Cyanobacterial blooms and their detrimental effects on water quality have become a worldwide problem. Vancouver Lake, a tidally influenced shallow temperate freshwater lake in Washington state, U.S.A., exhibits annual summer cyanobacterial blooms that are of concern to local resource managers. Our objectives were to describe changes in phytoplankton community composition in Vancouver Lake over seasonal, annual, and interannual time scales, and to identify strong water quality predictors of phytoplankton community structure, with an emphasis on cyanobacterial blooms, from 2007 through 2010. Cluster analysis, indicator species analysis, and non-metric multidimensional scaling were used to identify significantly different phytoplankton community groupings and to determine which environmental factors influenced community changes. From 2007 through 2009, depletion of NO3-N followed by elevated PO4-P concentration was associated with increased biomass and duration of each cyanobacterial bloom. Time-lag analysis suggested that NO3-N availability contributed to interannual changes within the summer phytoplankton community. Specifically, in summer 2010, a distinct cyanobacteria community was not present, potentially due to increased NO3-N and decreased PO4-P and NH4-N availability. Our study provides a comprehensive assessment of species-level responses to water quality variables in a shallow non-stratifying temperate lake, contributes to a better understanding of phytoplankton dynamics, and may aid in predicting and managing cyanobacterial blooms.
Eutrophication (and associated cyanobacterial blooms) and biological invasions are increasingly common problems in aquatic ecosystems, yet their effects on zooplankton community dynamics are not well understood. We examined zooplankton community dynamics from 2005 to 2011 in a tidally-influenced shallow temperate lake (Vancouver Lake, Washington, USA), with particular emphasis on the effects of eutrophication and biological invasions. Cluster analysis, indicator species analysis, and non-metric multidimensional scaling analyses were used to explore interactions between the zooplankton community and multiple environmental stressors. Our results suggest that interannual differences in seasonal zooplankton community succession may be influenced directly by turbidity, cyanobacterial blooms, predatory zooplankton, and invasive crustacean zooplankton, and indirectly by PO 4-P availability and temperature. Based on these results, we suggest that two separate management goals-alleviating eutrophication and managing the spread of invasive species-may be in conflict. We recommend future studies on the competition between native and non-native species to better understand the effects of cyanobacterial blooms on the success of non-native species, and the potential long-term consequences of non-native species invasions on zooplankton community dynamics.
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