Large natural island at Chippewa Flowage, Wisconsin
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Natural floating islands occur in a number of unique settings around the world. These include mangrove mats in coastal equatorial settings, pools and other waterways associated with volcanic activity, and waterways associated with arboreal forests (typically around the 45th parallel in both the Northern and Southern Hemispheres).
Variations of floating islands have been built by humans for at least 2,000 years. |
However, until the advent of BioHaven floating islands, none of the human-designed systems purposely bio-mimicked nature's floating island models. Instead, they relied upon conventional buoyancy factors to achieve “freeboard” (the volume of a floating structure that lies above the waterline) to grow crops or provide communal living space. BioHaven floating islands are designed to replicate arboreal forest-based islands (Van Duzer, 2004).
Natural floating islands are typically peat-based and are essentially biofilm reactors. Biofilm- generating bacteria grow on the surface area of plant roots within the peat and on the surface area of the peat itself. Much of the island buoyancy is not associated with conventional factors such as low-density materials or entrained air. Instead, these islands float because of biogas (gases produced by bacteria within a biofilm) contained between the water table and the top of the island. This zone of trapped biogas can actually extend below the waterline on the inside of the island. This buoyancy contributes substantially to floating islands’ durability, longevity and size, which can encompass dozens of acres and support thousands of full-size trees.
Based on research funded by the State of Montana and Floating Island International (FII) and carried out at Montana State University's Center for Biofilm Engineering, aerobic, anoxic and anaerobic zones quickly develop on the matrix of BioHaven floating islands, when the surface area of the matrix is exposed to nutrient-laden water, especially when combined with circulation. Biofilm-generating microbes typically grow so fast that they are the only common life form to potentially take up nutrients more rapidly than phytoplankton (algae).
Natural floating islands are typically peat-based and are essentially biofilm reactors. Biofilm- generating bacteria grow on the surface area of plant roots within the peat and on the surface area of the peat itself. Much of the island buoyancy is not associated with conventional factors such as low-density materials or entrained air. Instead, these islands float because of biogas (gases produced by bacteria within a biofilm) contained between the water table and the top of the island. This zone of trapped biogas can actually extend below the waterline on the inside of the island. This buoyancy contributes substantially to floating islands’ durability, longevity and size, which can encompass dozens of acres and support thousands of full-size trees.
Based on research funded by the State of Montana and Floating Island International (FII) and carried out at Montana State University's Center for Biofilm Engineering, aerobic, anoxic and anaerobic zones quickly develop on the matrix of BioHaven floating islands, when the surface area of the matrix is exposed to nutrient-laden water, especially when combined with circulation. Biofilm-generating microbes typically grow so fast that they are the only common life form to potentially take up nutrients more rapidly than phytoplankton (algae).
Floating Treatment Wetlands schematic
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The primary biogases associated with floating islands are carbon dioxide (most microbial processes) and nitrogen (anoxic denitrification). Gases produced only by anaerobic processes are hydrogen sulfide and methane. FII can model nutrient cycling through BioHavens, and accordingly can estimate the volume of buoyant gas that can be generated within a cubic foot of island under variable nutrient loading conditions.
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For water quality improvement using BioHavens, FII has developed a spreadsheet model to estimate either the floating island size(s) required to meet water quality objectives, or the effect on a waterway of a given floating island size. Capital costs can then be estimated. Water quality parameters that dictate floating island requirements include ammonia, nitrate, phosphorus, total suspended solids and Biochemical Oxygen Demand.
BioHaven floating islands cycle nutrients from water into periphyton, which is a base material representing an alternative to free-floating algae. Periphyton is the microfloral and microfaunal community (bacteria, algae, protozoa, etc.) living attached to submerged surfaces. One of its primary values is that periphyton does not experience the massive bloom and die-off cycle of free-floating algae. Instead, it provides a continuous and perennial source of both food and oxygen for higher forms of life. Numerous studies have documented periphyton's relative value in triggering massive fish production (Azim 2005). With some stewardship, nutrients that would otherwise cycle into algae and ultimately reduce dissolved oxygen levels can be instead transitioned into fish. This cycling of nutrients contributes to BioHavens’ ongoing buoyancy.
FACTORS REDUCING BIOHAVEN FLOATING ISLAND BUOYANCY
Microbes that colonize a BioHaven are resilient. When seasonal or other environmental conditions are not optimal, these microbes have evolved strategies to ensure survival. When conditions become more favorable, microbes rapidly resume their nutrient cycling abilities. However, certain environmental conditions, such as exposure to broad-spectrum biocides or herbicides, can affect even resilient microbial populations. When this occurs, BioHavens generate less of the biogas that accounts for their ongoing buoyancy. As a design safety measure and means by which to provide initial buoyancy prior to mature biofilm development, typically a period of about one full growing season, BioHavens incorporate a proprietary blend of marine-based polyurethane foam as added buoyancy. To date, 4,800 BioHavens have been installed in a wide range of settings around the world, including wastewater ponds, stormwater ponds, lakes, streams, rivers and oceans. FII has seen no documented cases of island buoyancy failure. While there have been instances of reduced buoyancy associated with addition of chemicals such as biocides, BioHavens have always recovered.
