AQUATIC VEGETATION MANAGEMENT PLAN Wenck Associates Inc. Riley - - PowerPoint PPT Presentation

AQUATIC VEGETATION MANAGEMENT PLAN

Wenck Associates Inc. Riley Purgatory Bluff Creek Watershed District City of Eden Prairie

Project Objective

Develop an aquatic plant control program that defines the problems, identifies quantifiable management goals, and identifies specific management actions to improve lake conditions

Lake Issues

• Submerged aquatic vegetation is
• ver-abundant in the lake. The
• verabundance of submerged

aquatic vegetation limits lake uses such as:

• swimming in areas adjacent to property

and in larger areas of the lake including the public landing

• navigational access to most areas of the

lake

• fishing opportunities throughout the lake

due to the thickness of the vegetation

• aesthetics of the lake including water

quality and SAV matting

• Species diversity is limited in the

three lakes.

Aquatic Plant Management Premise

Diverse, native moderately abundant plant community Native, monotypic SAV community Monotypic SAV Dominated by Invasive species No Vegetation

DNR Regulations

• DNR does not allow aquatic plant control for

aesthetic purposes

• Allowed for recreational access, invasive control
• Mechanical control
• May not exceed more than 50% of the littoral area of

the lake

• Can create open water areas for recreational use
• Needs to be same location from year to year
• Herbicide use is limited to 15% of the littoral

area

• Accounts for drift of the herbicide
• Management of natives for recreational access

requires a plant management plan

• Mitchell Lake is a Natural Environment Lake

which prevents the use of herbicides without a variance

Eurasian Watermilfoil

Invasive Species

Recreational Management

Management Options

Harvesting Herbicides

Current and Historical SAV Community

Invasive Species Management Options

Red Rock Lake

• Control Curly-leaf

pondweed

• Eurasian Water

milfoil present in very low density

• No management

required at this time

Invasive Species Management Options

Mitchell Lake

• Mix of herbicide and

mechanical harvest

• Herbicide requires a

variance in Natural Environment lakes

• Herbicides more

effective for long term suppression

• Additional

mechanical control

Recreation Management – Navigation/Swimming

• Maintain navigable channels to
• pen water
• Create additional open water

area in south bay

• Harvesting 2-3x per year
• Supports swimming areas,

fishing areas, edge habitat

• Homeowners responsible for

channel maintenance from dock to open water

• Homeowners responsible for

individual swimming/fishing area

• Can hire harvesting company to

maintain area (2,500 sq-ft)

American Lotus

Recreation Management – Navigation/Swimming

• Maintain navigable channels to
• pen water
• Create additional open water

area in middle bay

• Harvesting 2-3x per year
• Supports swimming areas,

fishing areas, edge habitat

• Homeowners responsible for

channel maintenance from dock to open water

• Homeowners responsible for

individual swimming/fishing area

• Can hire harvesting company to

maintain area (2,500 sq-ft)

Plant Management Costs

Alternative Description Acres 15 Year Life Cycle Cost1 Average Annual Cost1 Cost/Acre/Year Mitchell Lake 1 Invasive Contract Harvesting 23 $265,000 $17,667 $771 2 Invasive Contract Herbicide 13 $156,000 $10,400 $783 3 Invasive Contract Harvesting and Herbicide 23 $279,000 $18,600 $809 4 Recreation Area Harvesting2,3 12 $152,000 $10,133 $854 Red Rock Lake 1 Invasive Contract Harvesting 23 $268,000 $17,866 $770 2 Invasive Contract Herbicide 13 $205,000 $13,667 $1,009 3 Invasive Contract Harvesting and Herbicide 23 $309,000 $20,600 $888 4 Recreation Area Harvesting2,3 30.5 $343,000 $22,867 $749

1Each annual cost adjusted to inflation and summed to obtain a total lifetime cost. 2Acreage is equal to the sum of area harvested throughout the year (Acreage = acres harvested x times harvested) 3Assumes lakeshore residents are responsible for their own channel from shore to recreational areas and

any private swimming area.

Long Term Management for Increasing Diversity and Reducing Abundance

• Plant abundance is driven

by light, carbon, temperature, nutrient availability, and sediment type.

• SAV get the majority of their

nutrients from the sediments and are likely N limited, focus on N reductions in lake

• Coontail is not a truly rooted

plant, so response to sediment nutrient reduction is difficult to determine

• Sediment bulk density is a

key factor in controlling SAV abundance

Woodchip Bioreactors Whole Lake Drawdown

Summary

• Manage invasives through to prevent dominance in SAV

community

• Some management can be completed to better support

recreational uses

• Navigation channels and open water areas
• Reduction in plant abundance and dominance by coontail

is difficult to control, but may be improved long term through nitrogen and sediment bulk density management

• Long term reductions in N inputs into the sediment
• Export of N from sediments through denitrification

Shallow Lakes Forum 2015

Saturday, April 25th from 8:30-12:30 Minnesota Landscape Arboretum McMillan Auditorium

Questions?