Progress Toward Restoring the Everglades The Ninth Biennial Review - 2022 (2023) / Chapter Skim
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Pages 137-168
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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... ...
High nutrient concentrations also have implications for the Central Everglades Restoration Plan and the plans to move more Lake Okeechobee water south into the remnant Everglades. High TP in Lake Okeechobee could challenge the capacity of stormwater treatment area infrastructure to meet the water quality discharge standards.
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From page 141... ...
Storms and High Hydraulic Loading. Storm events or prolonged wet weather can influence STA performance through changes in hydraulic loading.
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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... ...
or other sources of water storage, such as an FEB, can eliminate dryout conditions if suf ficient water is available. 20 STA-3/4 has a maximum inflow capacity of 6,475 cfs via the G-370 and G-372 pump stations (FDEP, 2017b)
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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... ...
. In addition, underwater photosynthesis by SAV creates an environment that facilitates abiotic immobilization of phosphorus from the water column.
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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... ...
After 20 years of operation, water column TP concentrations during regular flow events showed a plateau in the upstream areas of flow-way, followed by a steady decrease in water column TP concentrations in the downstream cells, suggesting reduced uptake in upper cells with phosphorus-saturated soils. A more pronounced plateau is observed under no-flow conditions where internal loading is offsetting any TP uptake.
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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... ...
This knowledge, in turn, could be used to optimize STA operations, inform routine maintenance and refurbishment schedules, and assess potential system modifications intended to increase phosphorous removal. Considering the recent advances in wetland water quality models and the insights that can be gained through their application, the committee judges that they should play a greater role within an adaptive management framework for WQBEL attainment.
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From page 162... ...
The 2018 Science Plan indicates that internal phosphorus loading is an understudied phenomenon in the STAs and that additional research is needed to examine the biological, chemical, and physi cal factors that influence this process (Orihel et al., 2017; Steinman and Spears, 2020) , with particular attention paid to dissolved organic phosphorus.
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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... ...
Different phosphorus removal mechanisms in EAV and SAV areas result in different soil types and biogeochemical processes. The more organic soils derived from EAV are capable of trapping particulate matter whereas the soils dominated by SAV are characterized by more mineral matter, are flocculent, and are easily suspended in the water column (Reddy et al., 2019a)
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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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