Stormwater Management for Nutrient & Sediment Control

For stormwater management, BioHaven floating islands efficiently treat runoff while delivering quality-of-life benefits. They act like a natural wetland, increasing the aesthetic value and wildlife abundance of any stormwater pond and farm pond. Easily installed, they protect the environment from harmful pollutants and sediments carried downstream by urban, industrial and agricultural runoff. In many US states, BioHaven floating islands have been approved as a BMP and can be used to gain nutrient credits.

Floating Islands for Stormwater Management

  • Effectively manage nutrients and sediment from urban and agricultural runoff
  • Capable of treating non-point source pollution throughout the watershed
  • Deployed in retention ponds to trap scum and particulates, which are then mechanically and biologically sequestered
  • Easily retrofit into existing stormwater ponds
  • Installation is non-disruptive to the environment
  • No need to remove plants – in fact, to do so is counter-productive
  • Ideal for fluctuating water levels
  • Straightforward sizing protocol
  • Quality-of-life restored to a functional waterbody
  • BioHavens have been proven by premier wetland scientists throughout the world!

Description of Floating Island Technology

BioHaven Floating Islands employ rooted, emergent macrophytes (similar to those used in surface and subsurface flow wetlands) growing as a floating mat on the surface of the water rather than rooted in the sediments. They tolerate wide fluctuations in water depths that are typical of stormwater systems. The plant roots hanging beneath the island provide a large surface area for biofilm growth and entrapment of fine suspended particulates that would otherwise remain in suspension in a pond system. Because the plants are not rooted in the sediment, they are forced to acquire their nutrition directly from the water column, which enhances potential rates of nutrient and element uptake into biomass.

It’s all about the matrix

The basis of the BioHaven solutions is the permeable, tiny fibers of the proprietary matrix, together with mature plants and extensive roots that grow through them. This makes up the massive surface area to support the growth of biofilm, a sticky substance that contains the microbes responsible for treating pollutants in stormwater. Through the processes of organic digestion, particle settlement, filtration, adsorption and direct uptake, BioHavens can treat oil and grease, excess nutrients and heavy metals such as copper and zinc. Put another way, pollutants are circulated through the islands and glom on to the sticky biofilm covering the root surfaces and island matrix. They either fall off into the sediments below when they get too heavy or are digested by the incredible food web inside the island and the plant-root mass.

Minimal Environmental Impact

BioHaven treatment approach to stormwater management requires zero land use, and has many other environmental benefits:

  • Standard BioHavens require no power to operate
  • Plants harmonize with the surrounding vegetation and create new habitat
  • Reduces or eliminates the need for chemical dosing
  • The manufacturing process is low-energy

Not all stormwater is created equal. Just look up-watershed and track the potential nutrient loading that could be happening. For example, is there heaving farming in the up-watershed region? In such a setting there is likely to be surges of nutrients. Say a storm event coincides with farm field fertilizer application. Or a flood irrigation system is inadvertently mishandled. And about a million other mishaps can explain why the downstream stormwater pond occasionally becomes a flat-out carpet of algae. The occasional burst of phosphorus, and nitrogen too, makes management of stormwater ponds particularly challenging.

  • Design and Deployment

     

    Flexibility

    BioHavens Floating Islands can be adapted to suit a wide range of situations with very little effort. For example, they can be:

    • Fit into any existing space or waterbody shape
    • Operated in extreme climate or environmental conditions
    • Designed to remove specific pollutants aerobically or anoxically
    • Effective in fluctuating water levels, without drying out or being inundated
    • Deployed to slow down flow and increase detention times
    • Can be installed in stages to meet changing treatment requirements.

    Design and Deployment Considerations

    Sizing a BioHaven solution is based on a proprietary model based on historical data collected from a host of BioHaven-specific studies. As far as possible, placement should take advantage of natural circulation to bring water into the treatment process. Aerators or circulators may be added to enhance circulation. Placement close to inflow and outflow is often most effective, though this may need to be balanced with aesthetic considerations. Depending on customer preference, BioHavens can be anchored or tethered to shore. Plants should be selected from a known range of species that thrive on BioHavens and produce a perennial, bushy root-mass. Hyper-accumulator plants can be recommended for specific parameters of concern (e.g. sulfates). Waterfowl may need to be considered.  They do not pose a threat to the islands, which are armored for protection, but may pluck out young plants.  FII recommends using netting around the islands until the plants are well established. BioHavens are very winter-hardy, withstanding cycles of freeze /thaw without impact. Perennial plants will revive along with their land-based counterparts. It may take up to 4 weeks after thaw for the islands to regain their normal buoyancy. Maintenance involves periodically checking tethers, anchor chains and placement. Invasive plants and volunteers may need to be weeded out. Plants do not need to be harvested but may be trimmed periodically for neatness or to promote root growth.


