The Rainbow River is located in Dunnellon, Florida, USA, in the southwest corner of Marion County, about 20 miles (32 km) southwest of Ocala, 100 miles (160 km) northwest of Orlando and 100 miles (160 km) north of the Tampa Bay area. It is formed by a first-magnitude spring (Rainbow Springs) that is ranked fourth in the state for volume of discharge. In addition to the springs located at the headwaters, there are many smaller springs that discharge from numerous caves, rock crevices, and sand boils the entire length of the river.
The Rainbow River is a gently winding river that is 5.7 miles (9.2 km) long and merges with the Withlacoochee River at Dunnellon, Florida. The headwaters, Rainbow Springs, is the anchor for Rainbow Springs State Park. This first-magnitude spring is not one large vent but is numerous vents that issue 400 - 600 million gallons of crystalline water every day. Rainbow Springs State Park is a popular destination to swim, snorkel, canoe, picnic, or stroll on the walking paths to enjoy the many plants and animals that abound here.
Once named Wekiwa Creek, Blue Spring, and Blue Run, archaeological evidence indicates that the waters of the Rainbow River have attracted and sustained human inhabitants for over 10,000 years. The crystal clear water, abundant with fish, wildlife and vegetation along with the constant water temperature of 73 degrees, has attracted a number of modern day activities.
Rainbow Springs and the Rainbow River became popular in the late 1880s when hard rock phosphate was discovered in the area. A small community called Juliette flourished near the springs during this "boomtown" era. In the 1930s the spring was developed as a tourist attraction. Sea walls, a lodge, gift shop, the waterfalls, and a reptile exhibit were developed. Under new ownership, the real heyday for the attraction occurred in the 1960s. During that time activity greatly increased with glass-bottomed boat rides, riverboat rides, log raft rides, a gift shop and cafe, an aviary, a leaf-shaped gondola/monorail system, a horse rodeo, and submarine boat tours. Not faring well when traffic began using I-75 instead of U.S. Highway 41, with many tourists heading to a new attraction called Walt Disney World, the attraction closed in 1974.
The Rainbow River was designated as a Registered Natural Landmark in 1972, an Aquatic Preserve in 1986, and an "Outstanding Florida Waterway" in 1987. The state purchased the original area that was the Rainbow Springs attraction in 1990. Volunteers cleared the overgrown park and opened the park on weekends to the public. The Florida Park Service officially opened Rainbow Springs State Park on a full-time basis on March 9, 1995.
Rainbow Springs State Park comprises 1,459.07 acres (590.46 ha) of upland (which includes around 100 acres (0.40 km2) of wetlands) and 12.83 acres (5.19 ha) that are submerged. The most significant natural feature is the first-magnitude headspring basin which produces between 400 - 600 million gallons of fresh water per day, forming the Rainbow River. The looking-glass waters of Rainbow Springs come from several vents, not one large bubbling spring. The river itself supports a wide variety of fish, wildlife, and plants, many within easy viewing by visitors. In total, the park contains 11 distinct natural communities, including sandhills, flatwoods, upland mixed forests, and hydric hammocks. Visitors are able to see a variety of wildflowers in season; oak, longleaf pines, magnolia, dogwood, redbud, and hickory trees; gray squirrels, red-shoulder hawks, swallowtail kites, barred owls, whitetail deer, and a wide variety of wading birds. The relative peace and quiet of the winter season offers much for the nature enthusiast. There is an interpretive room located in the visitor center displaying historical, natural, and cultural resources of the park.
