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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 5 Lake Okeechobee and Its Place in the Restoration of the South Florida Ecosystem Lake Okeechobee (Figure 5-1) is at the heart of the hydrologic system, with connections to the east and west coasts as well as downstream to the southern Everglades. The lake was a critical part of the pre-drainage hydrology because it was a primary storage mechanism that modulated downstream flows by storing water in wet years and gradually releasing water during dry periods. After artificial connections to the St. Lucie Canal to the east and the Caloosahatchee River to the west, with a dike around its perimeter, the lake became a diversion point. Large amounts of water that once flowed southward were instead diverted to the ocean, and the lake became much less of a controlling factor for downstream flows to the south, while large, fluctuating flows to the Caloosahatchee and St. Lucie estuaries and the Lake Worth Lagoon have had adverse impacts on them (see Figure 5-2). In addition, the lake’s water quality has been degraded by the external loading of nutrients, especially phosphorus (Engstrom et al., 2006). As a result, although the lake is the largest potential natural source of storage for water in the system, its water cannot be delivered to the often-parched remnant Everglades ecosystem because today’s stormwater treatment areas (STAs) do not have the capacity to treat increased volumes of nutrient-enriched water. Changes in water quantity and degradation of water quality (Havens and Gawlick, 2005; Johnson et al., 2007) have also adversely affected the lake’s ecological value as a habitat for diverse biotic communities as well as the lake’s recreational value. As in many other complex water management problems (Alexander et al., 2007; Feldman, 2008), extensive research on the lake makes clear that water quantity and quality are inseparably intertwined and need to be considered together in planning and implementing restoration plans (James and Havens, 2005; RECOVER, 2007c). For example, increases in water level (quantity) directly affect the amount of submerged aquatic vegetation (SAV), which in turn allows phosphorus-rich sediments to be mobilized into the water column (quality) (Johnson et al., 2007). Although for organizational reasons water quantity and
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 FIGURE 5-1 Lake Okeechobee. SOURCE: Adapted from http://www.evergladesvillage.net/sat/everglades/thumbs.html. © International Mapping Associates. quality are considered separately in places in this chapter, readers should keep their close connection in mind. This chapter explores several facets of the management of Lake Okeechobee and the potential role it might play in the Everglades restoration. The chapter also includes a discussion of the downstream effects of the disturbed lake, including
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 FIGURE 5-2 Lake Okeechobee within the South Florida ecosystem. © International Mapping Associates. impacts on the estuaries that receive direct flows from it. Allowing the lake to function as the heart of the Everglades as it used to in the pre-drainage system requires large additional restoration efforts. Therefore, the final section of the chapter addresses current and proposed restoration efforts and discusses additional options for restoring the system.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 THE CONDITION OF LAKE OKEECHOBEE Lake Okeechobee presently is plagued by both high and, more recently, very low water levels as well as poor water quality. These conditions have adversely affected the lake’s structure and functioning. Water Quantity Lake Okeechobee receives most of its inflow from Central Florida via the flows of the Kissimmee River. Until the late 1800s and early 1900s, no canals connected the lake to the Caloosahatchee or St. Lucie estuaries to the west and east, respectively (Blake, 1980; Brooks, 1974; Parker, 1974, Parker et al., 1955). In the rainy season, the lake levels sometimes increased to 21 or 22 feet above mean sea level, and lake waters also flowed southward through the central body of the Everglades via overland flow when the lake exceeded these levels (USACE, 1999). In rainy periods, some lake water also flowed west through wetlands into Lake Hicpochee, which served as the headwaters of the Caloosahatchee (Steinman et al., 2002a). Thus, the lake was a major source of water storage and supply for the entire Everglades ecosystem during periods of high water. Also, the lake, its watershed to the north, and the ecosystem to the south transmitted water fairly slowly. As a result, the seasonality of water level fluctuations in the lake and its watershed and the severity of most dry and wet periods in the ecosystem was considerably reduced compared to today’s system (Beissinger, 1986; NRC, 2005). The condition of Lake Okeechobee today differs distinctly from its historical condition. Lake Okeechobee has undergone major modifications; primary among these was diking that began with a small earthen dike in the 1910s, was expanded in the 1930s along the south shore of the lake, and gradually strengthened until the current Herbert Hoover Dike was completed in the 1960s (Blake, 1980; Brooks, 1974; Parker, 1974, Parker et al., 1955). The construction of the dike restricted the ability of the lake to expand in response to wet periods and reduced the total storage capacity of the lake. Today, the lake functions as a regional reservoir whose inflows and outflows are regulated based on water supply, flood control, and environmental needs (see Box 5-1). The area of the lake varies from about 300,000 acres at its historical low water level to about 470,000 acres (more than 730 square miles) when water levels reach 20 feet above mean sea level. When the lake is at an elevation of 9 feet, a very low level, it contains about 1.75 million acre-feet (MAF) of water; at the upper end of current operating policy of 17 feet, storage is about 4.8 MAF. Each additional
