Mapping Aquatic
Vegetation
While
lakes are well known
for their recreational
and aesthetic value,
traditionally, society
has considered wetlands
as nuisances and
problems that need
to be cleaned up.
Statewide, Minnesota
has drained over
half of the original
wetlands (around
4.5 million hectares)
for agricultural
and development
purposes, and many
of the remaining
wetlands are degraded.
A
frequent cause of
wetland degradation
is increased storm
water discharge
resulting from changes
such as increases
in impervious surface
area or installation
of storm water systems
in urban and suburban
areas, as well as
tiling and ditching
systems in agricultural
areas. Changes
in hydrology affect
the water quality
and quantity, and
may severely impact
the function of
wetlands. When too
many wetland plants
are removed or impacted,
water quality, wildlife,
and fish populations
can suffer. These
plants are important
because they help
protect water quality,
provide habitat
for fish and wildlife,
and provide economic
and aesthetic opportunities.
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Aquatic
plants in lakes
and wetlands are
beginning to be
recognized as important
ecosystem features
in need of protection.
As a result of this
greater appreciation
for aquatic plants
in wetland and lake
environments, aquatic
plant surveys and
assessments are
becoming part of
routine monitoring
efforts conducted
by consultants,
citizen groups,
and state and local
agencies. Aquatic
plant diversity
and abundance are
important indicators
of lake or wetland
health, but accurate
maps and data are
difficult to acquire.
Because ground-based
mapping requires
much time and human
resources, only
a small fraction
of this large resource
has been mapped
by natural resource
agencies.
The
objective of our
research is to evaluate
using high-resolution
satellite imagery
to map and classify
aquatic plant groups
by resource management
agencies. To date,
we have evaluated
the two forms of
commercially available
high resolution
satellite data:
IKONOS and QuickBird.
To evaluate IKONOS
imagery, we conducted
an aquatic plant
survey on Swan Lake
in Nicollet County,
Minnesota.
Swan
Lake is a large
(>3600
ha), “type-4” wetland
meaning it is classed
as a deep fresh
water marsh with
standing water and
abundant emergent aquatic
vegetation. To evaluate
the use of QuickBird
imagery for assessment
of submergent aquatic
plants in open water
lakes, we conducted
aquatic plant surveys
of two lakes south
of Lake Minnetonka.
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