Progress Toward Restoring the Everglades The Fourth Biennial Review, 2012 (2012) / Chapter Skim
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4 Ecosystem Trajectories Affected by Water Quality and Quantity
4 Ecosystem Trajectories Affected by Water Quality and Quantity
Pages 95-148
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From page 95... ...
In light of the ongoing declines and the slow pace of restoration progress, NRC (2010) recommended "a rigorous scientific analysis of the short- and long-term tradeoffs between water quality and quantity for the Everglades ecosystem." In this chapter, the committee explores recent trends, possible future trajectories, and timescales for recovery of 10 ecosystem attributes of the remnant Everglades to better understand the implications of the current slow pace of progress and the potential consequences of focusing on water quality at the expense of water quantity, or vice versa.
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Finally, the committee identifies key conclusions. CONTEXT FOR WATER QUALITY AND QUANTITY ISSUES The problems in the central Everglades result from hydrological conditions that make some areas often too dry, while other areas are often too wet.
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loads, interior TP concentrations, soil phosphorus, cattail (Typha domingensis) , periphyton, fish mercury concentrations, peat depth, ridge-and-slough topography, tree islands, and snail kites.
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to D (seriously degraded; e.g., peat, tree islands, ridge and slough, fish mercury)
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These timescales reflect the committee's qualitative estimates of the time required after substantial degradation has occurred to recover the losses in that ecosystem attribute (i.e., snail kites, tree islands, ridge-and-slough topography, periphyton, peat, cattail) or to attain established restoration criteria (i.e., phosphorus concentrations and loads in the water and soil, fish mercury concentrations)
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From page 100... ...
Recovered communities may not be the same as prior to disturbance Peat D Degrading 0 ++ ++ Centuries in dry areas Tree islands D Degrading 0 +5 +5 Decades to centuries; may require active restoration Ridge and D Degrading 0 + ++ Centuries; could slough involve adaptive management Snail kite F Degrading 0 + + Years to irreversible Fish mercury D Stable – + + Years to decades continued analysis also helps to prioritize the focus: stabilizing and ultimately reversing declines of attributes that would take a long time to recover merit higher priority than attributes that would recover more quickly, all other things being equal, especially if other aspects of the restoration depend on them. Observations The committee's qualitative analysis (explained in more detail in the a ttribute-specific sections later in the chapter)
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From page 101... ...
3 Timescales of recovery reflect the committee's qualitative estimates of the time required after substantial degradation has occurred to recover the losses in that ecosystem attribute (i.e., snail kites, tree islands, ridge-and-slough topography, periphyton, peat, and cattail) or to attain established restoration criteria (i.e., phosphorus concentrations and loads in the water and soil, fish mercury concentrations)
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From page 102... ...
. The committee considered improved hydrology to address flow volumes, flow velocity and direction, flow variability and frequency, and water depths and their spatial distribution, timing, and duration.
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Attributes most directly influenced by hydrology are continuing to decline and are the most difficult to recover (e.g., peat, tree islands, ridge and slough) , making addressing them a high priority.
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From page 104... ...
, periphyton, fish mercury concentrations, peat, tree islands, ridge-and-slough topography, and snail kites. Phosphorus The wetlands of the historical Everglades were primarily low‑nutrient, p hosphorus-limited systems.
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From page 105... ...
. 250 Annual 5-Yr Moving Average 200 Target TP Concentration, ppb 150 100 50 0 5 7 9 1 3 5 7 9 1 3 5 7 9 1 8 8 8 9 9 9 9 9 0 0 0 0 0 1 19 19 19 19 19 19 19 19 20 20 20 20 20 20 FIGURE 4-2 Annual average concentrations of phosphorus in Lake Okeechobee.
