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| Florida Science Center |
SIR 2005-5052
Prepared in cooperation with the:
City of Orlando
Orange County Public Utilities
Orlando Utilities Commission
Reedy Creek Improvement District
St. Johns River Water Management District
South Florida Water Management District
2005
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CONTENTS Abstract Introduction Purpose and Scope Previous Investigations Acknowledgments Description of the Study Area Environmental Setting Surface Drainage
Population, Land Use, and Water Use Precipitation, Streamflow, and Lake Levels Water Quality Hydrology Annual, Seasonal, and Daily Variation Precipitation Streamflow
Lake Levels Precipitation Streamflow Low-Flow Characteristics Annual Mean Flow High-Flow Characteristics Lake Water Levels
Streamflow Duration and Recurrence Intervals Major Ions and Nutrients in Streams Major Ions and Nutrients in Lakes Trace Elements in Streams and Lakes Pesticides in Streams and Lakes
Household and Industrial Waste Compounds in Streams and Lakes
A. Annual rainfall totals for selected National Oceanographic B. Summary of water-level measurements for selected lakes C. Summary of lake water-quality data
D. Field measurements and concentrations of major ions, nutrients, and trace
E. Concentrations of pesticides in samples collected from lakes and
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Orange County, Florida, is continuing to experience a large growth in population. In 1920, the population of Orange County was less than 20,000; in 2000, the population was about 896,000. The amount of urban area around Orlando has increased considerably, especially in the northwest part of the County. The eastern one-third of the County, however, had relatively little increase in urbanization from 1977-97. The increase of population, tourism, and industry in Orange County and nearby areas changed land use; land that was once agricultural has become urban, industrial, and major recreation areas. These changes could impact surface-water resources that are important for wildlife habitat, for esthetic reasons, and potentially for public supply. Streamflow characteristics and water quality could be affected in various ways.
As a result of changing land use, changes in the hydrology and water quality of Orange County’s lakes and streams could occur. Median runoff in 10 selected Orange County streams ranges from about 20 inches per year (in/yr) in the Wekiva River to about 1.1 in/yr in Cypress Creek. The runoff for the Wekiva River is significantly higher than other river basins because of the relatively constant spring discharge that sustains streamflow, even during drought conditions. The low runoff for the Cypress Creek basin results from a lack of sustained inflow from ground water and a relatively large area of lakes within the drainage basin.
Streamflow characteristics for 13 stations were computed on an annual basis and examined for temporal trends. Results of the trend testing indicate changes in annual mean streamflow, 1-day high streamflow, or 7-day low streamflow at 8 of the 13 stations. However, changes in 7-day low streamflow are more common than changes in annual mean or 1-day high streamflow.
There is probably no single reason for the changes in 7-day low streamflows, and for most streams, it is difficult to determine definite reasons for the flow increases. Low flows in the Econlockhatchee River at Chuluota have increased because of discharge of treated wastewater since 1982. However, trends in increasing 7-day low streamflow are evident before 1982, which cannot be attributed to wastewater discharge.
Some of the increases in 7-day low flows may be related to drainage changes resulting from increased development in Orange County. Development for most purposes, including those as diverse as cattle grazing and residential construction, may involve modification of surface drainage through stream channelization and construction of canals. These changes in land drainage can lower the water table, resulting in reductions of regional evapotranspiration rates and increased streamflow. Another possible cause of increasing low flows in streams is use of water from the Floridan aquifer system for irrigation. Runoff of irrigation water or increased seepage from irrigated areas to streams could increase base streamflow compared to natural conditions.
Water-level data were analyzed to determine temporal trends from 83 lakes that had more than 15 years of record. There were significant temporal trends in 33 of the 83 lakes (40 percent) over the entire period of record. Of these 33 lakes, 14 had increasing water levels and 19 lakes had decreasing water levels. The downward trends in long-term lake levels could in part be due to high rainfall accumulation in 1960-1961, which included precipitation from Hurricane Donna (September 1960). The high rainfall resulted in historical high-water levels in many lakes in 1960 or 1961.
A large range of water-quality conditions exists in lakes and streams of Orange County (2000-01). Specific conductance in lake samples ranged from 57 to 1,185 microsiemens per centimeter. Values of pH ranged from 3.2 to 8.7 in stream samples and 4.6 to 9.6 in lake samples. Total nitrogen concentrations ranged from less than 0.2 to 7.1 milligrams per liter (mg/L) as nitrogen in stream samples, and from less than 0.2 to 6.0 mg/L as nitrogen in lake samples. Concentrations of total nitrogen less than 1.0 mg/L as nitrogen are considered background levels. Concentrations of total nitrogen greater than about 1.6 to 2.0 mg/L as nitrogen probably are considered elevated and could indicate contamination from surface runoff. The most commonly detected trace elements in streams were aluminum, barium, boron, iron, manganese, and strontium.
Water-quality data from four sites (Econlockhatchee River, Boggy Creek, Bonnet Creek, and Whittenhorse Creek) had significant temporal trends in at least two of the seven constituents. Values of specific conductance and concentrations of chloride increased at the Boggy Creek, Bonnet Creek, and Whittenhorse Creek sites. Bicarbonate concentrations increased at the Econlockhatchee River, Boggy Creek, and Bonnet Creek sites. Sulfate concentrations increased at the Boggy Creek site. Concentrations of nitrite plus nitrate and ammonia plus organic nitrogen decreased at the Econlockhatchee River site. Phosphorus concentrations significantly decreased at the Econlockhatchee River and Boggy Creek sites. Many of these changes probably are related to changes in land use. However, decreased nitrogen and phosphorus concentrations in the Econlockhatchee River site near Chuluota are the result of constructing a waste-water treatment facility in 1982, providing secondary treatment of wastewater discharged into the river. This facility was upgraded to include nitrogen and phosphorus removal on the Little Econlockhatchee River, a tributary of the Econlockhatchee River.
Multiple sources probably contribute to the occurrence of pesticides that were detected in surface water. The most commonly detected pesticides were atrazine, prometon, simazine, tebuthiuron, and diazinon. Atrazine had the highest concentration (0.716 microgram/liter). Because the surface-water samples were collected during baseflow, runoff probably did not contribute to pesticide concentrations in streams. However, runoff to lakes during wet periods could have contributed pesticides, which can persist during dry conditions. Pesticide detections in samples from relatively pristine sites, such as the pond at Tosohatchee State Reserve, indicate that airborne sources could contribute pesticides to surface water in Orange County.
German, E.R., and Adamski, J.C., 2005, Hydrology and Water Quality of Lakes and Streams in Orange County, Florida: U.S. Geological Scientific Investigations Report 2005-5052, 103 p.
U.S. Department of the Interior
U.S. Geological Survey
Suite 1006
224 West Central Parkway
Altamonte Springs, FL 32714
egerman@usgs.gov
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