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 FIGURE 5-3 Elevations of Lake Okeechobee surface 1912–2006. SOURCE: Daily water level data for April 12, 1912–May 22, 2008, accessed at http://waterdata.usgs.gov/nwis/nwisman/?site_no=02276400&agency_cd=USGS. foot of elevation above 17 feet adds about 425,000 to 525,000 acre-feet of storage, up to 26 feet elevation (Abtew et al., 2007). Natural lake functioning was also altered by the establishment of new connections to the east via the St. Lucie Canal and to the west via a canal to the Caloosahatchee River, and the construction of levees, water control structures, and locks (Rogers and Allen, 2008). Large releases of water that are frequently made through canals to the Caloosahatchee and St. Lucie estuaries during wet periods are adversely affecting the vitality of those ecosystems (as discussed later in this chapter). Water levels are currently maintained at much lower levels than historical levels. The U.S. Army Corps of Engineers (USACE) estimated that before the first dike was constructed, the lake had a mean stage of 20.5 feet (USACE, 1999), but today the USACE aims to maintain the water level at about a 12-foot elevation to protect the integrity of the Herbert Hoover Dike (USACE, 2006). A 1999 report showed that at an elevation of 18 feet, 3 of the 13 components of the dike are
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 BOX 5-1 Average Annual Water Budget for Lake Okeechobee The lake is fed from several watersheds north and west of the lake and the Everglades Agricultural Area (EAA) (see Figure 5-2). Total stream-flow input to the lake averages 1.62 million acre-feet (MAF) (based on data between 1965–2000), with an additional 1.67 MAF direct rainfall input resulting from an annual average rainfall of about 50 inches (4.2 feet) per year over the lake (see Figure 5-4). However, precipitation is more than offset by evapotranspiration, which amounts to 2.09 MAF per year. Not considering evapotranspiration, total outflow is 1.43 MAF, 29 percent of which is discharged to the Caloosahatchee River (as regulatory discharges and environmental releases), 12 percent to the St. Lucie River (as regulatory discharges and environmental releases), 7 percent to the lower east coast (as regulatory discharges), and 4 percent to the Water Conservation Areas (as regulatory discharges). Water supply applications (mostly agriculture) in these basins receive 38 percent of the outflows from Lake Okeechobee, and the remaining 10 percent is accounted for in other outflows. Inflows and outflows are highly variable within annual periods and from year to year. FIGURE 5-4 Average water balance of Lake Okeechobee based on the current Lake Okeechobee Regulation Schedule (LORS) and precipitation data from 1965–2000. NOTE: All flows are in thousands of acre-feet. Diagram depicts all flows greater than 0.1 percent of the total water budget (including evapotranspiration), with the exception of 141,000 acre-feet in “other outflows.” These other outflows include flow to small basins around the lake, the Seminole Tribe, and the Florida Power and Light Reservoir. SOURCE: Data from J. Obeysekera, SFWMD, personal communication (2008).
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 classified as hazardous, with high probabilities of failure; at 21 feet, 8 of the 13 are hazardous, with 4 having probabilities of failure of 0.89 or higher; and at 26 feet, 11 of the 13 are hazardous, with 7 virtually certain to fail (USACE, 1999). In 2000, the U.S. Congress authorized the USACE to rehabilitate the dike, and initial construction of a 4.6-mile section of the 140-mile-long dike began in 2005. Completion of all improvements is scheduled over a 25-year period (USACE, 2006), contingent on congressional appropriations. Water Quality Historically, water flowing into Lake Okeechobee came primarily from the Kissimmee River, whose extensive wetland floodplain filtered nutrients from the water. This kept nutrients at extremely low concentrations throughout the system, particularly with respect to phosphorus, the contaminant of greatest concern. The extensive spread of agriculture in the upstream drainage basins, plus the channelization of the river and the creation of canals conveying storm-water from agricultural areas directly to the lake, resulted in high phosphorus loads to the lake (Engstrom et al., 2006). A large proportion of phosphorus loaded to the lake accumulated in sediments. The role of phosphorus as a controlling factor in eutrophication of freshwater ecosystems has been recognized for several decades. High phosphorus concentrations in the