Invasive species interactions affect nutrient cycling in a shallow reservoir: a mesocosm experiment

Shivers SD, Golladay SW, Waters MN, Wilde SB, Marzolf NS, Covich AP. 2023. Invasive species interactions affect nutrient cycling in a shallow reservoir: a mesocosm experiment. Lake Reserv Manage. 39:278–290.Nonnative species’ introductions can affect nutrient dynamics as new combinations of species form novel ecosystems. This experiment investigated how combinations of 3 invasive species, one submerged macrophyte (Hydrilla) and 2 benthic invertebrates (Corbicula and Pomacea), affected nutrient cycling in a shallow reservoir, Lake Seminole, Georgia, United States. To assess these effects, an in-reservoir mesocosm array was installed using different combinations of the invasive species. Eight physical and chemical parameters of water quality were measured in all the mesocosms (1 control, 7 treatments) weekly for the duration of the 5 wk experiment. Nitrogenous compounds were strongly affected by Hydrilla and Pomacea presence, with NO3-N concentrations decreasing in Hydrilla mesocosms and NH4-N and total nitrogen (TN) increasing in Pomacea mesocosms. Corbicula, when present, helped to mitigate increases in N concentrations, presumably as filter feeding reduced water column TN concentration. Overall, Hydrilla growth reduced inorganic N concentration. Pomacea grazing converted stored N to available organic and particulate N. Total phosphorus concentrations were not impacted by the invasive species treatments and increased in all mesocosms during the experiment. In short, Hydrilla and Corbicula are contributing to the uptake, conversion, and sequestration of nutrients that may increase eutrophication, while Pomacea is releasing potentially eutrophying nutrients. As climate change and human influence continue to create new combinations of species, it is important to understand the effects produced by novel combinations of species.