BioHaven floating islands cycle nutrients from water into periphyton, which is a base material representing an alternative to free-floating algae. Periphyton is the microfloral and microfaunal community (bacteria, algae, protozoa, etc.) living attached to submerged surfaces. One of its primary values is that periphyton does not experience the massive bloom and die-off cycle of free-floating algae. Instead, it provides a continuous and perennial source of both food and oxygen for higher forms of life. Numerous studies have documented periphyton's relative value in triggering massive fish production (Azim 2005). With some stewardship, nutrients that would otherwise cycle into algae and ultimately reduce dissolved oxygen levels can be instead transitioned into fish. This cycling of nutrients contributes to BioHavens’ ongoing buoyancy.
FACTORS REDUCING BIOHAVEN FLOATING ISLAND BUOYANCY
Microbes that colonize a BioHaven are resilient. When seasonal or other environmental conditions are not optimal, these microbes have evolved strategies to ensure survival. When conditions become more favorable, microbes rapidly resume their nutrient cycling abilities. However, certain environmental conditions, such as exposure to broad-spectrum biocides or herbicides, can affect even resilient microbial populations. When this occurs, BioHavens generate less of the biogas that accounts for their ongoing buoyancy. As a design safety measure and means by which to provide initial buoyancy prior to mature biofilm development, typically a period of about one full growing season, BioHavens incorporate a proprietary blend of marine-based polyurethane foam as added buoyancy. To date, 4,800 BioHavens have been installed in a wide range of settings around the world, including wastewater ponds, stormwater ponds, lakes, streams, rivers and oceans. FII has seen no documented cases of island buoyancy failure. While there have been instances of reduced buoyancy associated with addition of chemicals such as biocides, BioHavens have always recovered.
Periphyton on the FTW matrix
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Dutchy Lake, Oregon, where a 20,000-ft2 FTW is covered with six inches of crushed rock
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Dutchy Lake FTW partially submerged after rainfall
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Other factors can lead to partial island submergence. These include exposure to heavy rainfall and snow loads as well as exceptional wildlife events, like large alligators that have used islands as convenient sunning locations. In all cases, BioHavens have fully recovered. For example, when the freeboard becomes saturated after a large rainfall event, an island will ride somewhat lower in the water until evaporation reduces the added weight.
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Island freeboard can also decrease with high atmospheric pressure. This is due to the corresponding reduction in the diameter of gas bubbles contained within biofilm coating the BioHaven matrix surface area.
The Elfin Cove walkway in southeast Alaska that experienced up to a 45-inch snowfall load
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Seawater biota thriving on the underside of the floating island, which did not reduce buoyancy
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It should be noted that marine FTWs have withstood up to a five-foot tidal surge.
FACTORS DAMAGING BIOHAVENS
Beaver, nutria, Canada geese and alligators have been known to dig holes into BioHavens. While such holes represent a cosmetic blemish, in no instances has such damage resulted in island failure. Muskrat are also suspected of damaging BioHavens on occasion but again, in no instances has this resulted in catastrophic failure or sinking of an island.
PROJECTED LONGEVITY
As BioHavens mature, they develop biofilm, diatom and phytoplankton forms of periphyton, which produce biogases and serve to maintain island buoyancy. Islands also become thicker as they mature. This results from plant humus accumulating on top of islands and other organic residue growing within islands. FII believes that young BioHavens correspond to the early- stage, peat-based, naturally occurring islands that they bio mimic. Such islands do not normally create the “pressurized vadose zone” seen in older, mature natural islands. Large, mature natural islands can be as much as six meters thick within 20 meters of their perimeter. Because of their low permeability, this thickness serves to contain biogas and contributes to long-term buoyancy. Accordingly, FII predicts that BioHavens will also develop pressurized vadose zones over time as they mature.
Monitoring of BioHavens indicates that their dry weight can nearly double over the course of a single growing season, with a 72% increase in mass measured over an 11-week period (Kania, 2013). However, based on monitoring of the same 520-square-foot island, thickness only expands slightly to accommodate this mass buildup. Currently the “520” island located at FII’s research center in Shepherd, MT has grown about nine centimeters thicker over an eight-year period, or approximately one half-inch per year.
BioHavens are composed almost entirely of a polyester-based, nonwoven, filter-like material. This material is composed of fine threads of matrix and is vulnerable to ultraviolet light degradation. FII and its seven island manufacturers provide quality assurance guidelines that call for islands to be covered with either bedding soil or a blanket-like material (typically composed of coir or jute) at island launch. In some settings, where islands tend to very quickly develop a carpet of macrophyte cover, clients have opted to not incorporate this protective material. To date, FII knows of no island failures associated with any of these protection strategies.
