Restoration Strategies Science Plan

Quantifying Phosphorus Uptake and Release from Periphyton and Phytoplankton Communities

Description/Objective
Microbial communities of bacteria, algae and fungi, are found attached to plants (periphyton), soils (epiphyton), or in free floating form (phytoplankton). They play an important role in Phosphorus (P) cycling within the Everglades Stormwater Treatment Areas (STAs) through uptake, growth and senescence. The amount of cycling through periphyton can affect P reduction in STAs.

This study quantifies periphyton processes of growth, senescence, and nutrient dynamics within the STAs. This information will indicate the significance of periphyton in P cycling and retention reduction within the STAs. The results may support the management of the STAs especially at the outflow regions where P concentrations are very low.

This study includes two phases:

• Phase I - Literature survey and analysis of periphyton-related research conducted in the STAs.
• Phase II - Benchtop and field study plan development and implementation.

Study Plan Overview

Activities Completed and Current Status

Phase 1 – Literature survey: Studies on similar wetlands were reviewed. Results from published literature showed that periphyton community structure is affected by light intensity, temperature, and nutrient availability. Methods and measurements used to estimate periphyton growth, senescence and nutrient dynamics were summarized. Only a few published rates applicable to subtropical systems were found. Methods to measure periphyton community structure, productivity, decomposition and senescence include pigment analysis (chlorophyll, phycocyanin), biovolume, cell counting, oxygen content, mass, accumulation via sediment traps, carbon isotopes (¹⁴C), and genetic techniques, such as amplicon sequencing (metagenetics), metagenomics, metatranscriptomics. Nutrient uptake rates can be measured through dissolved inorganic carbon, periphyton tissue nutrients, enzyme activity, phosphorus isotopes (³¹P, ³²P), nitrogen isotopes (¹⁵N), combustion (measures particulate or solid phase nitrogen), Acetylene Reduction Assay, and Membrane-Introduction Mass Spectrometer analysis.

Part 2 of Phase I - Analysis of the unpublished research from STAs and Water Conservation Areas: this is on-going. The information gleaned from Phase I should identify any data gaps and guide additional future research approaches in the next phases.   

Phase II: Bench top and field experiments: pending approval.

Reports and Publications

1. Laughinghouse, H. D., Berthold, D. E, Barbosa, M., and Lefler, F. W, May 2019, A Review on Tropical and Subtropical Periphyton and Phytoplankton Processes and Methods of Quantification, draft.

Improving Resilience of Submerged Aquatic Vegetation in the Stormwater Treatement Areas

Description/Objective

To understand how Phosphorus (P) is processed and removed within well performing Stormwater Treatment Areas (STAs), this multi-component study was undertaken. This study evaluates the mechanisms and factors that affect P reduction from the water column particularly in the outflow regions of the STAs. The components include assessments of flow-way (FW) water quality, internal phosphorus loads, soil, microbial enzymes, vegetation, particulate transport and settling, fauna, and organic P speciation. In addition, a data synthesis and integration component was used to evaluate the collected data that 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.

A detailed study plan can be found here:

Detailed Study Plan

Activities Completed, Results and Current Status

The overall study began in 2013 and all nine sub-study components have been completed: 

• Flow-way Water Quality Assessment: P cycling in three well-performing STA FWs was evaluated under different flow conditions: high, moderate, low and no flow.  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, resuspension via entrainment 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 also increased during no flow periods, which indicate internal P loading from vegetation mining of soils and turnover. This increasing P trend, evaluated with a computer model, indicated 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.

P sorption and desorption were influenced by vegetation type, depth in the profile and distance from the inflow. The floc and RAS were more reactive than underlying soils. SAV-dominated sites generally exhibited a greater potential to retain P at lower surface water P concentrations.  EAV-dominated sites exhibited reduced potential to retain P at low surface water P concentrations.  No trend was found for P sorption or desorption from the inflow to the outflow regions. P desorption tended to be higher under 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.

• 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. To understand the impact of flow conditions on the microbial communities, enzyme activity in the surface water, floc, litter, and periphyton was measured along the flowways from inflow to outflow and within the major plant communities (EAV and SAV).

The level of enzyme 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. During flow conditions, often the level of enzyme activity in the surface water was below detection. In the floc, flow resulted in more N-limited conditions in the EAV areas 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.

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. 

• 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 the inflow region of this cell.   

     Tests of the sediments from SAV areas at relatively low and stable water velocities (< 0.5 cm/s) indicate that water column particulates 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 study.

• Organic P Speciation: Biomarkers (lignin phenols, amino acids, and pigments) estimated the quality of organic matter (OM) found in the treatment wetland STA-3/4 and a reference wetland WCA-2A. Linkages between C and P cycling were assessed within these two systems using these biomarkers. 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.

• 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.

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., 2019, Measurement of internal phosphorus loading rate (iPLR) in a low-P stormwater treatment wetland. Prepared in fulfillment of 4600003029‐WO01 on Technical Environmental Services in Support of the Restoration Strategies (RS) Science Plan.
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 Flrodia 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.

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 includes 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”. 

Detailed Study Plan

Activities Completed and Current Status

• Phase I is complete.
• Phase II is ongoing.

Results

UAS identified floating wetlands 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. A buoyancy model based on this literature review will be developed in Phase II.

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 May 2021): 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 2020): 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 resuspend soils, including particle disturbance, ingestion and defecation).
• Task III – (Ongoing through October 2021): 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 2020): Calibrate electrofishing by comparing biomass of non-native fish collected by electrofishing to known numbers of these fish stocked in enclosed test cells.
• Task V – (to begin in 2020) Estimate the effect of herbivory on SAV production

Activities Completed and Current Status

The STAs support a high biomass of aquatic fishes 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.

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.