Benthic BarriersBenthic Barriers

What is a Benthic Barrier?What is a Benthic Barrier?

Benthic barriers, also known as benthic mats or bottom screens, are mats that are installed on the bottom of a lake to inhibit the growth of invasive aquatic plants. Barriers consist of dark, light blocking fabric that is held at the bottom of the lake by weights. The benthic screen limits light The benthic screen limits light to the bottom of the lake, thus helping to to the bottom of the lake, thus helping to preclude the growth of aquatic vegetation. preclude the growth of aquatic vegetation. Barriers can be porous or solid. Barriers can be porous or solid.

Appropriate LocationsAppropriate Locations

Benthic barriers are most appropriate for small areas, such as around docks or boat launches or in swimming areas. This technique is not suitable for controlling widespread invasive plant infestations.

AdvantagesAdvantages

Highly flexible control Reduces turbidity from soft bottom

sediments Can cover undesirable substrate Can improve fish habitat by creating

edge effects

DisadvantagesDisadvantages

May cause anoxia at sediment-water interface

May limit benthic invertebrates Non-selective interference with

plants in target area May inhibit spawning/feeding by

some fish species

Porous Barrier - subject to less billowing, but will allow settling plant fragments to root and grow; annual maintenance is therefore essential

Solid Barrier - generally prevent rooting in the absence of sediment accumulations, but will billow after enough gases accumulate; venting and strong anchoring are essential in most cases

Information for Proper ApplicationInformation for Proper Application

Mapping of area to be covered by barrier, with information on plant types and density

Knowledge of sediment features, along with any obstructions or other interference factors

Inventory of biological features of the target area, especially the presence of any protected species

Plan for installation and maintenance

Installation ProcessInstallation Process

Proper application requires that the screens be placed on the sediment surface and staked or securely anchored. This may be difficult to accomplish over dense plant growth, and a winter

drawdown can provide an ideal opportunity for application in exposed areas. Late spring application has also been effective, despite the presence of plant growths at that time, and barriers applied in early May have been removed in mid-June with no substantial plant growth through the summer. Scuba divers normally apply the covers in deeper water, which greatly increases labor costs.

Installation Considerations Installation Considerations

The size of the area to be treated Bottom features and possible

obstructions Costs: product, application and

maintenance Possible impacts to non-target

organisms in the installation area. Deployment & Anchoring Method

PermittingPermitting

Depending on size of installation, will Depending on size of installation, will require filing of Request for require filing of Request for Determination of Applicability or a Determination of Applicability or a full Notice of Intentfull Notice of Intent

Material CostsMaterial Costs

Aquatic Control Technologies - .85 per Aquatic Control Technologies - .85 per square foot (price includes installation)square foot (price includes installation)

Lake Bottom Blanket – 10 x 40’ lake Lake Bottom Blanket – 10 x 40’ lake bottom blanket $200bottom blanket $200

Typar 12 x 300 foot (3,600 sq feet) roll Typar 12 x 300 foot (3,600 sq feet) roll approx $350, or about 10 cents per square approx $350, or about 10 cents per square foot. foot.

Aquascreen, a product marketed for the Aquascreen, a product marketed for the purpose of benthic barrier applications, is purpose of benthic barrier applications, is sold for about 50 cents per square foot.sold for about 50 cents per square foot.

ScreenScreen

Material CostsMaterial Costs

There are a variety of methods to There are a variety of methods to anchor the screening; anchor the screening;

Cinder BlocksCinder BlocksRebarRebarWood FrameWood Frame

Anchor MaterialAnchor Material

Permit Fees & Installation Permit Fees & Installation

At a minimum a RDA with the local At a minimum a RDA with the local conservation commission is required; in conservation commission is required; in some cases Notice of Intent may be some cases Notice of Intent may be requiredrequired

If installed professionally, labor costs must If installed professionally, labor costs must be factoredbe factored

In many installations; homeowner can In many installations; homeowner can installinstall

If diver services needed due to depth; If diver services needed due to depth; diver costs must be factoreddiver costs must be factored

Case Study of Benthic Case Study of Benthic Barrier InstallationBarrier Installation

Lake Holland, Belchertown, MALake Holland, Belchertown, MA20072007

Much of the area treated was being Much of the area treated was being choked by invasive milfoil stands. The choked by invasive milfoil stands. The water column and growing along on the water column and growing along on the surface. The water is hot and stagnant, it surface. The water is hot and stagnant, it does not circulate, and is a noxious habitat does not circulate, and is a noxious habitat favorable to insect breeding. favorable to insect breeding.