lake adversely impact biota by altering the structure and functioning of both the lake and downstream ecosystems. The overall increase of phosphorus loading in the past decades has resulted in conversion of a phosphorus-limited system to a nitrogen-limited system. This has resulted in many changes in the lake, including increased frequency of algal blooms and an increasing abundance of nitrogen-fixing cyanobacteria (Havens et al., 2007). Unless phosphorus in Lake Okeechobee’s water can be reduced, there are serious constraints to discharging large volumes of water to the south for use in Everglades restoration. The phosphorus problem is exacerbated because much of the phosphorus accumulates in soils, ditches, wetlands, and lake bottoms where it can remain for a long time; such stored phosphorus is often referred to as legacy phosphorus. Legacy phosphorus is problematic both in the Lake Okeechobee watershed and in the lake itself, because the soil- and sediment-associated phosphorus can serve as steady sources of phosphorus to the water column. When it does so in the watershed, it contributes to the external phosphorus load to the lake; when it does so in the lake, it creates an internal phosphorus load to the lake water. The effects of legacy phosphorus on water quality can last several decades.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 External Phosphorus Loads Most of the current external phosphorus load to Lake Okeechobee comes from agricultural and urban activities in the watershed. Phosphorus is added to uplands in fertilizers, organic solids (e.g., sewage sludge, animal wastes, composts, crop residues), wastewater, and animal feeds. South Florida uses approximately 50 percent of the phosphorus fertilizer imported into the state of Florida (Reddy et al., 1999). Some of the phosphorus is exported from the drainage basin as agricultural products (i.e., harvested biomass), but a significant amount of the phosphorus applied to the land ends up in upland soils and sediments of ditches and streams, and a portion is then transported by river flow to the lake, where it accumulates in lake sediments (Engstrom et al., 2006) and contributes to eutrophication. The Lake Okeechobee watershed consists of approximately 3.5 million acres, and primary land cover/land uses include: natural areas such as wetlands (37 percent), improved and unimproved pastures (20 and 4 percent, respectively), sugarcane (12 percent), citrus (7 percent), and urban use (11 percent) (SFWMD and FDEP, 2008a). The export of phosphorus to Lake Okeechobee was exacerbated by the channelization of the Kissimmee River in the 1950s and 1960s and the transport of large volumes of phosphorus-laden sediments. Approximately 10 percent of the phosphorus imported into the Okeechobee basin is eventually exported into the lake, although current estimates are based on limited data sets. The residual mass and annual load from legacyphosphorus in the watershed is not currently quantified (Reddy et al., 1996; SWET, Inc., 2008a, 2008b). A total maximum daily load (TMDL) of 140 metric tons (mt)1 of phosphorus per year was established for Lake Okeechobee using a goal of phosphorus concentration in Lake Okeechobee of 40 ppb (FDEP, 2000). Based on modeling studies, the Florida Department of Environmental Protection (FDEP) selected 40 ppb as a threshold concentration in nearshore waters for preventing imbalance in the composition of biotic communities (Havens and Walker, 2002). An estimated 35 mt per year of the load is atmospheric deposition (primarily as dust), leaving a target of 105 mt per year as the waterborne TMDL. Average total waterborne phosphorus loads to Lake Okeechobee in the past 5 years were 630 mt per year—six times greater than the target waterborne TMDL. The recent loads represented a decline from the previous 5-year average of 715 mt, largely due to the drought in 2007 when the total phosphorus load to the lake was 203 mt (Figure 5-5). Over the past 5 years, the average phosphorus concentration in the lake water column has been 179 ppb—4.5 times the target concentration (SFWMD and FDEP, 2008a). Intensive phosphorus-management strategies are 1 One metric ton equals 2,200 pounds.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 FIGURE 5-5 Annual phosphorus loads into Lake Okeechobee between 1981 and 2007. SOURCE: Data for 1974–2005 from James et al. (2006); data for 2006–2007 from James and Zhang (2008). needed to reduce loads from the basins and meet the current TMDL of 140 mt of total phosphorus in Lake Okeechobee by 2015. Internal Phosphorus Loads Excessive external phosphorus loads to the lake have accumulated in mud sediments in the center of the lake (Figure 5-6), and they create the current internal phosphorus loads to the lake water column. The phosphorus-rich mud sediment in Lake Okeechobee covers an area greater than 197,684 acres (40 percent of the lake bottom) and has a volume of approximately 162, 142 acre-feet. Currently, there are nearly 30,000 mt of phosphorus that have accumulated in the upper 10-cm of these mud sediments (Fisher et al., 2001; see Figure 5-6), representing approximately 60 years’ worth of external phosphorus loads. Phosphorus accumulated in sediments shows a dramatic increase in loading, beginning about 1950, coincident with elemental tracers of phosphate fertilizers (Engstrom et al., 2006).
