Terrestrial Salmon Carcass Decomposition: Nutrient and Isotopic Dynamics in Central Idaho

Abstract

Terrestrial salmon carcass decomposition and nutrient dynamics have been reported for coastal marine ecosystems of the Pacific Northwest but are lacking for semi-arid inland ecosystems of this region. Understanding these processes is a critical step in accurately understanding the biochemical responses to natural salmon deposition and appropriately mitigating for its loss. Additionally, the movement of carcasses for nutrient enhancement poses the risk of spreading pathogens and disease. Freezing and pasteurization of the carcasses reduces this risk. However, the effect of these treatments on decomposition processes is unknown. Decomposition rate and nutrient dynamics were investigated in semi-arid central Idaho by decomposing salmon carcasses in soil-filled microcosms. Rapid thermal accumulation in this semi-arid climate resulted in completion of soft tissue decomposition (skeletonization) in 16 days. Soil dissolved organic C (DOC) and dissolved total N (DTN) increased dramatically with respective increases from pretreatment concentrations of 7 and 48 fold by the time skeletonization occurred. Isotopic analysis of fluids beneath the carcasses revealed up to a 6‰ change in fluid δ13C and δ15N during decomposition as well as an overall 4‰ enrichment in mean fluid δ515N, relative to whole reference carcasses. Freezing and pasteurization of carcasses only yielded differences during the first few days of decomposition relative to the fresh carcasses. These results suggest that decomposition of carcasses in inland riparian forests proceeds very rapidly and that treated carcasses are suitable surrogates for fresh carcasses in semi-arid regions of central Idaho.