The nutrient legacy left by salmon tissue on riparian soils in Southeast Alaska

Abstract

AbstractSalmon‐derived nutrients (SDN) are a distinctive aquatic subsidy to terrestrial ecosystems. Streamwater nutrient increases in response to SDN have been documented but uncertainties about the magnitude and persistence of their effects in riparian areas remain. A key research gap is the response of specific soil types to the nutrient subsidy over time. To address this question, an Entisol and a Spodosol commonly found in riparian zones of Southeast Alaska were delineated adjacent to streams with abundant spawning salmon for experimental nutrient additions. Salmon nutrient additions were applied to track the fate of N and P through time to investigate the patterns of nutrient retention and loss in the Entisol and Spodosol. Salmon additions to Entisols across eight watersheds revealed a large and consistent residual concentration of available NH4+–N but a high variability in NO3−–N after a 30‐d incubation. A comparison of Entisols and Spodosols in two watersheds tracked salmon tissue additions for ∼1 yr, where nutrient concentrations at 240 d decreased relative to 30 d but a flush of available nutrients occurred at 340 d, with higher values in the salmon‐amended soils. The magnitudes of extractable N and P retained in the extractable fraction were similar in the Entisol and Spodosol but dissolved N loss measured via resin beads at the base of the measurement cores indicated higher leaching of NO3−–N from the surface in Entisols. Identification of specific soil types can advance the understanding of nutrient processing, uptake, and loss from SDN additions on riparian landforms.