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 FIGURE 5-6 Lake Okeechobee showing the location of fine mud sediments on the lake bottom that can be resuspended by hurricanes and other wind events. SOURCE: Adapted from Fisher et al. (2001). Internal loads of phosphorus to Lake Okeechobee’s water can be substantial (approximately 200 mt per year) and comparable to external loads (Fisher et al., 2005). These internal loads occur through diffusive flux of phosphorus from sediments to overlying water and during resuspension of surface sediments into the water column during wind events. After three hurricanes (Frances, Jeanne,
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 and Wilma) moved directly over the lake in 2004 and 2005, sediments became resuspended, and nutrient budgets showed that these sediments became a source of phosphorus to the lake water rather than a sink. Resuspension of sediments also creates turbidity in the lake and prevents light penetration, resulting in poor establishment of SAV. In most hypereutrophic lakes, the bottom sediments are largely derived from deposition of planktonic materials, and the sediments are highly organic in nature. In contrast, one of the sources of Lake Okeechobee’s bottom sediments is clay mineral matter derived from the Kissimmee River basin, and these low-density colloidal materials are easily redispersed following wind-driven mixing events and settle very slowly (Harris et al., 2007), which could have long-term impacts on water quality. The origin and composition of the existing mud sediments and current sediment loads are pertinent to phosphorus management in the lake. At present, sediments delivered to the lake contain magnesium silicates. These colloidal sediments remain suspended in the water column for long periods. This may decrease the longevity of prospective dredging benefits by maintaining resuspended sediments in the water column. Also, the concentration of calcium in the water column can affect flocculation of suspended particles. At this time, very little is known about the reactivity of suspended particles with respect to phosphorus release and retention and the role of altered water chemistry on sediment resuspension. Implications of Legacy Phosphorus Once the external phosphorus loads from uplands are curtailed through the implementation of best management practices (BMPs) and other phosphorus management strategies in the drainage basin, the critical question concerns how the lake will respond to reduction of the external phosphorus load (Havens et al., 2007). Legacy phosphorus will continue to leach into the water even after other external loads have been reduced, extending the time required for the lake to meet environmental goals (Fisher et al., 2005). Given these conditions, how long will it take for Lake Okeechobee to reach background or alternate stable conditions? For example, in Lake Okeechobee, phosphorus accretion rates have increased about fourfold since the 1900s (from about 0.25 g P/m2/year before 1910 to 0.85 g P/m2/year in the 1980s; Brezonik and Engstrom, 1998), and most of that increase occurred since the 1950s (Engstrom et al., 2006). Although accretion of sediment-bound phosphorus suggests that particulate phosphorus flux is downward (i.e., from the water column to sediments), the dissolved reactive (bioavailable) phosphorus flux is upward (i.e., from sediments to the water column) in response to concentration gradients established at the sediment-water interface (Reddy et al., 2007). Average phosphorus flux from sediments is estimated
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 balance analysis should be done for water and total phosphorus, as well as other critical contaminants that impact the Everglades ecosystem (i.e., sulfur, mercury, nitrogen). The transport and cycling of elements (e.g., phosphorus, carbon, sulfur) are generally closely coupled with one another (e.g., inputs of sulfur influence the transport and fate of phosphorus and mercury), and thus comprehensive material balances of contaminants of concern and associated major constituents will provide insight on ecosystem response to perturbations. Increasing Water Storage A fundamental premise of the CERP is that significantly increased water storage is needed to improve the condition of the South Florida ecosystem, including Lake Okeechobee, the estuaries, and the remnant Everglades ecosystem. As discussed previously in this chapter, modifications to the system (e.g., levees, canals, lake operations) have reduced the amount of water stored naturally in the ecosystem. As a result, some parts of the ecosystem are water starved while other parts are submerged, and the natural timing and amplitudes of highwater and drying events have been severely disrupted. Construction of storage for water in the Lake Okeechobee region is the single largest component of CERP and is proposed primarily in two forms: surface reservoirs and aquifer storage and recovery (ASR) wells. The Yellow Book plan proposed to provide approximately 5.5 MAF of new water storage, of which approximately 4 MAF can be attributed to ASR systems (assuming 30 percent injection loss) (NRC, 2005). ASR pilot projects are currently under way to address technical feasibility issues associated with ASR (NRC, 2001, 2002a). Two ASR pilot project systems have been constructed and are about to begin cycle testing. “To date, no ’fatal flaws’ have been uncovered…that might hinder the implementation of CERP ASR” (SFWMD and USACE, 2008), but the final technical ASR program assessment based on the operation of the pilot systems is not anticipated until 2012. The high costs of ASR, however, have caused SFWMD leaders to publicly question the scale of the proposed ASR effort (King, 2008). The ASR contingency plan still has not been completed, and therefore, discussions of alternative water storage options have been repeatedly postponed until this document is released. Meanwhile, some stakeholders question whether the CERP, even with ASR, provides sufficient storage to support rehabilitation of the estuaries and Lake Okeechobee, given uncertainties in future climate and precipitation patterns (Audubon of Florida, 2007).
