Progress Toward Restoring the Everglades The Third Biennial Review - 2010 (2010) / Chapter Skim
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5 Challenges in Restoring Water Quality
5 Challenges in Restoring Water Quality
Pages 149-204
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From page 149... ...
Yet, water quality and water quantity are inextricably linked. Restoration planners cannot design projects to move large quantities of water south into the Everglades Protection Area to meet CERP goals without first ensuring that the water will meet established water quality criteria.
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From page 150... ...
derived primarily from atmospheric deposition. Any phosphorus inputs from Lake Okeechobee overflows were gen erally thought to have been assimilated by the former pond apple swamp that existed between the lake and the sawgrass plains (Noe et al., 2001)
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From page 151... ...
into Lake Okeechobee and the Everglades Protection Area. In general terms, one set of criteria was established for water quality within the Everglades and other standards set limits on the actual discharges of phosphorus into water bodies.
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From page 152... ...
. Water Quality Standards for the Everglades Protection Area In 1988, the United States sued the state of Florida and the South Florida Water Management District (SFWMD)
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From page 153... ...
.5 That rule states that for Class III waters in the Everglades Protection Area, the phosphorus criterion is a long-term geometric mean of 10 ppb, but not lower than natural conditions, taking into account temporal and spatial variability. Achievement of the criterion in Everglades National Park is governed by methods in Appendix A of the 1991 Settlement Agreement, and achievement of the criterion in the WCAs is evaluated across a network of sampling stations using a four-part test6 to determine whether a violation of Class III standards has occurred.
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From page 154... ...
. The data overwhelmingly demonstrate that even low levels of enrichment in total phosphorus concentrations result in elevated phosphorus in macrophyte tissues, soil, the water column, and periphyton, leading to undesirable changes in periphyton and macrophyte biomass and productivity and faunal communities.
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From page 155... ...
Following a 1999 Consent Decree,8 Florida enacted the Lake Okeechobee Protection Act in 2000 (Chapter 00-103, Laws of Florida) , requiring limits on phosphorus inflows into the lake.
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From page 156... ...
The cost of attaining and maintaining the standards may be considered during formulation and implementation of water quality management programs, but options for doing so are quite burdensome. As discussed later in this chapter, attaining water quality standards in the Everglades system may take decades of sustained effort at very substantial costs.
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From page 157... ...
The 10 ppb TP criterion for the Everglades Protection Area was not affected by the proposed rule. A protective TN and TP load for Lake Okeechobee also was not calculated, because a total maximum daily load (TMDL)
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From page 158... ...
Implementing a similar strategy in the Everglades Protection Area would require significant changes to existing policy. The CWA offers to states two options to address an unattainable standard, namely the use of attainability analysis and discharge-specific variances, neither of which may be appropriate to the Everglades ecosystem.
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From page 159... ...
. Internal loads from sediments in Lake Okeechobee to the water column are also significant, especially from the mud zone sediments.
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From page 160... ...
, then it is likely that the lake would recover in the next 10 to 20 years and reach an alternate stable condition. Tracking Phosphorus Fluxes in the South Florida Ecosystem Annual average inflows and outflows of phosphorus over water years 2005 2009 are shown in Figure 5-3 for the principal components of the South Florida ecosystem.
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From page 161... ...
WCD = water control district; ECP = Everglades Construction Project. bitmap SOURCE: SFWMD and FDEP (2008b)
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From page 162... ...
Mass balances do not exist for either the EAA subareas or the sub-basins, and connections between subareas/sub-basins and the STAs are incomplete. Data on atmospheric deposition of phosphorus is only available for the Lake Okeechobee basin, and, based on 2005 reported data, atmospheric deposition appears to be a sizeable component of the phosphorus load in the Everglades Protection Area.
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From page 163... ...
Source Control Strategies One of the approaches for improving and maintaining water quality in the South Florida ecosystem has been the implementation of source controls, or BMPs. BMPs are applied to both agricultural and non-agricultural lands, and on both field and watershed scales.
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From page 164... ...
164 Progress Toward Restoring the Everglades FIGURE 5-4 Location of source control basins within the South Florida ecosystem. Figure 5-4.eps SOURCE: SFWMD (2009c)
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From page 165... ...
In February 2008, the SFWMD released the Lake Okeechobee Watershed Construction Project: Phase II Technical Plan, a comprehensive plan to implement the Northern Everglades and Estuaries Protection Program. The preferred plan identifies a combination of STA construction, agricultural and urban BMP implementation, ecosystem services projects, chemical and wetland treatment projects, as well as other projects for increasing water storage north of the lake.
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From page 166... ...
Thus progress on reducing phosphorus loads from the Lake Okeechobee water shed to the lake has not yet been achieved. In water year (WY)
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From page 167... ...
Furthermore, the C-139 basin primarily contains sandy (mineral) soils, more like those of the basins north of Lake Okeechobee than the organic (muck)
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From page 168... ...
