In past decades, visitors to Rainbow River enjoyed crystal-clear water and sandy, rocky river bottoms. Today’s visitors will find something else — portions of the river filled with a slimy aquatic plant.
Since the 1990s, Rainbow River has experienced elevated levels of a native algae species that overcrowds areas of the middle and lower river. Many experts attribute this growing algae population to rising nitrate concentrations in the water.
The algae and nitrate imbalances are affecting the water quality and plant diversity of the river and are causing concern among experts and visitors, said Todd Osborne, assistant professor in the UF Soil and Water Science Department.
These threats may negatively impact the system in the long run unless action is taken, Osborne said.
The Rainbow Springs springshed, which spreads into northwest Marion County and eastern Levy County, is Florida’s fourth-largest spring, according to the Rainbow Springs State Park website. The river is formed by the springs, which are fed by the same underground aquifer that helps supply Florida’s drinking water, Osborne said.
Rainbow Springs park manager Charles Smith said the park welcomed 398,808 visitors and generated $1,091,511 in 2014. The springs are a popular recreational destination and an economic engine for the surrounding communities. They are also home to an abundance of wildlife vital to Florida’s culture.
“The long-term view is that if the springs aren’t maintained or restored to their function and their beauty, that we lose out on a lot of fronts,” Osborne said. “We lose the habitat and the environment, we lose the cultural aspect and we lose the economic aspect.”
He said nitrate naturally enters the springshed, the area surrounding the springs, when rainfall seeps into the ground, joins the aquifer and eventually empties into the springs. The human contribution to the nitrate increase in the springs occurs when fertilizers, septic tanks and agricultural practices release nitrate into the groundwater.
Combined, horse and cattle farms along with fertilizer application to crops release about 66 percent of the nitrate currently in the aquifer that feeds the springs, according to a study done by the Florida Department of Environmental Protection.
Sky Notestein, senior environmental scientist for the Southwest Florida Water Management District, said nitrate levels have been increasing for the past 70 years. He attributes the rise to Florida’s growing population.
Southwest Florida Water Management District’s most recent nitrate measurement for Rainbow Springs and Rainbow River is from April and has a concentration of 2.29 mg/L, Notestein said.
Although the drinking water standard allows for levels of nitrate of up to 10 mg/L before it is considered a health risk, the current and continually increasing nitrate levels are still cause for concern.
“The drinking water is coming from a shared source, same as the water going through the river, so any pollution or increased nutrients we see in the river are also potentially in our drinking water, and it’s in everyone’s interest to keep nutrients and other pollutants at as low of a level as possible,” Notestein said.
Nitrate is a vital nutrient source for plants but is best for the environment when maintained at a certain level. When levels start to rise, plant species tend to grow in population because there is more food available, Notestein said.
Aggressive plant species like algae compete with other plants for space and light and push out other native species. In Rainbow River, this process threatens the river’s aquatic diversity, he said.
The algae is threatening desirable native plants like eelgrass, which is an important habitat and food source for fish, insect, turtle and crustacean populations. Its thin blades leave the river bottom with plenty of room for fish and other aquatic life to nest and lay their eggs, he said.
Unlike algae, Eelgrass also has roots that grow into the river’s soil and stabilize sediments. This tends to improve water clarity, he said.
In contrast to plants like eelgrass that make the water look greenish-blue, algae is a thick, slimy plant that makes the water appear grayish-black and hides the river’s white sand and rocky bottom. It isn’t aesthetically pleasing to tourists.
“You know, [visitors] have memories particularly in the past, and they would like their kids or their relatives to have those same fun memories or opportunities to swim and play in clean water that’s not choked full of algae,” Notestein said.
Nelson Anderson, a master’s student at the UF School of Forest Resources and Conservation, said a large drop in Rainbow Springs’ water output may also be causing the algae growth downstream.
“The algae problem has been around for awhile, and the nitrate is so high right now,” he said. “It’s really going to be hard to reduce it, and we really don’t have any proof that reducing it will reverse the effects of the algae appearing.”
Although not everyone agrees on the proper solution for the springs’ pollution or all of the damage this pollution causes, they agree it’s crucial to take action now to prevent future harm.
The Florida Department of Environmental Protection is a major force that is currently taking action. It is in the final stages of adopting a long-term basin management action plan, or BMAP, which aims to decrease the springs’ high nitrate levels. The department believes this will improve water quality and stabilize or even decrease the algae population.
The department first determined the ideal level of nitrate concentration for the Rainbow Springs system to perform at its best, said Terry Hansen, an environmental consultant for the FDEP. It came up with a total maximum daily load, or TDML, of .35 mg/L of nitrate, which means nitrate levels in the springs will have to decrease by at least 82 percent of its current level of 2.29 mg/L to reach this goal.
The BMAP outlines 98 plans of action that focus on reducing the springs’ levels of nitrate toward the TDML. Examples include decreased fertilizer usage, the replacement of septic tank usage for sewer systems that more efficiently filter nitrate, and the abandonment of some package plants in Marion County to improve wastewater treatment facility emission, he said.
Hansen said the long-term plan will be reviewed and evaluated after five years, at which point the BMAP will be re-evaluated to see what worked and what didn’t before it is modified as a phase-two BMAP. The changes won’t happen overnight.
“This isn’t designed to be a quick fix; this is a long term project,” he said. “You want people to be committed and invested in it.”