ECODYNAMIC ASSESSMENT OF THE SUBMERGED AQUATIC VEGETATION IN LAKE OKEECHOBEE, FLORIDA UNDER NATURAL AND ANTHROPOGENIC STRESS

摘要

Lake Okeechobee, a large, shallow lake in southern Florida, is the liquid heart of the Everglades. The lake's hydrodynamic patterns and water depths have been impacted by four major hurricanes in the past decade, including Irene (1999), Frances and Jeanne (2004), and Wilma (2005), and intermittent water level variations due to droughts in 2000-2001 and 2007-2008. In the past few decades, conditions in Lake Okeechobee have changed significantly, largely as a result of nutrient inputs to the ecosystem from agriculture and other human activities in the watershed. The excessive phosphorus loads from the lake's watershed have led to an increase in eutrophication and contributed to the accumulation of phosphorus-rich mud sediments on the lake bottom. The cumulative effect of these continuous natural hazards and anthropogenic impacts in Lake Okeechobee resulted in resuspending a large quantity of sediment, lowering light transparency, and releasing a large amount of nutrients into the water column, followed by long-standing shallow water depths. Such collective impacts led to a drastic change of sediment bed and ecosystem stability, especially the submerged aquatic vegetation (SAV). This study quantifies the ecodynamics of SAV to elucidate the coupled impact of natural and anthropogenic stress by a numerical model, the Lake Okeechobee Environment Model (LOEM) that links the spatial and temporal distributions of SAV as a whole.