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The Rogue Phosphorus Conundrum in Lake Okeechobee and the Everglades



E. Allen Stewart III P.E. 6/20/18

Preface: Before reading this Blog please understand that I fully support expeditious implementation of the proposed deep, above ground reservoir and expanded Stormwater Treatment Area (STA) presently under consideraton to help reduce the discharges to the Caloosahatchee and St. Lucie Rivers from Lake Okeechobee, and to reduce phosphorus loading to the Everglades National Park. These however are temporary remedies, the need for which has emerged from decades of failure to effectively assess and resolve the ecological disruptions associated with excess phosphorus and inadequate water management within Lake Okeechobee and the Everglades. Within  this Blog is presented a sound argument for implementing an aggressive long-term phosphorus removal, recovery and redistribution program. The present approach taken by the involved agencies to continue to store phosphorus internally through some of the Best Management Practices (BMP) strategies, the Stormwater Treatment Areas (STA) and deep above ground reservoirs is not a sound or scientifically viable long-term program. Actual removal, recovery and redistribution of phosphorus eventually will need to be implemented if any semblance of environmental protection of existing resources is to be realized.

In spite of the scientific evidence that the 9,000 (+/-) square mile Kissimmee-Okeechobee-Everglades Ecological Amalgamation (KOEEA) has become saturated with excess phosphorus, or what has been called “legacy” phosphorus, or perhaps more accurately, “rogue” phosphorus, and that it is this rogue phosphorus which is now spilling over from Lake Okeechobee and being diverted to tourist centers on both of Florida’s Coasts, the involved agencies continue to allow loading of the KOEEA with external phosphorus and to rely upon internal storage of phosphorus within the KOEEA. This is a general denial of the basic principle of conservation of mass associated with classical mechanics, combined with the faulty presumption that the KOEEA has the capability of sequestering this excess phosphorus within wetland  and lake sediments without significant long-term changes in the ecology or hydrology of these wetlands. While some realize there may come a time to remove this stored phosphorus through what they call “adaptive management”, there appears to be little effort being directed towards development and economic assessment of these adaptive management technologies, nor is there evidence that solid plans are being developed to confront this expanding problem. Instead, the agencies continue to rely upon internal storage as a viable solution to excessive phosphorus loading. Neither magic dust nor wishful thinking qualify as adaptive management. The present strategy is a dangerous rejection of sound science.  Such denial of science is and will continue to be problematic. Remember the Humpty Dumpty Axiom—rejecting or denying science does not eliminate the inevitability of its influence! Drawing by Maggie O’Leary

Neither restoration nor reasonable reclamation of Lake Okeechobee or the Everglades will be realized as long as there continues to be importation and storage of extensive loads of phosphorus within the system. This excess phosphorus has now accumulated to the point that the involved agencies call it “legacy” phosphorus, but a more applicable term is “rogue” phosphorus. The University of Florida[1] recently announced that more than 110,000 metric tons (240 million pounds) of readily available reactive phosphorus—rogue phosphorus-- is now held within the Lake Okeechobee Basin alone. They noted this to be sufficient quantity, even if all external inputs were immediately terminated, to sustain the present loading rates of about 500 metric tons annually to Lake Okeechobee for nearly 200 years! For reference the Total Maximum Daily Load or TMDL[2] allocation for Lake Okeechobee is 140 metric tons per year with an in-lake total phosphorus concentration of 40 µg/L. The present loading and concentration exceed these allocations by about a factor of three! The only plausible way phosphorus can be effectively managed in Lake Okeechobee and the Everglades is to 1) capture it and convert it to a resource of some value; 2) effectively recycle this captured and converted phosphorus internally to replace imported phosphorus to the extent practical; and 3) distribute the remainder to regions disconnected to the Lake Okeechobee and the Everglades watersheds. This of course has to be done in concert with meaningful expansion of water storage capabilities, such as would be achieved through procurement and appropriate modification of the 700,000 acre Everglades Agricultural Area (EAA) as well as expanding shallow storage zones in other regions of the KOEEA.[3]


[1] Options to Reduce High Volume Freshwater Flows to the St. Lucie and Caloosahatchee Estuaries and Move More Water from Lake Okeechobee to the Southern Everglades March 2015 An Independent Technical Review by the University of Florida Water Institute, Gainesville, Florida

[2] The TMDL or Total Maximum Daily Load Program is a Federal program adminisered typically by the States, by which in accordance with section 303(d) of the Clean Water Act critical impaired waters are identified, and allocations are developed for controlling pollutants, such as Phosporus in the case of Lake Okeechobee. Compliance with the TMDL is inteded to bring he impaired water in compliance with water quality sandards.