The area was about 3,000 sq ft. (1/15th of The area was about 3,000 sq ft. (1/15th of an acre). an acre).

The area is bounded by a thick wetland, The area is bounded by a thick wetland, deep water. deep water.

MaterialsMaterials The fabric utilized was a non-woven polypropylene that is water and The fabric utilized was a non-woven polypropylene that is water and

gas permeable but opaque. It is sold by Dupont under the brand name gas permeable but opaque. It is sold by Dupont under the brand name Typar and is commonly used for house-wrap in construction, riprap Typar and is commonly used for house-wrap in construction, riprap (shoreline structuring), sandbags and road construction to separate (shoreline structuring), sandbags and road construction to separate aggregate from soil. It is very durable and could be moved and re-aggregate from soil. It is very durable and could be moved and re-used. There is much experience with Typar as a benthic barrier. The used. There is much experience with Typar as a benthic barrier. The following is from the Lake Sutherland (Washington State) Association following is from the Lake Sutherland (Washington State) Association Newsletter regarding Typar:Newsletter regarding Typar:– ““The new barriers have been the key to our success. Made of The new barriers have been the key to our success. Made of

porous, non-woven fabric, not plastic, the material is rolled out porous, non-woven fabric, not plastic, the material is rolled out underwater and secured with gravel-filled bags….The old barriers underwater and secured with gravel-filled bags….The old barriers were made of burlap which degraded within a year, sometimes were made of burlap which degraded within a year, sometimes less, any stray milfoil readily established on top. The fabric barrier less, any stray milfoil readily established on top. The fabric barrier is much better. By preventing fragments from getting established, is much better. By preventing fragments from getting established, the new barriers have allowed us the breathing space to return and the new barriers have allowed us the breathing space to return and remove stray plants as they re-grow or try to re-established.” remove stray plants as they re-grow or try to re-established.”

Typar is slightly buoyant with a gravity rating of .9 , technique requires Typar is slightly buoyant with a gravity rating of .9 , technique requires secure anchoring. As weeds decompose gases will accumulate and secure anchoring. As weeds decompose gases will accumulate and cause billowing to some extent even though the fabric is gas cause billowing to some extent even though the fabric is gas permeable, and this must be managed. This is the same challenge for permeable, and this must be managed. This is the same challenge for any fabric. any fabric.

Work PlanWork Plan

Crew - Homeowner & 2 individuals. Crew - Homeowner & 2 individuals. Most of the target area is very shallow but scuba will likely be necessary for some of the placement Most of the target area is very shallow but scuba will likely be necessary for some of the placement

work. (Diving to be done by property owner who is a PADI Rescue certified diver with much work. (Diving to be done by property owner who is a PADI Rescue certified diver with much experience in various conditions including lakes. ) experience in various conditions including lakes. )

In preparation, some of the weeds to be removed by hand. This step is not necessary to the In preparation, some of the weeds to be removed by hand. This step is not necessary to the technique but pre-clearing some of this biomass would make it easier to install the barriers in the technique but pre-clearing some of this biomass would make it easier to install the barriers in the shallows and it will reduce the amount of rotting matter during treatment, which may reduce shallows and it will reduce the amount of rotting matter during treatment, which may reduce maintenance later. maintenance later.

The fabric will be cut from the bolt into tailored pieces. These will be re-rolled, taken to the site, The fabric will be cut from the bolt into tailored pieces. These will be re-rolled, taken to the site, unrolled and sunk, pinned at the corners and along the sides with sandbags. A number of unrolled and sunk, pinned at the corners and along the sides with sandbags. A number of overlapping pieces will be assembled to cover a contiguous area. overlapping pieces will be assembled to cover a contiguous area.

Optionally, instead of covering one contiguous area, depending on circumstances, gaps may be left Optionally, instead of covering one contiguous area, depending on circumstances, gaps may be left to allow hand-pull after installation. The idea is that these gaps, if cleared quickly, would help to allow hand-pull after installation. The idea is that these gaps, if cleared quickly, would help restore the area post treatment, and would add to the amount of edge effects that is a side benefit restore the area post treatment, and would add to the amount of edge effects that is a side benefit of the barriers to fish. of the barriers to fish.

