Progress Toward Restoring the Everglades The Ninth Biennial Review - 2022 (2023) / Chapter Skim
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4 STA Water Quality and CERP Progress
4 STA Water Quality and CERP Progress
Pages 113-170
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From page 113... ...
. In response to this degradation, in 1988 the United States sued the State of Florida.1 Under the Consent Decree reached in 1992 and subsequent enhancements, the state constructed 57,000 acres of treatment wetlands, termed stormwater treatment areas (STAs)
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From page 114... ...
Finally, the committee recommends strategies to support the state's ongoing efforts to meet the water quality discharge requirements and sustain STA performance over the long term. EVERGLADES WATER QUALITY OBJECTIVES AND CRITERIA The federal Clean Water Act (33 U.S.C.
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From page 115... ...
Remedial measures under the Consent Decree included a commitment by the SFWMD to construct 35,000 acres of STAs and for the state to develop and implement an interim and long-term regulatory program to ensure that all discharges from the Everglades Agricultural Area (EAA) meet Clean Water Act standards.
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From page 116... ...
. The data overwhelmingly demonstrate that even low levels of enrichment in TP concentrations result in elevated phosphorus in macro phyte 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 117... ...
STA Water Quality and CERP Progress 117 FIGURE 4-1 Location of water quality monitoring stations used to assess water quality conditions in the Everglades Protection Area and mean TP concentrations for WY 2021. For WY 2021, 83 percent of interior marsh sites had annual geometric mean TP concentrations in water of less than or equal to 10 µg/L and 89 percent had annual geometric means of 15 µg/L or less.
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From page 118... ...
In response to the Amended Determination, in 2012 the SFWMD developed the Restoration Strategies Regional Water Quality Plan (hereafter, Restoration Strategies Plan; SFWMD, 2012) , which provides for expanding existing STA acre age and additional infrastructure improvements to meet the WQBEL (Box 4-2; Figure 4-2)
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From page 119... ...
and the locations of Restoration Strategies projects, including expansion of STAs, STA earthwork, and flow equalization basins (FEBs)
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From page 120... ...
to Construction completion expected in 2024 Improvements the west Subregional Source Reduce inflow loads from Pilot projects completed in 2015 and 2017; Controls hotspots in the basin conceptual project planning ongoing Central Flow Path A-1 FEB Attenuate flow into STA-2 and Construction completed 2015, now operational STA-3/4 Western Flow Path STA-5/6 Internal Improve the performance of Construction completed 2020, now in optimization Improvements STA-5/6 period C-139 FEB Attenuate flow into STA-5/6 Construction completion expected in 2023 SOURCES: Data from Chimney et al., 2022a; Shuford et al., 2022. However, once the Miami Canal is plugged, if inflows do not meet the WQBEL, the redistribution of water as sheet flow through WCA-3A could increase TP concentrations in interior areas not previously affected (see Figure 4-1)
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From page 121... ...
ll features of the state's Restoration Strategies must be completed and meet state water quality standards prior to initiating any operations which would allow water from the Federal EAA project to enter any of the state's Restoration Strategy facilities." Until the WQBEL is met for the Restoration Strategies STAs, "the EAA reservoir may only be operated to flow the amount of water that the new EAA A-2 STA alone can treat to meet all federal and state water quality standards, as well as any additional treatment necessary for passage of water to Everglades restoration" (USACE, 2020c) .11 Under this policy, before the A-2 Reservoir is allowed to operate at full capacity, the prior 5 years of data 10 Following release of the prepublication version of the report, this paragraph was modified to correct its description of the compliance process.
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From page 122... ...
Modeling for the EAA Reservoir planning process calculated that the A-2 STA could treat an average of 162,100 AF/year (out of the 370,000 AF/year that the CEPP was projected to provide on average) and the remaining 207,900 AF/year would be treated by STA-2 and STA-3/4 (SFWMD, 2018a)
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From page 123... ...
In the balance of this chapter the committee turns its attention to a review of the underlying science, engineering, design, and operations of the STAs and a discussion of the progress to date under Restoration Strategies, with the goal of helping inform the state's efforts to meet the WQBEL criteria by 2027. OVERVIEW OF STAS Constructed treatment wetlands are used globally to remove nutrients and other contaminants from inflow waters and to maintain desired outflow water quality (Kadlec and Wallace, 2009; Vymazal, 2022)
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From page 124... ...
