Restoration Strategies Science Plan

L-8 FEB Study

The L-8 Flow Equalization Basin (FEB), is a 950-acre basin that can store nearly 45,000 ac-ft of water. The primary purposes of the L-8 FEB are to reduce peak stormwater flows, temporarily store stormwater runoff and improve water delivery to Stormwater Treatment Areas (STAs) STA-1E and STA-1W. This improved water delivery should enhance STA performance to achieve state water quality standards in the Everglades.

In water year 2018 (WY2018: May 2017 to April 2018), the flow weighted mean concentration (FWMC) of total phosphorus (TP) in outflow from the L-8 FEB was higher than inflow. Potential sources of the increase TP in outflow include groundwater, levee sediment erosion, benthic sediment resuspension, and phosphorus release from aquatic plants and animals.  The objective of this study is to determine the potential sources of this excess TP and to provide operational guidance to limit the occurrence of higher TP outflow compared to TP inflow.

The study includes three phases:

• Phase I - Evaluate vertical and horizontal water column phosphorus concentrations to determine if increased TP is related to water levels and/or groundwater interactions.
• Phase II - Investigate the potential of levee sediment erosion and benthic sediment resuspension on TP concentration increases.
• Phase III – (if needed) Investigate biological sources of P.

More Information can be found here:

Study Plan

Activities Completed and Current Status

Phase I sampling of groundwater and waters within the L-8 FEB found much lower TP concentrations in groundwater samples than surface water samples. This result indicates that groundwater does not contribute to the intermittent high TP concentrations at the outflow site. Particulate phosphorus (PP) constitutes the major fraction of TP in the surface water suggesting that resuspension, or introduction of sediments may be the source of PP in the FEB surface water, which could contribute to the occasionally observed high TP concentrations at the outflow site.

For Phase II, sediment was sampled in and around the FEB along with four surface water quality sampling events that collected water under contrasting hydrologic conditions. Sediments from the FEB banks had low TP content compared to benthic sediments making them unlikely candidates to explain periods of relatively high TP in water column. Large flows of water at the G538 inflow structure contributed significant loads of nutrients and suspended materials into the FEB. Additionally, these large flow events may have disturbed benthic sediments resuspending into the water column. These suspended particulates release dissolved P into the water column, which can then be converted into algal biomass resulting in temporarily elevated TP in the water column. Whether these suspended particles originate outside the FEB or are resuspended inside the FEB will be investigated in future Phase II sampling activities.   

Reports and Publications

1. DB Environmental, 2019, L-8 FEB Surface Water and Groundwater Quality Monitoring, Deliverable #A3.5 Sampling Report. Prepared in fulfilment of Contract 4600003883 on Inter-Agency Agreement to Conduct Scientific Studies Relevant to the Stormwater Treatment Areas. South Florida Water Management District, West Palm Beach, FL.
2. DB Environmental, 2020, L-8 FEB Targeted Surface Water and Sediment Assessment, Deliverable #A3.7 Sampling Report. Prepared in fulfilment of Contract 4600004075 on Inter-Agency Agreement to Conduct Scientific Studies Relevant to the Stormwater Treatment Areas. South Florida Water Management District, West Palm Beach, FL.

Evaluation of Inundation Depth and Duration for Cattail Sustainability

Description/Objective
Cattail (Typha domingensis) communities are an important component of Stormwater Treatment Areas (STAs). They remove particulate phosphorus (PP) by reducing water turbulence allowing the particles to settle. PP in moving water also may be removed by sticking to plant leaves.  Soluble P is removed by algae attached to cattail leaves. Algae and particulate P can settled onto soils, where this material can be buried or  degraded, releasing soluble forms of P.  The soluble P may be taken up by cattail roots and stored in roots, rhizomes, shoots or leaves of the plant.

Rows of cattail planted at intervals throughout STAs support other aquatic vegetation by reducing water flow velocity in the STA and blocking the effects of winds from major storm events.

Cattails are hardy plants, but they can die off if water levels are too deep for a long period. 

Phase I of this study evaluated cattail in the field through seasonal monitoring of water depths, cattail density, leaf elongation, photosynthesis, and plant biomass in a number of locations in STA-3/4 Cell 2A with varying water depths. Declines in any of these measures are an indicator of poorer cattail health.  

Phase II of this study evaluated the effects of water depth on cattail health in a more controlled environment:  half-acre test cells in which water depths were maintained at constant water levels between 40 and 124 cm.  The results of this study will support operation of STAs by defining optimal water depths and the length of time suboptimal (deep) water depths can be maintained to support cattail communities in the STAs.

More information can be found here:

Detailed Study Plan

Activities Completed, Results and Current Status

Phase I field monitoring occurred from Water Year (WY: May through April) 2016 to WY2018. Cattail densities during the wet seasons were lower in the deeper inflow region of STA-3/4 Cell 2A than in the shallower outflow region. Cattail densities declined in the inflow region due to water depths >91 cm for long periods of time in the 2016 and 2017 wet seasons. Leaf elongation rates were consistently higher in the inflow region. Photosynthetic rates and total live biomass were not different between the inflow and outflow regions. Throughout the STA cell, cattail biomass declined over time. The belowground biomass:leaf ratio declined over time in the inflow region indicating that the cattail population was stressed more in this region.

Phase II water depth experiments were carried out in the STA-1W Northern Test Cells (see photo above). Phase I results were used to develop the experimental design of this test cell experiment, which includes treatment water depths of: 1) 1.3 feet (40 cm, 2) 2.0 feet (61 cm), 3)  2.75 feet (84 cm), 4) 3.4 feet (104 cm), and 5) 4.1 feet (124 cm). Each treatment was replicated in 3 treatment cells, with the 1.3 foot test cells serving as the controls.

Test cells were refurbished in 2016 to improve soil and water control. Seedling cattails were planted, and cattail seeds were scattered in the test cells from May and June 2018. Cattail plants were fully mature in the spring of 2019. The water depth experiments started on July 1^st, 2019.

Cattail abundance and water quality were evaluated at least monthly from July 2019 to late April 2020. Final cattail biomass sampling and processing were completed late July 2020. Initial results indicate that the deep (3.4 feet) and extremely deep (4.1 feet) treatments stressed cattail plants more as observed from differences in density, leaf area index, leaf elongation and final biomass than those observed in moderate (2.75 feet) and shallow (2.0 feet) depth treatments. These preliminary results agree with the Phase I in-situ study. This study will determine more precisely the water depth and duration Cattail can tolerate without a decline in health.

Figure 1. STA-3/4 Cell 2A survey plot (red) and water level logger (blue) locations.

