Re-Engineering Water Storage in the Everglades: Risks and Opportunities (2005)

The planning framework, boundary conditions, and planning constraints that are found in the Restoration Plan are themselves the result of a process of adaptation to the interests and concerns of the myriad stakeholders in south Florida. The constraints and conditions that emerged during the initial stages of planning were necessary to allow the project to move forward. The committee is concerned, nevertheless, that at some future time circumstances may evolve in ways that will require reconsideration of these initial boundaries and constraints if the project is ultimately to be effective and successful.

A project the size of the Florida Everglades Restoration Project will be subjected to many surprises, some caused by exogenous forces and some the consequence of the project itself. As noted earlier, project planners will need to create adaptive plans that will allow considerable flexibility in responding to unanticipated change. There are two important lessons that should guide the efforts at adaptive planning. First, it seems obvious that there will be many changes that cannot be anticipated and that will have to be accommodated through adaptations with relatively short lead times. This means that it will be vitally important to deal with changes that can be anticipated in a timely and proactive way so as to minimize surprises and retain maximum flexibility to respond to change that cannot be anticipated. The progressive loss of soil in the Everglades Agricultural Area is an example of a change that can be anticipated and should be planned for promptly as the project develops. Second, in responding to change, it may be necessary to rethink and reconsider some of the boundaries and constraints that were part of the early planning and now characterize the planning framework.

Mayer (2001) provided a useful discussion of interactions among policies unrelated to the Everglades restoration, economics, and the choice of storage options in south Florida. It simply may not be possible to protect all of the existing interests and conditions or to proceed with the project while preserving certain hydrologic and social features of the landscape in south Florida that were initially thought to be worth preserving. One example is Lake Okeechobee. The intent of existing plans is to continue to manage Lake Okeechobee in accordance with the prevailing hydrologic performance indices that govern the lake level and thereby tend to protect the existing littoral zone. This will severely constrain the extent to which Lake Okeechobee might be used for storage. With time and change, it could turn out that the only way to complete the project as envisioned would be to use Lake Okeechobee for additional storage and possibly sacrifice, to some extent, the continued preservation of the current littoral zone.

This chapter focuses on these two lessons, illustrating the importance of anticipating change and reacting to it by using the full range of available options.

The Everglades Agricultural Area (EAA) immediately south of Lake Okeechobee is characterized by rich peat soils (histosols). The area is devoted primarily to the production of sugarcane with small acreages devoted to vegetables, rice, beef cattle, and sodgrass. The annual value of production in this area in the early 1990s totaled $640 million (Alvarez et al., 1994). It is known that the peat soils oxidize on contact with the atmosphere, and this oxidation has caused the land surface to subside as progressive increments of the peat itself were lost though the twentieth century. The ultimate demise of Everglades agriculture was first predicted over 50 years ago, but there has been a long controversy over the rates of oxidation and the exact time when there would be insufficient soil over the bedrock to permit agriculture to be practiced (Douglas, 1947; Stephens and Johnson, 1951). Moreover, some have argued that agriculture could be practiced on the remaining mineral soils on a long-term sustainable basis. Indeed, economic rather than strictly agronomic factors may affect the near-term fate (next 5-20 years) of agriculture production in the EAA. Much of the EAA is devoted to sugarcane production, which effectively is subsidized by import duties on foreign-grown sugar and shielded from Cuban sugar production by import restrictions that have been in place since the 1960s (e.g., Mayer, 2001). Those restrictions may well change if there are changes in the government of Cuba, its policies, or those of the U.S. government.

Another economic stimulus for removing EAA land from agricultural production is the continuing strong migration of people to south Florida, which shows no sign of abating. At some point in the perhaps not too distant future, agricultural interests may decide that some of their land is more valuable for development into retirement communities, golf courses, and related land uses than for agricultural production. If this were to happen, it would create additional problems for the Everglades restoration because it would impose continued demands for reliable water supplies and at the same time decrease the amount of land that could be used for water storage and also possibly make it more difficult to use adjoining lands for storage.

