Influences of the environment and plankton community interactions on toxic cyanobacterial blooms in Vancouver Lake, Washington, a temperate shallow freshwater system

Occurrences of cyanobacterial blooms are in freshwater systems are increasing in frequency and intensity largely in response to urbanization of landscapes, eutrophication, and climate change. Cyanobacterial blooms negatively affect water quality which leads to a broad range of environmental, social, and economic concerns. In particular, cyanobacteria are known to produce a suite of toxins that have been linked to changes to the aquatic food web, small animal mortality and illness, and adverse health risks to humans. Vancouver Lake, located in southwest Washington state, is a tidally influenced shallow freshwater lake that exhibits annual summer cyanobacterial blooms that have been an on-going concern for public health and natural resource managers. Thus, the purpose of this project was to investigate the biotic and abiotic interactions associated with bloom events in a shallow, freshwater system. The main objectives were: 1) analyze phytoplankton community dynamics with an emphasis on the cyanobacterial community in relation to water quality factors; 2) identify and quantify toxin producing cyanobacterial populations in relation to water quality factors; 3) assess the potential effects of cyanobacterial blooms on zooplankton community dynamics; and 4) develop a model on the potential effects of wind-driven waves on internal phosphorus loading as a potential mechanism contributing to seasonal cyanobacterial blooms. Our findings suggest that nutrients, dissolved inorganic nitrogen and dissolved inorganic phosphorus, significantly influence cyanobacterial blooms dynamics, and more specifically with toxin producing cyanobacteria. In relation to zooplankton community dynamics, we found that while cyanobacterial blooms may have some influence, but also non-native invasive crustacean zooplankton may interact with cyanobacterial blooms affecting the summer zooplankton community. In spite of Vancouver Lake being a model large shallow lake highly susceptible to wind driven sediment resuspension, simulations of seasonal orthophosphate availability did not support observed measurements, suggesting other mechanisms such as redox related processes and bioturbation, should be examined in assessing potential management considerations for restoring Vancouver Lake.