Spatial and Temporal Hypoxia Dynamics in Dense Emergent Macrophytes in a Florida Lake

Many aquatic systems worldwide have experienced significant changes in littoral macrophyte communities from altered hydrology in the form of water controls structures (e.g., dams). Water level stabilization for flood control can cause persistent occurrence of dense stands of emergent macrophytes, which can affect the physicochemical environment for fishes. We evaluated dissolved oxygen (DO) concentrations in five emergent macrophyte species (cattail Typha spp., pickerelweed Pontedaria cordata, smartweed Polygonum spp., torpedograss Panicum repens, and water primrose Ludwigia spp.) at three levels of macrophyte coverage (i.e., 50-64, 65-79, and 80-95%) at Lake Istokpoga, Florida during July-August (summer) and October-November (fall) 2007. Dissolved oxygen exhibited substantial spatial and temporal variability at small scales (i.e., meters and hours), with the lowest DO and highest probability of hypoxia occurring in smartweed and water primrose habitats relative to other macrophyte types. The probability of hypoxia increased with macrophyte coverage for all macrophyte species tested. Dissolved oxygen was influenced by the structural differences (e.g., stem density and size) and spatial orientation (e.g., proximity to open water) associated with the individual macrophyte habitats. Restoration efforts that create open water pathways and maximize edge areas might improve DO concentrations and habitat quality and quantity for freshwater fishes.