. In the soil and water column, phosphorus is present in organic and inorganic forms, which can be present as dissolved and/or particulate forms (Box 4-3; Appendix B)
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From page 125... ...
Particulate phosphorus (PP) fractions are considered those in water that do not pass through a 0.45 µm filter: Particulate inorganic phosphorus (PIP)
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From page 126... ...
In treatment cells containing SAV, underwater photosynthesis and primary productivity promote alkalization and calcium carbonate (CaCO3) formation in the water column that is deposited as a fine particulate sediment.
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From page 127... ...
Small areas with deep water zones near STA inflows are sometimes colonized by FAV. Although FAV can assimilate phosphorus in the biomass, it is generally undesirable in STA operations because it spreads rapidly, depletes water column oxygen, lowers pH, and interferes with the underwater growth of shoots of EAV.
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From page 128... ...
King, SFWMD. and function of periphyton, the soil from the PSTA cell is initially removed down to the underlying limestone caprock to reduce potential internal phosphorus loading from existing soil.
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From page 129... ...
are now operational, and a third is under construction. EVALUATION OF CURRENT CONDITIONS AND STRATEGIES OF INDIVIDUAL STAS TOWARD THE WQBEL The recent performance of each of the five Everglades Construction Project/ Restoration Strategies STAs are briefly summarized in this section by flow path, and more detailed descriptions and diagrams of each STA are provided in Appendix B
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From page 130... ...
, completed in 2015, helps attenuate peak inflows to both STA-3/4 and STA-2 and also significantly reduces TP concentrations in the FEB outflows, essentially acting as a large supplemental STA. All Restoration Strategies actions have been completed for STA-3/4, and if best practices and optimal operational metrics are continued, this STA is poised to maintain outflow TP concentrations required by the WQBEL.
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From page 131... ...
and phosphorus loading rates are much larger than those of the Central Flow Path (Table 4-2)
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From page 132... ...
Neither STA has experienced average annual discharges below 19 μg/L during the past 6 years. Significant work is now under way through Restoration Strategies to address performance issues, including efforts to mitigate hydraulic short circuiting, excessive dry downs, and high phosphorus loading rates.
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From page 133... ...
Additional concepts are expected to be developed as these discussions continue." In summary, significant progress is under way in STA expansion and refurbishment in the Eastern Flow Path, but no progress in reducing loads is apparent through additional Restoration Strategies subregional source control practices despite a decade of effort. STA-5/6 (Western Flow Path)
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From page 134... ...
Assessment Across All STAs Efforts undertaken as part of Restoration Strategies are expected to improve the performance of all STAs. The impressive performance of STA-3/4 shows that sustained discharge with TP concentrations below 13 μg/L is possible, especially if associated with low phosphorus inflow concentrations and loading rates.
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From page 135... ...
ever, the challenge of meeting the WQBEL starting in WY 2027 is substantial. A helpful way to illustrate key challenges across the different STAs is to calculate phosphorus treatment efficiency based on either average flow-weighted mean inflow and outflow TP concentrations or inflow and outflow TP loads.18 Phosphorus treatment efficiency of STAs based on average inflow and outflow concentrations over the most recent 6 years (WY 2017-2022)
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From page 136... ...
Efforts are also under way through Restoration Strategies to reduce phos phorus loading rates by increasing the STA treatment area in the Eastern Flow Path. Moreover, Restoration Strategies envisioned efforts to reduce phosphorus loads through subregional source control efforts, although no source reduction projects have been implemented.
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From page 137... ...
Key external drivers include inflow phosphorus concentrations and loading rates, hydraulic loading, and inflow water chemistry, which all can be affected by the source of the inflow water (e.g., EAA, C-139 Basin, Lake Okeechobee water)
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From page 138... ...
Phosphorus Loading Rates. One of the most consistent external factors driving STA performance is phosphorus loading rates from external sources.
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From page 139... ...
Increasing the size of the STA footprint, as is under way in the Eastern Flow Path, can help address conditions with high phosphorus loading rates. Construction of shallow, naturally vegetated FEBs, as are part of Restoration Strategies in the Central and Western Flow Paths, can reduce both phosphorus loading rates and inflow concentrations.
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From page 140... ...
The TMDL was established to achieve a TP concentra tion below 40 µg/L to improve the structure and function of the lake ecosystem. Annual phosphorus concentrations in Lake Okeechobee have increased from the earliest mea surements in the 1970s through WY 2021 (see Figure 4-13)
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From page 141... ...
