Hydrology and water quality of Reedy Creek in the Reedy Creek Improvement District, central Florida, 1986-89

The Reedy Creek Improvement District encompasses an area of about 43 sq mi in southwestern Orange and northwestern Osceola Counties in central Florida. The District operates a wastewater-treatment plant that discharges through two forested wetland areas and a percolation-pond system into Reedy Creek. Discharges from these wetland systems provide a relatively steady base flow which maintains streamflow in Reedy Creek during periods of low rainfall. Streamflows during the study were characterized by relatively long periods of below-average discharge interspersed with periods of high discharges. The highest mean discharges were recorded in 1988 and the lowest mean discharges were recorded in 1989. Water-quality data collection included the operation of four continuous water-quality monitors recording hourly water temperature, specific conductance, and dissolved oxygen concentration, and the collection of water-quality samples. Dissolved oxygen concentrations were similar for all stations on Reedy Creek and frequently were less than the minimum Florida standard of 5.0 mg/L. These low dissolved oxygen concentrations probably are the result of natural conditions. Nutrient analyses of water-quality samples were used to compute loadings into and out of a wetland conservation area in the southern part of the District and in the reach of Reedy Creek downstream from the wastewater discharges. Overall retention percentages for 1986-89, not including atmospheric and precipitation inputs, were 59.1 percent for total ammonia nitrogen: 3.4 percent for total organic nitrogen, which was the predominant nitrogen species: 33.2 percent for total nitrate nitrogen; 27.0 percent for total phosphorus; and 26.0 percent for total organic carbon. Highest loading inputs to the wetland conservation area were from the reach of Reedy Creek receiving wastewater discharge. Discharges from the wetlands receiving wastewater and entering the wetland conservation area during 1988 carried 16.3 percent of the total nitrogen load, and 25.0 percent of the total phosphorus load: during 1989 the discharges carried 22.0 percent of the total N and 21.0 percent of the total P.