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From page 106... ...
have fluctuated in a narrow range around the 10 ppb level since 2000. 300 300 Annual Annual 250 250 5-Yr MA Annual Load, Annual Load, 5-Yr MA metric tons metric tons 200 200 150 150 100 100 50 50 0 0 1980 1990 2000 2010 1980 1990 2000 2010 WCA 1 WCA 2 300 30 Annual Annual 5-Yr MA 250 25 Annual Load, Annual Load, 5-Yr MA metric tons metric tons 200 20 150 15 100 10 50 5 0 0 1980 1990 2000 2010 1980 1990 2000 2010 WCA 3 ENP FIGURE 4-3 Annual total phosphorus loads and five-year trailing moving averages of annual loads on individual components of the Everglades Protection Area.
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From page 107... ...
LNWR, WCA-2, WCA-3, and Everglades National Park (ENP) are protected by the water quality standards established in Florida's Administrative Code Chapter 62-302.540, but compliance with the phosphorus limits in the E verglades Protection Area is determined by two complex rules:
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. Compliance tests for Everglades National Park are based on flow-weighted mean concentrations in inflows to Shark River and to Taylor Slough and Coastal Basins.
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project (Reddy et al., 2005) showed similar spatial patterns in soil phosphorus concentrations in surface (0-10 cm)
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When the vegeta tion dies and decomposes, through the processes of peat accretion, the detrital material accumulates and the plant phosphorus is cycled back into the soil. Soil pore ater phosphorus concentrations in the nutrient-enriched areas are w approximately 10 times higher than water column phosphorus, creating steep concentration gradients (Koch and Reddy, 1992)
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. Based on this information, the committee judges that soil phosphorus may now be stabilizing, although more recent soil phosphorus analyses across a broad spatial scale would be needed to confirm this trend.
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will help to reduce soil phosphorus enrichment in soils. However, cattails are extremely efficient at recycling phosphorus from aging and dying plant materials, inhibiting the export of phosphorus from dense cattail stands, even under conditions of reduced phosphorus loads.
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. This spread is associated with elevated phosphorus loads and altered hydroperiods (Newman et al., 1996)
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) shows that existing high phosphorus concentrations in the soils of cattail marshes represent a source of phosphorus that will continue to impact downstream marshes even if canal phosphorus loading decreases substantially (see also previous section on soil phosphorus)
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raster iamge
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. FIGURE 4-10 Upper Taylor Slough surface water quality and weather monitoring sites.
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However, the committee estimated that the large internal reservoirs of soil phosphorus would lead to minor to moderate (rather than major) improvements in current trends.
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. Periphyton was once found abundantly in the Everglades ecosystem, with the largest expanses in WCA-3 and Everglades National Park (Gleason and Spackman, 1974)
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raster iamge reduced or even completely eliminated because of exposure to high phosphorus loads and, in some areas, replacement by dense cattails (McCormick and O'Dell, 1996; McCormick et al., 1996)
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. Analysis of periphyton m etrics in 2005 and 2006 demonstrated a general north to south trend of increas ing periphyton biomass and decreasing periphyton TP concentration over the Everglades Protection Area (Figure 4-12a)
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Predictions under Various Scenarios Continued or increased input of above-ambient phosphorus concentrations will both increase severity of enrichment effects near canals and cause p eriphyton deterioration effects to cascade downstream. In contrast, enhanced water treatment will promote periphyton recovery.
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, should be monitored in STAs, CHIP, and other manipulated settings. Fish Mercury Mercury contamination is a chronic environmental problem in the South Florida ecosystem.
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. These long-term declines in sulfate are linked to long-term declines in fish mercury concentrations.
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This spatial pattern reflects variations in the processes controlling fish mercury concentrations. Under high sulfate concentrations in waters adjacent to the EAA, as in the STAs, microbes produce high sulfide con centrations that inhibit the production and bioavailability of methyl mercury (Benoit et al., 2003)
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The two major drivers of fish mercury concentrations that might be affected by restoration management changes are: (1) agricultural sulfate inputs that control the production of methyl mercury and (2)
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, it is anticipated that fish mercury concentrations would decrease. With the restoration of sheet flow the interaction of water with wetlands will likely facilitate the removal of sulfate, thereby reducing methyl mercury formation and fish mercury concentrations.
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. Figure 4-16 ferentiated ridges from sloughs, and, in many cases, tree islands from sloughs.
