Restoring the Greater: Everglades Ecosystem

Abstract

Illustration courtesy of Thinkstock/Val_Iva Pelican photo courtesy of Thinkstock/kojihirano In 2003, Todd Osborne was presented with an “opportunity,” he quips: the chance to collect the samples for a soil map of all five million acres of Florida's southern Everglades. Osborne was a University of Florida graduate student at the time, and his adviser, Ramesh Reddy, had funding with Sue Newman of the South Florida Water Management District to conduct the sweeping project. Now Reddy needed the labor, so Osborne spent the next nine months flying by helicopter “everywhere, I mean everywhere” in the southern Everglades, he says: from the Loxahatchee wildlife refuge in the north to Everglades National Park at Florida's tip. Todd Osborne collecting samples in the Everglades. He retrieved soil from 1,356 locations in all, gaining along the way a perspective on the ecosystem that other researchers might acquire only after decades. Then the lab work began. Samples were analyzed for an all-inclusive list of properties, including carbon, nitrogen, phosphorus, and other nutrients; contaminants, such as mercury; and a host of physical parameters. Afterward, these point data were woven together by a team of collaborators into a full-scale map of the Everglades landscape. Many reports and scientific publications followed. The work was intensely rewarding, but also exhausting. “It's been almost 10 years, and it seems like yesterday. I'm still tired,” Osborne says with a laugh. Joking aside, the scope of the effort underscores the deep concern among government agencies, conservation groups, scientists, and the public about the fate of the greater Everglades ecosystem and how desperately people want to see it restored. Once a vast, free-flowing “river of grass” stretching from the Kissimmee Chain of Lakes near Orlando down through central Florida's Lake Okeechobee and into the southern Everglades, the same lands and waterways are now drained, diked, compartmentalized, and controlled. As a result, areas like Everglades National Park receive too little water. Others, such as Lake Okeechobee, get far too much. And nutrients abound most everywhere, driving wholesale changes in plant communities, aquatic life, and wildlife populations. Top: Excessive phosphorus (P) has fueled both the loss of native sawgrass and the spread of invasive cattail in the Everglades. Bottom: In areas that are not impacted by high P levels, native vegetation remains. Excessive phosphorus, for instance, has fueled both the loss of native sawgrass and the spread of invasive cattail—and where cattail dominates, other changes soon follow. Cattail often grows so densely that alligators, turtles, wading birds, and other native wildlife can't move through it. Frequent wildfires also helped maintain the astounding ecological diversity of the historical Everglades, but fire is less common now because cattail burns poorly. The soil also isn't immune. It transforms under cattail into a flocculent, detritus-rich “vegetable soup” that breaks down quickly and fails to build organic matter, says Osborne, now an assistant professor of soil biogeochemistry at the University of Florida. This last point may seem minor to those who care about saving endangered plant and animal species, but the importance of soil in Everglades restoration has actually been recognized for a long time. It's one big reason why Reddy's and Newman's 2003 soil mapping project went forward. Yet, even before then—from the beginning, in fact—soil was on people's minds. When restoration efforts first got under way in the late 1980s, Osborne explains, two soil-based criteria for tracking restoration success were set: There would be no net loss of organic soils, and the load of nutrients, especially phosphorus, would be reduced. “That's huge because most of the time soil ends up being on the bottom, and I don't mean that as a pun,” he says. “People usually don't consider soil when it comes to ecosystem restoration projects.” To appreciate why they did in this case, it helps to understand the magnitude of change in the Everglades over the past 100 years. A century ago, water would flow from Shingle Creek near Orlando, down through the Chain of Lakes, and into the Kissimmee River. From there, it collected in Lake Okeechobee—the Southeast's largest freshwater lake and the “life blood” of the greater Everglades system, says ASA and SSSA member Patrick Bohlen, a University of Central Florida ecologist. During a talk at the 2013 ASA, CSSA, and SSSA Annual Meeting, he explained this means that “during the rainy season, the lake would spill over with a volume of water most of us couldn't comprehend.” The wave would then fan out southward, creating the marshes, sloughs, and ridges of the southern Everglades. Top: The Everglades before 1880. Each year, Lake Okeechobee used to overflow its southern rim in the rainy season and start the Everglades water supply flowing southward unobstructed to the Gulf of Mexico. Bottom: Today, agriculture, cities, roads, canals, levees, dams, locks, and pumps now interrupt or drain the natural flow. The Everglades must now compete for water with cities and agriculture. The images to the left are part of a display at the Everglades National Park. Courtesy of Flickr/afagen. Although early settlers were awed by their beauty, the Everglades were a soggy, inhospitable place to live. So, early in the 20th century, people began re-engineering the region's hydrology, and one of their first actions was to build a dike around Lake Okeechobee. Expanded to its current form in the 1960s, the dike prevents the lake's historical spillovers and protects downstream residents and farmlands from floods. But it also creates problems. Most notably, water from the entire northern watershed still pools in Lake Okeechobee; however, because the lake is extremely enriched now with nutrients—including 600 parts per billion (ppb) phosphorus—very little is allowed to travel its natural path to the sensitive, protected Everglades