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

Abstract

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 1 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.