; that were not flagged to have vegetation disturbance with phosphorus loading rate greater than 1.3 g/m2-yr (middle panel) ; and that were flagged to have experienced vegetation disturbance (right panel)
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From page 142... ...
High hydraulic loading can also increase water depth within an STA. Water depths in EAV treatment cells exceeding 3 feet result in physiological stress in plants, reducing biomass and plant density and ultimately decreasing phosphorus removal (Diaz, 2022)
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From page 143... ...
STA Water Quality and CERP Progress 143 FIGURE 4-16 Relationship between annual volume-weighted mean concentrations of TP in outflow and annual phosphorus loading during the operation period of WY 2006-2022 for STA-1E and WY 2004-2022 for the other four STAs. Dashed red lines represent the requirements of the WQBEL (13 μg/L and 19 μg/L TP)
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From page 144... ...
Overall, on an average annual basis, the STAs collectively responded to low phosphorus loading rates of less than 1 g/m2-yr and produced outflow TP concentrations of less than 25 μg/L once the disturbance event subsided. SOURCES: Data from Chimney, 2014, 2015a, 2017, 2018, 2019, 2020, 2021, 2022a,b; Germain and Pietro, 2011; Goforth et al., 2005; Ivanoff et al., 2012, 2013; Pietro, 2016; Pietro et al., 2006, 2007, 2008, 2009, 2010.
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From page 145... ...
Regulatory releases from Lake Okeechobee to STA-1E, -1W, and -2 (Figure 4-18) have also increased chronically high phosphorus loading rates and have added more stress to STAs that have been unable to meet the WQBEL.
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From page 146... ...
Storms can be associated with high winds and wave action, which can damage vegetation and suspend sediment, respectively, again resulting in a deterioration of phosphorus removal efficiency (DB Environmental, 2022)
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From page 147... ...
. However, nitrogen availability within STAs is likely an under-recognized potential driver of phosphorus treatment efficiency.
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From page 148... ...
SOURCES: Data from Chimney, 2015a, 2017, 2018, 2019, 2020, 2021; Pietro, 2016. managed or intensively researched, but differences in nitrogen loads and removal efficiency among the STAs hint at the potential importance of nitrogen to STA performance.
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From page 149... ...
At present the relative proportion of dissolved organic nitrogen entering STAs from external sources compared to that produced through internal biogeochemical processes is not known. Additional research on abiotic and biotic biogeochemical processes regulating the fate of phosphorus and nitrogen forms within the STA soil and water column would enhance the understanding of STA performance.
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From page 150... ...
. Overall, low N/P ratios in the water column coupled to soil phosphorus enrichment may indicate reduced phosphorus removal efficiency and opportuni
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From page 151... ...
. Underwater photosynthesis increases water column pH during the daytime and promotes CaCO3 formation and deposition into floc, which increases conditions for accumulation of phosphorus (Pederson et al., 2013; Pelechaty et al., 2013)
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From page 152... ...
, primarily reflecting variation in hydraulic loading rates and SAV activity that influence the production of CaCO3. At present, calcium dynamics in STAs are relatively understudied and merit additional attention in future research, monitoring, and assessment in relation to STA performance given that additional Lake Okeechobee inflows (~50 mg/L calcium)
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From page 153... ...
Vegetation EAV and SAV play pivotal roles in STA performance in reducing phosphorus concentrations. Overall, the biogeochemical processes of STAs are regulated by vegetation through uptake of nutrients and production of litter, which serves as organic substrate to microbial communities (Chimney and Pietro, 2006; DeBusk and Reddy, 2005; Reddy and DeLaune, 2008)
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From page 154... ...
. Continuous phosphorus loading into the STAs has resulted in distinct phosphorus gradients in the soil and water column with high v alues in upstream areas and low levels in downstream areas.
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From page 155... ...
. Approximately one-third of stored phosphorus is highly reactive and susceptible to release from the sediment into the water column via advective and diffusive flux, resulting in high internal loads, especially in upstream areas of treatment cells.
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From page 156... ...
soils, thus raising concerns about the long-term capacity to achieve and maintain desirable outflow TP concentrations. Phosphorus removal efficiency and TP concentrations in upstream treatment cells can serve as an indicator of phosphorus saturation status of the soil and pro vide early warning signals of the need for management actions.