Reports and Publications

1. Diaz, O., Appendix 5C-5: Evaluation of Inundation Depth and Duration Threshold for Cattail Sustainability., in South Florida Environmental Report – Volume I. 2018: South Florida Water Management District, West Palm Beach, FL.
2. Diaz, O. and K. Vaughan., Appendix 5C-2. Evaluation of Inundation Depth and Duration Threshold for Cattail Sustainability: In-Situ Study., in 2019 South Florida Environmental Report – Volume I. 2019: South Florida Water Management District, West Palm Beach, FL.

Use of Soil Amendments or Soil Management to Control Phosphorus Flux

Description/Objective

Stormwater Treatment Areas (STAs) remove phosphorus (P) from agricultural and urban runoff before discharging into the Everglades and have been constructed to a large extent on former agricultural lands. Once the STAs are flooded, P in the soils can be released (flux) into the water column. This study was intended to screen methods that could reduce P flux from the flooded soil by application of soil amendments and/or management techniques. Effective methods may be useful at appropriate locations within the STAs to lower outflow P concentrations.

This study was to include three phases:

• Phase I – Review existing information on soil amendments and/or management techniques applicable to wetlands.
• Phase II – Conduct small-scale experiments to screen soil amendments or management techniques identified in Phase I
• Phase III – Conduct large-scale field trials of the most promising technologies identified in Phases I and II.

More Information can be found here:

Detailed Study Plan

Activities Completed and Current Status

Phase I:  Completed. Technologies to reduce soil-P flux in wetlands or lakes were reviewed from the literature and past SFWMD projects. The technologies were evaluated for their potential to scale up to field trials in the STAs.

Phase II: This phase was cancelled due to uncertainties of long-term treatment effectiveness of soil amendments, potential negative effects on STA operations, high costs to implement at full-scale in the STAs and potential negative effects to the downstream Everglades flora and fauna.

Phase III: Ongoing. The scope of this phase was scaled back and now includes only an evaluation of the efficacy of soil management, specifically soil inversion in the STA-1 West (STA-1W) Expansion Area (EA).

Results
A comprehensive review of available technologies and soil amendments indicated that many potentially could lower P flux from flooded soils. However, due to the uncertainties listed above, all further evaluations were cancelled, with one exception: soil inversion (i.e., soil management without amendments).

Soils in the STA-1 West Cell 7 expansion were inverted as a remedial action to bury high copper concentrations that resulted from past agricultural practices. Soils in the adjacent Cell 8 were not inverted and are considered a control. Prior to flooding these cells, soils were collected and incubated to determine the amount of soluble P that could be released.  Phosphorus release from inverted soils was less than non-inverted soils. All STA-1W EA cells have since been flooded but are not operational. Once this facility begins treating water, P concentrations will be monitored at Cell 7 and 8 inflow and outflow sites to evaluate treatment performance in these cells.

1. Chimney, M., 2015, Phase I Summary Report for the Use of Soil Amendments/Management to Control P Flux Study. Technical Publication WR-2015-006.  South Florida Water Management District, West Palm Beach, FL.
2. Josan, M., B. Taylor, and K. Grace, 2019, Appendix 5C-3: Use of Soil Inversion to Control Phosphorus Flux. In: 2019 South Florida Environmental Report – Volume I. South Florida Water Management District, West Palm Beach, FL.

Improving Resilience of Submerged Aquatic Vegetation in the Stormwater Treatment Areas

Description/Objective

Submerged aquatic vegetation (SAV) communities are important for Stormwater Treatment Area (STAs) performance as they remove phosphorus (P) from the water column.  This occurs primarily by chemical reactions where phosphate coprecipitates with calcium (Ca) as CO₂ is removed from the water column during photosynthesis. This removal of P, especially at low P concentrations, is a major mechanism that supports P reduction from the STA water column prior to discharge into the Everglades.

To understand SAV species distribution, persistence, colonization, and recovery in Stormwater Treatment Areas (STAs), the objectives of this study are to investigate SAV biology, water chemistry, soil chemistry, soil physical characteristics, herbivory, and their interactions.

The study has two phases:

• Phase I – Review of literature and analysis of historical SAV data to develop a detailed study plan for Phase II.
• Phase II – Evaluate potential stressors of SAV growth and persistence with field surveys and experiments using mesocosms or enclosures to evaluate the effects of marl, muck, or aged muck soils; hydraulic and P loading rates; drying out wetland soils; and herbivory by fish.

More Information can be found here:

Detailed Study Plan

Activities Completed and Current Status

Phase I: SAV survey datasets between 2000 and 2018 were compiled and key data gaps were identified. Literature and historical data of selected STA flow-ways were reviewed. Field monitoring methods were evaluated and optimized. This phase is complete

Phase II: of the three experiments initiated, two have been completed.

Results
Phase I - SAV growth, persistence, and sustainability can be affected by numerous factors. These include: P and nitrogen loading, turbidity, Ca concentrations, water depth, sediment accretion, dry down/reflood events, wind/wave disturbance events, herbivory, and physiological senescence.  

Results of SAV surveys indicate that, 1) SAV standing crop biomass and tissue P content decreases with distance in an STA flow-way, 2) floating aquatic vegetation (FAV) encroachment into SAV areas, followed by herbicide treatment of FAV biomass, may reduce SAV densities and  P removal performance, and 3) random environmental events (e.g., high flows, drawdown or cold temperatures) can change SAV community distribution.

Phase II – Experiment 1 compared SAV growth on farm muck, aged muck (older muck soils from STAs), or marl soils and found that plants grew well with no significant differences among all soils. Tissue macro-nutrients (P) and micro-nutrients (Zn, Cu, Fe) for plants grown on marl were lower than those grown on farm muck, suggesting reduced nutrient availability to the SAV standing crop as STAs “age”.

Experiment 2 is ongoing and has demonstrated that Chara (a common SAV species) can acquire nutrients relative to the supply in the water column. If the nutrient supply is high, Chara concentrates its biomass near the water surface. This creates reducing and frequent anoxic conditions in the bottom waters, which could stress the SAV community and reduce P removal efficiency. Under lower nutrient supply, the biomass is more diffuse and oxygenated conditions are more homogenous throughout the water column.

Experiment 3 examined germination and growth rates of SAV on previously dried soils versus soils that remained hydrated. Germination was highest on previously dried soils, and shallow rooted SAV (e.g. Chara) germinated more robustly. More deeply rooted plants were less successful on dried soils, and overall SAV growth rates did not vary between soil types.