Aside from its potential use for construction of surface reservoirs, an EAA that no longer was used (in whole or part) for agricultural production also could be flooded and allowed to revert to its natural wetland condition. It would take many centuries for the wetland to accrete the amount of peat soil present before drainage and agriculture production began, but a semblance of a natural marsh system probably could be established rather quickly. This system would tend to act as a giant stormwater treatment area, removing nutrients as the water slowly moved south. As Odum and Odum (2003) pointed out, such an approach could reestablish the original pattern of “longitudinal succession” within the Lake Okeechobee-Everglades system–that is, nutrient-rich water from the lake would pass through a eutrophic slough south of the lake and lose nutrients by plant growth and peat accretion before entering the oligotrophic Everglades to the south.

Often called the liquid heart of the Everglades, Lake Okeechobee is near the geographic center of the series of ecosystems constituting the Greater Everglades. Given the attention it has received and its actual and potential importance in the Everglades restoration, it is treated in some detail here.

In terms of surface area, Lake Okeechobee is the second largest freshwater body located wholly within the United States (Lake Michigan is the largest), but its volume is very small

compared with any of the Great Lakes. It also has been the center of many controversies in recent decades concerning its function in the larger system and the most appropriate strategies for its management (e.g., Steinman et al., 2001; Havens, 2002; Bachmann et al., 2003). Historically, the lake served as the key hydrologic link between the mostly upland ecosystems in its large drainage basin mostly to the north and the sawgrass marshes and prairies of the Everglades proper to the south. Water storage provided by the large lake moderated the effects of variations in rainfall (wet-dry climatic cycles) on water levels in the Everglades. The lake also serves as a drinking water supply for several communities along the southern shore, and it is renowned as a sport fishery, especially for largemouth bass. The economic importance of the sport fishery is considerable.

This section describes the physical setting of Lake Okeechobee, its historical development, current uses, and limnology. We focus on the recent history of water-quality studies and management efforts to control the large lake’s nutrient problems. Preliminary analyses conducted in the Restudy regarding the lake’s potential to provide water storage are summarized, and issues are identified that should be considered in detail in a contingency-planning exercise to evaluate the advantages and disadvantages of relying more on Lake Okeechobee for water storage in the overall Everglades restoration program.

According to Brooks (1974), the earliest recorded name for the lake (by Solis de Mera in 1567) was “Mayaimi,” a Caloosa Indian word meaning “big water.” The present name, Okeechobee, is derived from a Seminole Indian composite of “oki” (water) and “chubi” (big) (Bloodworth, 1959 cited in Brooks, 1974).

Although Lake Okeechobee occupies a marine depression formed in the Pliocene by oceanic currents (Hutchinson, 1957), the modern lake itself is much younger, owing its existence to the accumulation of peat deposits along the southern rim of the depression. The peat deposits also underlie what is now the 310 mi² (~800 km²) Everglades Agricultural Area south of Lake Okeechobee. The process of peat accumulation began about 6,300 years ago, probably as a response to climatic changes (increased rainfall) in south Florida (Gleason et al., 1974). The early lake encompassed a larger area than the present lake and included parts of the current Water Conservation Areas. According to Brooks (1974), the modern lake, with “an ever increasing elevation as the result of organic deposition along its southern rim began to develop just over 4,000 years ago,” and the historic maximum level was reached only in the third century A.D.

Under pre-drainage conditions, the lake’s boundaries were diffuse and spatially variable (depending on rainfall conditions). According to Parker (1974), at lake stages exceeding about 14.6 ft NVGD (National Vertical Geodetic Datum, essentially equivalent to mean sea level) outflow from the lake occurred as diffuse overflow across the peat sill into the Everglades along two large segments of the southern shore, but Leach et al. (1971) described outflow as occurring along “a narrow reach.” Some diffuse outflow also occurred to the southwest to Lake Hicpochee, the headwaters of the Caloosahatchee River (Brooks, 1974). Overflow along the south shore became more general at a stage of about 18 ft NVGD, and “sizeable volumes of water moved slowly in flat, broad sloughs toward tidewater” (Parker et al., 1955, as quoted in Leach et al., 1971). However, except during “extremely wet” years, there was no direct surficial hydrologic connection of the lake to the Everglades (Leach et al., 1971).