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From page 157... ...
A vigorous adaptive management program is merited for an initiative as large and as consequential as Restoration Strategies, which is based on complex natural biogeochemical process whose interactions and dynamics are not fully
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From page 158... ...
For the STAs, WQBEL compliance beginning in WY 2027, following the full implementation of Restoration Strategies, represents the key quantitative objec tive. However, given the importance of WQBEL compliance to the full opera tion of other CERP features, such as the EAA Reservoir, the committee recom mends that the SFWMD establish intermediate milestones for each STA, so that managers remain fully informed about whether the STAs are on their expected trajectories and can address unexpected issues as early as practicable, ideally well before the first year of WQBEL compliance assessment in WY 2027.
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From page 159... ...
Evaluation of Inundation Depth and Duration for Cattail Sustainability -- completed 2021 4. Investigation of STA-3/4 PSTA Performance, Design and Operational Factors -- completed 2018 (monitoring continuing)
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From page 160... ...
Focused cell-by-cell data would help managers understand how a cell is responding to Restoration Strategies rehabilitation efforts, whether phosphorus saturation is occurring that could compromise the removal of phosphorus necessary to attain the WQBEL, and whether additional near-term management steps are needed, such as those discussed later in this chapter. Modeling, Machine Learning, Data Analysis, and Integration Models have been primarily used to inform STA design (e.g., Dynamic Model for Stormwater Treatment Areas [DMSTA]
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From page 161... ...
, employs a tank-in-series hydraulic framework with simple expressions for flow-dependent phosphorous removal and internal phosphorus loading (Juston and Kadlec, 2019)
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From page 162... ...
The influence of fish and wildlife on STA performance, 5. Management of internal phosphorus loading, and 6.
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From page 163... ...
, it remains unclear to what extent effective phosphorus removal was due to p eriphyton uptake or other factors such as low phosphorus inflow concentrations and/or lime rock exposure. These uncertainties underscore the need to understand the phosphorus removal efficiencies of different growth forms (e.g., submergent versus emergent vegetation)
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From page 164... ...
Near-term options to improve STA performance include improving hydraulic loading rates, reducing phosphorus concentra tions and loading rates, managing vegetation, and managing floc and soil. The SFWMD is actively using these tools to improve phosphorus removal efficiency, although some additional considerations are noted below.
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From page 165... ...
26 Prior to the STA expansions, STA-1E and STA-1W included approximately 11,400 acres. The addition of 5,820 acres through Restoration Strategies will increase the total STA acreage in the Eastern Flow Path to approximately 17,220 acres.
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From page 166... ...
Alternative Agricultural Management A potentially effective approach to reaching phosphorus targets is to control the phosphorus concentrations and loads entering STAs from external sources. Additional attention to source reduction, particularly in the Eastern and Western Flow Paths, may ultimately be necessary and may well prove cost-effective in
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From page 167... ...
For example, if STAs are not performing adequately, instead of moving water south through the STAs, managers theoretically could opt to reduce hydraulic and phosphorus loading rates by discharging the water to the coastal estuaries. This outcome would result in a cascade of adverse effects by reducing the flow of water south and by increasing the discharge of nutrients to the estuaries.
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From page 168... ...
Talented and experienced SFWMD scientists and engineers are working on the STAs, as evidenced by the phosphorus removal performance to date, and substantial research is under way through the Restoration Strategies Science Plan that should be useful to STA management. Nonetheless, the extent of phosphorus removal needed to meet and sustain the WQBEL will likely require even stronger science support for decision making, cell-by-cell monitoring, new modeling tools, detailed analysis of available data, and frequent feedback between science and management to support rapid, science-informed decision making and to reduce the likelihood of water quality impeding CERP progress.
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From page 169... ...
Dissolved organic and particulate phosphorus can represent substantial fractions of TP concentrations in STA outflows, but current management efforts are generally focused on TP rather than individual forms of phosphorus. The interplay between nitrogen and phosphorus and the significance of nitrogen-limiting conditions deserves additional atten tion in understanding factors that affect phosphorus removal efficiency.
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From page 170... ...
. Restoration Strategies includes all three approaches in some capacity to reach the WQBEL, with most efforts devoted to improving phosphorus removal efficiency, but little progress has been made to reduce subregional phosphorus loads in the Eastern Flow Path.
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