Transitioning From A River To A Lake PDF Download

Freshwater ecosystems, which include lakes and reservoirs, are important sites for biogeochemical cycling on both a regional and global scale. Reservoirs affect the storage and transformation of nutrients as water moves through a watershed transporting municipal and agricultural runoff. Water quality is often a major concern because reservoirs provide a reliable source of water for human consumption and are used for recreational fishing and boating; both can be threatened by the accumulation of excessive nutrients. Because reservoirs attract many different users, they can also facilitate the spread of invasive species. The goal of this research project was to investigate how abiotic and biotic factors affect nutrient processing within a reservoir. The study area features extensive coverage by the invasive plant Hydrilla verticillata, which affects water quality within the reservoir through nutrient uptake and storage. Therefore, this study quantified the spatial coverage of submerged aquatic vegetation (SAV) using annual vegetation surveys between 2012 and 2014. Coverage changed dramatically by decreasing from 35.6 km2 to 18.3 km2. High precipitation and flooding during early spring increased turbidity and reduced light availability needed for growth. These high flows through the reservoir resulted in decreased SAV coverage and changes in nutrient storage. This study also investigated how these changes in SAV coverage affected nutrient cycling and organic matter processing through a water quality monitoring program that quantified nutrient concentrations in the inflows and outflow of the lake. Concentrations of NO3-N were lowest during the period of lowest SAV coverage. Consequently, flooding affected the coverage of SAV, which was driving nutrient cycling within the reservoir. To investigate the effects of Hydrilla and two other invasive species in the reservoir (Corbicula fluminea and Pomacea maculata), a mesocosm experiment was designed featuring different combinations of these species. The experiment demonstrated strong effects on nitrogenous compounds with Hydrilla reducing inorganic N, Pomacea converting stored N to available particulate N, and Corbicula mitigating the effects of Pomacea by reducing total N. Because Pomacea was recently introduced to the lake and the extent and rate of spread was unknown, snail egg mass surveys were completed during 2013 and 2014 to determine the spatial extent of the Pomacea population. Presence of Pomacea was found to be extensive in the reservoir and range expansion occurred in the second year of surveys. The expanding snail population has the potential to alter.