[3] KOEEA or Kissimmee-Okeechobee-Everglades Ecological Amalgamation includes a complex sstem of connected ecosysyems within south central Florida as described in the PASOP Blog Of November 28, 2017 The Kissimmee-Okeechobee-Everglades Ecological Amalgamation--Understanding its Beginnings and its Dynamics.

In 1987, shortly after the creation of the second Lake Okeechobee Technical Advisory Committee (LOTAC II), I wrote a letter to the committee through a staff member of the South Florida Water Management District in which I offered the following:

“Phosphorus management must be done through carefully developed programs with the emphasis not only on removal but on recovery and long term cost effectiveness……..The LOTAC is placing great confidence in the presumption that biological availability of phosphorus within the lake will be reduced and that the sediment held stores cannot be biologically exploited, a presumption in which I personally have little confidence”

This was over thirty years ago, and these concerns have proven to be well founded—as verified by the University of Florida in their recent report as cited in the lead paragraph. Over the years following 1987 the South Florida Water Management District, in spite of these concerns, decided not to pursue a removal and recovery program regarding phosphorus, but rather centered their efforts on what are known as Best Management Practices (BMP), as well as non-harvested constructed wetlands known as Stormwater Treatment Areas or STA’s. In addition, water management was to rely largely upon deep, elevated reservoirs and Flow Equalization Basins (FEB), and these were also presumed to be effective in reducing phosphorus.


In the Lake Okeechobee and Everglades Watersheds, Best Management Practices relate primarily to efforts to reduce the loss or release of phosphorus and other pollutants from agricultural operations. These actions may include, but are not limited to, reduction of imports; more efficient use of fertilizers and feeds; recovery and recycling of manures and other wastes; and establishing Waste Stabilization Ponds. While such BMP’s can certainly be helpful, their effectiveness in providing significant reduction of phosphorus loading to Lake Okeechobee has been minimal. Based upon South Florida Water Management District data as presented within the previously cited University of Florida study, total phosphorus loading to the lake has averaged 503 metric tons per year since 1978, and the annual variability appears to be more directly associated with rainfall than BMP implementation, with loading down during dry years, and increasing during wet years. It is noteworthy also that the in-lake total phosphorus concentration has increased substantially since 1978 from about 65-75 µg/L to about 140-150 µg/L. The graph below reflects this loading data on a 5-year moving average and the in-lake total phosphorus concentration. Just looking at this trend it appears that the BMP program alone will not achieve the TMDL allocations for total phosphorus.

Total Phosphorus loading and in-lake Total Phosphorus concentration Lake Okeechobee 1978-2015 (graph generated by Allen Stewart from existing data)

In the January 2018 meeting of the Everglades Coalition at Hutchinson Island, I remember someone talking about the BMP program in the Lake Okeechobee Watershed. An Environmental Professional well known to everyone there, asked the simple question--why over the years have not the BMP’s worked that well? I thought this was a reasonable question. And of course, the answer is rogue phosphorus—although I do not remember that being the answer given. There is so much phosphorus saturating the soils, canals, streams and groundwaters in the Okeechobee Basin that BMP efforts to manage incoming sources do little to solve the problem. As noted by the University of Florida, this rogue phosphorus will deliver loads of around 500 metric tons of reactive, biologically available, total phosphorus per year for 200 years, even if all agricultural activity stopped tomorrow. In fact, when action was taken to buy-out existing dairies as part of the 1987 Surface Water Improvement Act (SWIM), I recall that there was virtually no change in phosphorus loading to the lake—testimony to the rogue phosphorus influence.

In all fairness, the BMP programs can be helpful, they just are not the sole answer to the rogue phosphorus issue—the symbolic 500-pound Gorilla in the room—or should I say the 500-metric ton Gorilla. The farmers in the Lake Okeechobee watershed have generally been cooperative in adjusting their operations to meet the BMP requirements, even though such adjustments often make a difficult business even more difficult. I have been a farmer in the Lake Okeechobee Basin, and I can tell you first hand it is a risky business with typically small margins, and constant vulnerability to the whims of the market, the weather and regulations.

The question then is how can the farming community be supported while at the same time protecting the ecological stability of Lake Okeechobee? Most of the people I have worked with in Okeechobee County, including the farmers, love the lake and the fishing, hunting and tourism it supports. They, more than most, appreciate how valuable a resource it is. What is missing are well developed strategies which include long-term solutions to positively remove, recover and export this rogue phosphorus while equitably distributing the costs and shared benefits. I have some ideas regarding such strategies which I refer to as “agricultural solutions to agricultural problems”. I will be sharing these ideas in future blogs.