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 Early CERP Storage Projects A number of CERP projects that are designed to increase water storage and benefit Lake Okeechobee and the northern estuaries are under way. The C-43 Basin Storage Reservoir (Figure 3-2, No. 1) (170,000 acre-feet)is intended to improve the quantity and timing of freshwater flows to the Caloosahatchee Estuary by holding water to avoid excessive discharges and releasing water to maintain salinity gradients in the estuary. The C-44 Basin Storage Reservoir (Figure 3-2, No. 8) (50,600 acre-feet) and STA are components of the larger Indian River Lagoon-South restoration project and are designed to decrease and attenuate excess water flow and reduce the salinity impacts on the St. Lucie Estuary. A 6,300-acre STA will capture and treat some or all of the discharge from the reservoir before it enters the St. Lucie Canal and flows to the St. Lucie Estuary and Indian River Lagoon. The Indian River Lagoon South project (Figure 3-2, No. 8) will provide 195,000 acre-feet of water storage in four reservoirs and three natural storage areas to benefit the St. Lucie Estuary. The project also includes STAs and habitat restoration initiatives (e.g., muck removal in the estuary), described in Box 3-1. The North Palm Beach County project (Figure 3-2, No. 13) includes a water storage reservoir (48,000 acre-feet), intended to improve the timing and deliveries of flow to the Lake Worth Lagoon and Loxahatchee Estuary, enhance hydroperiods in the Loxahatchee Slough, and increase base flows to the North-west Fork of the Loxahatchee River. This project also includes habitat restoration and water treatment components. Site 1 Impoundment (Figure 3-2, No. 2) (13,280 acre-feet) is intended to reduce water demands on Lake Okeechobee and the Arthur R. Marshall Loxahatchee National Wildlife Refuge. The Everglades Agricultural Area Storage Reservoir, Phase 1 (Figure 3-2, No. 14) (190,000 acre-feet) is expected to moderate high stages in Lake Okeechobee and discharges to the estuaries. These projects are among those scheduled for early implementation in the CERP (see Figure 3-2 for project locations). The C-43 and C-44 reservoirs, the EAA Phase 1 Reservoir, and the Site 1 Impoundment projects were all included under the state of Florida’s Acceler8 program. Also, the L-8 reservoir in the North Palm Beach County project was expedited by the state under a separate initiative. Construction is under way on the C-44 reservoir, the EAA Phase 1 Reservoir, and the L-8 reservoir (status reports for these projects are provided in Table 3-1). The
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 Indian River Lagoon-South and the Site 1 Impoundment projects were congressionally authorized in the 2007 Water Resources Development Act. A number of issues have emerged as a result of technical review and stakeholder input with regard to the degree to which the CERP projects will achieve restoration goals. First, the storage capacity of the CERP plan, including ASR, is not large enough to detain peak freshwater discharges—such as resulted from the hurricanes of 2004 and 2005—sufficiently so as to prevent impacts from high flows into the estuaries. The impacts of excessive freshwater discharges to the estuaries could be further alleviated if more of the Lake Okeechobee outflow were allowed south through the EAA to the southern Everglades. However, as discussed previously, this is constrained by seepage management issues and water quality requirements in the Everglades, as well as flow capacity into Everglades National Park as facilitated by the Modified Water Deliveries to Everglades National Park (Mod Waters) project (see Chapter 4). Also, unmanaged flows from the Caloosahatchee watershed rather than from Lake Okeechobee may be significant (Figure 5-7) and may require additional efforts by landowners to store water. Second, there may be conflicts between human and environmental demands on these water storage reservoirs once they are operational. During dry seasons and droughts, demands to deliver fresh water from the reservoirs for agricultural and municipal water uses may result in inadequate flows to the estuaries to maintain desired salinity gradients or inadequate lake levels to support the lake biota. Meeting those human demands may come at the expense of meeting environmental freshwater requirements (see Chapter 2). Also, several of the reservoirs are intended to support recreational uses, including boating and fishing. Once established, recreational users may oppose management actions, including water level fluctuations and drainage, required to achieve environmental benefits. Finally, the water quality of this new water and potential adverse effects on the ecosystem need to be carefully considered. STAs are not included for the C-43 reservoir as they are for the Indian River Lagoon-South reservoirs. This deepwater reservoir is not expected to reduce phosphorus or nitrogen concentrations greatly because of its lack of macrovegetation, frequently limited residence time, and susceptibility to sediment resuspension; thus, nutrient loading to the Caloosahatchee Estuary may exceed that needed to achieve water quality objectives. A third draft of the EAA Reservoir Phase 1 project is now in development, primarily due to inadequate plans to address the water quality implications of the reservoir on the Everglades ecosystem.