The hydrology and morphometry of Lake Okeechobee and its drainage basin have been modified greatly over the past 125 years, and the current system bears little resemblance to conditions that existed when early explorers visited the region in the early and mid-nineteenth century (Tebeau, 1971, 1974). Modifications began in 1881 when Hamilton Disston dredged canals connecting a series of large lakes in the upper part of the Kissimmee River basin and enlarged a shallow outlet to Lake Hicpochee and the Caloosahatchee River on the southwest side of the lake (Brooks, 1974). Disston actually was not the first to construct drainage canals around the lake. Apparently, even the Caloosa Indians and their predecessors did so (Will, 1964).

A much more drastic modification of the Kissimmee drainage basin occurred in the 1960s, when the Kissimmee River was channelized by the U.S. Army Corps of Engineers, converting a 100-mile long, slow-moving, and highly meandering river with extensive riparian wetlands into a 50-mile long, nearly straight channel. Incorporation of five locks and dams in the waterway provided a constant depth for navigation. Channelization had dramatic effects on the drainage basin, river, and Lake Okeechobee. By accelerating the movement of runoff downstream, the new channel opened large areas of the watershed that previously were inaccessible to use for cattle grazing and other agricultural pursuits. The faster travel time of runoff through the system decreased its ability to retain nutrients, and the nearly straight, steep-sided channel provided much less habitat for wetland plants and animals than the original meandering river had.

Concern about negative environmental impacts of the channelization began even before the project was completed in 1973, and efforts began to restore the river by removing the new channel. The State of Florida initiated an Everglades restoration project in the mid-1980s that included a demonstration project to restore the Kissimmee. In 1990, Congress appropriated funds to the Corps of Engineers to pursue Kissimmee River restoration, and it authorized the dechannelization of the Kissimmee River in 1992. The restoration program is still under way. The original channelization project cost an estimated $30 million, and although the dechannelization project thus far has cost an estimated $300 million, it will not restore the entire river length. Because of encroachment of human settlements on the floodplain of the lower river (near its entrance into Lake Okeechobee), it was not considered feasible to restore the original channel below approximately 12 km upstream from the river mouth.

Because the landscape of southern Florida, including the area surrounding Lake Okeechobee, is very flat, the shoreline of the lake expanded and contracted considerably, depending on rainfall conditions. Consequently, construction of levees to constrain expansion of the lake began fairly early in the history of European settlement, which began on the southern end of the lake in the late nineteenth century. By the early 1920s, a series of low, muck levees that were constructed around the southern and southwestern shore of the lake eliminated sheet flow from the lake to the Everglades and facilitated farming operations in the rich muck soils just south of the lake. The levees were not sufficient to hold back the lake waters during large flooding events, however. Major hurricanes that moved through south Florida in 1926 and 1928 breached the levees, resulting in disastrous flooding and the loss of more than 2,000 lives (Will, 1964). The 1928 disaster was caused by a giant wind-induced, resonant tide, or seiche, that formed when the eye of a hurricane passed across the north end of Lake Okeechobee on September 16. The loss of life and extensive property damage prompted federal action that resulted in the construction of a large earthen dike around the southern side of the lake by the Corps of Engineers from 1930 to 1937. In 1960-64, the levee (called the Hoover dike) was extended around the entire lake and raised to a height of 25 feet above normal lake stage, which is 15 ft above mean sea level.

By early 1883, the natural flood channel toward the Caloosahatchee River had been widened to a shallow canal (Leach et al., 1971). Construction of major drainage canals began early in the twentieth century to allow more rapid release of water from the lake, and the period 1905-1921 saw the connections of the lake to the coast via the Hillsborough Canal, the North New River Canal, the West Palm Beach Canal, and the Miami Canal (Leach et al., 1971; Light and Dineen, 1994). The St. Lucie Canal was completed in 1924 and was the main controlled outlet for regulation of the lake until about 1946 (Leach et al., 1971). Most of these historical drainage features remain a part of the south Florida landscape. Following major flooding in south Florida in 1947, a series of drainage canals was constructed (1948-63) around the southeastern side of the lake. The Everglades Agricultural Area (EAA) was formed in 1948, and although it was not a part of Lake Okeechobee’s natural watershed, it became so as pumps were installed to “back-pump” water draining from the EAA into the lake for storage purposes. A large low-head pumping station (designated S-2 by the SFWMD) was constructed in 1957 to connect the lake to the Hillsboro and North New River canals near Belle Glade. Because of concerns about detrimental effects of the nutrient-rich and generally low-quality agricultural drainage water on Lake Okeechobee, the South Florida Water Management District agreed in 1979 to cease the back-pumping practice except under extreme circumstances.

