Restoration Strategies Science Plan

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

Description/Objective
Evaluate factors that affect phosphorus (P) treatment performance of the Stormwater Treatment Areas (STAs), particularly those that are key drivers at the lower reaches of the treatment flow-ways (FWs). This study will provide critical information to explain factors and processes that influence STA performance and will serve as basis to develop or improve management options to reduce total P (TP) discharge concentrations from the STAs.

There are multiple components (sub-studies) to this study, including:

1. Data Mining
2. Flow-way Water Quality Assessment
3. Microbial Enzyme Activity
4. Vegetation Assessments
5. Organic P Speciation
6. Soil Characterization
7. Particulate Dynamics
8. Phosphorus Flux Dynamics
9. Role of Fauna

Detailed Study Plan

Activities Completed and Current Status
Data mining was completed in 2017. Flow event and sub-study data collections will continue through 2019. The individual sub-studies are in different stages of implementation. Transects samples, microbial samples, porewater samples and flux measurements were taken for six separate flow events. Particulate samples were collected using traps in STA-2 FW 3 and STA-3/4 Western FW; these samples are being analyzed for nutrient content. Erosion, velocity and meteorological measurements have provided important information of the effects of flow on particulate transport. Soil and vegetation biomass were sampled in all study flow-ways. Vegetation coverage surveys, biomass measurements and fauna surveys in both emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) cells are continuing according to the study plan.

Results*

^{* (For detailed information on each sub-study, please see Reports and Publications.)}

• Data Mining: This sub-task showed the importance of nitrogen (N) and phosphorus coupling on STA P reduction. The analysis revealed a zonal pattern of components along the flow-way (soil, vegetation and surface water characteristics) and the significance of labile soil P as a consistent and sensitive indicator of P flux.
   
• Flow-way Water Quality Assessment: A distinct TP concentration gradient along the treatment flow-ways was observed at all periods of the flow events. However, average TP concentration reduction was higher for FW 1 than for FW 3. Soluble reactive P (SRP) accounted for a majority of the reduction in FW 1 while particulate P (PP) accounted for most of the reduction in FW 3. In FW 3, TP concentrations increased under stagnant condition following a period of high flow but not after low flow. The TP increase was largely due to increase in particulate P (PP), particularly at stations closer to the inflow. At the outflow region of both flow-ways, residual P was comprised mainly of PP and dissolved organic P (DOP). SRP was reduced early in the flow-way and reached minimum detection limit (2 µg/L) at the mid-region of both flow-ways.
   
• Flux Measurements: Vertical diffusive flux likely produced an internal load to water column P in the inflow and midflow regions, but not at the outflow region. However, the chambers measuring flux rates showed positive net fluxes in the outflow region. P flux declined from inflow to outflow. The sources of these fluxes, especially at the outflow regions have yet to be determined. Additional controlled flow event monitoring is underway in STA-2 FW 1.
   
• Microbial Assays: Trends in enzyme activity for two P-acquiring enzymes, one carbon (C)-acquiring enzyme and one N-acquiring enzyme were variable between the surface water and periphyton, between seasons and during flow or stagnant conditions for the flow events conducted in STA-2 FW 3 in 2016. Enzymatic activity in the periphyton for all enzymes was greater under stagnant conditions than flowing conditions, while enzymatic activity was less in the water column for stagnant conditions than flowing conditions. P and C enzyme activity in the periphyton increased along the nutrient gradient from inflow to outflow, but there was no consistent trend in surface water samples. For both surface water and periphyton, enzymatic activity was lowest in the summer compared to the spring and fall events.
   
• Vegetation Assessments: TP storage in the vegetation was substantially higher at the inflow region for EAV compared to SAV. TP concentration in vegetation tissues decreased from the inflow to the outflow of STA-2 FW 1 and FW 3. TP concentrations in SAV tissues at the inflow region of FW 3 were higher than in EAV tissues at the inflow region of FW 1, indicating higher P uptake by SAV; this trend reversed at the middle and outflow regions.
   
• Soil Characterization: High P enrichment of floc and soil were found near the inflows with concentrations decreasing toward the outflows. Enrichment of floc and recently accumulated soil in STA-2 FW 1 (EAV-dominated) was substantially higher and more spatially extensive than in STA-2 FW 3 (SAV-dominated). TP in the floc and recently accumulated soil from FW 1 was predominantly organic, while TP from FW 3 was primarily inorganic. P storage in FW 1 was higher than FW 3 due to higher bulk density of floc and accumulated material in FW 1. Spatial trends in floc and soil TP concentrations and storage in STA-3/4 Cell 3A (EAV) and Cell 3B (SAV) were similar to those observed in STA-2.
   