The Rainbow River is located in southwest Marion County near the town of Dunnellon, approximately 20 miles southwest of Ocala (Figure 1). The first magnitude spring system that forms the Rainbow River has an average discharge rate of 763 cubic feet per second (cfs), or 493 million gallons per day (mgd) and is one of 33 first magnitude spring systems in the State. The river flows south from the headspring complex approximately 5.7 miles to the tannic Withlacoochee River. The Rainbow River supports numerous listed and unlisted wildlife species through a variety of habitats in and along the river. Accordingly, the unique ecological attributes of Rainbow River/Rainbow Springs were recognized by the state of Florida when the system was designated an aquatic preserve in 1986 and an Outstanding Florida Water (OFW) in 1987. The Florida Park Service opened Rainbow Springs State Park in 1995. The local economy is supported by both recreational and commercial activities associated with the distinctive habitat and wildlife of the Rainbow River. However, land use changes in the watershed and groundwater recharge basin have occurred and threaten the water quality and associated natural systems in the Rainbow River. In recognition of the need to place additional emphasis on restoration, protection, and management of the surface water resources of the State, the Florida Legislature, through the Surface Water Improvement and Management (SWIM) Act of 1987, directed the State's water management districts to "design and implement plans and programs for the improvement and management of surface water" (Section 373.451 F.S.). In 1989, the Southwest Florida Water Management District (District) adopted the Rainbow River as a SWIM water body and developed the first Rainbow River SWIM Plan. The 1989 SWIM plan identified a variety of projects that included public education, habitat restoration, baseline vegetation and wildlife surveys, and sediment analysis. These projects were diagnostic in nature with a focus on obtaining a basic understanding of the system. As projects were completed and the District staff's understanding of the system increased, SWIM plans were periodically updated. The Rainbow River SWIM plan was updated in 1995 and again in 2004 to evaluate management issues and to determine which areas to focus management strategies in the future. As each SWIM plan was updated, management issues shifted from the area immediately surrounding the river to more regional issues within the 735 square-mile groundwater recharge area. The purpose of this technical summary is to provide a synopsis of projects that have been completed to date, specifically those completed since the latest Rainbow River SWIM Plan of 2004.Similar to other spring-fed rivers in the state as well as the District, the natural systems and water quality of the Rainbow River have been impacted by development. Over the last century this system has experienced a variety of land use changes within its watershed. The Rainbow River and its immediate surroundings were mined for phosphate in the early part of the 20thcentury. From 1934 to 1973 the headspring complex was used as a tourist attraction that included glassbottom boats and mermaid shows. These are just a few of the land use changes that have led to altered surface and groundwater chemistry, reduced wetlands in the watershed, hardened natural shorelines, increased nutrient loading to the system, disturbed natural sediment regimes, the introduction of exotic plant and animal species, and increased disturbances related to recreational activities. Since its inclusion as a SWIM priority water body in 1989, the District, with a variety of state and local government partners, have worked together to identify management issues and develop strategies to protect and improve conditions in this unique first magnitude system. The management issues and strategies identified and implemented to date are summarized in this report. Management Issues & Water Quality
Current management issues related to water quality on the Rainbow River focus on nutrient loading. The primary nutrients of concern are nitrogen and phosphorus. These nutrients occur naturally in low concentrations and support natural processes associated with aquatic ecosystems. However, excess nutrients from man-made sources fuel the growth of phytoplankton, epiphytic algae and nuisance filamentous algae. Additionally, numerous studies have also suggested that there are toxic effects of nitrogen enrichment on aquatic fauna (Mattson, 2007). The first SWIM plan for the Rainbow River was developed in 1989 and focused primarily on point source discharges associated with wastewater treatment plants (WWTP) as a source of water quality degradation. These facilities discharged large amounts of nutrients into the Rainbow River. In the late 1980's and early 1990's, many of the WWTP's were either taken off-line or required to significantly improve treatment methods. As a result, concerns about point source discharges subsided and subsequent SWIM plans began focusing on more regional management issues. By the time the second SWIM plan was developed in 1995, several Rainbow River diagnostic studies had been completed. The Diagnostic Studies of the 6 Rainbow River report (Water and Air Research, 1991) identified an apparent trend of increasing nitrate concentrations in groundwater discharging from the springs. Because of the concern for increased nitrate loading in the Rainbow River, the 1995 SWIM plan recognized the need to establish a Pollutant Load Reduction Goal (PLRG). A PLRG is an estimated numeric reduction in pollutant loading needed to preserve or restore designated uses of receiving bodies of water and maintain water quality consistent with applicable state standards. Pursuant to State Water Policy, Chapter 62-40, Florida Administrative Code (FAC), a PLRG is to be developed for each SWIM water body and adopted as part of the SWIM Plan. Because the District was in the process of determining the source of increasing nitrates, an interim pollutant load reduction goal of zero was established. This means that the goal was to prevent nutrient levels from increasing beyond the current levels. The 2004 updated Rainbow River SWIM Plan identified a continuing need for water quality monitoring both within the Rainbow River system and its associated groundwater recharge area. The PLRG was maintained at zero, however nitrate levels have continued to rise as shown in Figure 2. The data shown in Figure 2 was collected by the WQMP from 1994 to 2008 following Florida Department of Environmental Protection (FDEP) sampling protocols.