Experiment 4 measured growth rates of common SAV species and herbivory effects within a flow-way that previously supported them, but are now absent. SAV was inoculated into netted enclosures (1.5 m² area) in monocultures and polycultures, and select enclosures included exotic nuisance fish. Shallow rooted species had the highest growth grates, and more deeply rooted plants had higher growth rates when mixed compared to when grown in monoculture. SAV biomass development was significantly reduced in enclosures than included fish compared to enclosures without fish.

References

1. DBE, 2018, Deliverable A1.1 under Agreement No. 4600003883, SAV Resilience Study Work Plan: Studies on Improving the Resilience of SAV in the STAs. . Prepared by DB Environmental, Inc.for South Florida Water Management District, West Palm Beach, FL.
2. DBE, 2019, Deliverable A1.5 under Agreement No. 4600003883, SAV Resilience Study Report 4: Studies on Improving the Resilience of SAV in the STAs. Prepared by DB Environmental, Inc.for South Florida Water Management District, West Palm Beach, FL.
3. DBE, 2020, Deliverable A1.5 under Agreement No. 4600003883, SAV Resilience Study Report 4: Studies on Improving the Resilience of SAV in the STAs. Prepared by DB Environmental, Inc.for South Florida Water Management District, West Palm Beach, FL.

Evaluation of Factors Contributing to the Formation of Floating Tussocks in the Stormwater Treatment Areas

Description/Objective

Floating tussocks (wetlands) in Stormwater Treatment Areas (STAs) can uproot Emergent Aquatic Vegetation (EAV), shade out submerged aquatic vegetation (SAV), increase turbidity, block gates and other water control structures, and create short circuits. All these actions can reduce STA performance.  This study evaluates factors that cause the formation of floating wetland areas in STAs, methods to determine current coverage of these floating areas, and an assessment of strategies to reduce their occurrence.

The study includes two phases:

• Phase 1 included 4 tasks:

1. A literature review of floating wetland types, buoyancy mechanisms, formation, and controls.
2. A nomenclature of floating wetlands based on soils, plant communities, size, and location.
3. Classification maps of floating wetland communities in STA 1W Cell 2A and STA 2 Cell 7 using unmanned aerial systems (UAS).
4. Thermographic imagery to detect floating vs. emergent vegetation.

• Phase II will build on the findings from Phase I to determine potential causes and methods to reduce the occurrence of floating wetland formation. 

1. Evaluate relationships between occurrence and distribution of floating wetlands and potential environmental and management factors that are likely to trigger floating wetland formation,
2. Refine UAS methodology and workflow, then apply to all STA emergent aquatic vegetation (EAV) cells, and
3. Develop a Typha Wetland Buoyancy Model to develop a metric of soil cohesion that can be used to quantify the soils “holding capacity”. 

More information can be found here:

Detailed Study Plan
 

Activities Completed and Current Status

Phase I: All Tasks are completed.

Phase II: Task 1 – Data mining and environmental factors related to floating tussock formation was completed in June 2020; Task 2 – Refine UAS methodology and workflow; and Task 3 – Typha wetland buoyancy model, was significantly delayed due to University of Florida COVID-19 travel and field activity restrictions. The timeline for these remaining deliverables has been changed to account for these delays until the first quarter of 2021.  

Results

Floating wetland communities were identified in two EAV cells using multispectral drone imagery. Typha floating wetlands complexes were discovered that otherwise would not be apparent in satellite imagery.  Floating wetlands were identified based on observed flattened vegetation, presence of fern seedlings, and nearby open seams. Thermographic imagery was difficult to interpret. However, midday imagery was most useful and could complement the other spectral interpretation. A nomenclature of floating wetlands (tussocks, mats, islands, and complexes) was developed from the literature review. Historical data from the STAs were analyzed to identify significant predictors of floating wetlands communities across EAV cells. Results suggested a higher likelihood of floating vegetation occurrence in treatment wetlands cells with greater high-water levels, cells that had lower TP soil storage at the start of cell operations, and cells built on agricultural land that were farmed prior to cell construction. A buoyancy model based on this literature review will be developed in Phase II.

Reports and Publications

1. Clark, M., and K. Glodzic. 2019. Assessment of Floating Wetlands Coverage in STA EAV Cells. Task 3a Submitted by Soil and Water Science Department, University of Florida, Gainesville FL, to South Florida Water Management District, West Palm Beach, FL.
2. Clark, M., and K. Glodzic. 2020. Data Mining and Statistical Analysis of Environmental Factors Related to Floating Tussock Formation. Task 1 Submitted by Soil and Water Science Department, University of Florida, Gainesville FL, to South Florida Water Management District, West Palm Beach, FL.

Investigation of the Effects of Abundant Faunal Species on Phosphorus Cycling in the Everglades Stormwater Treatment Areas

Description/Objective
Aquatic fauna: fish and large invertebrates such as crayfish, may significantly affect phosphorus (P) cycling within Stormwater Treatment Areas (STAs). This study evaluates the potential of aquatic fauna to affect P reduction in STA surface waters. The study should provide management recommendations for aquatic fauna to improve STA treatment performance.

The study includes five tasks:

• Task I – (Ongoing through June 2022): Estimate biomass of fish and aquatic invertebrates (STA-2) and aquatic faunal community composition (STAs 1E, 1W and 3/4); analyze P and nitrogen (N) storage in tissues of individuals of abundant fishes (STA-2).
• Task II – (Ongoing through May 2021): Estimate P excretion rates of selected abundant fishes to estimate contribution to STA P budgets. Evaluate benthic (sediment foraging) fish species to determine their contribution to water column nutrients through bioturbation (i.e. activities that re-suspend soils, including particle disturbance, ingestion and defecation).
• Task III – (Ongoing through October 2022): Use biomass and excretion estimates to calculate areal (per ha) P excretion by the entire aquatic faunal population in STA-2 (i.e. rates of P released to the water column via excretion, μg P/ha/ h).
• Task IV – (to begin in July 2021): Calibrate electrofishing by comparing biomass of non-native fish collected by electrofishing to known numbers of these fish through block net collection.
• Task V – (to begin in 2021) Estimate the effect of herbivory on SAV production

More information can be found here:

Work Plan

Activities Completed and Current Status

The STAs support a high biomass of fish and macroinvertebrates. By comparison, the biomass per unit area was approximately 2-15 times more than in other Everglades regions.

Ten of the most abundant fish species stored one metric ton of P and 3.7 metric tons of N within their body tissues, and excreted >0.626 kg of P per hour and >3.897 kg of N per hour. These calculations demonstrate that storage and excretion by fishes are important processes of P and N cycles within STA habitats. Future research will focus on refining the current estimates and incorporating the effects of fish into nutrient budgets for the STAs.

