characteristics and potential correlations with biological and physicochemical attributes.…”

“…These studies include delivery of nutrients to aquatic systems via direct application of inorganic liquid or slow-release pellet fertilizer (Kline et al 1990, Gulis andSuberkropp 2003), natural spawning events of semelparous salmon and manipulative carcass additions and exclusions (Minshall et al 1991, Wipfli et al 1998, Ambrose et al 2004, Chaloner et al 2004, Lang et al 2006, and use of pasteurized salmon carcass analogue (SCA) , Pearsons et al 2007, Kohler et al 2008). These investigations encompass a variety of trophic transfer pathways and demonstrate unique and variable responses in auto-trophic, heterotrophic microorganism, and macroinvertebrate and fish consumer communities across a range of lotic and lentic environments.…”