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

The objectives of this study were to evaluate nutrient delivery, storage, and trophic transfer between the Horsefly River spawning channel and its riparian zone during the 2011 sockeye salmon run and subsequent 2012 spring. The hyporheic zone was investigated as a pathway for nutrient exchange, transformation, and storage by analyzing water movement and ammonium (NH⁴⁺) concentration. Using stable isotopic analysis, the assimilation and storage of marine-derived nutrients (MDN) were evaluated through multiple trophic levels. Results identified lateral hyporheic flow as a dominant pathway for MDN delivery to deep-rooted vegetation, specifically willow trees <7-m from the streambank. Amphipods and chironomids appeared to assimilate MDN in the fall and maintained high spring biomass, indicating an important nutrient linkage in the salmon feedback loop. Finally, a temporal reversal in NH⁴⁺ concentration across the stream-riparian interface and a seasonal shift in nutrient fluxes revealed reciprocal subsidies that highlight the interconnectedness of these adjacent systems. --Leaf ii.