But now let’s turn to another agency preferred phosphorus management approach known as Stormwater Treatment Areas or STA’s. As noted, this technology has been adopted as the primary long-term water quality enhancement approach by the involved agencies, which include among others, the South Florida Water Management District, the Florida Department of Environmental Protection, and the U.S. Army Corps of Engineers. Stormwater Treatment Areas are what can be called passive wetland treatment—i.e. the use of wetlands for transferring nutrients from the water column to aquatic plants and wetland sediments without active harvest and nutrient recovery from the system.

The use of wetlands for surface water nutrient management emerged from efforts associated with implementation of the Clean Water Act of 1972—PL92-500—or CWA. As surface water pollution associated with the discharge of the nutrients nitrogen and phosphorus became more problematic—particularly as manifested by excessive growths of suspended algae in lakes and estuaries—a need for technological innovations and advancements became obvious. Wetland based treatment was soon recognized as a potentially viable approach to nutrient management.  

Initial investigations into the use of wetlands were largely conducted during the 70’s and 80’s. These investigations led to the emergence of two distinctly different approaches. The first was the use of native and constructed wetlands in a passive manner, e.g. STA. The second was to actively cultivate aquatic plants within engineered systems. These aquatic plants included algae as well as highly productive vascular plants such as water hyacinth. In this case cultivate means the purposeful promotion of high productivity accompanied by frequent harvesting and the potential generation of usable products. This set of cultivated wetlands eventually became known as Managed Aquatic Plant Systems or MAPS.

Of the two approaches, the passive system appeared more attractive from an operational perspective, as it was less labor intensive. In addition, passive systems did not require the development, processing and marketing of products. Even though there was some effort by the agencies to assess MAPS facilities, it was not surprising therefore that those agencies involved in the protection and “restoration” of Lake Okeechobee and the Everglades showed a clear preference for the passive approach—it represented the low hanging fruit. Their commitment to passive systems led to the construction and operation of a demonstration scale wetland in the Everglades watershed in 1994-1999 known as the Everglades Nutrient Removal Project (ENRP). This project served as a vanguard project for future STA facilities. From the ENRP, design and operational criteria were established, and a first-order model (Design Model for STA or DMSTA) was developed for sizing and projecting performance of the larger STA’s. Now there is over 57,000 acres of STA within that region south of Lake Okeechobee known as the Everglades Agricultural Area (EAA).     

In terms of transferring phosphorus from the water column to the wetland sediments, the STA’s have been very effective. In the 2018 South Florida Water Management District’s Environmental Report (, as noted in Chapter 5B of Volume 1, a total of 57,045 acres of total STA area have been established in the Everglades watershed. In 2018 these STA’s received 1,090,000 acre-ft of inflow (about 973 million gallons per day or 973 MGD). Within this flow, the average total phosphorus concentration was 96 µg/L (sometimes referenced as parts per billion or ppb), with the total phosphorus load for the year at 129 metric tons (one metric ton is about 2,200 pounds). The effluent (outflow) total phosphorus concentration was 15 µg/L with the effluent total phosphorus load at 20 metric tons. Consequently, it was estimated that about 109 metric tons of phosphorus remained in the STA’s.

This is excellent performance, and it is hard to criticize the agencies for initially selecting the STA approach. It may be the quickest, most cost-effective means for addressing immediate and short-term needs.

But there are two serious issues which make passive systems such as STA’s sub-optimal on a long-term basis.

First of all, the STA’s do not address the critical need to remove rogue phosphorus from the KOEEA, but rather exacerbate the issue through continued accumulation of phosphorus. The STA’s do not actually remove any phosphorus from the system, but rather just retain and store phosphorus. Therefore the net mass of phosphorus within the KOEEA increases, and as a result the system will continue to purge itself of rogue phosphorus through diversionary discharges, largely through the Caloosahatchee and St. Lucie Rivers, or Southward through the Everglades National Park. Such diversionary discharges are deleterious both ecologically and economically.

The second issue with long term STA performance relates to the build-up of sediments within the STA, which has influence upon the hydrological and biological dynamics of the STA. This was demonstrated at a 1,200 acre treatment wetland known as the Orlando Easterly Wetland or OEW, owned by the City of Orlando, which was placed in operation in 1988. In 2006, after 18 years of operation, the wetland sediments had accumulated to the point that hydraulic performance was being negatively impacted, as was phosphorus removal efficiency, based upon data presented by the City of Orlando. It was decided to physically remove these sediments from the front end cells of the system—about 90 acres. The photograph below shows the removal activity during the 160 day project.   