Completion of the levee, drainage canals, and water-control structures (including various pumping stations) changed Lake Okeechobee from a natural lake characterized by wide fluctuations in water levels and areal extent between wet and dry periods to a highly regulated reservoir with only minor changes in area except during major droughts. A lake-stage regulation schedule (see Figure 3-4) has been used to manage lake levels for decades. In general, the schedule provides for maximum lake stage in winter and lower stage during summer and fall to provide storage capacity for inflows associated with the summer rainy period and hurricane season.

The modern lake still has extensive areas with sandy bottom sediments, but a “mud zone” with organic-rich fine sediments covers most of the northeastern portion of the open lake. These sediments have elevated levels of phosphorus, and wind-induced resuspension of these sediments is a major factor in the internal loading (recycling) of phosphorus to the water column, which maintains the lake’s eutrophic and somewhat degraded water quality. The mud-zone sediments generally are underlain by marl deposits (unconsolidated calcium carbonate formed within the lake). Localized areas of peat deposits are found on the southern edge of the lake, but they constitute only a small fraction of the lake area. A ridge of exposed limestone limits water exchange between the main body of the lake and the southern bays and littoral areas, especially when water levels are low. Extensive areas of emergent aquatic vegetation occur in a large littoral zone on the western side of the lake, and a large freshwater marsh occupies the southwest section. Littoral areas on the southern end of the lake have mixed areas of submergent and emergent vegetation, but the eastern and northeastern sides of the lake have very limited areas with littoral vegetation.

The first significant investigation on the chemical and biological characteristics of Lake Okeechobee was conducted by the U.S. Geological Survey in 1969 and 1970 (Joyner 1971, 1974), and an extensive and nearly continuous monitoring and research program has been conducted by the South Florida Water Management District on the lake and its tributaries since the

early 1970s. The primary focus of this work has been on nutrient-related water-quality issues. Sufficient tributary monitoring data are available for more than twenty years of annual nutrient (phosphorus and nitrogen) budgets (e.g., Janus et al., 1990; James et al., 1995), and extensive lake monitoring data are available to characterize both temporal trends and spatial variability in nutrient concentrations and related water-quality conditions such as chlorophyll levels and water clarity (Secchi disk transparency) (Aumen, 1995). Other studies have focused on the important role of the lake’s sediments as an internal source of phosphorus and suspended sediment to the water column (e.g., Maceina and Soballe, 1990; Reddy et al., 1993; Sheng, 1993; James et al., 1997; Brezonik and Pollman, 1999).

Nutrient-budget studies in the 1970s focused on contributions of specific source waters to the lake and showed that Taylor Creek and Nubbin Slough (Figure 2-5), which provide minor amounts of water to the lake, were substantial contributors of phosphorus. This was attributed to extensive dairy and cattle operations in these watersheds. Four sub-basins north of Lake Okeechobee, including the Taylor Creek-Nubbin Slough basin and three sub-basins in the lower Kissimmee River, still contribute about 35 percent of the current phosphorus loading to the lake although they comprise only about 450 square miles (~12 percent of the total contributing land area in the lake’s watershed). The SFWMD recognizes them as priority basins for phosphorus management and has ongoing projects to develop and implement best management practices in the basins.

Back-pumping of water from the EAA also was found in early studies to be a major nutrient source, especially for nitrogen, and EAA discharge water also was found to be generally poor in quality—high in dissolved solids and colored natural organic matter from the peat soils (e.g., Brezonik and Federico, 1975). These studies led to a decision by the SFWMD in 1979 to stop the practice of pumping EAA discharges into the lake, and except during periods of extreme drought, such as occurred in 2001 (SFWMD, 2001), back-pumping of drainage water from areas south of the lake has not been practiced.

