Cheng Y.,Georgia Institute of Technology |
Stieglitz M.,Georgia Institute of Technology |
Turk G.,Georgia Institute of Technology |
Engel V.,South Florida Natural Resources Center
Geophysical Research Letters | Year: 2011
Wetland ecosystems are often characterized by distinct vegetation patterns. Various mechanisms have been proposed to explain the formation of these patterns; including spatially variable peat accumulation and water ponding. Recently, short-range facilitation and long-range competition for resources (a.k.a scale dependent feedback) has been proposed as a possible mechanism for pattern formation in wetland ecosystems. We modify an existing, spatially explicit, advection-reaction-diffusion model to include for a regional hydraulic gradient and effective anisotropy in hydraulic conductivity. This effective anisotropic hydraulic conductivity implicitly represents the effect of ponding: a reduction in the long-range inhibition of vegetation growth in the direction perpendicular to the prevailing hydraulic gradient. We demonstrate that by accounting for effective anisotropy in a simple modeling framework that encompasses only a scale dependent feedback between biomass and nutrient flow, we can reproduce the various vegetation patterns observed in wetland ecosystems: maze, and vegetation bands both perpendicular and parallel to prevailing flow directions. We examine the behavior of this model over a range of plant transpiration rates and regional hydraulic gradients. Results show that by accounting for the effective x-y anisotropy that results from biomass-water interaction (i.e., ponding) we can better understand the mechanisms that drive ecosystem patterning. Copyright © 2011 by the American Geophysical Union.
Wang X.,University of Miami |
Sternberg L.O.,University of Miami |
Ross M.S.,Florida International University |
Engel V.C.,South Florida Natural Resources Center
Biogeochemistry | Year: 2011
The tree island hammock communities in the Florida Everglades provide one of many examples of self-organized wetland landscape. However, little is understood about why these elevated tree island communities have higher nutrient concentration than the surrounding freshwater marshes. Here we used stable isotopes and elemental analysis to compare dry season water limitation and soil and foliar nutrient status in upland hammock communities of 18 different tree islands located in the Shark River Slough and adjacent prairie landscapes. We observed that prairie tree islands, having a shorter hydroperiod, suffer greater water deficits during the dry season than slough tree islands by examining shifts in foliar δ13C values. We also found that prairie tree islands have lower soil total phosphorus concentration and higher foliar N/P ratio than slough tree islands. Foliar δ15N values, which often increase with greater P availability, was also found to be lower in prairie tree islands than in slough tree islands. Both the elemental N and P and foliar δ15N results indicate that the upland hammock plant communities in slough tree islands have higher amount of P available than those in prairie tree islands. Our findings are consistent with the transpiration driven nutrient harvesting chemohydrodynamic model. The water limited prairie tree islands hypothetically transpire less and harvest less P from the surrounding marshes than slough tree islands during the dry season. These findings suggest that hydroperiod is important to nutrient accumulation of tree island habitats. © 2010 Springer Science+Business Media B.V.
Seavey F.,South Florida Natural Resources Center
Bryologist | Year: 2010
Although Cladonia cinerella Ahti does not appear on the North American checklist of lichens and lichenicolous fungi, it was collected once from the Everglades of Florida in 1909. Ironically, I encountered a large colony deep within the interior of Everglades National Park exactly one century plus one day after the original encounter. In this paper I present some additional observations to Ahti's description based upon living Everglades material illustrated by photos and propose the addition of C. cinerella to the above checklist. © 2010 The American Bryological and Lichenological Society, Inc.
Surratt D.,National Park Service |
Shinde D.,South Florida Natural Resources Center |
Aumen N.,National Park Service
Environmental Management | Year: 2012
Recent appearance of cattail (Typha domingensis) within a southern Everglades slough-Upper Taylor Slough (Everglades National Park)-suggests ecosystem eutrophication. We analyze water quality, nutrient enrichment, and water management operations as potential drivers of eutrophication in Upper Taylor Slough. Further, we attempt to determine why surface water phosphorus, a parameter used commonly to monitor ecosystem health in the Everglades, did not serve as an early warning for eutrophication, which has broader implication for other restoration efforts. We found that surface water total phosphorus concentrations generally were below a 0.01 mg L-1 threshold determined to cause imbalances in flora and fauna, suggesting no ecosystem eutrophication. However, assessment of nutrient loads and loading rates suggest Upper Taylor Slough has experienced eutrophication and that continued total phosphorus loading through a pointsource discharge was a major driver. These nutrient loads, combined with increases in hydroperiods, led to the expansion of cattail in Upper Taylor Slough. We recommend other metrics, such as nutrient loads, periphyton and arthropod community shifts, and sediment core analyses, for assessing ecosystem health. Monitoring surface water alone is not enough to indicate ecosystem stress. © Springer Science+Business Media, LLC.
