Lake Okeechobee Watershed Nutrient Loading
Project Chief: Michael J. Byrne Sr.
Cooperator: Florida Department of Agriculture and Consumer Services, South Florida Water Management District (SFWMD)
Period of Project: October 2003 - September 2013
Problem Statement
Figure 1. Location of regional basins, sub-basins, and monitoring sites in the Lake Okeechobee Watershed Project (LOWP) area. SFWMD, South Florida Water Management District; USGS, U.S. Geologoical Survey.
Lake Okeechobee is a large, shallow lake located in southern-central Florida. With a surface area of 730 square miles, it is the second largest lake within the contiguous United States and has an average depth of 9 feet. Lake Okeechobee is the heart of southern Florida’s water supply and flood control system and is the major source of water for the Everglades.
The lake’s drainage area covers more than 4,600 square miles. Major inflows to the lake include rainfall (50%), the Kissimmee River (25%), and drainage from canals, smaller creeks and tributaries north of the lake (25%). The drainage area north of the lake is known as the Lake Okeechobee Watershed (LOW) Project area (fig. 1).
An increase in phosphorus concentrations has shifted the natural balance of nutrients in the lake, led to conditions that are favorable for blue-green algal blooms, and contributed to the accumulation of phosphorus-rich bed sediments over an extensive area of the lake. Flood control has exacerbated the lake’s phosphorus problems and has contributed to a decline in health of the lake’s littoral zone. The canals that discharge excess floodwaters from Lake Okeechobee to the St. Lucie and Caloosahatchee estuaries have severely impacted both estuaries.
The LOW Project incorporates 4 of the 68 major components of the Comprehensive Everglades Restoration Project (CERP) and has 3 major objectives: 1) to improve water quality in tributaries and discharges to Lake Okeechobee; 2) to increase storage capacity for watershed runoff and lake water; and 3) to enhance and restore wetlands in the watershed.
Objectives
The general objective of the USGS project was to quantify the nutrient loads, specifically phosphorus and nitrogen, for 15 canals located throughout the LOW project area.
The specific objectives of the sub-basin-scale monitoring conducted by the USGS were to: (1) compute loads for phosphorus, nitrogen, and total suspended solids in selected sub-basins with no current load monitoring; (2) characterize spatial distribution of loads across the LOW Project area; (3) establish a baseline of water quality and stream-flow information at the sub-basin level; (4) provide data to cooperators for planning management measures for restoration of Lake Okeechobee; and (5) provide data for evaluating changes in the watershed, particularly the cumulative effect of restoration management measures at the sub-basin level.
Approach
The USGS maintained hydrologic gages for the purpose of determining stream flows. The South Florida Water Management District personnel collected weekly water samples near the gages in order to calculate nutrient loads from the canals.
Results
Tributaries east of the Kissimmee River have elevated concentrations of phosphorus. However, tributaries on the western side of the Kissimmee River contribute most of the flow to the river. Variation in nutrient loading from tributaries is controlled by rainfall. Throughout the study, numerous hurricanes followed by a long drought, made it difficult to determine if management decisions improved the water quality of the lake.
Information Product
Byrne, M.J., Sr., and Wood, M.S., in review, Concentrations and Loads of Nutrients in the Tributaries of the Lake Okeechobee Watershed, South-Central Florida, Water Years 2004–2008: U.S. Geological Survey Data Series 613, 22 p.
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U.S. Department of the Interior |
U.S. Geological Survey
