Managed Aquatic Plant Systems (MAPS)--A Strategy for Phosphorus Removal and Recovery within the Kissimmee-Okeechobee-Everglades Ecological Amalgamation (KOEEA)

E.Allen Stewart III P.E. August 7, 2018

Presented within the next two Blogs is a proposed long-term strategy for management of excess phosphorus within the Kissimmee-Okeechobee-Everglades Ecological Amalgamation or KOEEA. Biologically available forms of phosphorus have saturated the soils throughout the KOEEA, which has resulted in sustained high levels of phosphorus within Lake Okeechobee. These rising phosphorus concentrations are critical in sustaining favorable conditions for promotion of heavy blooms of cyanobacteria (Blue-Green Algae) during the wet season. These blooms not only have been deleterious to Lake Okeechobee, the diversion of excess waters from the lake to the Caloosahatchee and St. Lucie estuaries have contributed to serious water quality degradation and toxic conditions in and around these estuaries. This deteriorating water quality has caused extensive mortality of animal life and seagrasses, has negatively impacted the tourist based economy,  and could create serious threats to human health.

The existing Comprehensive Everglades Restoration Plan (CERP) has been assessed as lacking sufficient scope or timing to address these developing problems. While construction of additional water storage is critical to protecting both the estuaries and the downstream Everglades and Water Conservation Areas from seasonal excesses and deficiencies of water, it is also vital that phosphorus, both as long-term accumulations known as legacy or rogue phosphorus, as well as new imports, are removed, recovered and exported or recycled as value added products.

This first Blog is offered as a cursory introduction to a technology known as Managed Aquatic Plant Systems (MAPS). The complexity of the existing problems in the KOEEA and how a MAPS program could be effectively implemented is presented in the second Blog.

MAPS can provide and sustain cost effective, high rates of phosphorus removal and recovery, and have the potential for reduction of both rogue and net phosphorus imports, something that is critical for ecological stability within the Everglades as well as the impacted estuaries. MAPS technology involves the cultivation of aquatic plants through purposeful and frequent harvesting, processing and removal/recycling.

MAPS are capable of removing nutrients from the water column and incorporating them at predictable rates into the harvested aquatic plant biomass, and as such, MAPS can be seen as a type of agriculture—but an agriculture that does not pollute, but actually treats water while recovering nutrient resources, such as phosphorus, protein, fiber, carbon, fats, minerals, vitamins and other  beneficial compounds.

Although there are several versions of MAPS, some of which include chemical precipitation processes and the use of  non-harvested/recovered water hyacinth systems, both of which are presently being investigated by the South Florida Water Management District (SFWMD), within these two Blogs I am limiting my review to just four types of MAPS. These, shown in the following photographs are:

  1. Floating Aquatic Plant Systems (FAP-MAPS) involving cultivation of such floating plants as water hyacinth and water lettuce. 

  2. Attached Algal Floways (AAF-MAPS) such as the Algal Turf Scrubber® as developed at the Smithsonian and now applied in Florida as full scale systems.

  3. Floating Mats (FM-MAPS) which are used to support emergent vegetation within an engineered mat, such as BeeMats™[1].

  4. Stormwater Treatment Systems (STA-MAPS) which are periodically harvested of plants and sediment accumulations, and accordingly represent a conversion of the passive STA to an actively managed STA.

[1] Floating vegetative mats as offered by BEEMATS LLC, New Smyrna Beach, Fla.

Cultivation of the floating aquatic plant, the water hyacinth, likely represents the initial modern effort to develop effective Floating Aquatic Plant-Managed Aquatic Plant Systems (FAP-MAPS), with early investigations dating to the sixties. Noted in this picture is a pond in which water hyacinths were cultivated in 2003, just north of Lake Okeechobee in the S-154 watershed. At this facility the water hyacinth crop demonstrated an ability to reduce both phosphorus and nitrogen from nutrient impaired surface waters at high removal rates. The S-154 project was jointly funded by the Florida Department of Agriculture and Consumer Services (FDACS), the Florida Department of Environmental Protection (FDEP) and the South Florida Water Management District (SFWMD). This was a successful demonstration project. The technical report is available within this website.  