Removal of excess sediment from the Orlando Easterly Wetland –from Mark D. Sees circa 2011. The Orlando Easterly Wetland Strategies for Prolonged Phosphorus Removal. City of Orlando, Florida

The actual removal of accumulated sediments is expensive. Just for consideration, within a 2001 analysis of the Orlando Easterly Project by K.R. Reddy and others  at the University of Florida[1], it was estimated that sediment removal in two cells of the OEW—about 90 acres—would cost “$1-2 million per cell” in 2001 dollars, or about $20,000 per acre. It is not clear if this includes hauling and disposal costs. In today’s dollars, to draw-down, clear, dewater, excavate, and haul and dispose (not sure where these sediments would be disposed) of 57,000 acres of wetland sediments would likely be well over $2 billion dollars.

So how often would this need to be done?  In a television interview circa 2003, when confronted with the issue of long-term build-up, a manager with the South Florida Water Management offered the following:

“We are actually building up soil (in the STA’s) at a very slow rate, in the order of 1 centimeter per year, which means in perhaps 20 to30 years we will have to come back and address that. We may take a cell off-line, dry it out, scrape it out, we are not sure.”

This uncertainty about how to manage the STA units over the long term is unsettling, especially considering the potential for very high costs. The effort to shut down all or a significant portion of 57,000 acres of treatment area and remove, haul and dispose of 30-50 years of accumulated, phosphorus enriched wet sediment would mean handling as much as 180 million cubic yards of material. How would it be removed, and where would it be taken? If hauled off by the standard 16 yard dump truck, this would amount to over 10 million loads. Even if this were done over several years, the disruption and costs could border on prohibitive. It might be better to devise a program through which smaller quantities of accumulations are more frequently removed through a carefully developed harvesting/removal strategy, and are more efficiently recovered and processed, and eventually distributed as products of value.

As might be expected, the issue of the life expectancy of an STA has become somewhat controversial. There are some that do not believe wholesale removal of sediments will be necessary, or that any required removal will be limited, relatively easy and inexpensive. The quote cited from 2003 by the South Florida Water Management District might be seen as indicative of this attitude.

Again we need to heed the words of Dr. Reddy and his team in their assessment of the OEW as previously cited:

“The past decade of operations in the OEW has led to a dramatic accumulation of sediments, particularly in cattail communities near the inflow region. Sediment accumulation can be detrimental in two respects: first, it reduces the wetland volume or “live storage”, and secondly the accrued sediments may contribute P (Phosphorus) to the water column. The amount of P released into the water column by the sediments will be related to the P concentration of the overlying water, as well as to the physico-chemical characteristics of the sediment-water interface. Inflow region sediment buildup is not unique to the OEW, and ultimately will become a concern in most

natural and constructed wetlands used for water treatment.” 

While the OEW phosphorus loading rates were considerably higher than the Everglades STA units, sediment accumulations remain a concern with STA’s. Such was noted by Dr. Reddy in a 2014 paper on the sediment accretion rates within the Everglades STA[2]:

“Studies carried out in water conservation (WCA)-2A showed decreases in P uptake from the overlying water with the enrichment of floc and soil layer…….knowledge of accretion rates in a treatment wetland can be useful for optimizing design criteria and to estimate functional life of a wetland before soil buildup reduces flow volume and the residence time, necessitating extensive engineering interventions.”

In summary, STA technology as presently practiced does not remove, but rather retains phosphorus, and hence offers no relief to the continued accumulation of rogue phosphorus within the KOEEA. In addition, STA’s are not sustainable—i.e. they have a finite life—and once performance deteriorates, recovering functionality could likely involve very expensive and disruptive interventions.



In March of 2017 a group of us with experience in MAPS technology, and with several decades involvement with water quality issues in the KOEEA, delivered a letter to Colonel Jason A. Kirk, District Commander and District Engineer U.S. Army Corps of Engineers in Jacksonville, in which we expressed concerns regarding, among other things, the potential water quality problems which could arise from deep, above ground reservoirs. From this letter:


“deep water storage areas, developed without pre-treatment or continual treatment, could become production facilities for cyanobacteria with the possible release of extensive loads of microcystin—a known toxin which can jeopardize the health of fish, wildlife, and humans. From a scientific perspective, water storage and water quality management should be jointly considered during system design and implementation.”