168 FIGURE 5-5 EAA basin observed (measured) total phosphorus loads compared to predicted (calculated)
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From page 169... ...
Assessment of the compliance of each basin is based on monitoring phosphorus loads at the basin level, not at the farm level. However, to ensure that BMP plans between different permittees are comparable and equitable, a system of BMP equivalents was developed by assigning points to BMPs within four basic categories: water management practices, nutrient management practices, control of sediment and particulate matter, and pasture management (where applicable)
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From page 170... ...
The maps and tables show that although many farms in the EAA are achieving substantial reductions in phosphorus loads (with some reductions >90 percent compared to baseline) , the reductions are not consistent across the basin.
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From page 171... ...
Costs of Enhanced BMPs South of Lake Okeechobee. To the committee's knowledge no cost-effectiveness analyses of source controls in the EAA or of other agricultural lands in the South Florida ecosystem have been published.
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From page 172... ...
One approach to reduce phosphorus loads in the South Florida ecosystem is to manage the phosphorus released from sediment within the lake. Only limited phosphorus management actions have been taken to date within the lake.
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From page 173... ...
Given the magnitude of the phosphorus challenges, the SFWMD should reconsider the costs and benefits of in-lake actions, perhaps combined with aggressive source control strategies in the Lake Okeechobee watershed. Costs of In-lake Treatment In a 2003 study of options for phosphorus treatment in Lake Okeechobee, the SFWMD provided detailed cost estimates for two approaches: hydraulic dredging and in-place chemical precipitation with aluminum compounds.
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From page 174... ...
Overview of Everglades STAs Phosphorus management through STAs has been a major focus of the SFWMD through the Everglades Construction Project (see Box 2-3) and the dis trict's Long-Term Plan for Achieving Water Quality Goals (Burns and McDonnell, 2003)
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From page 175... ...
inflow phosphorus. Hurricanes severely impacted the STAs during WY 2005 and WY 2006 with large volumes of inflows and phosphorus loads.
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From page 176... ...
Phosphorus loading rates for WY 2009 (1.4 g/m2/year) were within the design criteria established for STAs,12 although STA-2 and STA-3/4 were loaded at much lower rates than The design criteria listed by Burns and McDonnell (1994)
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From page 177... ...
In addition to STAs in the EAA, two STAs have been recently constructed in "nutrient hotspots" in the Lake Okeechobee watershed: the Taylor Creek STA (142 acres effective area) and the Nubbin Slough STA (773 acres effective area)
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From page 178... ...
. Phosphorus loading rates during the first 10 years of operation ranged from 1 to 1.5 g/m2/year, but extreme weather conditions (i.e., hurricanes and drought)
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From page 179... ...
Challenges in Restoring Water Quality 179 (a) STA -1W Water column TP, µg/L Inflow Outflow STA-Age, years (b)
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From page 180... ...
Although reduced inflow loads do not guarantee low outflow concentrations, reduced loading is clearly an important component of STA management, albeit challenging in the variable climate conditions of South Florida (see Box 2-2)
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From page 181... ...
Thus, phosphorus removal and stability of the stored phosphorus in STAs is regulated by inflow water chemistry, including nitrogen, sulfur, calcium, and magnesium, and transformations of these chemicals within the STAs. The concentrations of calcium and other inorganic chemicals should be monitored as part of routine performance assessments.
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From page 182... ...
. Phosphorus enrichment in the floc and surface soil decreases the potential phosphorus uptake from the overlying water column.
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From page 183... ...
) without the addition of substantially more acreage to the STAs, more vigilant maintenance of accreted sediments, and careful control of inflow phosphorus loads.
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From page 184... ...
Research and Monitoring Needs to Support Long-Term STA Sustainability Understanding the factors and processes that control long-term perfor mance is essential to optimizing the efficiency and the long-term sustainability of STAs. Focused research efforts directed at improving STA management and For this analysis, CERP flows were assumed to be 1.86 MAF/year to the Everglades Protection 13 Area, compared to current flows of 1.38 MAF/year.
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From page 185... ...
, differences between STA cells built on historical wetlands and on previously farmed soils (Juston and DeBusk, 2006) , and the efficacy of STA systems at low loading rates (Juston and DeBusk, 2006; Gu and Dreschel, 2008)
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From page 186... ...
In particular, research is needed to assess the long-term ability of STA units to sustain or improve upon their current level of functioning. The committee also identified several areas where additional research might lead to improved STA operation and phosphorus removal efficiency: • Determine the stability of phosphorus stored in floc and soils and deter mine how phosphorus-retention capacities change with period of operation of the STA, flow rates, climatic conditions, and altered water chemistry; • Determine the inter-relationships between phosphorus and other elemen tal cycles (e.g., nitrogen, calcium, sulfur)
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From page 187... ...