Reports and Publications

1. Evans, N., J. Trexler, and M. Cook, 2018, The Effects of Faunal Communities on Water Quality in the Everglades Stormwater Treatment Areas. In: . 2018 South Florida Environmental Report – Volume I, , in Appendix 5C-3: Evaluation of Phosphorus Sources, Forms, Flux, and Transformation Processes in the Stormwater Treatment Areas,, O. Villapando and J. King, Editors.: South Florida Water Management District, West Palm Beach, FL.
2. Evans, N., et al., 2019, Appendix 5C-4:  Effects of Abundant Faunal Species on Phosphorus Cycling in the Stormwater Treatment Areas. In 2019 South Florida Environmental Report – Volume I, . South Florida Water Management District, West Palm Beach, FL.
3. Evans, N., et al., 2020, Appendix 5C-1: Estimating Phosphorus and Nitrogen Excretion in Fishes in the Everglades Stormwater Treatment Areas  In 2020 South Florida Environmental Report – Volume I, . South Florida Water Management District, West Palm Beach, FL.

Data Integration Study

Description/Objective
The purpose of the Data Integration and Analysis Study (Data Integration Study) is to synthesize and summarize results from the Restoration Strategies Science Plan (RSSP) Studies, and other STA scientific activities, to provide a comprehensive understanding of phosphorus (P) dynamics and factors affecting Everglades Stormwater Treatment Area (STA) removal performance, and to develop STA design, operation and management guidance to achieve optimal STA performance.

The tasks to accomplish the Data Integration Study include:

1. Document Review – Document major findings from STA research and Science Plan studies that define P movement and transformations throughout these constructed wetlands and evaluate how the various components interact to support or inhibit P removal from the water column. 
2. Data Analyses - Analyze data to support the document review and modeling efforts
3. Modeling - Develop and/or update models that describe STA P dynamics at various functional and spatial scales. Information from RSSP reports and data will be used to enhance existing models and/or create new models.
4. Gap Analysis – Use the results of the first three tasks to determine where gaps in understanding of the P cycling process in STAs may be essential to manage P removal.  Develop methods to fill gaps through literature and/or statistical methods using Science Plan and/or STA data
5. Guidance Document - Develop a guidance document that supports the design, operation, and management of STAs to achieve compliance with the WQBEL.

More information can be found here:

Detailed Study Plan

Activities Completed and Current Status

Three separate substudies are currently underway.

1) Microbial data integration- this study is compiling the microbial research in STAs with specific focus on Periphyton (attached algae), processes, biomass, and enzyme activity.

2) Biogeochemical and CASM models – Phase I will review the literature to determine the direct interaction of significant P components within the STAs and develop conceptual biogeochemical and CASM models that represent P cycling in the STAs. Phase II will develop the models which include the mathematical formulations of interactions of the components.

3) STA and Water Conservation Area 2A evaluation- this study will develop a statistical model of the water quality data in the STAs, evaluate the change in P in the STAs over space and time, and compare and contrast the similarities and differences in WCA and STA-2 to determine if there are management activities that can be undertaken in the STAs to attain lower P concentrations in the outflow water.

Results

All three of these substudies have collated and reviewed literature from past studies and from peer reviewed journals.  The Microbial Data Integration Study and the STA and Water Conservation Area Study have compiled historical data. The Biogeochemical and CASM Models Phase I have developed preliminary interaction matrices of STA components as well as preliminary conceptual SAV and EAV models.

Biomarker Study

Description/Objective

The stormwater treatment areas (STAs) were created to decrease phosphorus (P) inputs into the Everglades. Phosphorus can come in many forms, some of which is associated with particles (particulate P) and organic matter (organic P). These forms of P may be stored in the soils and plants of the STA, consumed by organisms like fish and microorganisms and then recycled into other P forms (internal cycling), or exported to the Everglades. However, we do not yet know all the conditions (drivers) that control the fate of P in the STAs.

A Pilot study indicated that this approach could provide information on P sources and sinks within the STA. This study will measure the forms of P in the STAs, where they may originate, and what factors (light, microbial decomposition) may affect them in the STAs.

This study includes three phases:

• Phase 1: Characterization of STA source waters
• Phase 2: Identification of fish biomarkers
• Phase 3: Experiment to test mechanisms of P turnover in the STAs

More Information can be found here:

Work Plan

Activities completed and current status

The project was initiated in September 2020, work has been begun for all three phases:

Phase 1. Characterization of STA source waters. Source water samples have been collected from eight locations of source water to the STAs and are currently being analyzed at the University of Florida for various organic components (such as amino acids, lignin, and sterols) as well as molecular weight, Xray absorbance, size fraction and P speciation.  These analyses may help to identify the degradability and origin of the P molecules.

Phase 2. Identification of fish biomarkers. In collaboration with researchers at Florida International University, samples from fish excretion studies have been collected and are being analyzed to identify fish excretion “fingerprints.” These fingerprints will assist to determine the contribution of fish excretion to internal P cycling within the STAs.

Phase 3. Experiment to test mechanisms of P turnover in the STAs. This experiment will be conducted in late spring/early summer of 2021 and will evaluate how light and microbial decomposition influence P turnover in the STAs.

Reports and Publications

1. Morrison ES, Shields MR, Bianchi TS, Liu Y, Newman S, Tolic N, Chu RK. 2019. Multiple biomarkers highlight the importance of water column processes in treatment wetland organic matter cycling. Water Res 168: 115153. Elsevier Ltd. doi: 10.1016/j.watres.2019.115153

Evaluate Phosphorus Sources, Forms, Flux and Transformation Processes in the Everglades Stormwater Treatment Areas

Description/Objective

To understand how Phosphorus (P) is processed and removed within well performing Stormwater Treatment Areas (STAs), this multi-component study evaluated mechanisms and factors affecting P reduction from the water column particularly in the outflow regions of the STAs. The study measured flow-way (FW) water quality, internal phosphorus loads, soil, microbial enzymes, vegetation, particulate transport and settling, fauna, and organic P speciation. In addition, these data were synthesized to explain factors and processes influencing STA performance and will serve as the basis to develop or improve management options to reduce total P (TP) discharge concentrations from the STAs.

More Information can be found here:

Detailed Study Plan

Activities Completed, Results and Current Status

The Study was completed in 2019

Vegetation type, depth in the profile and distance from the inflow affected P sorption and desorption. The floc and RAS were more reactive than underlying soils. SAV-dominated sites generally exhibited a greater potential to retain P at low surface water P concentrations, than EAV-dominated sites.  No trend was found for P sorption or desorption from the inflow to the outflow regions. P desorption tended to be higher for EAV than SAV-dominated sites. P sorption was strongly related to extractable and total Fe and Al for EAV-dominated FWs, and Ca and Mg in SAV-dominated FWs.

