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SFS Annual Meeting

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Shallow ponds and lakes constitute over 91% of the number of standing water bodies and are important in global carbon cycling. Many small ponds exist in alternative stable states: either turbid, phytoplankton-dominated or clear, macrophyte-dominated. State may be regulated by either bottom-up or top-down mechanisms. We examined the rates of ecosystem metabolism (EM; gross primary production, respiration and net ecosystem production) in four ponds in Minnesota: one with brook stickleback, dominated by phytoplankton; three fishless, dominated by macrophytes. We assessed EM by measuring changes in O2 levels every 10 minutes from May-October, 2018. We measured phytoplankton biomass (Chl a) every two weeks, and mapped relative abundance of macrophytes. Components of EM varied daily with no obvious seasonal trends. On average the ponds were heterotrophic. Water temperature had a greater impact on the components of EM than surface light availability. The presence of macrophytes influenced EM potentially by influencing atmospheric oxygen exchange. The variability among fishless ponds exceeded the difference between ponds with and without fish. The alternative state of a pond has less impact on EM than more local factors.

Dan Hornbach (Primary Presenter/Author), Macalester College,;

Emily Schilling (Co-Presenter/Co-Author), Augsburg University,;

Holly Kundel (Co-Presenter/Co-Author), Augsburg University,;