  • Treatment Benefits

    BioHaven Floating Islands can effectively treat ponds, streams and ditches to restore a watershed to health:

    • Effectively reduce algae blooms, cyanobacteria and Golden Algae
    • Reduction in phosphorus and nitrogen halts widespread loss of aquatic life
    • Reduction in fecal coliforms makes water healthier for humans and animals to drink
    • Sediment trapping and removal prevents choking of pristine waters
    • Prevention of erosion maintains stream and river bank integrity
    • Prevention of midgefly, mosquito, and other nuisance pest infestation

  • Case Studies and Research
    • Mermaid Pool: Passive Biohavens remove phosphorus in a New Jersey stormwater pond

      several adults bending in water to help with the installation of floating islands

      Mermaid Pool, Somerset County, New Jersey

      This study, undertaken by Princeton Hydro, demonstrates that even without added aeration, BioHaven floating islands qualify as a BMP for removal of phosphorus from stormwater ponds. They are effective even at low concentrations of 0.1 mg/L.

    • Successful treatment of industrial stormwater runoff using Floating Island Technology at a site in Billings, MT

      several floating islands positioned in an area that collects storm water

      Metra Park Industrial Area, Billings, MT, USA

      This two-year study documents the success of an FTW installation in treating light industrial stormwater runoff.

    • BioHavens north of Chicago win storm water BMP award for local conservation group

      floating islands line the shoreline of a small lake with trees and a mountain in the background

      Barrington, IL

      The Citizens for Conservation used BioHaven floating islands to augment a wetland for storm water treatment in a housing sub-division in Barrington, IL. Their algae problem disappeared and dissolved oxygen levels went up – and Sandhill cranes successfully reared chicks on the islands.

  • Related Reading

a pond backed by a large apartment building dotted with floating islands and a fountain

a floating island positioned in a storm water runoff

several floating islands positioned in an area that collects storm water

a pond by some residences that is covered in algae and lined with brown plants

a floating island placed in a pond by some residences

a floating island on the edge of a pond

shows small floating island products being planted and prepared for launch

floating island products in an island acting as fish aggregation device

a man lifting up a bed of floating islands to expose the roots underneath


Urban stormwater poses significant threats to waterways because it transports pollutants.

Loads of pollutants, such as nutrients, heavy metals, sediment, indicator organisms, and hydrocarbons, tend to be higher in urban areas than in rural areas.

The added volume of stormwater that is conveyed from impervious surfaces causes stream bank erosion, degradation of aquatic habitat, and loss of real estate. Therefore, federal, state, and local legislation in the U.S. mandates the use of stormwater control measures (SCMs) to combat these negative consequences of urban growth. Examples of SCMs include innovative stormwater practices, such as bioretention, permeable pavement, water harvesting, and infiltration devices, which are often integrated into Low Impact Development (LID) strategies.

Nutrient reduction goals have been set with strict TN (total nitrogen) and TP (total phosphorus) load limits for new and existing development. Since existing developments often have limited space for retrofitting stormwater practices, methods to improve currently in-ground stormwater practices’ performance for nutrient removal are crucial. One potential retrofit for reducing nutrients in wet detention ponds is the use of floating treatment wetlands (FTWs), or Floating Islands (FIs).

FTWs function in a similar manner to hydroponic systems, where plants and microbes inhabit a floating mat and uptake nutrients as they grow.

A laboratory study of floating treatment wetlands (Tanner and Headley 2011) showed positive removal of Copper, Zinc, and fine suspended particulates. A study using them to treat raw domestic wastewater showed removal efficiencies of 22-42% for total ammoniacal nitrogen (TAN), total nitrogen (TN), and total phosphorus (TP) (Van de Moortel et al. 2010).

Evaluation of Floating Wetland Islands (FWIs) as a Retrofit to Existing Stormwater Detention Basins, sponsored by NCDENR – Division of Water Quality study completed in 2012 in North Carolina (NC) provided data for the performance of FTW as retrofits to stormwater wet ponds.

They studied two ponds, called the DOT pond and the Museum pond. During the post-retrofit monitoring period, the DOT pond significantly reduced concentrations of seven of nine analytes studied (all except TAN and PBP), while the Museum pond with FIs significantly reduced concentrations of all pollutants studied. Results suggest that a larger number of unit processes were provided during the post-retrofit period, presumably due to the addition of the floating wetland islands. The addition of the floating wetland islands also appeared to reduce variability in effluent concentrations.

Pollutant load reductions occurred for every pollutant studied except OP. Sediment load reductions in the pond were between 72-95% for the two ponds.

Please request the full report here.