of the south. Instead, excess lake water is shunted artificially to two estuaries—one on Florida's east coast and one to the west—where, unfortunately, it also causes harm. The water brings excess nutrients, for one, and it also upsets salinity levels in the brackish estuary ecosystems. The situation reached a crisis last summer. After the lake became engorged with runoff from unusually heavy rains and began straining against its dike, the Army Corps of Engineers was forced to release a deluge to the east and west. Although a definitive connection hasn't been made, these heavy flows of Lake Okeechobee water are suspected of contributing to problems in the estuaries, which have been plagued by die-offs of eelgrass, manatees, and pelicans; huge blooms of algae; and zones of oxygen-starved water, Bohlen says. In the meantime, once-flooded areas are now unnaturally dry, resulting in another worry: soil subsidence. Many soils of the southern Everglades are organic and peaty, making them excellent for growing crops. That's why agriculture is well established throughout the region, especially in the 700,000-acre Everglades Agricultural Area (EAA) just south of the lake. But draining these peatlands for farming also has caused them to oxidize. Since the late 1800s, the EAA alone has lost an average of 5.5 feet of peat, according to Tom Dreschel of the South Florida Water Management District, reporting this fact at the Societies’ Annual Meeting last November. Such tremendous losses of soil and organic matter are of grave concern to farmers, but soil subsidence affects natural areas, as well. Native vegetation in the Everglades is patterned along gentle elevation gradients (i.e., ridges and sloughs) that are mainly determined by differences in peat and soil buildup. When peat soils dry out and subside, this corrugated topography disappears, leaving behind “a flat, wet prairie,” Osborne says. “So you lose some of the uniqueness and function of the ecosystem.” There is yet another issue with soil subsidence, he adds: Organic soils release nitrogen and phosphorus when they dry. “These soils are natural sinks for nutrients, so exposing them and oxidizing them only exacerbates the water quality problem,” Osborne says. Top: Alan Wright, associate professor at the University of Florida, stands next to a post showing the loss of soil due to subsidence just south of Lake Okeechobee over the last 80 plus years. Photo courtesy of Ramesh Reddy. Bottom: Native vegetation in the Everglades is patterned along gentle elevation gradients (i.e., ridges and sloughs) that are mainly determined by differences in peat and soil buildup. When peat soils dry out and subside, this corrugated topography disappears, affecting the uniqueness and function of the ecosystem. To be sure, landowners, government agencies, policy makers, and conservation groups have done a lot to improve the Everglades’ water quality over the past several decades. “Things are working in the right direction,” Osborne says. By implementing a stringent set of best management practices (BMPs), for example, farmers in the EAA have curbed the phosphorus leaving their fields by more than 50% on average each year—more than twice what state law requires. But turning down the spigot on any “new” phosphorus entering the system is less than half the battle. Most of the nutrient load into Everglades’ waterways today comes from phosphorus that has accumulated in soils from past human activities—or “legacy” phosphorus, says Reddy, an ASA and SSSA Fellow who has studied the Everglades for more than 30 years. Although producers are much more careful nowadays, farmlands both north and south of Lake Okeechobee were once heavily fertilized, with much of the excess nutrients winding up in the soil. Past engineering projects, too, have mobilized phosphorus, Osborne says. When the Kissimmee River was channelized in the 1960s and 1970s, miles and miles of river and existing channels had to be dredged. The dredging cut through several layers of geologic clays that were rich in phosphorus, releasing it downstream. Many areas now contain so much legacy phosphorus, in fact, that Reddy and Osborne estimate that decades, or even centuries, will pass before all of it moves out of the system. In a talk at the 2013 Annual Meeting, Reddy explained how average annual phosphorus loads entering Lake Okeechobee from the northern watershed have held steady at around 500 metric tons for nearly 40 years, despite widespread efforts to curb them. And if even 15% of the remaining legacy phosphorus leaches from the drainage basin, it could maintain that same 500 metric tons per year load for the next 60 years. “So, that's a pretty alarming number,” he said. Similarly, even though farmers in the south have done much to cut phosphorus losses, the annual load moving downstream from the EAA still averages 170 metric tons due to the release of stored phosphorus from drained and decomposing organic soils. “So how do we strategize to reduce the loads? BMPs alone aren't going to do it,” Reddy said during his talk. “We need to find another way to retain the phosphorus before it goes into these water bodies.” The South Florida Water Management District, for example, has built 57,000 acres of wetlands, known as Stormwater Treatment Areas (STAs), to intercept and store phosphorus moving south from the EAA. The agency is also now constructing “flow equalization basins” to capture heavy runoff during storms, create a more steady flow to the STAs, and hold even more phosphorus. In the meantime, though, another means to achieve this aim could lie miles to the north in the Everglades ecosystem above Lake Okeechobee. To reduce the overwhelming volumes entering the lake and relieve pressure on its dike and the estuaries, people have been searching for ways both to retain water in the upper watershed and slow its movement southward, Bohlen explains. The eventual goal is to store between 900,000 and 1.3 million acre-feet above Lake Okeechobee, he adds. One proposed solution is to create giant reservoirs or