In spite of extensive efforts to limit or manage nutrient inputs to the lake from watershed sources over the past ~30 years, phosphorus concentrations in the lake actually appear to have increased since the early 1970s (Figure 5A in Havens and Walker, 2002). For example, annual average total phosphorus concentrations in the lake’s pelagic (open-water) zone were in the range 50-60 mg m^-2 yr^-1 in the period 1973-1977, increased to approximately 80-90 mg m^-2 yr^-1 in the period 1979-1983, and varied between ~90 and 120 mg m^-2 yr^-1 over the period 1987 to 1999. Water clarity (as measured by Secchi disk transparency) similarly declined over this period—from an average of about 60 cm in the mid-1970s to about 40 cm in the late 1990s (Havens et al., 2003).

Nutrient loadings, especially phosphorus loadings, remain substantially higher than stated SFWMD goals. Annual phosphorus inputs have increased from about 230 mg m^-2 yr^-1 to 850 mg m^-2 yr^-1 from 1910 to the 1990s (Brezonik and Engstrom, 1998). The total phosphorus input into the lake is about 498 t per year (Walker, 2000). In contrast the proposed target loading is 140 t per year. The target load is based on a model prediction of the phosphorus loading needed to attain an average total phosphorus concentration in the lake’s pelagic (open-water) zone of 40 mg m^-2 yr^-1 (Havens and Walker, 2002). The latter value is the proposed in-lake goal for phosphorus that was used in the total maximum daily load (TMDL) process for Lake Okeechobee (Havens and Walker, 2002).

Factors controlling primary production by algae and the composition of the phytoplankton community in Lake Okeechobee have received considerable attention over the past 30 years.

The former issue is complicated by the spatial and temporal variability of nutrient levels in this large lake; at different times and locations, either phosphorus or nitrogen may be the potentially limiting nutrient for planktonic primary production (e.g., Brezonik et al., 1979), but light conditions usually are the actual limiting factor (Phlips et al., 1997; Bachmann et al., 2003), especially in the open-water area, where wind-induced sediment resuspension is responsible for low water clarity (Maceina and Soballe, 1990). Secchi disk transparency in the open lake typically is in the range of 30 to 60 cm; as a rough approximation, the euphotic zone, which is defined as the depth at which light penetration is sufficient for primary production to just exceed respiration, is about twice the Secchi depth; this is thought to occur at ~1-2 percent of incident light. Low light availability also has been suggested as a regulator of cyanobacteria (blue-green algae) species in the lake (Havens et al., 1998) and low nitrogen:phosphorus ratios in the lake water also have been used to predict the recent dominance of cyanobacteria (Havens et al., 2003).

The complexity of factors influencing phytoplankton concentrations in the lake has led to substantial disputes about the merits of developing a TMDL for phosphorus to control algal blooms in the lake. Havens and Walker (2002) concluded that the TMDL goal of 40 micrograms per liter for long-term average total phosphorus concentration in the pelagic zone of the lake would reduce the frequency of near-shore algal blooms to 2-9 percent compared with 5-33 percent under present conditions. In contrast, Bachman et al. (2003) contended that a stringent TMDL for phosphorus would not result in improved water quality; they argued that the lake has been eutrophic for over a century and had a high phosphorus loading rate (~377 metric tons per year) even in presettlement times. Such a high rate seems unlikely, however, given pre-settlement hydrology and the major agricultural and other anthropogenic phosphorus sources known to be important in the drainage basin at present. The contention that the lake was eutrophic in pre-settlement times does not agree with the descriptions of some early explorers. For example, in 1887 Heilprin, as quoted by Brooks (1974), described the lake in the following way:

In addition, paleolimnological evidence based on lead-210 (²¹⁰Pb) dated sediment cores from eleven sites in the mud zone of the lake indicates that annual phosphorus accumulation rates in the lake’s sediments have increased about fourfold since pre-settlement times, with most of the increase occurring in the past 50 years (Brezonik and Engstrom, 1998). Although difficulties were encountered in interpreting ²¹⁰Pb dating of cores from some locations (probably because of sediment resuspension problems), reliable dates were obtained from most sites. These studies also suggested that the lake had very low rates of accumulation of organic-rich muck sediments in pre-drainage, pre-settlement times.

