Water Quality Trends in Shallow South Florida Lakes and Assessment of Regional Versus Local Forcing Functions

Abstract

Seven large shallow lakes in South Florida, including five of the Kissimmee Chain of Lakes (KCOL) and Lakes Istokpoga and Okeechobee, have been the focus of long-term water quality monitoring since 1981, 1988, and 1972, respectively. Analysis of these long-term data, rare for a subtropical region, allowed the authors to evaluate trends and the extent to which observed temporal patterns are driven by regional climate-related forcing functions (e.g., rainfall and discharge) versus local forcing functions including nutrient load reductions and in-lake rehabilitation projects conducted by management agencies. Recent changes occurring in 2004 and 2005 were likely a result of major tropical storm events that affected sediment resuspension. While more localized phenomena including land use, sediment–water interactions, and management of aquatic plants appear to overwhelm synchronous patterns for water quality, activities that reduce a significant amount of external load, such as diversion of wastewater treatment effluent, and large infestations of Hydrilla have resulted in improvements of water quality in some of these lakes.

KEYWORDS:

• shallow lakes
• water quality trends
• hydrology
• environmental management
• synchrony
• nutrient loads
• South Florida