On April 12, 2017 Colonel Kirk responded with the clarification that the Army Corps of Engineers does not include water quality improvement as an objective. Note the following two paragraphs from this letter:  

“The ongoing Lake Okeechobee Water Restoration Project (LOWRP) is focused on developing storage options north of Lake Okeechobee to improve the quantity, timing and distribution of flows into Lake Okeechobee to maintain ecologically desired lake stage ranges, limit damaging discharges to the northern estuaries, increase the spatial extent and functionality of wetlands and increase water supply availability for existing legal users. Water quality improvement is not a project objective or within existing authority of the U.S. Army Corps of Engineers. Water quality improvement within the project area is the responsibility of the project’s partner, the South Florida Water Management District (SFWMD) and the Florida Department of Environmental Protection (FDEP) as part of the Lake Okeechobee Basin Management Plan BMAP).

The Lake Okeechobee Water Restoration Project has many opportunities for public involvement through the monthly Project Delivery Team (PDT) meetings. NEPA process public meetings and public workshops. Your participation at any of these meeting is welcomed.”


It is interesting that Colonel Kirk did not list the SFWMD or FDEP as copied on either letter, as I would think these “partners” might be interested in the water quality issues presented. And concerning the public meetings, I have not only attended many of these, I have responded in writing with detailed concerns similar to those expressed in the March, 2017 letter to Colonel Kirk. The responses to my letters were either a short “Thank you for your comments and suggestions”, or a short paragraph explaining again that the Corps is not responsible for water quality matters, but the deep reservoirs will incidentally provide nutrient removal through storage within the reservoir sediments.


I certainly am not the first person to be concerned that these reservoirs could become hot spots for harmful algae blooms (HAB). In fact I remember circa 2000 talking to Richard Harvey, a well-respected and experienced scientist, about these proposed reservoirs. Richard at the time was overseeing the South Florida office of EPA. If I recall, he was concerned that the nutrient enriched water and the extended hydraulic detention times associated within these reservoirs could elicit toxic algal blooms. In 2005 he expressed this openly, warning that these reservoirs could become incubators for toxic algal blooms[3]. In 2007 his involvement with Everglades’ restoration was terminated. Like many scientists in the past, including Art Marshall[4] who as a scientist managed to get removed from the Boards of two Water Management Districts, Richard Harvey, made the mistake of noting the Emperor’s nakedness.


Incidentally, Richard Harvey accurately projected that diversionary discharges from Lake Okeechobee to the two coasts would cause serious water quality problems. Humpty Dumpty strikes again—ignoring, rejecting or denying science does not eliminate the inevitability of its influence.    


The summer of 2018 promises to be a repeat of 2016, with deterioration of coastal waters and negative impacts upon tourism. It will be interesting to see if in the near future, the Sierra Club, the Heritage Foundation, the Stuart/Martin County Chamber of Commerce, and the Sanibel and Captiva Islands Chamber of Commerce find a way to join forces in a significant lawsuit against the SFWMD, FDEP and the Army Corps of Engineers. Crises make strange bedfellows!    




[1] K. Ramesh Reddy presently Graduate Research Professor and Department Chair, Wetland Biogeochemistry Laboratory, University  of Florida, Gainesville Florida. Dr. Reddy has been involved in wetland dynamics in and around the Everglades, as well as other regions of Florida for several decades and has been a leading scientist in developing understanding of wetland systems, particularly as applied for nutrient reduction.  He reviewed and conducted field evaluations of the Orlando Easterly Wetland providing comments in a proposal to the City of Orlando entitled Preliminary Design of Vegetation Modifications and Pilot Development of Sediment Management Protocols for the City of Orlando’s Easterly Wetland’s Treatment System A Proposal for City of Orlando Prepared by J. R. White, K. R. Reddy-University of Florida - Soil and Water Sciences Department Gainesville, FL and T. A. DeBusk DB Environmental, Inc. Rockledge, FL November 2001

[2] Bhomia, R.K, P.W. Inglett and K.R. Reddy (2015) Soil and phosphorus accretion rates in sub-tropical wetlands: Everglades Stormwater Treatment Areas as a case example.  Science of the Total Environment 533 (2015) 297-30

[3] Tampa Bay Times November 19, 2007, Craig Pittman EPA Removes Expert who Criticized Everglades' Program

[4] See          Blog        Near and Far from Equilibrium, Significant Dependence on Initial Conditions, Seep and Creep, and the Curse of Dissolved Rocks. March 30, 2018

Comments Welcome as always.

Will we see 2018 as a repeat of 2016, with rogue phosphorus from Lake Okeechobee, and from other sources stimulating toxic algae blooms, resulting in fish kills, and economic damage to tourist dependent regions? Photo permission of Florida Today



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