EAV in STA-2 had higher concentrations of P, N and C in plant material compared to SAV.  Of the SAV species, Chara had the highest nutrient storages of all species.  EAV biomass and performance were consistent throughout the study in FW 1 while FW 3 experienced a decline in performance following the significant loss of SAV. 

• Flow-way Water Quality Assessment: P cycling in three well-performing STA FWs was evaluated under high, moderate, low and no flow conditions.  TP concentrations were high at the inflow region--consisting primarily of inorganic phosphate--and low at the outflow region--consisting primarily of particulate P (PP) and dissolved organic P (DOP). These results were consistent for all flow conditions in all FWs. More P was removed from the water column of emergent aquatic vegetation (EAV) regions than submerged aquatic vegetation (SAV) regions. In SAV regions, TP increased under no flow condition--primarily as particulate P (PP)--which could be from internal loads caused by periphyton sloughing, litter fragmentation, or bioturbation. P concentrations were slightly higher in SAV systems than in EAV systems under no flow condition.   


• Flux Measurements: P concentrations in field chambers increased during no flow periods, indicating internal P loading from vegetation mining of soils and turnover. This increasing P trend, evaluated with a computer model, suggested that internal loading was a significant contributor to the P cycle. Internal loading was highest at inflow regions and lowest in outflow regions of the FWs.


• Soil P Characterization: P concentrations in floc and recently accreted soils (RAS) declined from higher values at the inflow regions to low values at the outflow regions. Phosphorus in floc and RAS was higher and more spatially extensive in EAV than SAV areas of the STAs. The decreasing trend of P from inflow to outflow resulted in increasing trend of N:P ratio from inflow to outflow. P was primarily in an organic form in EAV and inorganic mineral form in SAV areas. P accretion rate was higher in SAV than in EAV due to accumulation of material high in inorganic matter.


• Microbial Enzymatic Patterns: Within the STA flowways, the microbial communities play an important role in nutrient cycling, especially when nutrient limiting conditions exist. Required nutrients (i.e., C, N, or P) can be released from the dissolved organic compounds by enzymes produced by the microbes. Enzyme activity--a measure of microbial community activity--was affected by flow conditions among each component and differing responses were observed along the flowways and within the vegetation communities. The level of enzyme activity was highest in the periphyton and lowest in the surface water. Enzyme activity in the surface water during flow conditions, was often undetectable.  With regard to enzyme response and nutrient conditions, flow resulted in more N-limited conditions in the EAV areas for floc and more P-limited conditions in the SAV areas. In the periphyton, C-limited conditions increased during flow in the EAV areas, but an opposite effect was observed in the SAV areas. In both plant communities, N-limiting conditions in the periphyton was greatest during no flow periods. In both the floc and periphyton, greatest P-limiting conditions were observed at the outflow locations. These variable responses indicate that flow conditions have a complex effect on the microbial responses within each component and that nutrient limiting conditions change along the flowways and within the major components.


• Vegetation Assessments: Satellite images of STA areas in wet and dry seasons detected differences in SAV and EAV spectral signatures. SAV areas dominated by a single species, specifically Chara, could be accurately identified. Mixed SAV species beds were more difficult to distinguish. When cross-validated with ground observations, the spectral analysis correctly classified 96% of reference samples.


• Particulate Transport and Settling: Water velocities in the STAs are affected by gate operations, wind, and distance to remnant agricultural canals and ditches, with highest velocities near inflow and outflow structures and remnant canals/ditches. Inflow regions had the highest observed sediment settling/resuspension and net accumulation rates. Measured net P accumulation rates into floc were similar in magnitude to net P storage estimated from mass balance for STA-2 FW 3.  STA-3/4 Cell 3B had lower storage rates, which is attributed to lower accumulation, higher erosion, and/or more spatial variability at this cell’s inflow regions. At relatively low and stable water velocities (< 0.5 cm/s), water column particulates likely originate from sloughed SAV biomass rather than sediments and are caused by wave related stress rather than flow driven stress. PP resuspension and settling measurements in SAV areas are approximately 10 times higher than total P loading and accumulation rates derived from mass balance. Therefore, the potential for large swings in P storage or loss may be expected depending on the factors that drive these fluxes. 


• Fauna Study: STA fish nutrient content and nutrient ratios were similar to values reported for enriched areas of Water Conservation Area 2A. Fish tissues contained an estimated 1 metric ton of TP and 3.7 metric tons of TN in STA-2 Cells 3, 4, 5, and 6. Because of the substantial fish population, further analyses on the contribution of fauna to the water column P in the outflow regions of STAs is being investigated as a separate Fauna Study.


• Organic P Speciation: Biomarkers (lignin phenols, amino acids, and pigments) as a measure of organic matter (OM) quality were compared between STA-3/4 and a reference wetland WCA-2A. More vascular plant-based OM was found in EAV areas, and more algal-based OM was found in SAV areas. OM was fresher and more degradable in treatment SAV sites than reference wetland sites. Other than dense cattail areas, water column particulate OM in SAV areas was primarily from microbial sources. Amino acid degradation indices and organic P were positively correlated with bacterial amino acid biomarkers, suggesting microbial abundance was associated with “fresher” OM. This multi-biomarker approach may evaluate the relative “freshness” of OM pools, identify sources of OM, and provide relative measures of water column processes in P cycling in STAs. Due to the significant results further analysis is being conducted under a separate Biomarker Study.


• Data Synthesis and Integration: This effort focused on two major approaches.  One using a numerical version of a conceptual model that incorporated a number of different (yet connected) data sets. This “bottom up approach” model identifies specific fluxes and transformations among major P reservoirs within the STAs.  When integrated with existing data, key processes (settling, resuspension, etc.) were captured well with a better model-data match for EAV than for SAV. The “top down approach” model focused on two major controlling variables, internal load and flow. This model evaluated transect data and the effects of varying flows on outflow P concentrations. Model results suggest that internal loading and flow affected outflow P concentration dynamics. Further synthesis and integration beyond the P Flux study is being conducted in the Data Integration Study.

Reports and Publications

1. Villapando, R. and J. King, 2019, Appendix 5C-3: Evaluation of Phosphorus Forms. Flux, and Transformation Processes in the Stormwater Treatment Areas in Volume I 2019 South Florida Environmental Report.