EVERGLADES NATIONAL PARK, Florida — The shallow coastal waters of Florida Bay are famed for their crystal clear views of thick green seagrass – part of the largest stretch of these grasses in the world. But since mid-2015, a massive 40,000-acre die off here has clouded waters and at times coated shores with floating dead grasses. The event, which has coincided with occasional fish kills, recalls a prior die-off from 1987 through the early 1990s, which spurred major momentum for the still incomplete task of Everglades restoration. “It actually started faster as far as we can tell this year,” said James Fourqurean, a Florida International University marine scientist who studies the system. “In the ’80s, it continued to get worse for 3 years.” Fourqurean and government Everglades experts fear they’re witnessing a serious environmental breakdown, one that gravely threatens one of North America’s most fragile and unusual wild places. When most people think of the Everglades, they envision swamps — but seagrass is just as important, if less romanticized. Besides being the home to majestic sea turtles, dolphins, and manatees, Florida Bay also hosts pink shrimp, spiny lobsters, spotted seatrout, and much more – sport fishing alone here is worth $ 1.2 billion per year, according to the Everglades Foundation. And although there is at least some scientific dissent, Fourqurean and fellow scientists think they know the cause of the die-off. It’s just the latest manifestation, they say, of the core problem that has bedeviled this system for many decades: Construction of homes, roads, and cities has choked off the flow of fresh water. Without fast moves to make the park far more resilient to climate change and rising, salty seas, the problem will steadily worsen. The Everglades ecosystem “being out of balance at a time of climate change is really going to have a huge impact on South Florida, if we don’t do something about it,” said Interior Secretary Sally Jewell, who surveyed the seagrass die-off last week during an Everglades Trip. Holding dead grasses in her hand in a National Park Service boat in the more than half-a-million-acre estuary, Jewell told a group of staff and reporters, “This is what we get when we don’t take care of Florida Bay.” Florida Bay encompasses roughly one-third of Everglades National Park. And like the park’s mangroves and sawgrass prairies, it relies on the same broad water system. Both need fresh water to flow southward from Florida’s Lake Okeechobee, and the central part of the state, to preserve their unique characteristics. And both have suffered from highway and water management projects that have blocked or diverted much of this water away. “It’s basically a permanent manmade drought, created by the drainage and development patterns to the north in the Everglades,” said Robert Johnson, director of the National Park Service’s South Florida Natural Resources Center, on the boat trip with Jewell. The seagrass die off, according to Johnson, was caused when this perennial problem was further exacerbated by a 2014-2015 South Florida drought. Flows through Shark River Slough, which feeds water to the Everglades and eventually Florida Bay, plunged to just 200,000 acre-feet in 2015. That’s just a quarter of standard annual flows, which themselves are less than half of historic flows of 2 million acre-feet per year before major projects blocked and redirected the Everglades’ water. The center of the bay then heated up last summer, saw considerable evaporation, and became quite salty – for some parts of the bay, twice as salty as normal sea water. “It’s a really delicate balance between how much freshwater comes in each year, how much rainfall falls, and then how much evaporation occurs,” Johnson said. “In the absence of rainfall, salinity takes off in the bay, and we get a lot of harmful impacts of that.” In very salty conditions, waters hold little of the oxygen that seagrasses need to live. At the same time, other marine organisms turn to a different “anoxic” process – one that goes forward without oxygen – that has a nasty by-product: hydrogen sulfide. The chemical “is a notorious toxin,” said Donald Boesch, president of the University of Maryland Center for Environmental Science. “It kills life, including human.” And that’s just the beginning. Once the seagrass dies off, it becomes a feedback – the water becomes filled with dead grasses that release nutrients, and those can stoke huge algal blooms (which happened the last time around, but so far have not appeared en masse). That clouds the water and prevents light from reaching remaining seagrasses, which then also die, because they need the light for photosynthesis. “You have this water that’s notoriously gin clear water, because the seagrasses and the biology kept the light penetrating, and then all of a sudden it changes pretty dramatically to a system without grass, and very turbid waters,” Boesch said. Granted, there are some dissenters. Brian LaPointe, a researcher with Florida Atlantic University, contends that Florida Bay seagrass die-offs are caused by the runoff of too many nutrients, like nitrogen, into the Bay’s waters, which