Seasonal Carbon Budget Succession in Lake Erie's Western Basin

Lake Erie's Western Basin is a eutrophic region and likely hotspot for carbon transformation. While this basin has received much attention for its high nutrient loads from the Maumee River and recurring harmful algal blooms, carbon has gone understudied. To investigate the seasonal and spatial variability in inorganic and organic carbon budgets, we completed three surveys in spring, summer, and fall on a transect from the Maumee River to South Bass Island. In each survey, we observed higher spatial variability of all carbon species within 11 km of the Maumee River mouth relative to sites outside of Maumee Bay. This variability was driven by pulses of direct river water carbon, steep nutrient gradients, and patchy bloom conditions. Seasonal variability was also greater in Maumee Bay, with the highest river discharge in June adding large amounts of dissolved inorganic and organic carbon and pCO2 flux out of the water when productivity from the diatom bloom was smaller. In August, when and where we observed a Microcystis bloom, particulate organic carbon increased in concentration, and pCO2 flux switched directions into the water. In October, Chl-a concentrations and oxygen saturations were lowest, indicating a seasonal slowdown in productivity, and river discharge was the lowest, resulting in the lowest total carbon observed and dissolved organic matter chemistry indicating less contribution from the terrestrial watershed. In the open water outside of Maumee Bay seasonal and spatial carbon budget dynamics were more stable, highlighting the importance of riverine inputs on lake carbon cycling. The Maumee River has a large influence on the water quality of Lake Erie's Western Basin. Past research in this region focused on the connection between nutrients, such as phosphorus and nitrogen, and harmful algal blooms. Carbon, which is a water quality indicator and can serve as a component of greenhouse gases, is less studied. The goal of this project was to quantify changes in carbon over space and time along a gradient from the Maumee River into the Western Basin. We performed research cruises in spring, summer, and fall and collected samples for dissolved inorganic carbon, dissolved organic carbon, and particulate organic carbon. We found the Maumee River influenced the carbon budget due to direct inputs of carbon as well as nutrient inputs that fueled algal blooms. In the spring and summer when the Maumee River had high flow, much of the carbon in Maumee Bay was from the river, but later in the year as flow decreased an larger percent of the carbon came from the algal bloom, which changed which kind of carbon was most common due to photosynthesis. Throughout the study the open water of the basin had less variability in carbon compared to Maumee Bay. Carbon in the Western Basin of Lake Erie is heavily influenced by river input Spatial and temporal variability of inorganic and organic carbon is high in Maumee Bay Seasonal bloom dynamics transform carbon