A significant percentage of these nutrients associated with the S-154 project were periodically removed through harvesting of the water hyacinths. Harvesting was conducted about two to four times a month, depending upon seasonal conditions and nutrient levels. Harvesting was done using a specially designed light weight grapple powered through a tractor PTO (Power Take-Off) to remove a portion of the plants at a rate greater than 10 wet tons per hour

Another MAPS program involves attached algal floway systems (AAF-MAPS), such as the Algal Turf Scrubber® or ATS™ developed at the Smithsonian Institute in the seventies. The ATS™ was included as a unit process at the S-154 project. Attached algal systems involve cultivation of a community of attached algae and associated organisms, known as algal turf. This algal turf is grown on a flat, mildly sloped floway down which water is delivered in a continuous shallow laminar flow. The facility shown here is known as the Egret Marsh Stormwater Park in Indian River County, Florida. It treats 10 MGD of stormwater and has been in active operation for six years.  As the water flows down this system, nutrient pollutants within the water are taken up by the algal turf and incorporated into its growing biomass

The harvested plants were placed in a transport canal and picked up by a conveyor system, and deposited into a chopper system modified to accommodate the high moisture content of the plants. Chopping significantly increased the bulk density, while expanding surface area, making the crop easier to handle and amenable to direct windrow composting without addition of a bulking agent. At this facility much of the chopped hyacinth material—about 100 wet tons—was delivered to a nearby Dairy Farm, where it was fed to dairy cattle as an additive to their green chop program. In the past, chopped water hyacinths also proved effective in the generation of a usable biogas and in the development of fiber products.

Through photosynthesis, the algal turf releases oxygen, much of which is dissolved within the overlying water. The resulting effluent therefore is of high quality, being reduced in nutrients, suspended solids and other pollutants, while enhanced with increased levels of dissolved oxygen (DO).The biomass, or algal turf, is composed of periphytic and epiphytic algae and associated microbes and invertebrates. As the biomass increases, the system is harvested, and the harvest is recovered and converted to usable products such as compost. Noted in these two pictures are the initial harvesting and the harvest rake. Harvesting occurs about once weekly during the warm season and about every 14 days during the cool season.

A comparatively simple method of processing biomass associated with MAPS harvests is composting. The compost piles shown here are from an ATS™ facility. This compost can be developed into a marketable product, such as that shown in the picture below (Lagoon Saver™).

This is a picture of the water body which receives effluent from the Egret Marsh ATS™ in Vero Beach (Indian River County) Florida. If you look just to the right of the small cypress tree inside the encircled area you can see a large bass. The fish choose to gather around the discharge area because of the high dissolved oxygen levels and the abundance of small minnows and invertebrates which also flourish in the water.



These before and after pictures show the improvement in water quality on the right after the flow from the drainage canal on the left is treated through the Egret Marsh ATS™

Floating Mat Systems (FM-MAPS) such as the BeeMats™ shown in these three photographs can be used in ponds, lakes, streams and canals to capture nutrients and solids and deter blooms of suspended algae (phytoplankton) such as blue-green algae, by shading and competition for nutrients. These mats expand the shoreline (littoral) zone, thereby providing an additional sink for nutrients and habitat for visiting wildlife and a diverse community of aquatic species. The mats can be retrieved periodically and the plants removed for either further processing (such as compost) or as a source of native plants for wetland creation and mitigation. Also high value domesticated plants, such as various herbs and lettuces may also been grown on the mats.   

Of course the STA-MAPS associated with high quality input are more emulative of the original Everglades, and with innovative designs can be developed to attract certain endangered and threatened species. The wetland shown in the picture to the right was designed for the Indian River County Egret Marsh Stormwater Park to receive effluent from the ATS™, specifically for the wood stork. As can be seen in the photograph, this design approach has proven quite effective. 