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 Changes in Lake Operations The USACE manages water levels in Lake Okeechobee through operation of a series of structures that can release water to the Caloosahatchee Estuary to the west, the St. Lucie Estuary to the east, and to outlet canals to the south of the lake. Safety concerns regarding the Herbert Hoover Dike, combined with high lake levels over the period 2003–2005, led to a number of damaging high water releases to the estuaries. Therefore, the USACE launched a review of the lake operating rules (called the Water Supply and Environmental [WSE] regulation schedule), which were adopted in 2000 and based on a historically drier time period. Given the constraints on lake water discharges, there is a limited range of options for modifying the operating policy. Large releases to the Everglades ecosystem will be possible only with the appropriate conveyance and seepage management structures in place and reduced phosphorus concentrations, either from additional STAs or improvements to lake water quality. In the Lake Okeechobee Regulation Schedule Study, several alternatives were evaluated using the South Florida Water Management model, with 36 years’ worth of historical records. The model was used to calculate stage duration curves (relative frequencies at which the lake is at or below stages varying from 8 to 18 feet) for a range of alternatives and compared to the WSE (No Action). At all relative frequencies, all of the proposed alternatives resulted in about a 1-foot decline in surface elevation compared to the WSE, thus reducing the total storage capacity of the lake by about 450,000 acre-feet. The alternatives had a positive effect on low flows to the estuaries, but they had no impact on very high flows (Table 5-4) (USACE, 2007b). As a result of this study, a new regulation schedule was approved by the USACE in April 2008, and a new operation regime is now being implemented for an interim period. The new operation schedule consists of complex decision tree where releases are governed by hydrologic conditions at selected locations throughout the system. The new schedule incorporates improved climate fore- TABLE 5-4 Comparison of the Frequencies of Flows into the Caloosahatchee Estuary under the Lake Okeechobee Regulation Schedule and the “No Action” Alternative for a 36-Year Simulation Ranges of Flow (cfs) No. of Months in Flow Ranges No Action Tentatively Selected Plan < 450 198 131 450–2500 160 237 2500–4500 45 35 > 4500 29 29 SOURCE: http://www.saj.usace.army.mil/cco/docs/lorss/LORSS_PM_Pres-6Aug07.pdf.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 casts as part of decision trees, and it allows longer and lower rates of release to the WCAs and the estuaries to reduce the impact of sudden pulse releases. Water Storage in the Northern Everglades The preferred plan for the Northern Everglades and Estuaries Protection Program includes water storage capacity ranging from 0.9 to 1.3 million acre-feet, including three reservoirs upstream of the lake, three large reservoir-assisted STAs, and a variety of other storage projects. The plan (SFWMD et al., 2008), however, does not provide full details on all the potential projects. Three non-CERP storage projects are described, with a combined volume of 441,000 acre-feet; three reservoir assisted STAs, with a capacity of 474,000 acre-feet, are listed in Table 5-4; and a variety of other specific projects have a combined capacity of 102,000 to 139,000 acre-feet. The balance of 250,000–280,000 acre-feet is not specified. Only 29 percent of the total storage capacity in the plan was represented by management measures with the highest level of implementation certainty (Level 1; see Table 5-1). Sixty-nine percent of the remaining planned storage capacity reflects Level 4 management measures with low implementation and projected benefits certainty. The Northern Everglades Regional Simulation Model was used to examine the effects of the alternative plans on flows in the watershed compared to current base conditions and future base conditions without additional reservoirs. If these projects in the preferred plan are realized, there would be substantial improvement in all performance measures listed relative to current and future base conditions without those projects (Table 5-5). Synergistic Opportunities from the Repair of the Herbert Hoover Dike As discussed in the previous section, concerns about the structural integrity of the Herbert Hoover Dike currently limit the capacity to store water at higher stages in Lake Okeechobee, which creates more frequent high and damaging discharges to the northern estuaries. Optimal lake levels, however, are also determined by the desire to enhance conditions for lake biota and protect the lake’s littoral zone. Nevertheless, rehabilitation of the Herbert Hoover Dike may offer synergistic opportunities for creating additional CERP storage and managing water levels for the benefit of the littoral zone, and the costs, benefits, and hydrologic and ecological viability of these options should be considered in any analysis of CERP storage alternatives. Alternative Dike Configurations. Localized outward movement of the Herbert Hoover Dike was considered in the Yellow Book but not adopted. The concept
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 TABLE 5-5 Performance Measures for Water Quantity Target Current Base Future Base Preferred Plan Lake Okeechobee (percent of the time) Extreme Low Lake Stage 100 91.7 94.1 99.1 Extreme High Lake Stage 100 83.6 87.9 95.4 Below Envelope—Weekly Average 100 61.0 66.0 89.2 Above Envelope—Weekly Average 100 58.0 65.9 80.3 Caloosahatchee Estuary (number of months out of 432) Mean Monthly Flow > 2,800 cfs 3 82 55 51 Mean Monthly Flow > 4,500 cfs 0 38 25 18 Number of months Lake Okeechobee regulatory releases >2,800 cfs 0 21 13 9 Mean Monthly Flow < 450 cfs 0 90 32 18 St. Lucie Estuary Mean Monthly Flow > 2,000 cfs and < 3,000 cfs 0 37 38 33 Mean Monthly Flow > 3,000 cfs 0 28 21 18 Mean Monthly Flow < 350 cfs 31 134 26 15 Water Supply (percent of target) Annual Percent Demand not Met (%) 0 4.7 4.2 2.4 Lake Okeechobee Service Area Mean Annual Percent Demand Not Met (%) 0 4.4 4.6 1.5 SOURCE: Data from SFWMD et al. (2008). entails moving the dike outward in some locations so that the littoral zone can also move and support essential biotic functions in a different location of the lake. After all, the littoral zone did not exist at its current location historically; rather, it developed based on the management of the lake at lower water levels. An expanded dike configuration, if politically and societally feasible, could allow the lake to function at higher water levels once the dike has been rehabilitated. Although this committee makes no recommendations on this option, it echoes the advice of an earlier NRC committee (NRC, 2005) to keep an open mind about various water storage options, especially if current plans for storage are more expensive or less effective than expected. Establishing a Flow Way. One option that has long been considered, and often rejected to date, is the concept of a flow way, a direct connection between Lake Okeechobee and WCA-3A to the south. With cost and feasibility of ASR still an issue, the flow way continues to appear among options for transporting water