From the shore or from a row boat, one person will hold the rolled fabric and dole it out while a From the shore or from a row boat, one person will hold the rolled fabric and dole it out while a second person in a row boat or canoe pulls the fabric across the water. The four corners of the second person in a row boat or canoe pulls the fabric across the water. The four corners of the section will be weighted and the weights dropped into approximate position. Then a sandbag is section will be weighted and the weights dropped into approximate position. Then a sandbag is dropped in the center of the barrier. Then the fabric will be pressed down, flattening it outwards dropped in the center of the barrier. Then the fabric will be pressed down, flattening it outwards from the center sandbag, crushing the plants as much as possible. This would be done either from from the center sandbag, crushing the plants as much as possible. This would be done either from the boats using hands and canoe paddles and/or a swimmer with snorkel and mask in shallows or the boats using hands and canoe paddles and/or a swimmer with snorkel and mask in shallows or scuba diver in deeper water. More sand bags are positioned as the barrier is flattened, and scuba diver in deeper water. More sand bags are positioned as the barrier is flattened, and adjusted as necessary. adjusted as necessary.

While the barriers are in position site to be checked daily for billowing, which can either be pushed While the barriers are in position site to be checked daily for billowing, which can either be pushed to the sides or the fabric can be cut to vent the gas without affecting the treatment. to the sides or the fabric can be cut to vent the gas without affecting the treatment.

The fabric can be removed or moved to an adjacent location after 4 to 8 weeks. However, because The fabric can be removed or moved to an adjacent location after 4 to 8 weeks. However, because the fabric is porous, does not degrade quickly and is inexpensive, it is possible to leave some the fabric is porous, does not degrade quickly and is inexpensive, it is possible to leave some pieces in place. This is similar to the use of Typar as a separator in road construction and riprap. In pieces in place. This is similar to the use of Typar as a separator in road construction and riprap. In some cases this might be desirable, e.g. where the muck layer is shown to be the source of nutrient some cases this might be desirable, e.g. where the muck layer is shown to be the source of nutrient loading in the water column, or for longer term control with less maintenance requirements. loading in the water column, or for longer term control with less maintenance requirements.

Installation Images

Before PicturesBefore Pictures

Taken October 8, 2007

After PicturesAfter Pictures

Project CostsProject Costs

A 12 x 300 foot (3,600 sq feet) roll of A 12 x 300 foot (3,600 sq feet) roll of Typar cost approx $350, or about 10 cents Typar cost approx $350, or about 10 cents per square foot. Aquascreen, a product per square foot. Aquascreen, a product marketed for the purpose of benthic marketed for the purpose of benthic barrier applications, is sold for about 50 barrier applications, is sold for about 50 cents per square foot. Aquascreen has one cents per square foot. Aquascreen has one advantage over Typar: A specific gravity of advantage over Typar: A specific gravity of 2.5 as compared to .9 for Typar, which 2.5 as compared to .9 for Typar, which means that Typar is slightly bouyant. means that Typar is slightly bouyant.

SourcesSources 2004 Practical Guide to Lake Management in 2004 Practical Guide to Lake Management in

Massachusetts, Executive Office of Massachusetts, Executive Office of Environmental AffairsEnvironmental Affairs

Aquatic Control Technologies Aquatic Control Technologies http://www.aquaticcontroltech.com/physical_treathttp://www.aquaticcontroltech.com/physical_treatments.htmlments.html

Lake Project Net – Lake Holland Project Lake Project Net – Lake Holland Project http://lakeproject.net/LHRDA_Planhttp://lakeproject.net/LHRDA_Plan

Instructions for building a benthic barrier; wood Instructions for building a benthic barrier; wood frame construction frame construction http://www.cayugalake.org/images/resources/benhttp://www.cayugalake.org/images/resources/benthic_barriers.pdfthic_barriers.pdf

Lake Bottom Blanket Lake Bottom Blanket http://www.lakebottomblanket.com/product.htmlhttp://www.lakebottomblanket.com/product.html

Lycott Environmental Lycott Environmental http://www.lycott.com/benthic_screening.htmlhttp://www.lycott.com/benthic_screening.html