Created wetlands for water treatment have been given the name Stormwater Treatment Areas (STA) by the South Florida Water Management District (SFWMD) within the KOEEA. The higher the quality water entering these created wetlands the longer the time before the system requires removal of its sediments and standing crop of aquatic plants. If  periodic harvesting is planned as part of the operational plan, the STA becomes a MAPS, or STA-MAPS. Design of these STA-MAPS which allow compartmental isolation and in-situ dewatering/composting of sediments and biomass would provide sustainable, uninterrupted performance and reduced costs. [The wetland to the left shows Thalia geniculata (alligator flag) and Hibiscus gandiflorus (rose mallowI)]. It would seem reasonable to design such STA-MAPS as a polishing system following treatment by the other MAPS systems. 

It is scientifically and economically reasonable to expect the application of MAPS to reduce the rogue phosphorus stores as well as intercept and recover the net phosphorus imports into the Okeechobee Basin, and therefore bring the lake into compliance with the TMDL requirements of 149 tons of phosphorus per year loading and 40µg/L in-lake total phosphorus concentration.


Furthermore, a well-designed MAPS strategy involving serious long-term public-private partnerships in concert with enhanced system design, and development of marketable products, could create a new, revolutionary agri-industry. This new approach to agriculture would offer water quality improvements, more effective accommodation of existing markets, the opening of new product markets, and enhancement of the efficiency and environmental sensitivity of some of existing agricultural endeavors, such as but not limited to dairy farming.

Cultivation of aquatic plants has shown a capability of producing higher levels of protein and fiber per acre when compared to conventional crops, such as soy beans. High rate protein production means more nutritional value per acre of cultivation, and fits well into developing strategies for meeting the growing demands throughout the world. As an example, just a few miles from Lake Okeechobee a private company by the name of Parabel is cultivating the floating plant duckweed (Lemna sp.) and are achieving unprecedented rates of production, processing and sale of the plant protein, lentein.


Much of this I will present in the follow-up Blog. But just to give an idea of how MAPS might be applied on a large scale, to remove 1,500 tons of phosphorus annually it is projected that 64,000 acres of MAPS process area would be required in a treatment train that could be similar to that shown in Figure 1. This might require a total facility area of perhaps 90,000 acres, which would include pumping, power stations, access, security, flood protection, stormwater management, product processing and storage, and operational and maintenance support facilities. Envisioned is a series of about 70 modules placed around the lake and at the interface with southern reservoirs and control structures, with each module at 1,000-2,000 acres, as shown schematically in Figure 2. These units would act as kidneys, returning highly oxygenated, lower nutrient water back to the system, while generating about 30,414 tons per year of protein and 60,000 tons per year of fiber. The expected protein yield of about 950 lb/acre annually, is nearly three times the rate for soy beans. If 64,000 acres of aquatic plant agriculture sounds like a lot, remember sugar cane cultivation now encompasses about 400,000 acres, and if non-harvested STA’s were used alone without MAPS to remove 1,500 tons/year of phosphorus, at the documented removal rate for STA's of about 1g/sm-year or 8.9 lb/acre-yr, it would require over 336,000 acres!

Obviously 90,000 acres of MAPS facilities are not going to be built overnight, and while the water treatment capabilities of MAPS technologies has been well documented, there remains much work to identify and develop the most efficient design strategies and the most feasible and valuable product(s) from the harvested biomass. Design and operational refinements, such as more efficient harvesting methods, less expensive construction, effective pest and disease control, and energy efficient pumping systems need to be thoroughly evaluated. The potential products would require extensive market analysis, and objective determination of overall cost effectiveness and economic impacts.

How do we address these issues, and how might MAPS be most effectively implemented? That is the subject of the next Blog.

In closing, let me offer a disclaimer. I have been involved throughout my career of some forty years with the development and implementation of some of the MAPS technologies included within this Blog. I am now retired, and I do not have patent rights, or stock or ownership in any companies that develop and sell MAPS. However, I do at times promote these technologies, not in anticipation of substantial financial returns, but rather because I believe they can be applied to protect Florida’s waters and can have an overall positive influence on the quality of life for ourselves, our posterity and for the other living organisms with which we share this special environment. I do have a small consulting group— ASBRO LLC, involving myself and another manager (owner) and no employees. I use this LLC as a way to assist in resolving engineering and environmental issues. Much of my consulting is done pro bono or at much reduced rates, and most of what little I earn I typically return to worthwhile causes.