constructed marshes like the southern STAs. A massive effort to restore the historic flow patterns and floodplains of the Kissimmee River is also under way. But because the Everglades acres north of the lake are mostly privately owned—mainly by cattle ranchers—a leading idea is to pay these landowners to store water on their properties instead. It's estimated, for instance, that ranchlands above Lake Okeechobee contain more than 450,000 acres of wetlands. “Almost every ranch you visit has pastureland and wetland mixed together,” says Sanjay Shukla, a University of Florida biological engineer who collaborates with Bohlen. “That's the typical landscape of South Florida.” So, by restoring these wetlands to retain water, it's hypothesized that large volumes could be kept from entering the lake. And that got Bohlen and Shukla thinking about nitrogen and phosphorus. “If water isn't leaving [the upper watershed] as quickly or in the quantities it used to,” Bohlen says, “the theory is that, well, you'll also be holding back some of the nutrients.” They have both tested that hypothesis now in a series of pilot projects on both experimental and working ranches. A stormwater treatment area (STA) in the Northern Everglades surrounded by sugarcane fields. Courtesy of USGS. In a four-year study published in 2011 in the Journal of Environmental Quality (40:989–998), Bohlen and his collaborator Odi Villapando examined whether they could curb nutrient losses by retaining water in experimental pastures rather than letting it flow off unimpeded. For nitrogen, this was definitely true, Bohlen says: nitrogen loads in outflowing water dropped significantly when flow rates were reduced. The effect on phosphorus was more equivocal. Although, phosphorus loads were 27% lower under reduced-flow conditions, the result wasn't statistically significant. Moreover, the researchers saw evidence that flooding the land also released legacy phosphorus, thanks to fluctuating anoxic and oxygenated conditions in the soil. “So even though you're holding more water and nutrients back,” he says, “[the benefit] is offset a little bit by that release.” In more recent research, however, retaining water on a working ranch produced much more encouraging findings. On the Lykes Brothers ranch near Lake Okeechobee, Bohlen and Shukla collaborated on a project that pumped water from a nearby public canal into an existing reservoir on the ranch. The system was designed to hold the water for “treatment,” before sending it back into the canal, which drains directly into the lake. During three years of monitoring, the scientists found that retaining water in the reservoir dropped phosphorus loads in the outflow by more than 70% on average. In one year, more than 90% of the phosphorus was removed. “I was so surprised that I asked my postdoc to go back and make sure of the number again,” Shukla says with a laugh. “That level of retention, it's just not seen in a typical treatment system.” Although he's still not certain why so much phosphorus was removed, Shukla suspects some combination of uptake by plants and phosphorus adsorption by the soil was responsible. One thing he and Bohlen are sure of, though, is the potential for these methods to help restore the ecosystem—and so, for that matter, is the State of Florida. Based on these and other data, the state is now paying some ranchers to hold water on their lands through practices such as wetland restoration, flooding of pasture, or the creation of “private water treatment systems” like the one on the Lykes property. Not only can ranchers store water more easily and for far less money than a public works project, but these systems may also have ecological benefits. Shukla and his students are now asking whether holding water on ranches also increases wildlife populations and desirable plant species. Patrick Bohlen (left) and Sanjay Shukla inspect a culvert on a ranch just north of Lake Okeechobee being used to retain water. UF/IFAS Photo by Tom Wright. At the same time, he and Bohlen caution that more tracking of water volumes and nutrient loads are needed, particularly as people try to model the impacts of implementing private water-holding practices widely across the ecosystem. “In south Florida, especially in the Everglades watershed, you will see a lot of estimates,” Shukla says. “But how much of that estimate is derived from actual evidence based on measurements? There is a gap there, definitely.” Shukla also isn't ready to say how much of a risk legacy phosphorus will pose when drained pasturelands are inundated again. Although he and Bohlen have both observed some phosphorus loss in the short term, he'd like to analyze the nine years of data now gathered from one site before making any solid conclusions. It's the same with nearly every research effort in the Everglades. It will likely takes years or decades for the system to recover, which means most questions about its recovery will also take years to answer. The STAs, for example, are very effectively reducing phosphorus loads for now. But concern is mounting that this removal capacity will diminish over time, and indeed there is already evidence of this, Reddy says. Another long-term question is how the Everglades will respond to climate change, especially as sea level continues to rise and more saltwater floods the system. But the most enduring puzzle is this: How are the Everglades doing as a whole, and is the ecosystem responding to the pricey interventions ($9 billion and counting) being made on its behalf? “That's the really hard part,” Osborne says. “Determining: Has something changed?” He, Reddy, Newman, and their collaborators hopefully made that question easier to address when they captured the baseline state of the entire southern Everglades back in 2003. Scientists will know better once a second survey—now under discussion—is carried out. A continuing emphasis on soil should also help. “Soils provide a long-term signature for what's happening in the system,” Reddy says. “They are a ‘hub’ for all ecosystem functions.”