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As long as sur raster iamge face water covers the peat, anaerobic conditions prevail within the soil profile, and peat accumulation outpaces peat oxidation. If the water table drops below the surface, air enters the portion of the profile above the water table and allows aerobic microbial oxidation of the organic matter to occur.
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Shark River Slough-Slough 137 Cs 1.3-5.4 Clark and Reddy (2007) Taylor Slough 210 Pb 3.0 Meeder et al.
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, with soil oxidation, subsidence, and peat fires as the causes. Upper and lower limits of peat loss between 1946 and 1996 show significant loss in northern WCA-3A, -3B, -2A and Northeast Shark River Slough in Everglades National Park (Figure 4-20; Scheidt et al., 2000)
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Figure 4-18 R02233 (Everglades 4) raster iamge slough and tree islands depend upon.
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Predictions under Various Scenarios Overall, accretion of organic matter in the central Everglades is very slow, and it takes centuries to accumulate significant amounts of organic matter under oligotrophic conditions (Table 4-2)
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If impoundments are not removed, and if a sloped water surface parallel to the sloped ground surface is not restored (i.e., sheet flow) , then the impounded portions of the remnant Everglades will remain on a trajectory to become a series of disjointed flat steps, without the slope necessary to sustain the ridge-and-slough landscape.
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. The ridge-and-slough terrain extended hundreds of miles from the sawgrass plains south of Lake Okeechobee to the end of Shark River Slough, covering about 1.5 million acres (McVoy et al., 2011)
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Ecosystem Trajectories Affected by Water Quality and Quantity 135 FIGURE 4-21 Two aerial views of ridge-and-slough topography in WCA-3A. Above, an example of a functional ridge-and-slough system from the central part of WCA-3A showing features with distinctive linear orientation reflecting flows.
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The growth of sawgrass or wet prairie vegetation in the sloughs as a result of consistently shallow water depths thus disrupts the entire ridge-and-slough process. Woody vegetation may invade ridges that are subject to long-term dry conditions.
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Figure 4-23 R02233 (Everglades 4) raster iamge
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Fixed teardrop-shaped tree islands are associated with topographical variations in the mineral substrate and extend from WCA-3 to Shark River Slough in Everglades National Park (van der Valk and Sklar, 2002)
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From page 139... ...
. Nevertheless, for Shark River Slough tree islands, water levels deep enough to protect the thin peat covering from both microbial oxidation and fires were critical to the elevated areas' ability to support woody species.
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The northern tree islands in WCA-3A have also become more vulnerable to fires than their southern counterparts. If water depths are substantially reduced for extended periods of time, then peat will oxidize, lowering the elevation of the island.
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. Hence, the detrimental effects of altered water depths and duration are expected to exceed the effects of water quality on tree islands.
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The Everglade kites are the only snail kites in the United States, and the population has been designated as endangered because of its limited distribution and declining numbers. The decline of the snail kite in South Florida reflects the degradation of the ecosystem on which it depends.
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These conditions and the accompanying loss of tree islands that serve as nesting sites might explain the lack of kite nesting in some former nesting areas, such as eastern WCA-3A (Figure 4-25)
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. WCA-2 has experienced extensive loss of the tree islands (Sklar et al., 2009)
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, and there have been a few nests there in some years and none in others. Some nesting has occurred in Everglades National Park, but the dry season water levels there tend to be too low.
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. CONCLUSIONS An assessment of the status and trajectories of 10 ecosystem attributes reveals that conditions for tree islands, ridge-and-slough landscape, snail
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From page 147... ...
The velocity, depth, and duration of water in the Everglades are important controlling factors for the distinctive terrain of the Everglades: tree islands, ridge-and-slough topography, and peat accumulations. These landscape components have been severely degraded by flow alterations during past decades.
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From page 148... ...
148 Progress Toward Restoring the Everglades ing and ultimately reversing declines of attributes that would take a long time to recover, particularly if other aspects of the restoration depend on them. Because of its focus on the remnant Everglades and accelerated planning, the Central Everglades Planning Project conceptually provides promise for rehabilitating the remnant Everglades.
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