Nutrient Enrichment with Salmon Carcass Analogs in the Columbia River Basin, USA: A Stream Food Web Analysis

Anadromous fishes represent an important ecosystem linkage between marine and inland aquatic and terrestrial habitats. These fishes carry organic matter and marine-derived nutrient (MDN) subsidies across a vast landscape, often with profound influences on recipient ecosystem food web structure and function. In the Columbia River basin, century-long declines in the abundance of anadromous fish populations have focused attention on potential mitigation efforts to address MDN deficits. In this study, we evaluate components of the stream food web response (periphyton, macroinvertebrate, and fish) to pasteurized salmon carcass analog (SCA) treatments in 15 streams across the Columbia River basin. Periphyton standing crop, macroinvertebrate density, and salmonid fish growth rates and stomach fullness measures increased following the addition of SCA. We found no significant change in dissolved nutrient concentrations after treatment, suggesting that biological demand exceeded supply. Nitrogen stable isotope signatures confirmed trophic transfer from SCA to lower trophic levels but were noticeably weak in fish tissue samples despite our marked growth and stomach fullness measures. These data indicate that SCA has the potential to increase the productivity of nutrient-limited freshwater ecosystems and may provide a nutrient mitigation tool in ecosystems where MDNs are severely limited or unavailable.