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Allen's Blog

November 26, 2019

Harvesting Hydrilla in Florida Lakes

A Long-Term Strategy for Large-Scale Removal of Legacy Phosphorus and Maintenance of Viable Habitat

The Blue-Green Algae Task Force (TASK FORCE) was created in 2019 by Florida's Governor Ron DeSantis in response to increased public concern over recent explosive blooms of Cyanobacteria, also known as blue-green algae, within Lake Okeechobee, the Caloosahatchee River, and the St. Lucie River. And these are not the only water resources impacted by such blooms. Lake Apopka, a 33,000 acre lake in Central Florida, and the headwaters of the Oklawaha River, has been in a continuous Cyanobacteria bloom for over fifty years, and flow from the lake has degraded water quality within downstream lakes and rivers including Lake Dora, Lake Eustis, Lake Griffin, and ultimately the St. Johns River and its associated lakes. In addition, Florida's springs have also suffered from explosion of the Cyanobacteria species Lyngbya sp. which has displaced much of the native submerged freshwater grasses such as eel grass (Vallisneria americana) and their associated  ecosystems.  

In the  TASK FORCE Consensus Report of October 11, 2019 it is clearly noted that the intent of the TASK FORCE  is to serve as an "advisory body------to aid the Department of Environmental Protection in fulfilling its mission to protect, conserve and manage the state’s natural resources and enforce its environmental laws. The Task Force, through its discussion and deliberations, provides guidance and specific, science-based recommendations with the goal of expediting improvements and restoration of Florida’s water bodies that have been adversely affected by blue-green algae blooms."

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(left) Blue Green Algae bloom in South Florida 2016     

(center) Typical healthy lawn of eel grass in a Florida Spring         

(right) Invasion of an eel grass lawn by the Blue-Green Algae Lyngbya (now Microseira) wollei in a Florida Spring

photos by UF/IFAS Center of Aquatic and Invasive Plants


Included in the Task Force Consensus report is a comment related to the need to "expedite legacy nutrient removal." 

"Legacy nutrients, as indicated previously, are a concern in the South Florida landscape, and the task force recommends that their contribution to loading figure prominently in the Lake Okeechobee, Caloosahatchee and St. Lucie River and Estuary BMAPs (Basin Management Action Plan). The task (force) further recommends that projects with the demonstrated potential to expedite legacy nutrient removal merit special attention and be designated as priority projects."

The entire consensus report may be seen by clicking the button provided below this text.

In a recent PASOP blog on the PAY-FOR-PERFORMANCE strategy (see button above), legacy nutrients were identified as excess nutrient loads which remain in the sediments of a drainage basin (including lake sediments), and which can become available under the right environmental conditions. The TASK FORCE identified legacy nutrients as "nitrogen and phosphorus sequestered in soils, groundwater and sediments, (which can) contribute also to excessive nutrient loading of surface waters throughout the state." While the scientific community has been aware for decades of legacy nutrients and the problems they present, it was the recent Cyanobacteria blooms that forced serious Institutional and Political consideration of their potential deleterious impact. In a 2015 report by the University of Florida Water Institute [1] it was noted that over 110,000 metric tons of biologically available legacy phosphorus is held within the sediments of the Lake Okeechobee Basin. If  this legacy phosphorus were to be effectively removed, about 2,000 tons would need to be removed each year for fifty years. Like any challenge this  may be seen by some as insurmountable, while others might see it as a great opportunity. I prefer the latter perspective. So how can we make chasing  and recovering this legacy phosphorus an opportunity without sounding like someone who believes in Unicorns and magic dust?  

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(a) Harvesting and loading transport barge--Hydrilla West Lake Tohopekaliga Florida 2019 (photo by Texas Aquatic Harvesting 2019) 

(b) Barge Transport of Hydrilla to Land Base Depository (photo by Texas Aquatic Harvesting 2019)   

(c) Chopping of Aquatic Plants (Water Hyacinth) (photo by HydroMentia, Inc.)   

(d) Windrow Composting of harvested Aquatic Plants (photo by HydroMentia, Inc.) 

Well, in the Pay-For-Peformance blog previously referenced I presented the idea of using Managed Aquatic Plant Systems (MAPS) as one way of removing substantial legacy nutrient loads through direct plant uptake. The MAPS approach is centered around sustained cultivation of specific aquatic plants as agricultural crops which rely solely upon legacy nutrients as their nutrient source. If we apply some critical thinking to the MAPS challenge, we can surmise that such cultivation will require periodic harvesting and the subsequent processing of this harvest which would result in a viable product of significant market value while also removing substantial quantities of legacy nutrients. In other words MAPS would become a legitimate agricultural endeavor which also helps resolve water quality issues--it would be "an agricultural solution to an agricultural problem" [2].  We also should recognize that such culivation could be done as land-based operations external to the water body itself--where the MAPS would serve as a "kidney" to the contiguous water resource. But it could also be done internally within the lake through mechanical harvesting of aquatic plant overgrowth. This is presently being done in China as I reported in my blog of October 8, 2018 [3]. We could call such internal MAPS programs as in-situ MAPS.  

