Introduction--Monitoring and Assessment
In general, aquatic vegetation control efforts have been designed to eradicate the
target nuisance species. More often then not, the target species is not eliminated
and occasionally either use impairment worsens and/or unintended negative environmental
impacts occur. The traditional philosophy of aquatic vegetation control has evolved
from chemical and physical control of weed species in an agricultural setting. The
purpose of conventional agricultural pest management is, in essence grow a monoculture
of the crop, with maximal yield at a minimum expense. The integrity of the field's
"natural" ecosystem has generally not been of major concern to farmers. More recently,
in order to reduce negative environmental consequences, some farmers have embraced
Integrated Pest Management (IPM), optimization of chemical application rates or
"organic" culturing.
IPM is the design of a program which consists of a mix of physical, chemical and
biological techniques, in order to maximize crop yields and pest (weed) control,
while attempting to minimize negative environmental impacts, chemical application
rates and monetary costs. Organic culture is also an integrated program which utilizes
only physical and biological techniques. Pesticide application rate optimization
consists of incremental adjustment of cultural factors in response to real-time
in-field monitoring of the crop, pests and environmental indicators. An effective
Integrated Aquatic Plant Management Plan (IAPMP) should be derived from each of
these three progressive philosophies.
The purpose of this discussion is not to guide the reader in the development of
a IAPMP, but rather to explain the linkage between plan development and implementation,
and plant monitoring and assessment. The various components of such a plan are adequately
summarized in Cooke et. al (1986), Kishbaugh, Bloomfield and Saltman (1990) and
USEPA (1990) and the assessment of specific plant control strategies has also been
discussed in Chapter V. Please refer to this material for more details.
Linking Biotic Monitoring and Management Plan
Design
Remarkably, the first question that a lake manager should ask is "Is there really
a problem?" A dandelion is a pretty yellow flower, that is unless a few thousand
are dotting your prize Kentucky bluegrass lawn. Each user that shares the lake shoreline
and surface will have a different view of the extent of nuisance conditions caused
by aquatic plants. Some people are revolted by a few water lilies or cattails. People
who fish often seek out the edge of large beds of submerged plants, as a location
for catching the "big lunker". The presence of scattered Eurasian watermilfoil plants
in a clear, deep, unproductive mountain lake is often enough to create widespread
ecological hysteria. A small shallow pond that has always been weedy may not cause
any concern to its owner, unless it shows signs of filling in. However, it is clear
that most lake users will agree that widespread use impairment exists when aquatic
vegetation grows at great densities within 0.5 meters of surface, along much of
the usable lake shore and surface (Photo 1).
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Photo 1
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The above definition creates the distinction between the broad classes of management
plan types (Figure 3). First, a lake may neither have species with nuisance potential
present nor show any use impairment. Second, a lake may have these problem species
present, but the densities are too low to create use impairment. Third, and most
commonly, some use impairment exists. The fourth case would be widespread use impairment.
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Figure 3
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Surveys of lake user opinions can be helpful in defining the extent of use impairment.
A Citizens "Plant Watcher" program (see Nuisance or Exotic Species) can also be
useful in this regard. Neither effort is a substitute for professional monitoring
of plant populations, but rather a good first step. The results of a user survey
will only indicate the degree of concern or perception by various user groups over
the aquatic vegetation problem. Such a survey may be at odds with the technical
data on the plant populations.
If the results of the user survey indicate the lack of any use impairment caused
by aquatic plants, then the management plan should be protectionist in nature. The
plan should embrace any activity that will tend to preserve the lake's plant community
in its present state. In order to detect any subtle change in that state, a low
level of monitoring is required. The appropriate monitoring program would consist
of a combination of citizen "Plant Watchers", water quality measurements and possibly
aerial photography. User opinion surveys should also be repeated every few years.
Should the user opinion survey demonstrate that a well-defined problem exists, the
second step is obtain voucher specimens of all the common aquatic plants and have
each identification verified by a taxonomist. This step determines the nuisance
potential of the existing plant community. The presence of a few specimens of such
species as Eurasian watermilfoil, Curly-leaf pondweed or Waterchestnut would indicate
a high potential for future problems. In any case, a professional aquatic botanist
should be retained to better define both the structure of the plant community and
the degree of use impairment. The botanist will likely direct semi-quantitative
diver "swimovers" of key shoreline areas (see Species List ). These swimovers may
be done in conjunction with aerial photography. The end product of this stage will
likely be a map of these locations, showing the predominant species and the areas
of obvious impairment. If the lake is profoundly impacted, technical emphasis should
shift to design of control measures. More detailed monitoring of the plant community
(transects, biomass determinations, etc.) should be done only to demonstrate the
efficacy and environmental impact of individual control techniques.