• Particulate Dynamics: Current and suspended sediment concentrations followed a diurnal pattern driven by peak winds in the afternoons in STA-2 FW 3. The effects of wind speed were greatest at the inflow where a long fetch and lack of vegetation in the water column allows for more wind-driven flows compared with the midflow and outflow. Sediments accumulating in STA-2 FW 3 show P sequestration with TP concentrations showing a declining gradient from inflow to outflow. Vertical traps and videos have shown particle settling, accumulation and resuspension in the water column. Sedimentation rates decreased from inflow to outflow and the particle size in the water column increased from the inflow to the outflow regions.
   
• Fauna Study: The STAs support substantial fish, waterfowl and invertebrate populations. The mean density of fish and invertebrates is greater in the STAs than in other similar wetland areas in the region (Shark River Slough and WCAs 3A and 3B). The effect of these high populations in the STAs can be significant. Based on bird population estimates and SAV consumption, approximately 4% of STA-1 West's TP external loading could be attributed to coot (a waterfowl) grazing on SAV thus affecting the overall P cycling in the STAs.

Reports and Publications

• Villapando, R and J. King. 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.
   

Use of Soil Amendments or Soil Management to Control Phosphorus Flux

Description/Objective
Determine if flux of phosphorus (P) from the soil to the overlying water column can be reduced by application of soil amendments and/or soil management techniques and thereby lowering outflow P concentrations.

The original study plan includes three phases:

• Phase I – Review existing information.
• Phase II – Small-scale experiments to screen amendments or soil management techniques identified in Phase I for their ability to inhibit soil P flux.
• Phase III – Field trials of the most promising soil amendment or management techniques based on Phases I and II.

Detailed Study Plan

Activities Completed and Current Status

Phase I was completed in October 2015 with three tasks:

1. Literature review of technologies for controlling soil-P flux in wetlands or lakes.
2. Review data from past SFWMD supported projects relevant to this study.
3. Determine feasibility of implementing any of these technologies at full-scale in the Stormwater Treatment Areas (STAs).

Phase II was canceled.

Phase III soil management, specifically soil inversion, will be evaluated in STA-1 West (STA-1W) expansion area starting in 2019.

Results
A comprehensive review of available technologies and amendments indicated that many could lower outflow P concentrations. Due to many uncertainties regarding long-term treatment effectiveness of soil amendments, potential effects to STA operations, high costs to implement at full-scale in the STAs and their effects to downstream Everglades flora and fauna, no further evaluation was considered, with one exception. The study is proceeding to Phase III with an evaluation of the benefits of soil inversion (i.e., soil management with no amendments), which will be investigated in the STA-1W Expansion Area in early 2019.

Reports and Publications

• 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.
   

Stormwater Treatment Area Water and Phosphorus Budget Improvements

Description/Objective
Improve the annual water and phosphorus (P) budgets for selected Stormwater Treatment Area (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 phosphorus budgets for STA-3/4 (all cells) and STA-2 Flow-ways 1-3.

Detailed Study Plan

Activities Completed and Current Status
Phase I evaluation was completed in 2014. Phase II is ongoing.

Period of record flow data for STA-3/4 (all cells) and STA-2 Flow-ways 1 to 3 have been improved. Work is underway to improve the SFWMD's Water Budget Tool. Improved POR water and phosphorus budgets for STA-2 Flow-ways 1 to 3 were completed in 2017 and STA-3/4 (all cells) were completed in 2018 and will be reported in 2019.

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%. 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. Improved POR flow and stage data for STA-2 inflow and outflow structures were used in the analyses. The data and the configurations for the water budgets were reviewed and updated. Rainfall measurements were added. 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 annual P reduction efficiency.

Reports and Publications

• Polatel, C., W. Abtew, S. Krupa and T. Piccone. 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.
   
• 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.
   

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

Description/Objective
Develop tools and methods to support operational guidance and regional operation plans to optimize Flow Equalization Basins (FEBs) and Stormwater Treatment Areas (STAs) to achieve the Water Quality Based Effluent Limits for Total Phosphorus (TP).

The study includes 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.

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

• 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).
   
• 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.
   
• Lal, A. M. W. 2017. Mapping Vegetation-Resistance Parameters in Wetlands Using Generated Waves. Journal of Hydraulic Engineering 143(9).
   
• 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.

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) or the time of day. 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

• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
Determine if current sampling and monitoring techniques accurately measure total phosphorus (TP) concentrations, and if not, evaluate factors that influence results.

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

• 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
Determine if rooted floating aquatic vegetation (rFAV) enhance low-level phosphorus (P) removal in back-end submerged aquatic vegetation (SAV) communities of Stormwater Treatment Areas (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.

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. 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.