SPECIES OCCURRENCE AND ECOSYSTEM SIZE LIMIT AN ALTERNATIVE STATE IN FRESHWATER LAKES AND PONDS
Freshwater systems are infamous for abrupt changes in community and ecosystem states, such as shallow lakes that switch between clear-water (submerged vegetation) and turbid-water (phytoplankton) states in response to nutrient levels. Another alternative regime that replaces submerged vegetation in some agricultural ditches and wetlands is dominance by unrooted, free-floating vegetation. I used surveys of 201 freshwater lakes and ponds in the northeastern United States to ask: 1) Are aquatic plant regimes bimodal, suggesting alternative states? 2) Is there a linear, non-linear, or hysteretic (i.e., alternative states) relationship between total phosphorus, a driving variable, and the plant regime? and 3) What other factors influence the relationship between nutrients and floating plant regime? The floating plant regime was limited by waterbody size (it occurred only in waterbodies <5 ha.) and floating plant presence (>50% of waterbodies lacked floating plants). Floating plants cover was nonlinearly related to total phosphorus and waterbodies were found in either a submerged plant state or a floating plant state over a wide range of nutrient conditions, suggesting a complex threshold between regimes, with the possibility of alternative states.
McCann, M. J., Stony Brook University , USA, email@example.com
Location: Oregon Ballroom
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