The upper bound is a "worst case" that assumes refurbishment after 20 years and again after 40 years, and uses the high-end estimates of annual O&M, monitoring, and refurbishment costs. Using
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From page 188... ...
of phosphorus over a 50-year period. Using average values for O&M, monitoring, and refurbishment costs and assuming refurbishment after 25 years, the total present value cost per pound of phosphorus removed is $109.
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From page 189... ...
The cost analysis should also examine alternative restoration sequencing and water supply approaches that may be able to address water quality and water quantity concerns in a more efficient manner. For instance, planners should consider whether water quality issues necessitate higher priorities for seepage management projects, which would retain high quality water in the Everglades Protection Area.
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From page 190... ...
According to Figure 4-2, 243,000 acre-feet of water from the WCAs are transferred each year for urban and agricultural water supply. Elevated phosphorus levels are less of a concern for urban and agricultural water uses, and, if feasible, a water management approach that separates ecosystem water storage from urban and agricultural water storage could reduce overall treatment requirements and costs.
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From page 191... ...
Elevated concentrations of sulfate can enhance the supply of phosphorus from wetland soils to surface waters (Lamars et al., 1998; Smolders et al., 2006) , although experiments to date in the Everglades FIGURE 5-13 Concentrations of sulfide in porewaters of the Everglades during May 2005 (left)
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From page 192... ...
About 60 percent of the Everglades Protection Area currently exceeds background sulfate concentrations of <1 ppm (Scheidt and Kalla, 2007)
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From page 193... ...
The warm water temperatures, the large supply of biodegradable organic carbon and reducing conditions, and elevated inputs of sulfate in the Everglades promote sulfate reduction and the net methylation of ionic mercury. Finally the Everglades is extremely low in nutrients (oligotrophic)
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From page 194... ...
conducted a pre liminary mass balance of sulfur for Lake Okeechobee, the EAA, Water Conservation Area (WCA)
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From page 195... ...
. Ecosystem-wide sampling indicates that zones of elevated methyl mercury production appear to be controlled by sulfate transport, which varies in time and space.
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From page 196... ...
Restoration of sheet flow within the Everglades ecosystem will help pro tect sensitive areas like the WCAs, Everglades National Park, and Big Cypress National Park from the effects of sulfate contamination. Canals promote distant transport of sulfate under oxidizing conditions.
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From page 197... ...
, a key indicator plant for undisturbed communities. The conductivity of water in the interior of WCA-2A is generally in the range of 1,000 μS/cm; in contrast, within Everglades National Park, specific conductances are rarely above 600 μS/cm, despite thin peat and greater surface water-groundwater exchange in that region.
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From page 198... ...
Calcium Trends and Implications In contrast to the pattern of elevated calcium and alkalinity observed in the WCAs in association with inputs from the EAA, Lake Okeechobee has shown trends of decreasing calcium concentrations since the 1970s (Figure 5-16)
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From page 199... ...
specific conductivity, and (C) sulfate Figure 5-16.eps at eight long-term monitoring stations in Lake Okeechobee.
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From page 200... ...
Short-term immobilization of phosphorus in the STAs seems to occur by biological removal by periphyton and macrophytes and FIGURE 5-17 Relationship of phosphorus settling rate in Lake Okeechobee to calcium con centration in the water column, based on data from 1973 to 1999. Figure 5-17.eps SOURCE: Walker (2000)
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From page 201... ...
Legacy phosphorus storages in the Lake Okeechobee watershed, the lake itself, and the EAA suggest that current phosphorus release rates into the system will persist for decades. Attaining water quality goals throughout the system is likely to be very costly and take several decades of continued commitment to a systemwide, integrated planning and design effort that simultaneously addresses source controls, storage, and treatment over a range of timescales.
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From page 202... ...
In addition to considering additional treat ment and source control, this analysis should evaluate urban and agricultural water supply management approaches and accelerated sequencing for seepage management projects to determine whether changes could address water quality and water quantity concerns in a more efficient manner. A rigorous research, analysis, and modeling program is needed to develop improved best management practices and to examine the long-term sustain ability and performance of STAs to meet the desired outflow water quality.
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From page 203... ...
Long-term monitoring of the efficacy and costs of BMP implementation across multiple sites will be required to evaluate source control practices across variable hydrologic, geomorphologic, and soil regimes present in the South Florida ecosystem and to validate and build confidence in predictive models. Given that restoration as originally envisioned in the CERP remains decades away and the ecosystem continues to decline, CERP agencies should conduct a rigorous scientific analysis of the short- and long-term tradeoffs between water quality and quantity for the Everglades ecosystem.
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From page 204... ...
Likewise the transport and removal of phosphorus may be coupled with the supply of calcium in Lake Okeechobee, the STAs, and other portions of the Everglades. Additional research is also needed to clarify the linkages between water quality constituents to support sound multi contaminant water management decisions.
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