The exotic and invasive aquatic plant known as Hydrilla  is a potential candidate for an aggressive large scale in-situ MAPS  program. Hydrilla is a submerged plant that for a number of reasons has the ability to outpace native submerged plants such as Southern Naiad, tape grass and Coontail. In fact its growth is so explosive that it can rather quickly cover the surface of a water body ("topped out"),  as noted in the picture below. When Hydrilla tops out it renders the surface impassable to most boat traffic, and can deleteriously impact water quality by impeding oxygen exchange with the atmosphere, and by sloughing large quantities of necrotic tissue.  None of this is desirable, and it is not difficult to understand why there is a desire to eliminate Hydrilla, or at least control it so that it does not "top out" as shown in this picture. 

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Hydrilla "Topped out" on Florida's southern Withlacoochee River.     

Over the past few years, in light of the growing controversy over herbicide use within Florida's surface waters,  I have made an effort to gain a better understanding of the extent of the problem associated with Hydrilla, and the strategies adopted to facilitate some degree of control. I have talked extensively with those adamantly opposed to the application of herbicides, and those who see herbicides as the most cost-effective means of controlling Hydrilla. The opposition is composed largely of fishermen and fisherwomen (both professional and recreational); outdoors men and women; and environmental activists including many aboriginal indigenous people. All of these typically having extensive experience with the Florida environment, and many being native Floridians. Those who, to varying degrees, support herbicide use include those involved in the actual sales, distribution and application of herbicides; institutions conducting research and assessment of herbicide use; agency people assigned with the responsibility of managing aquatic plants; and a collection of impacted property owners, local governments, and commercial interests.


The common thread I found among most of these disparate groups is the recognition that herbicides are designed toxins whose long-term impact on aquatic ecosystems, while touted to be minimal, are in reality not that well understood, and that if we could replace the use of these toxins with a more environmental protective method(s), it would be supported. With such a shared perspective you would think we would see aggressive efforts to reduce herbicide use. But such is not the case. Why is this? 

Let me offer two of my thoughts as to why we persist in widespread application of herbicides. The first  thought -- this is an industry which appears particularly vulnerable to corruption.  I say this because there is a great deal of money involved in the sales, distribution, research and application of herbicides. As an engineer and scientist however I do not have the skills needed to investigate such matters, I can only express my concerns.  I realize all of this is only speculation, and I will leave the pursuit of this possibility to others. 

My second thought is a concern that the agencies and institutions involved in environmental management, including aquatic plant management,  are focused solely upon their specific charge, and hence do not recognize the overlap they may have with others. For example, aquatic plant management can have profound influence on water quality, but the FWC and their support institutions have consistently told me water quality is not their concern--that is the realm of the FDEP. On numerous occasions I suggested to FWC that they could benefit from the environmental services associated with nutrient reduction by actually removing aquatic plants using mechanical harvesting through a Pay-For-Performance arrangment. This way they would be contributing greatly to TMDL compliance and water quality enhancement. The silence of a positive response to this suggestion was deafening.

Similarly, FDEP has shown little interest in the idea that harvesting aquatic plants on a sustainable basis could remove legacy nutrients and help meet the TMDL limits. The USACOE have actually sent me written confirmation that they do not bother with issues related to water quality, as their primary concern is with water quantity.[4]  All of this denial of overlap reminds me of the failure of the FBI and CIA to share information--a sharing which might have prevented the 9/11 event.

The FWC is charged by the legislature through the Aquatic Plant Management Act (FS 369-20) with the responsibility to “direct the control, eradication, and regulation of noxious aquatic weeds and direct the research and planning related to these activities . . . so as to protect human health, safety, and recreation and, to the extent possible, prevent injury to plant and animal life and property.” There is little question  that the directive is centered around aquatic plant management, but how can it be interpreted that they are not responsible for water quality impact as well? Just how would you interpret "prevent injury to plant and animal life and property"? Is not the welfare of aquatic animals and plants, including fish, hugely dependent upon water quality? Am I missing something? 

If we envision a Venn diagram, under present operational strategies, we would not expect the activity circles for the involved agencies to touch as noted below left. In reality, there should be much greater overlap as noted in the diagram below right. All that is needed is for each group to climb over the edge of their box and play with others! The people of Florida deserve that.  

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After pondering this  second concern for sometime, I decided I needed to do more than talk, so I put together a conceptual plan by which a long-term extensive Hydrilla harvesting progam might be implemented on a large lake such as West Lake Tohopekaliga (West Lake)  in the upper reaches of the Lake Ockeechobee Basin. This conceptual plan includes a continual maintenance strategy involving about 12,000 acres, which would result in prevention of Hydrilla "topping out"; would provide viable habitat; would facilitate oxygen generation; would compete with cyanobacteria; and would remove over 500 tons each year of legacy phosphorus. And West Lake is used just as an example--this could be done on Lake Okeechobee, or Lake Istokpoga, or others, and of course could be modified to target floating or emergent aquatic plants. Use your imagination! Ultimately the harvested biomass would be converted to viable agricultural products, and through the Pay-For-Performance concept, would incentivize the private sector. This conceptual plan may be accessed using the button below.  

Implementation of such a plan would need to be proceeded by a two-year in-field demonstration project. This is required to establish critical design criteria such as growth rates, harvesting rates and costs, crop recovery rates, ecological impact, and eventually crop transport and processing options. A proposed Scope of Work for this demonstration project can be accessed through the button below.

I realize this is an agressive, bold approach that will require not only political will and a great deal of patience and obedience to science, but also a commitment to identify and implement effective and adequate funding mechnisms such as Pay-For-Performance. But  this approach has real potential not only as a way of enhancing desirable environmental features, but also to establish new sustainable economic opportunities.  







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