2. DBE, 2018 Field and Supplemental Laboratory Support for Evaluating Phosphorus Sources, Flux, and Transformation Processes in the Stormwater Treatment Areas – Annual Report. Prepared by DB Environmental, Inc. under Agreement 4600003029-WO01 for South Florida Water Management District, West Palm Beach, FL.

3.  DBE, 2019, Field and Supplemental Laboratory Support for Evaluating Phosphorus Sources, Flux, and Transformation Processes in the Stormwater Treatment Areas – Annual Report. Prepared by DB Environmental, Inc. under Agreement 4600003029-WO01 for South Florida Water Management District, West Palm Beach, FL.

4.  Jerauld, M., et al., 2020, Internal phosphorus loading rate (iPLR) in a low-P stormwater treatment wetland, Ecological Engineering,Volume 156.

5. King, J., and R. Villapando, 2018, Appendix 5C-3: Evaluation of Phosphorus Forms. Flux, and Transformation Processes in the Stormwater Treatment Areas in Volume I 2018 South Florida Environmental Report.

6.  King, J. and R. Villapando, 2020, Chapter 5C: Evaluation of Phosphorus Forms. Flux, and Transformation Processes in the Stormwater Treatment Areas in Volume I 2020 South Florida Environmental Report.

7. DBE, 2017, Field and Supplemental Laboratory Support for Evaluating Phosphorus Sources, Flux, and Transformation Processes in the Stormwater Treatment Areas – Annual Report. Prepared by DB Environmental, Inc. under Agreement 4600003029-WO01 for South Florida Water Management District, West Palm Beach, FL.

8. University  of Florida, 2019 Evaluation of Soil Biogeochemical Properties Influencing Phosphorus Flux in the Everglades Stormwater Treatment Areas (STAs) Final Report. Submitted to South Florida Water Management District, West Palm Beach, FL.

9. Gann, D., M. Bernardo, and J. Richards, 2019, Detection and Differentiation of Submerged Aquatic and Emergent/Floating Marsh Vegetation using Remote Sensing Methods -- Spectral Separability from WorldView Data (Pilot Study). Report Submitted to the South Florida Water Management District, West Palm Beach, FL.

10. Florida International University, 2019, Settling and Entrainment Properties of STA Particulates Draft Final Report.  Prepared under Agreement No. 4600003032-WO02-9500006758 for South Florida Water Management District,. West Palm Beach, FL.

11 Evans, N., et al., 2019, Appendix 5C-4:  Effects of Abundant Faunal Species on Phosphorus Cycling in the Stormwater Treatment Area in Volume I 2019 South Florida Environmental Report.

12. Morrison, E., et al., Multiple biomarkers highlight the importance of water column processes in treatment wetland organic matter cycling. J Water Research.,  168: p. 115-153.

13. Juston, J. and B. Kadlec., Data-driven modeling of phosphorus (P) dynamics in low-P stormwater wetlands. Environmental Modelling & Software 118: p.:226-240.

14. Julian, Paul II., et al., Evaluation of nutrient stoichiometric relationships among ecosystem compartments of a subtropical treatment wetland.  Do we have “Redfield wetlands”?  Ecological Processes (2019) 8:20.  https://doi.org/10.1186/s13717-019-0172-x

15. Julian, Paul II., et al., Understanding stoichiometric mechanisms of nutrient retention in wetland macrophytes: stoichiometric homeostasis along a nutrient gradient in a subtropical wetland.  Oecologia (2020) 1-12. https://doi.org/10.1007/s00442-020-04722-9
 

Development of Operational Guidance for Flow Equalization Basins and Stormwater Treatment Area Regional Operation Plans

Description/Objective
Management of water flow into the STAs is critical to maintain Stormwater Treatment Areas (STAs) to achieve their objective.  This study developed tools and methods to support regional operation plans and guidance to optimize the use of Flow Equalization Basins (FEBs) and distribution of flow to the STAs to achieve the Water Quality Based Effluent Limits for Total Phosphorus (TP).

The study included three tasks:

1. Evaluate relevant information on STAs and conduct field tests to evaluate hydraulics and water quality.
2. Define values for model equations needed to simulate hydraulics, hydrology and operational control of STAs.
3. Develop local (STAs/FEBs) and regional operating strategies and rules and application of system optimization tools.

More information can be found here:

Detailed Study Plan

Activities Completed and Current Status

The study was completed in 2017.

Field measurements of waves propagated by inflow discharges to STA-3/4 Cell 3A were evaluated in relation to low, medium and high flow rates and water depth. Wave speeds and heights along flow paths were used to calculate vegetation resistance to flow. Maps of flow and resistance were created using the equations that described resistance at different flow rates. A total variation diminishing Lax-Friedrichs (TVDLF) method was used in a simple model to simulate flow-through hydraulic gradients of STA flow-ways based on real-time water elevation observations and flows. An inverse model (iModel) for Restoration Strategy Operational Protocol (RSOP) was developed to optimize flow rates along the Central Flow Path for proper flow attenuation and treatment with and without the FEB.

Results

Field tests improved water depth estimates and residence times in real-world applications leading to improved accuracy of physically based models of the STAs. The patterns of resistance produced from these applications reflected the general patterns of the vegetation distribution. The applications represented vegetation resistance, topography effects, resistance due to blockages, short-circuiting and turbulent behaviors. This information can assist project planning and design. The values in the model equations can determine if the flow behaves like porous-media flow or short-circuiting stream flow. The simple TVDLF method can forecast seven-day predictions of water depths under multiple management scenarios/flow regimes. At present this tool assists the management of the western flow-way of STA-3/4.

The iModel-RSOP was applied to four alternative scenarios of different FEB and Lake Okeechobee water delivery configurations. By rearranging flow to optimize TP removal, the iModel predicted lower TP concentration in discharge for all the scenarios compared to observed values. While the iModel results are encouraging, many difficulties were encountered to provide an accurate statistical prediction of TP concentration suggesting room for improvement.

Reports and Publications

1. Ali, A. 2015. Multi-objective operations of multi-wetland ecosystem: iModel applied to the Everglades restoration. Journal of Water Resources Planning and Management 141(9).
    
2. Ali, A. 2018. Appendix 5C-1 iModel for Restoration Strategy Operational Protocol Development. In: 2018 South Florida Environmental Report – Volume I, South Florida Water Management District, West Palm Beach, FL.
    
3. Lal, A. M. W. 2017. Mapping Vegetation-Resistance Parameters in Wetlands Using Generated Waves. Journal of Hydraulic Engineering 143(9).
    
4. Lal, A.M., M.Z. Moustafa and W. Wilcox, 2015. The use of discharge perturbations to understand in-situ vegetation resistance in wetlands. Water Resources Research 51:2477-2497; doi: 10.1002/2014WR015472.

