Similar and Contrasting Drivers of Nutrient and Cyanobacteria Dynamics in Two Adjacent Shallow, Eutrophic Bays in Lake Champlain

Shallow lake systems are impacted seasonally by internal and external drivers and are also susceptible to impacts from global climate and land-use changes. Our study focuses on two shallows bays of Lake Champlain (Missisquoi and St. Albans) that experience intense cyanobacteria blooms in the late summer, primarily due to historical and current amendment of phosphorus in their catchments. The bays are within 18 km of one another, thus experience similar local weather patterns. However, the two sites differ in watershed to lake area, watershed land-use, and hydrologic connectivity to the northern Green Mountains and the mesotrophic waters of Lake Champlain’s inland sea. Thus, we posit that the two sites may exhibit different biogeochemical responses to both pheneological and episodic events. We use bi-weekly long-term monitoring data (1991-2016) to examine the differences and similarities in nutrient and bloom dynamics between the two sites on a seasonal scale. During wet and dry summers the bays exhibit contrasting patterns of TN and phytoplankton community composition. Conversely, both bays exhibit comparable, but precipitation-distinct TP and TN:TP patterns during dry and wet summers. Using the information gleaned from the historical biweekly data, we will use conceptual models of the drivers of nutrient and phytoplankton dynamics to develop hypotheses on the impacts of pheneological and stochastic events on the two systems. Our hypotheses will then be tested using recently deployed high-frequency biogeochemical and physical monitoring networks.