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 and has considerable advocacy among some environmental groups (e.g., A.R. Marshall Foundation, 2007). The concept involves “natural” flow of water south of Lake Okeechobee, through some areas of what is currently the EAA. Assuming a wetland environment, some water quality benefits might also accrue, although this would depend on the water depth. Some of its advantages and disadvantages as evaluated by this committee are outlined in Table 5-6. A major technical challenge is that subsidence and oxidation of peat have altered the historic land surface gradient between Lake Okeechobee and the WCAs, and some form of water management structures, including pumps, may be necessary to move the water through the region. If pumping is minimized, the storage areas themselves would need to be quite deep, functioning essentially like reservoirs. Perhaps the primary objection raised by agency evaluations is that a hydraulically unmanaged flow from the lake to the WCAs “would not be present in dry or even normal years” (USACE and SFWMD, 1999). The Yellow Book conclusion is that “The need for flow ways would have to be justified for other reasons rather than hydrology alone.” The A.R. Marshall Foundation (2007) argues that one such reason, apart from reestablishing the historic flow pathway, is that the flow way would be cost-effective relative to ASR by providing storage for large quantities of water in the subsided lands between the lake and the south. Of course, this assumes that a flow way, considering evapotranspiration losses, would provide storage equivalent to ASR. The biggest and most-often cited impediment to a flow way was the sociopolitical task of obtaining land for this project that is currently in agricultural and urban use, but this hurdle might now have been greatly reduced with the announcement by the state of Florida that it is negotiating the potential acquisition of 187,000 acres of U.S. Sugar Corporation land in the EAA just south of Lake Okeechobee. CERP planners now have an opportunity to consider restoration alternatives that previously were unavailable (e.g., vastly increased STAs, additional surface storage, increasing flow from Lake Okeechobee to the Everglades ecosystem during wet periods). These restoration opportunities would not be available if other kinds of development replaced agriculture as a primary land use in the EAA. Any reanalysis of the CERP should consider ways to optimize the restoration program and make it more cost-effective, while weighing the impacts of any associated trade-offs. The high costs of rehabilitating the Herbert Hoover Dike have led to suggestions that a spillway at some as-yet-undetermined lake level could negate the need for extensive dike repair. Flows discharged out of such a spillway might logically enter a flow way, although it is unclear as to the degree to which such flows could be integrated into CERP storage and conveyance needs, given the current water quality issues in Lake Okeechobee. CERP agencies continue to
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 TABLE 5-6 Positive and Negative Characteristics of a Flow Way Characteristic Advantages Disadvantages Ecosystem processes Creates hydrologic connection from the Northern to the Southern Everglades. Transports low-quality water south into the Everglades. Increases water storage capacity of the natural system. Reduces water quantity through additional ET from standing water in flow way. Mimics historic water flow path. Requires land currently in agricultural production. May provide option for treatment as it flows, hence acting in part as an STA. Water in flow way will likely be deep over most of its path if pumping costs are minimized. While sedimentation may be enhanced, wetlands vegetation growth may be inhibited. May increase habitat area available for certain species under wet and dry conditions. Actual design is uncertain. May not be “miles wide,” but rather more like a very wide canal. Contributes to “true” restoration of the Everglades. Good public perception. Potentially high releases to the flow way would reduce or eliminate damaging releases to the estuaries. Hydrologic issues Gravity feed from Lake O. to the WCAs. Gravity feed hampered by subsidence in EAA. Greatly altered topography from early 1900s. Will likely require pumps to get water out. Water flows “naturally.” Current conveyance system with pumps and hydraulic structures offers flexibility in operations. Lake O. dike renovation may offer opportunity for synergistic connection with “the spillway,” including opportunities for costsharing. May require compartmentalization of flow way into “boxes” in order to reduce wind fetch and wave setup and resultant threat to levee integrity and freeboard. Water may seep out of constraining levees into remaining EAA. Financial costs Cost analysis not done, but might reduce need for some currently planned CERP storage and/or additional STA construction. Cost of attaining additional EAA land is not documented. Alternative ASR life-cycle costs, including energy, may be more than capital and O&M costs of flow way. Flow way may have a smaller “carbon footprint.” Will require displacing communities and people at upstream end. Opportunities for cost sharing with HHD renovation.