Investigation of STA-3/4 Periphyton-based Stormwater Treatment Area Performance, Design and Operational Factors

Description/Objective
Investigate performance, design elements, operation and biogeochemical characteristics that have enabled the 100-acre PSTA Cell to achieve ultra-low outflow total phosphorus (TP) concentrations.

This study includes monitoring and surveys within the cell, as well as mesocosm and microcosm experiments that supplement these studies. Continuous TP measurements at inflow and outflow locations of the cell were also conducted.

More information can be found at:

Detailed Study Plan

Activities Completed and Current Status
The study was completed in 2018.

Inflow and outflow concentrations of TP and flows into and out of the cell were monitored continuously. Grab surface water samples taken at the structures were analyzed for various P species. Other data measured periodically within the PSTA Cell included conductivity, pH, temperature, dissolved oxygen, chlorophyll a, turbidity, water depth, light and ion concentrations. Effects of pulse flows, season, time of day, water depth, inflow P concentration, flow rate and seepage on cell performance were evaluated. Enzyme assays were also conducted to evaluate the role of microbial activity. Sediment accrual and vegetation nutrient contents were also analyzed. Reports and manuscripts have been completed. Final analyses will be reported in the 2019 South Florida Environmental Report.

Results
The PSTA Cell achieved annual outflow flow-weighted mean TP concentrations ranging from 8 to 13 µg/L for the period of record (2008 to 2017). Pulse flow events and associated higher P loads had no adverse effect on treatment performance. Outflow TP concentrations were not affected by two different operational water depths (average of 0.39 m and 0.55 m) the time of day, or longer periods of constant moderate flow. Generally, lower outflow TP concentrations were observed during the wet season. The optimal inflow TP concentrations to the PSTA Cell is 22 µg/L or less, which achieved outflow concentration of 13 µg/L or lower. Lateral seepage through the levee between the Lower Submerged Aquatic Vegetation (SAV) Cell and the PSTA Cell was the major source of seepage. The accumulated sediment in the cell is low in P and chemically stable, resulting in sustained P removal performance.

Reports and Publications

1. James, R.T. 2015. Evaluation of Remote Phosphorus Analyzer Measurements and Hydrologic Conditions of the STA-3/4 Periphyton-based Stormwater Treatment Area. Technical Publication WR-2015-002. South Florida Water Management District, West Palm Beach, FL.
2. James, R.T. 2017. Analysis of Effects of Sustained Moderate Flow at the STA-3/4 Periphyton-based Stormwater Treatment Area. Technical Publication WR-2017-003. South Florida Water Management District, West Palm Beach, FL.
3. Zamorano, M. F. 2015. Effects of Pulse Flow Events on the STA-3/4 PSTA Cell's Phosphorus Treatment Performance. Technical Publication WR-2015-007. South Florida Water Management District, West Palm Beach, FL.
4. Zamorano, M. F. 2017. Influence of Seepage on the STA-3/4 PSTA Cell's Treatment Performance. Technical Publication WR-2017-004. South Florida Water Management District, West Palm Beach, Florida.
5. Zamorano, M. F., Grace, K., DeBusk, T., Piccone, T., Chimney, M., James, R. T., Zhao H., and Polatel, C. 2018. Appendix 5C-2: Investigation of Stormwater Treatment Area-3/4 Periphyton-based Stormwater Treatment Area Performance, Design, and Operational Factors. In: 2018 South Florida Environmental Report – Volume I, South Florida Water Management District, West Palm Beach, FL.
6. Zamorano, M., Piccone, T. and Chimney, M.J. 2018. Effects of short-duration hydraulic pulses on the treatment performance of a periphyton-based treatment wetland. ecological engineering 111(1): 69-77.
7. Zhao, H., T. Piccone, and M. Zamorano. 2015. STA-3/4 Periphyton-based Stormwater Treatment Area (PSTA) Cell Water and Total Phosphorus Budget Analyses. Technical Publication WR-2015-001. South Florida Water Management District, West Palm Beach, FL

Evaluation of Sampling Methods for Total Phosphorus

Description/Objective

The objective of Restoration Strategies is to meet a stringent water quality based effluent limit (WQBEL) for phosphorus (P).  To assure that the WQBEL is reached, sampling and monitoring techniques must accurately measure total P (TP) concentrations The goal of this study is to determine the accuracy of the sampling and monitoring being used and to evaluate factors that may influence results.

More information can be found here:

Detailed Study Plan

Activities Completed and Current Status
The study was completed in 2017.

Various sampling methods were evaluated. Cameras were used to observe physical and biological disturbances that could affect sample quality. Methods were compared based on analytical results and sampling efficiency. Sample sets using different methods, including, Grab sampling, flow-proportional composite autosamplers (ACF) and discrete autosamplers based on time (ADT), were collected. These sets were compared with measurements from a remote phosphorus analyzer (RPA) deployed within the Stormwater Treatment Areas (STAs). Additionally, water quality sondes were deployed to measure conductivity, pH and turbidity.

Results
Data comparisons suggest that Grab and ADT collection methods are more reliable than ACF methods. Under some conditions, the ACF method may be biased and not meet the completeness (percent of acceptable samples collected based on planned number of samples to be collected) target of 90%. Completeness estimates differ, depending on whether they are based on time coverage and/or flow representation. Reverse, low or poorly defined flows interfere with ACF sampling and can lead to non-representative samples, particularly at sites with small water level differences from up to downstream. Data from the RPA method indicated a mid-day peak in TP concentrations.

Infrastructure and levees can function as habitat for wildlife and could be potential sources of TP. Some animals such as anhingas and turtles were observed interfering directly with sampling systems. Masses of submerged aquatic vegetation were also observed to accumulate often at the sample intake screens, but the influence of these events on TP results was not clear.

It is recommended that flow proportionality of autosamplers and comparison of ACF versus ADT at multiple locations be further investigated. The use of ACF method at structures with small water level differences from up to downstream should be discouraged. Evaluating the completeness of collection should be based on the amount of flow represented, rather than time. Also, methods for limiting wildlife impacts on surface water sampling should be studied further.

Publications

1. Rawlik, Peter 2017 Results from Project REST Remote Environmental Sampling Test. Technical Report WR-2017-002. South Florida Water Management District, West Palm Beach, FL.

Investigation of Rooted Floating Aquatic Vegetation in Stormwater Treatment Areas

Description/Objective

Rooted floating aquatic vegetation (rFAV) can make up a substantial amount of the vegetation in Stormwater Treatment Areas (STAs).  They could be a valuable method of removing phosphorus (P) as they can grow in deep areas where emergent (EAV) and submergent aquatic vegetation (SAV) cannot. This study was to determine if rFAV enhance low-level P removal in back-end SAV communities of STAs.