If the swimovers show no or only isolated use impairment, more detailed monitoring
should be conducted in the following fashion. First, where small areas of use impairment
are found, transects and biomass determinations should be conducted to establish
a baseline condition for future evaluation of control measures. This monitoring
will also serve to determine the "rate of spread" or expansion of the nuisance species
and/or the use impaired region. Second, non-impaired areas in key locations should
also be monitored periodically to screen for new local infestations. Some typical
key locations include boat launch sites, bathing beaches, fishing piers, shoreline
parks, freshwater wetlands, tributary mouths and navigation channels.
The next phase of plant community quantification will be associated with control
measure evaluation. The degree of monitoring and assessment detailed will be determined
be the nature of the control program. Obviously, a program of hand harvesting to
remove isolated nuisance specimens from sites, will dictate only cursory follow
up monitoring, in the form of citizen observation and infrequent swimovers. If the
management program results in successful containment of the nuisance species, detailed
monitoring will be needed at a few benchmark stations, specifically designed to
track reinfestation. However, if the control program is lakewide in scope and results
only in partial alleviation of the use impairment, quantification should be limited
to control measure evaluation. Examples of such lakewide programs would be those
that consist primarily of herbicide usage and mechanical harvesting.
In summary, the monitoring of aquatic plant communities is linked closely with the
development and implementation of the management plan. Initial simple monitoring
efforts dictate the scope of the management plan, which in turn determine the level
of long term monitoring. The process is iterative and should be tailored to lake-specific
conditions.
Allocation of Resources between Monitoring and Implementation
The successful conduct of any project depends on the quality and availability of
three resources: technical expertise, time and money. Projects fail, because often
one or more of these resources are in short supply. Since monitoring uses up resources,
it is logical to assume that no monitoring should be done and that all available
resources are applied to the reduction of nuisance conditions. In contrast, there
are scientists who, if asked, will "study the problem to death", thereby using up
all resources and precluding implementation.
Each extreme should be avoided, as they always result in ineffective and/or inefficient
management efforts. Whether the use impairment is widespread or just a potential,
the public will usually clamor for a "quick fix" at no expense. Unfortunately, the
entire spectrum of aquatic plant control techniques consists of low technologies;
they give partial relief in mild cases. The techniques that cost the least, are
the least effective or have the highest degree of side effects, or both! For example,
on the surface, the unit costs of utilizing aquatic herbicides to control nuisance
plants appear to be relatively low. However, herbicides often kill native plants,
gamefish and other aquatic life, along with the target species. With herbicide use
comes temporary restrictions on water usage. Costly chemical and biotic monitoring
programs may be required by regulatory agencies in order to document unintended
herbicide impacts.
In general, less than twenty percent of total project costs should be spent on environmental
monitoring (See Table 3, Budget for a Typical Management Program). This percentage
will be higher during the initial phases of a project. Lakewide mechanical harvesting
programs will probably need less monitoring, while herbicide-oriented programs will
need more. If a lake is in the initial stages of infestation, monitoring costs could
approach 100% of the project cost.
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Table 3
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Targeting Sites for Monitoring and Evaluating Control
Measure Efficiency
As previously discussed, the design of the management program will dictate the types
and locations of monitoring. Site targeting should be done in the following way:
1.
Herbicides. Aquatic plant, fish, macrobenthos and water chemistry
sampling should be done within the area where the herbicide is directly applied
(treatment zone). In addition, some estimates of biomass and percent bottom cover
should be done in adjacent critical habitats, such as identified fish spawning and
nursery areas and emergent wetlands. Control sites should be isolated from the treatment
area, such that water movement cannot transport toxic levels of herbicide into the
control site, under the potentially most extreme weather conditions.
2.
Harvesting. The amount of wet plant material that
is harvested should be entered into a log book. Measurement of the dry weight biomass
and nutrient content of the material may also be useful. The hours that the harvester
is operated and the location of operation should also be record in the log book
(see Table 4). It might also be useful to commission aerial photography of the harvested
region. Inadvertent fish capture studies can be conducted by seining both harvested
and unharvested areas for juvenile fish. Fish that are inadvertently captured by
the harvester can also be enumerated. A substantial number (5 to 10) small plots
(20 meters by 20 meters) should be selected within harvested areas for estimating
seasonal regrowth rates and changes in community composition. Plant heights, biomass
and bottom cover can also be measured. Control plots are simple to select, but a
big problem is marking both the harvested and control sites such that they can be
found at a later date.
3.
Hand and Suction Harvesting. Obviously monitoring should be done
within the treatment site. Community composition before and after harvesting should
be done by the swimover technique. The number and biomass of the plants removed
should be noted. The hours spent at each site should also be recorded.
4.
Barriers. Community composition prior to treatment should be
accomplished. Percent bottom cover of all species is acceptable, although limited
biomass sampling may be helpful. Monitoring of the plant communities adjacent to
the benthic barrier may be helpful. The accumulation of sediment and new plants
on top of the barrier should be recorded at least annually. Any tears in the material
should be noted and repaired. The condition of the plants under the barrier should
also be evaluated. If no plants are growing on, adjacent to or under the barrier
material, the mat may be removed and transported for use at another location. The
site should be examined on a regular basis for recolonization by nuisance species.