Potential Nutrient Subsidy Synergies Between Agriculture and Stocked Trout in New York Streams

Each year the New York State Department of Environmental Conservation stocks approximately 3.6 million trout and salmon, many of which are non-native, into almost 10,000 km of freshwater streams; thereby increasing areal density of trout in stocked sections. Despite increasing recognition of the importance of external resource inputs from migratory fish, few studies have investigated the nutrient contribution of stocked fish excretion into lotic systems. Furthermore, while many studies have demonstrated the importance of stream community nutrient dynamics and ecosystem subsidies separately, relatively few have studied subsidies within a nutrient framework. We quantified stocked trout nutrient loads by combining estimates of nutrient (NH₄+ and P) excretion rates with population density and biomass estimates on two 2^nd-3^rd order streams within watersheds with high and low agricultural land use in New York State. We then coupled the nutrient input model estimates with measures of areal nutrient uptake in order to better understand the relative contribution of stocked hatchery trout to stream nutrient dynamics in streams with differing levels of agricultural land use. Lastly, we calculated net flux of salmon derived nutrients in recipient streams using a mass-balance approach. By linking fish stocking practices to ecosystem level nutrient cycling, this study will provide a better understanding of the influence of species introductions on nutrient dynamics in streams within watersheds of high and low agricultural land use.