FACTORS DAMAGING BIOHAVENS
Beaver, nutria, Canada geese and alligators have been known to dig holes into BioHavens. While such holes represent a cosmetic blemish, in no instances has such damage resulted in island failure. Muskrat are also suspected of damaging BioHavens on occasion but again, in no instances has this resulted in catastrophic failure or sinking of an island.
PROJECTED LONGEVITY
As BioHavens mature, they develop biofilm, diatom and phytoplankton forms of periphyton, which produce biogases and serve to maintain island buoyancy. Islands also become thicker as they mature. This results from plant humus accumulating on top of islands and other organic residue growing within islands. FII believes that young BioHavens correspond to the early- stage, peat-based, naturally occurring islands that they bio mimic. Such islands do not normally create the “pressurized vadose zone” seen in older, mature natural islands. Large, mature natural islands can be as much as six meters thick within 20 meters of their perimeter. Because of their low permeability, this thickness serves to contain biogas and contributes to long-term buoyancy. Accordingly, FII predicts that BioHavens will also develop pressurized vadose zones over time as they mature.
Monitoring of BioHavens indicates that their dry weight can nearly double over the course of a single growing season, with a 72% increase in mass measured over an 11-week period (Kania, 2013). However, based on monitoring of the same 520-square-foot island, thickness only expands slightly to accommodate this mass buildup. Currently the “520” island located at FII’s research center in Shepherd, MT has grown about nine centimeters thicker over an eight-year period, or approximately one half-inch per year.
BioHavens are composed almost entirely of a polyester-based, nonwoven, filter-like material. This material is composed of fine threads of matrix and is vulnerable to ultraviolet light degradation. FII and its seven island manufacturers provide quality assurance guidelines that call for islands to be covered with either bedding soil or a blanket-like material (typically composed of coir or jute) at island launch. In some settings, where islands tend to very quickly develop a carpet of macrophyte cover, clients have opted to not incorporate this protective material. To date, FII knows of no island failures associated with any of these protection strategies.
A recently launched floating island with full UV protection
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BioHaven floating island lifespan is anticipated to be at least ten years (Stewart, 2013) but the maximum life is still unknown. Most of FII’s island manufacturers offer five-year warranties. Others offer seven-year warranties, and one offers a ten-year warranty. If the design continues to successfully bio-mimic naturally occurring peat-based islands, BioHavens will experience a life span much longer than ten years. Indications now are that current BioHavens are similar to early-stage natural islands.
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However, most naturally occurring islands grow in mesotrophic or oligotrophic waterways, while most BioHavens have been placed in eutrophic waterways (which is where they provide the most benefit). The added nutrients associated with eutrophic water suggests that BioHavens in such settings may outpace their naturally occurring counterparts in both growth and buoyancy. Current indications are that BioHavens become more buoyant over time.
In hyper-eutrophic settings, BioHavens could potentially extend all the way to the bottom of a waterway. If aerobic conditions are present in these conditions (which is unlikely), it is possible that macrophyte roots could tie into such a waterway’s benthic zone and permanently bond to the bottom of the waterway. In several settings, including high mountain spring creeks and streams associated with agricultural runoff, FII has successfully attached islands onto stream banks. In seasonal ponds, islands that were fully desiccated and apparently bonded to the dry waterway’s bottom have again floated after the waterway refilled. Where plants present on such islands were sustained and could continue developing roots, it appears likely that islands could mate permanently into the waterway’s benthic zone. It is unknown whether BioHaven’s biogas- based buoyancy, in combination with buoyancy from the polyurethane foam, would cause such an island to free itself.
In hyper-eutrophic settings, BioHavens could potentially extend all the way to the bottom of a waterway. If aerobic conditions are present in these conditions (which is unlikely), it is possible that macrophyte roots could tie into such a waterway’s benthic zone and permanently bond to the bottom of the waterway. In several settings, including high mountain spring creeks and streams associated with agricultural runoff, FII has successfully attached islands onto stream banks. In seasonal ponds, islands that were fully desiccated and apparently bonded to the dry waterway’s bottom have again floated after the waterway refilled. Where plants present on such islands were sustained and could continue developing roots, it appears likely that islands could mate permanently into the waterway’s benthic zone. It is unknown whether BioHaven’s biogas- based buoyancy, in combination with buoyancy from the polyurethane foam, would cause such an island to free itself.
Shoreline islands 20 months after installation
REFERENCES
Azim, M.E., 2005. Periphyton: Ecology, Exploitation and Management.
Kania, B., 2013. Personal communication.
Stewart, F.M., 2013. Estimate of the Useful Lifespan of BioHaven Floating Treatment Wetlands.
Van Duzer, C., 2004. Floating Islands: A Global Bibliography. Cantor Press, California, USA.
Azim, M.E., 2005. Periphyton: Ecology, Exploitation and Management.
Kania, B., 2013. Personal communication.
Stewart, F.M., 2013. Estimate of the Useful Lifespan of BioHaven Floating Treatment Wetlands.
Van Duzer, C., 2004. Floating Islands: A Global Bibliography. Cantor Press, California, USA.