The study includes two phases:

• Phase I – Evaluate P in the water column of rFAV and SAV patches to determine if differences exist.
• Phase II – Determine if Phase I findings are consistent among the STAs. Examine the mechanisms that account for the differences between patches.

More information can be found here:

Detailed Study Plan

Activities Completed and Current Status

The study was completed in 2018.

Phase I included water chemistry measurements to examine spatial within patch variability and temporal differences between rFAV and SAV patches. Expanded temporal sampling of additional patches was conducted to verify findings from primary patches. Measurements of soil characteristics and porewater from all patches, and sonde measurements, were conducted to determine factors that could explain patch differences.

Results
Water column P concentrations are different between rFAV and SAV areas for two of the three species evaluated [1]. Water column P concentrations in white water lily and American lotus patches were higher than their corresponding SAV patch, while water column P concentrations in a spatterdock patch were not different from SAV patch. Soils in white water lily patches were lower in bulk density, higher in organic content and lower in calcium content compared to its paired SAV patch. This low bulk density soil may be prone to resuspension and could be contributing to the higher particulate P concentrations in the water column. Dissolved oxygen and pH measurements indicate greater aquatic metabolism in the SAV patch relative to the rFAV patch. Greater aquatic metabolism results from increased photosynthetic rate in the water column, which leads to higher pH during the daylight hours. This higher pH may enhance co-precipitation of P with calcium resulting in more P removal. The soil from American lotus patches has a higher organic content than SAV patches but were similar otherwise.

Reports and Publications

• Powers, M. 2018. Role of Rooted Floating Aquatic Vegetation, in 2018 South Florida Environmental Report – Volume I Chapter 5C: Restoration Strategies Science Plan Implementation (D. Ivanov, T. Piccone, T. James, and J. McBryan Eds.). South Florida Water Management District, West Palm Beach, FL.

Stormwater Treatment Area Water and Phosphorus Budget Improvements

Description/Objective

Water and phosphorus (P) budgets are important tools that can be used to understand the treatment performance of Stormwater Treatment Areas (STA). Accurate water budgets are critical to develop accurate P budgets. The objective of this study is to improve the annual water and P budgets for selected  STA treatment cells or flow-ways.

The study includes two phases:

• Phase I – Evaluate the annual water budgets for STA-3/4 Cells 3A/3B; used as a test case. Evaluate sources of error and improve the annual water budgets.
• Phase II – Improve period of record (POR) flow data and water and P budgets for all cells of STA-3/4 and STA-2 Flow-ways 1-3.

More information can be found here:

Detailed Study Plan

Activities Completed and Current Status

• The study was completed in 2020.
• Phase I evaluation was completed in 2014.
• Phase II was completed in 2020.

Period of record flow data for all cells of STA-3/4 and STA-2 Flow-ways 1 to 3 have been improved. Work to improve the South Florida Water Management Districts's Water Budget Tool was completed. Improved POR water and P budgets for STA-2 Flow-ways 1 to 3 were completed in 2017 and all cells of STA-3/4 were completed in 2018. Annual and long-term average annual flow-way and treatment cell Total P (TP)  flow-weighted mean concentration (FWMC) in outflows, TP load retention percentage, and TP FWMC reduction percentage were calculated. The effect of annual hydraulic loading rate, annual phosphorus loading rate, annual average hydraulic residence time, inflow TP FWMC, and annual average water depth on annual outflow TP FWMC were evaluated.

Results

For STA-3/4 Cells 3A/3B, small differences in water levels across large culverts at mid-levees were the main source of error in annual cell-by-cell water budgets. The budgets were greatly improved by updating flows between the upper and lower portions of the flow-way. Annual errors for the water budgets were reduced to 8% or less. Rainfall, evapotranspiration, change in storage and seepage were minor contributors to these cells' annual water budgets and the current methods for estimating these components were found to be acceptable for Phase II.

Annual water and P budgets were developed for STA-2 Flow-ways 1 to 3 for Water Year 2002 (WY2002) to WY2016, and for STA-3/4 Cells 1A, 1B, 2A, 2B for WY2006 to WY2017 and for STA-3/4 Cells 3A and 3B for WY2009 to WY2017 [4]. Improved POR flow and stage data for STA-2 and STA-3/4 inflow and outflow structures were used in the analyses. Rainfall, evapotranspiration, and seepage estimates were included. A new calibrated seepage coefficient (1.1 cfs/ft/mi) was used for the water budgets. These efforts resulted in more reliable water and P budgets and other performance estimates including annual and long-term average annual hydraulic retention times, hydraulic loading rates, P loading rates, and P reduction efficiency. For the six flow-ways studied, a higher frequency of low-level outflow TP annual FWMC was achieved when the annual hydraulic residence time was longer than 14 days, annual hydraulic loading rate was less than or equal to 3.5 cm day⁻¹, the annual water depth was shallower than or equal to 0.65 meter, the annual P loading rate was smaller than or equal to 1.2 g m² yr⁻¹, or the annual inflow TP FWMC was less than or equal to 100 μg L⁻¹. This study demonstrated that TP settling rate alone is not adequate to evaluate STA treatment performance especially when hydraulic loading rates differ. This study also helped improve understanding of the factors that affect the treatment performance of large-scale constructed wetland flow-ways which consistently retained TP and reduced TP concentrations over a long-term operational period.

Reports and Publications

1. Polatel, C., et al., 2014, Stormwater Treatment Area Water and Phosphorus Budget Improvements – Phase I: STA-3/4 Flow-ways 3A and 3B Water Budgets. Technical Publication WR-2014-004. . South Florida Water Management District, West Palm Beach, FL.

2. Zhao, H. and T. Piccone, 2019, Appendix 5C-5 Summary Report for Water and Total Phosphorus Budget and Performance Analysis for Stormwater Treatment Area 3/4. In: 2019 South Florida Environmental Report – Volume I. South Florida Water Management District, West Palm Beach, FL.

3. Zhao, H. and T. Piccone, 2018, Appendix 5C-6 Summary Report for Stormwater Treatment Area 2 Flow-ways 1, 2, and 3 Water and Total Phosphorus Budget Analyses. In: 2018 South Florida Environmental Report – Volume I. South Florida Water Management District, West Palm Beach, FL.

4. Zhao, H. and T. Piccone,  Large Scale Constructed Wetlands for Phosphorus Removal, An Effective Nonpoint Source Pollution Treatment Technology. 145:. Ecological Engineering, 145.