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 provide negative evaluations of the technical feasibility and cost-effectiveness of a flow way compared to current CERP plans, despite new potential cost benefits associated with the rehabilitation of the Herbert Hoover Dike (e.g., Strowd and Punnett, 2007). CONCLUSIONS AND RECOMMENDATIONS Lake Okeechobee is a critical linchpin of the South Florida ecosystem. However, the lake presently is plagued by both high and, more recently, very low water levels as well as poor water quality, especially phosphorus, that have affected its structure and functioning. The challenges of water quantity and quality in the lake have important ramifications for the entire ecosystem because the lake supports important elements of the region’s biota, and it also has the potential to serve as a major source of water storage and water supply for downstream ecosystems. This potential will become more critical if other planned and proposed sources of water storage do not become available. An integrated, system-wide view of water quality management is essential to the achievement of restoration goals for the South Florida ecosystem. Good data are available for study to understand the local dynamics of phosphorus and other contaminants, but a system-wide accounting is lacking for water and phosphorus as well as other important contaminants, such as sulfur, mercury, and nitrogen. An integrated system-wide accounting in various components of the basin (including soils, sediments, vegetation, and water) is needed to determine the mechanisms of contaminant transport throughout the ecosystem—from the Kissimmee River to Everglades National Park—to assess the implications of upstream ecosystem changes on downstream habitats, to determine appropriate management actions, and to evaluate system-wide progress to improve water quality. It also is crucial to determine to what degree the current status of the lake represents a changed condition that will resist restoration. Recent water quality restoration initiatives in the Northern Everglades are not likely to achieve the stated water quality goals (40 ppb total phosphorus in the lake and 140 metric tons per year phosphorus input load) by the year 2015, and it might take decades for these goals to be met with current strategies. Using the “no-action alternative” to manage internal phosphorus loads in the lake is likely to delay achieving in-lake concentration goals by several decades, as concluded by the South Florida Water Management District. Also, although the Northern Everglades initiative’s technical plan identifies numerous management measures to reduce phosphorus loads and appropriately assesses the challenges and uncertainties in the proposed plan, the strategies probably are not adequate to reduce external phosphorus loads sufficiently. The Northern
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 Everglades initiative is appropriately focused on reducing phosphorus inputs to the lake as an initial step, but given the uncertainties associated with the current management measures, this committee judges it unlikely that the current TMDL of 140 mt of phosphorus input to the lake will be met by the year 2015. More significant remediation strategies in the lake and its watershed will probably be needed to reduce the legacy phosphorus in the system and meet the TMDL goal. Although the Northern Everglades plan represents a sizable effort, it will not be easy or inexpensive to reverse the lake’s decline in water quality. One of the greatest challenges to this program may be securing the necessary funding to fully implement the initiative. The lake’s importance in the ecosystem, however, justifies significant attention from researchers and planners and justifies the devotion of considerable resources to the lake. In the near term, restoration planners should consider the consequences of the likely failure to achieve the phosphorus goals and develop alternative approaches. Alternatives may involve significant reallocation of priorities among restoration projects and/or significant changes to water quality criteria for downstream deliveries. One structural option is to increase the number and size of STAs. Given questions concerning the long-term effectiveness of STAs in phosphorus removal, the current phosphorus loadings to the STAs suggest that their current configuration will be insufficient to achieve the 10 µg/L phosphorus criterion in the Everglades Protection Area. Meanwhile, failure to achieve the water quality goals in Lake Okeechobee will affect the condition of the lake and the northern estuaries, and it will reduce the amount of additional water that can be delivered to the Everglades ecosystem. Alternative approaches to addressing these water quality issues may involve significant reallocation of priorities among restoration projects. Restoration planners should carefully consider the needs for additional STAs, considering the opportunities that may be made available by the state’s potential land purchase in the Everglades Agricultural Area. In addition, methods of improving the long-term ability of STAs to remove phosphorus should be investigated. In-lake treatment of phosphorus may also be needed to expedite the rehabilitation of Lake Okeechobee as external loads are reduced. Given concerns about the financial and technical feasibility of aquifer storage and recovery (ASR) at the large scale proposed in the CERP, additional opportunities for water storage should be investigated, and Lake Okeechobee may be an important component of those alternatives. Several important water storage projects are under development through the CERP and Acceler8, largely intended to modulate flows to the northern estuaries, and additional opportunities for water storage upstream of Lake Okeechobee are being considered within the Northern Everglades initiative. Nevertheless, alternative storage options
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Progress Toward Restoring the Everglades: The Second Biennial Review - 2008 should be considered as possible contingencies to ASR—the primary source of new water storage for the CERP, but for which there are concerns about financial and technical feasibility—including synergistic opportunities related to modifications of the Herbert Hoover Dike. This committee makes no specific recommendations as to the most appropriate storage options, but it encourages CERP planners to consider a wide array of alternatives and their costs and benefits. Short-term and long-term trade-offs will be needed in the rehabilitation of Lake Okeechobee and northern estuaries. Moving appropriate volumes of water south into the Everglades and managing flows into the northern estuaries may pose conflicts with sustaining adequate water levels for the lake biota and other in-lake goals, and until the Herbert Hoover Dike is rehabilitated, the risk of its failure at high lake levels will constrain options. Given the current altered state of the whole system, goals for the lake, the northern estuaries, and other downstream interests might not be mutually compatible in all respects. As a result, trade-offs will have to be made. Modeling and adequate, reliable data will be needed to evaluate many of these trade-offs as discussed in NRC (2005) and Loucks (2006).