in turn stoke algal blooms. “There really isn’t a correlation over time of high salinity and problems in the Bay,” LaPointe said. Seagrasses, he said, “can handle pretty high salinities.” During the last dieoff, a large scientific debate erupted over whether changes in salinity were indeed the cause. But Boesch, who led a scientific review of the last die-off during the Clinton administration (which failed to reach a conclusion at the time), said that the high-salinity explanation “has now become kind of the mainstream scientific explanation,” although that now encompasses other related processes involving oxygen content of waters and buildup of hydrogen sulfide. It’s not just Florida Bay: Seagrasses the world over are threatened. In a 2009 study, scientists found that segrass extent had declined globally by 29 percent since the late 19th century. They concluded that seagrasses were just as threatened as their companion coastal ecosystem, coral reefs, though the latter tend to get far more attention. The Obama administration, in collaboration with Florida state agencies and local leaders, has been moving lately to simultaneously restore historic Everglades water flows and to try to safeguard the park against climate change. President Obama visited last year, telling his audience that “You do not have time to deny the effects of climate change…nowhere will it have a bigger impact than here in South Florida.” And this year Jewell visited the Everglades on Earth Day to announce a $ 144 million “bridging” project that will elevate 2.5 miles of Highway 41, more popularly known as the Tamiami Trail, which connects Miami to Tampa and runs through the Everglades. Constructed in the 1920s, the highway impairs water flow southward, from Lake Okeechobee, into the Everglades (and, eventually, the Bay). It’s like a dam across the famed “river of grass.” Lifting it could restore a substantial part of historic freshwater flow levels. But that will take years – the project should be completed in 2020 — too long to stop the current seagrass die off from running its course and perhaps having many cascading effects, scientists fear. And it’s not just nature that needs this fresh water: It’s people. South Florida, the home to 6 million people now and growing steadily, relies on the Biscayne aquifer, which is refilled by the Everglades, for drinking water. The aquifer’s water flows through limestone that is quite porous, which means that saltwater and freshwater can both penetrate it. In effect, two walls of water abut one another, facing off — and for the sake of nature and people alike, freshwater needs to hold its ground. If inadequate freshwater flows southward in Florida, then Florida Bay can get too salty even as the seas also creep into the Everglades, potentially causing land to subside and sink – but also penetrating the aquifer and threatening drinking water. In short, it’s bad news across the whole system. And even as governments at the local, state, and national level move faster to send the Everglades and the Bay more fresh water, the question remains just how much climate change will worsen problems like the seagrass die-off. After all, it will raise seas, increase air and water temperatures, and perhaps drive more droughts as well. “The questions I would ask, from a climate perspective, going forward, is first of all, are we going to have more conditions of really high temperature, due to, you know, the atmospheric warming, coupled with these extended periods of still water?” Boesch said. “Are we going to have longer periods of drought in the Everglades?” Boesch said that while higher temperatures are a given, precipitation patterns are difficult to predict, but notes that there is some reason to fear South Florida could get drier in the future. “What happened to the Bay is very much a climate change issue,” Jewell said in an interview during her Everglades tour. “It’s tied in to a drought. Now, is the drought tied to climate change? None of us could tie any single hurricane or storm event or drought to climate change, but we do know that the weather here is getting more extreme. And we do know that those extreme weather patterns are having a dramatic impact on our ecosystems, as we saw today on Florida Bay.” Still, much of Florida Bay remains unaffected – for now. That includes an area of lush seagrass meadow near a small island named Johnson Key. A trio of bottlenosed dolphins approached the National Park Service skiff there, and as the boat trolled slowly through the clear, only 3- to 4-foot-deep water, started to lead the way ahead of it. Nonetheless, the second major seagrass die off in three decades certainly suggests that something has changed recently in the system. “The really disturbing thing is, this unprecedented event has now happened twice in my career,” Fourqurean said. Six years later, we’re still learning how badly the BP spill damaged the environment This key psychological factor could explain why you care about the environment These striking numbers show just how fast we’re switching off coal For more, you can sign up for our weekly newsletter here, and follow us on Twitter here.