The structuring role of macrophytes in freshwater ecosystems

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Some ecosystems can exist in more than one state or regime. Discovering why some ecosystems remain in one state or another, and what perturbations can cause a shift between regimes, might allow prediction of how ecosystems will respond to invasion by new species or changing climate. The long-term goal of my research program is to understand relations between lake and river ecosystem structure and how those ecosystems function. My major hypothesis is that macrophytes are key structuring elements in both systems. In rivers, macrophytes affect dissolved oxygen through photosynthesis and respiration. Macrophytes provide cover for young fish, yet may also generate hypoxic zones if sufficiently metabolically active. In shallow prairie lakes, macrophytes affect water clarity by reducing sediment resuspension, trapping particles, providing refuge for large-bodied zooplankton and releasing chemicals that reduce phytoplankton growth.