Bachmann et al. (2003) proposed that water-level controls would be more effective in managing phosphorus levels (and associated algal blooms) in the lake. This is roughly in agree-

ment with the Restoration Plan’s proposed management plan for the lake (USACE and SFWMD, 2001; Havens, 2002) and is based on the findings of several earlier studies (Maceina, 1993; Havens 1997) of an association between higher water levels and higher total phosphorus concentrations in the lake. High water levels also facilitate the movement of suspended particles (and associated particle-bound phosphorus) from the mud zone in the central part of the lake to near-shore areas, especially in the south end of the lake, where a submerged limestone ridge at ~8 ft (NVDG) inhibits movement of water from the center of the lake to the southern bays at low lake stage but is ineffective at blocking large-scale circulation patterns at higher stages.

As the above description indicates, Lake Okeechobee is not just a potential water storage site for the Everglades; it is a key, albeit degraded, component of the Greater Everglades system, and it serves as an important drinking-water supply and recreational resource. It was identified as a system component to be restored by the Restoration Plan. Several parts of the comprehensive plan are focused on improving water quality in the lake. For example, the Kissimmee basin storage reservoir described in Chapter 2 is intended both to store water and to reduce nutrient loads to the lower Kissimmee River and Lake Okeechobee. This component will consist of a 17,500-acre above-ground storage reservoir and associated 2,500-acre stormwater treatment area (STA) in one of three counties north of Lake Okeechobee. A 5,000-acre reservoir and associated 5,000-acre STA in the Taylor Creek-Nubbin Slough area northeast of Lake Okeechobee is intended to serve the same purposes. The storage capacity of these two reservoirs (in sum about 250,000 acre-feet) essentially substitutes for storage that could be obtained by allowing a higher stage in Lake Okeechobee during wet periods. An increase in the maximum allowable lake stage of 0.5 feet would provide 227,500 acre-feet of additional storage (Table 4-1), over 90 percent of the storage of the two proposed reservoirs.

An increase in the maximum stage of Lake Okeechobee of 0.5 feet also would provide additional storage equivalent to about 82 percent of the total storage provided by the proposed Lake Belt. The actual stage of Lake Okeechobee reached the maximum allowable stage only a few times over the period 1931-2003.

Several additional Restoration Plan components to improve water quality in Lake Okeechobee are described in the Lake Okeechobee Surface Water Improvement Management Plan (SFWMD, 1997b). They include: (i) additional STAs on the north side of the lake; (ii) a plan to plug selected local drainage ditches, the net effect of which will be to restore about 3,000 acres of wetlands in the Okeechobee watershed; (iii) diversion of some drainage canals into wetlands; and (iv) dredging of phosphorus-rich sediment from 10 miles of primary canals in the watershed of the lake. However, despite concerns expressed by limnologists about the increasing importance of internal phosphorus loading by wind-induced resuspension of flocculent, phosphorus-rich, bottom sediments in maintaining high nutrient and algal conditions in the lake, no Restoration Plan components are designed to address this problem directly, and the plan does not include any in-lake restoration activities.

The Lake Okeechobee Surface Water Improvement Management Plan eschews a more prominent role for the lake in storing water for export to the Everglades during droughts because SFWMD limnologists believe that maintaining high water levels in the lake for extended periods would be detrimental to littoral plant communities primarily on the lake’s west side and also would cause poorer water quality (higher levels of turbidity and algae concentrations) in the open waters of the lake. Field data on the lake for periods of widely varying water levels during the 1990s (e.g., Maceina, 1993; Havens, 1997, 2002) support these conclusions. Nonetheless, the general argument and cited field observations that lower water levels are better for Lake Okeechobee appear at first to be contrary to a long-held limnological belief that deeper lakes tend to have better water quality because wind-induced sediment resuspension becomes less important as the depth of the water column increases. Also, a lake with a deeper mixed layer may have the same biomass of algae as a shallower lake, but in the deeper lake, the algae are suspended in a larger volume of water such that the concentration of algae is lower. However, when water levels in Lake Okeechobee are low, a submerged ridge along the southern edge of its central basin tends to interrupt circulation from the center of the lake, where fine sediments can be resuspended in windy conditions. It is possible that if the lake were regulated at levels several feet higher than it is at present, and if effective nutrient controls to the lake could be implemented, then poor water quality associated with higher lake levels would not be problematic.