Shortly after the 1995 SWIM Plan was adopted, the District's Water Quality Monitoring Program (WQMP) finalized a report investigating the source of nitrates in the Rainbow River groundwater recharge area (Jones, 1996). The report results showed that a 20-fold increase in nitrate concentrations had occurred in the last 40 years. The study noted that the average nitrate 7 concentration in the headspring complex was 0.89 mg/L, while background concentrations are considered to be 0.01 mg/L or lower. It was determined that the source of increased nitrate in the groundwater discharging from the various spring vents was inorganic fertilizer. At the time of the Jones (1996) report, agriculture was the dominant land use in the recharge area, although residential and golf course fertilizers as well as septic systems were identified as future threats due to expected land use changes. By 2001, nitrate concentrations in the headspring area were 1.0 mg/L (Champion, 2001). The District continues to monitor water quality for this system through various departments within the District, with assistance from FDEP. The Environmental Section is currently managing a surface water quality monitoring project in which nitrate concentrations at the Rainbow River headspring complex are consistently above 1.6 mg/L, and on several occasions approaching 2.0 mg/L. Additional monitoring efforts include the implementation of an Upper Floridan Nutrient Monitoring Network (UFANMN), priority pollutant screening, groundwater monitoring, and isotope sampling. Figure 3 shows the location of the various ongoing District monitoring efforts. Recent monitoring of nitrogen isotopes has not shown a change in the source of nitrates discharging from the springs. In recent years, the District has also been involved with monitoring for specific pollutants in targeted springs throughout the District. This project has been collecting data since 2002 and involves the monitoring of priority pollutants such as cyanide, mercury, heavy metals, pesticides, and volatile organic compounds. To date, no priority pollutants have been detected from samples collected from the spring vents. The District also recognizes that phosphorus is a nutrient of concern and it is monitored at the same frequency as nitrates. Phosphorus levels in the Rainbow River remain at or very near background levels averaging 0.03mg/L. Phosphorus contributions to surface water bodies are typically the result of surface runoff. Groundwater discharge accounts for 97-99% of the river flow with very little surface runoff from the watershed (Water and Air Research, 1991). The Rainbow River watershed is approximately 47,000 acres (73 sq. mi.) while the groundwater recharge area or "springshed" is 470,000 acres (735 sq. mi.) (FGS, 2007; Figure 3). It has been estimated that groundwater may take up to 30 years to reach the spring vents from the recharge areas. Therefore, management strategies applied within the groundwater recharge area may take up to 30 years to realize the "full" benefit in measured water quality at the headspring complex. However, BMPs and other management strategies applied closer to the springs may be realized much sooner. 8
Figure 3. Rainbow River Sample Stations, Watershed, and Springshed
It has been perceived by many that water clarity along the river has been decreasing over time. As described earlier, current management issues related to water quality on the Rainbow River focus on nutrient loading. Excess nutrients discharging from the spring vents fuel the growth of chlorophyll-producing organisms in receiving rivers and estuaries. The abundance of algal cells in the water column contributes to decreased water clarity or transparency, which impacts rooted aquatic vegetation. In 2002, the District began a surface water quality monitoring project to examine which water quality parameters, if any, impact water clarity along the Rainbow River. The result of the project was an optical model that explained both spatial and temporal variability in water clarity through chlorophyll concentrations using an exponential decay function (Anastasiou, 2006). Figure 4 shows the relationship between water clarity and chlorophyll concentration for the river reach. Figure 4.