COS 51-6 - Role of waterfowl in wetland biogeochemical cycling: Evaluating the effects of waterfowl on wetland nutrient cycling and algal community composition

Abstract: Freshwater coastal wetlands along Lake Erie provide essential habitat for migrating waterfowl (geese and ducks) and are also critical for reducing nutrient loads that enter the Great Lakes, which frequently experience harmful algal blooms. Waterfowl translocate large nutrient subsidies via guano along their migration routes. Resident waterfowl can also play a role in nutrient recycling in wetlands by foraging and excreting within one system. However, we know little about the role that waterfowl have on wetland nutrient budgets and algal growth in the Great Lakes region. Many coastal wetlands, especially along Lake Erie, are currently managed for waterfowl habitat but are now shifting to also include nutrient retention services in their management plans. Therefore, our objective was to understand how much nutrients (nitrogen [N] and phosphorus [P]) waterfowl supply to coastal wetlands, how these waterfowl-derived nutrients shape algal communities, and how efficiently coastal wetland sediments can remove bird-derived nutrients. We experimentally measured how waterfowl guano additions at different concentrations affect algal growth and algal community structure in laboratory microcosms. We also completed a microcosm experiment investigating how effectively wetland sediments can process waterfowl guano nutrient additions by measuring nutrient fluxes to indicate immobilization/release rates, specifically of phosphate, nitrate, ammonium, total phosphorus, and total nitrogen. Preliminary results indicate that waterfowl guano increases algal growth and causes shifts in the algal community composition. We found that guano additions increased the proportion of green algae and cyanobacteria and decreased the proportion of diatoms within the algal community. We found that sediments immobilize nutrients from guano more efficiently at low guano concentrations than high concentrations, with retention of P at low guano concentrations and N release at all guano concentrations. Waterfowl density measurements are ongoing and will be used to estimate total waterfowl nutrient loads throughout the year to coastal wetlands. We will compare these estimated waterfowl nutrient loads to previously measured nutrient loading from landscape runoff to better understand nutrient inputs to the system. This work will help inform management decisions that prioritize both waterfowl habitat and nutrient retention services to properly address nutrient reduction goals.