Although higher water levels may diminish the width of the littoral zone of emergent vegetation in the northwestern area of the lake, higher water levels actually may enhance the littoral zone in the southwest part of the lake. Under current operating conditions, the large expanse of marsh south of the mouth of Fisheating Creek and northwest of the city of Moore Haven on the lake’s southwest shore is very shallow and much of it cannot be traversed by boats because of insufficient water depths and dense vegetation. If maximum water levels in the lake were allowed to increase modestly (e.g., by 1-3 feet), it is likely that this large area would become more lake-like, but still littoral rather than pelagic, and less like a separate, nearly impenetrable marsh.

A recent study (Smith et al., 2004) found that low water levels (< 13-14 ft, NGVD) promote the spread of a nonnative invasive terrestrial species of grass, torpedograss (Panicum repens), in marshy areas of the lake where depths are less than 50 cm (1.6 ft). This exotic species has displaced more than 6,000 ha (15,000 acres) of native plants, including spikerush, and open-water habitat since it was introduced to the lake in the 1970s. (Although the plant is considered a terrestrial species, once established, it can grow in water depths of 75 cm or less, and it can survive extended periods at water depths up to 1 m.)

Given the above comments and the possibility that other storage options (e.g., ASR) may not provide the amounts of water needed to fulfill the restoration plan, the committee judges that it would be prudent to revisit the question of whether Lake Okeechobee can provide some of the sought-for water storage. A wide range of options exist. Some of them, including options explored early in the Restudy, would have extreme effects on lake levels and would diminish the value of the lake as an ecological resource and probably as a sport fishery. These options likely would be opposed by a wide range of stakeholder groups, including the sport-fishing community and environmentalists. The lake is widely considered to be a valuable aquatic resource, even in its somewhat degraded condition, and proposals that would relegate the lake primarily to use as a water-storage device are likely to be controversial. For this reason especially, any reconsideration of Lake Okeechobee’s role in storage would need to include careful consideration of socioeconomic and ecological factors, including short- and long-term financial costs.

One of the more extreme options involved splitting the lake into two sections with a large dike. One section would include the littoral zones on the west side of the lake, in which water levels would be maintained within a range that would promote a healthy littoral plant community. The other section would include most of the open water portions of the lake on the east side, and water levels would be allowed to fluctuate to rather extreme highs and lows. A second option considered in early Restudy modeling runs allowed the entire lake to be used for water storage, and although the runs demonstrated that maximal use of storage in Lake Okeechobee would be “cost effective and hydrologically efficient” (USACE and SFWMD, 1999), they produced extreme fluctuations in lake levels, which likely would adversely affect the lake ecosystem. More modest fluctuations in water levels, including relatively small increases in maximum lake stage, apparently were not explored in these runs.

Smaller fluctuations and smaller increases in maximum stage of Lake Okeechobee obviously would not provide the total amount of storage that the unaltered system of the nineteenth century had and that may be required to offset the loss of another major storage component, such as ASR, should it prove infeasible. Nonetheless, moderate changes in lake stage could contribute substantially to system storage. As noted previously, an increase in maximum lake stage of only 0.5 ft would provide a water storage volume nearly equal to that of the two reservoirs (total of 22,500 acres plus an additional 7,500 acres devoted to STAs) proposed to be constructed north of Lake Okeechobee (see Chapter 2). Such changes may have only small negative effects on lake quality in the long term, especially once the problem of excessive nutrient loading to the lake is finally solved, and it may even lead to positive changes, such as a larger open-water habitat and a more accessible littoral zone on the southwest side of the lake. Thus, there is the potential to provide ecological benefits earlier in the process. Other storage options, including the proposed storage reservoirs north of Lake Okeechobee, have their own environmental costs. Any such changes should be undertaken using adaptive management to maximize learning opportunities.