Recovery of submerged plants from high water stress in a large subtropical lake in Florida, USA

The spatial and temporal dynamics of submerged plants were examined in a large subtropical lake in Florida, USA. The objective was to characterize succession of the community following a natural experiment in 2000-2001, when release of water from the lake, followed by a severe drought, reduced water levels by 2 m, alleviating stress of multiple years of high water. A systematic survey of shoreline transects was used to compare attributes of submerged plants under pre-drought versus post-drought conditions. Initially, the plants did not respond to lower water because shoreline areas had high turbidity from resuspended sediments and, later algal blooms. In June 2000, approximately 2 months after the water level was lowered, Chara (a macro-alga) rapidly expanded across the near-shore landscape. For over I year, this plant strongly dominated the submerged plant community, with just scattered individuals or isolated beds of vascular plants, including Potamogeton, Vallisneria, and Hydrilla. This included a period when the lake reached a record low elevation, where much of the habitat became dry, and then subsequently re-flooded in late summer 2001. However, in November 2001, Chara rapidly declined and vascular taxa (Hydrilla and Potamogeton) became dominant. They subsequently increased their biomass and spatial extent, and the previous Chara dominance did not return. Just prior to the loss of Chara, a frontal system passed over the lake, with wind velocities in excess of 30 km h(-1) for 3 days. Concentrations of solids in the water more than doubled and uprooted Chara was observed floating in the water. In this large, wind-driven lake, Chara may only be an ephemeral pioneer because, lacking roots, it is probably more sensitive to excessive wind-related stress (e.g. wave energy and scouring) than vascular plants. (C) 2003 Elsevier B.V. All rights reserved.