A symposium was held at the 10th annual meeting of the North American Lake Management
Society to discuss methods of aquatic vegetation quantification and its application
to an aquatic plant management program. Topics discussed at this symposium included
the importance of accurate taxonomic identifications, the use of transect and biomass
sampling methods, development of manipulative experiments to evaluate management
techniques, and advances in remote sensing for aquatic plant quantification. These
technical approaches were then illustrated in an ongoing governmental aquatic plant
management program. Techniques used for aquatic plant quantification and the importance
of vegetation quantification to an ongoing management program are summarized.
The management of nuisance aquatic vegetation is one of the primary aspects of lake
management in North America. Despite the expenditure of millions of dollars every
year, only a small fraction is typically allocated to acquire reliable quantitative
data concerning the need for management or the effectiveness of most management
techniques. The acquisition of quantitative data is important for several reasons:
1. It is an objective measurement of plant distribution and abundance; relying on
subjective estimates leads to opinion, rather than fact, as the basis for management
decisions.
2. Quantification allows rigorous statistical and mathematical evaluation of plant
community trends and assessments of the need for and effectiveness of management
techniques.
3. Quantification of vegetation, as part of a monitoring program, may eliminate
costly but unproductive techniques or reduce the amount of costly elements in a
given management approach.
4. It allows individuals other than the observer to evaluate data.
Quantification, as part of a monitoring and assessment program, is also being required
by many granting or regulatory agencies as part of obtaining grants or permits.
Therefore, the above are convincing reasons for all aquatic vegetation management
programs to establish systematic quantitative data collection as part of an overall
management plan.
The Finger Lakes Water Resources Board, which funded the symposium, is an association
of 11 counties in the Finger Lake region of New York which is responsible for management
of waterbodies of the region. One of their major concerns is nuisance aquatic vegetation
control, on which approximately $5 million is spent annually. Since many of these
control projects are under lake association or county supervision, the Board desired
to unify attempts to monitor and assess vegetation in the project lakes, which gave
rise to the symposium. Three products were proposed to achieve a more unified approach
to vegetation quantification: 1) a symposium at the North American Lake Management
Society 10th annual meeting to address different aspects of vegetation quantification
by experts on those topics, 2) publication of these presentations in Lake and Reservoir
Management, and 3) publication of a final report to the Finger Lakes Water Resources
Board with specific recommendations (Madsen and Bloomfield 1992). Six presenters
were invited to give presentations at the 10th annual meeting of the North American
Lake Management Society on aquatic vegetation quantification: Dr. C. Barre Hellquist,
North Adams State College; Dr. John Titus, SUNY-Binghamton; Dr. John Madsen, US
Army Engineer Waterways Experiment Station; Dr. David Spencer, USDA-ARS Aquatic
Weed Laboratory (Davis, CA); Mr. Alan Cibuzar, A.W. Research Laboratories; and Dr.
Peter Newroth, British Columbia Ministry of the Environment. Five of the papers
are presented here.
Many approaches have been taken to characterize aquatic vegetation communities.
These have ranged from the simple (species lists) to the intensive ( biomass) and
from low-technology (visual observations) to high-technology (remote sensing) routines.
The following is a short review of some of the major techniques used (Table 1).
Presence/Absence
The simplest approach is to develop a species list for a given waterbody. These
surveys are typically relatively inexpensive, and can involve the assistance of
laypersons. The level of information resulting is also low in complexity. Species
surveys yield some important information, such as whether nonnative species could
pose a significant nuisance problem, or if rare species are a management consideration.
However, the exact meaning of the presence or absence of a given species from a
species list must be scrutinized based on the technique employed.
The presence of a species in a given waterbody is the most straightforward component
to the question at hand. However, the presence of the species on the list does not
indicate any information on its abundance or distribution. Some care must be taken
concerning the proper identification of a species by taxonomic experts, and in all
cases voucher specimens should be retained for future examination.
The absence of a given species is a more difficult issue. Species lists may result
from only a cursory examination of a few locations, so that even relatively common
species may be missed. In addition, it is likely that rare species may be missed
entirely from even detailed surveys. The best species lists result from a thorough
and systematic search of likely aquatic plant habitats.
Subjective Abundance Estimates
Commonly, individuals will visit a waterbody, ride around for a while, and then
make an estimate of how much of each type of plant there is - abundant, common,
or rare. More often than not, these estimates are given as a sum total for the entire
waterbody. This method is to be avoided for several reasons. First, the estimate
made is too subjective to be useful. Results cannot be compared between different
observers or between different lakes or times. Second, these observations are too
often made on very few sites in the lake, rather than a systematic survey of a waterbody.
Third, these surveys are too often made without viewing under the water, thus missing
species. Last, there is no information on species occurrences at different sites
around the lake.
Semiquantitative Survey
On a limited budget, the semiquantitative survey is the best compromise. A snorkeler
or SCUBA diver swims set segments of shoreline, recording the presence or absence
of species at the site or within each depth interval of each site, out to the maximum
potential depth range for aquatic plants in that waterbody. In addition, an estimate
of the abundance of plants using an abundance scale can be made for added information.
Sites are selected systematically around the waterbody and thoroughly examined for
all species. This method gives a good species list, is not biased against smaller
or rarer species, and does not bias the results based on distribution of species
around the waterbody. This type of survey also results in a good estimate of the
frequency of species around the waterbody if several sites are selected.
However, the semiquantitative survey does not replace more quantitative techniques,
because the results are not readily analyzed by statistics and have very few replicates,
or units of measurement.
Transect Methods
Transect methods utilize a graduated line or course along which a diver makes species
observations. Transects may be either parallel or perpendicular to shore. They should
be distributed around the waterbody in a systematic manner, to thoroughly cover
geographical variability. These methods involve a moderate level of input and result
in a moderate level of data intensity: sensitive to the distribution of plants but
somewhat insensitive to species abundance. Data is typically recorded from quadrats
placed along the transect (Photo 1), although line intercept (Photo 2)and point
methods are also used. Data is recorded for quadrats as either presence/absence,
or percent cover estimates.
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Photo 1
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Photo 2
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Transect methods are strong in indicating the species composition of communities
over relatively large areas, and charting the distribution of species across environmental
gradients or larger management areas. These are particularly useful in charting
the effect of management practices on species diversity.
Biomass Techniques
Biomass methods are very labor intensive, but provide the best information on species
abundance (Photo 3). For this reason, they are a preferred method for evaluating
the effects of management practices on the target species. Biomass studies are quite
common, but a large number of potential mistakes in designing and carrying out biomass
studies may render the data of limited usefulness. For instance, care must be taken
to randomize samples, and ensure that data comply with the assumptions of parametric
statistics if those statistical analyses are performed. Otherwise, biomass data
is very amenable to statistical analysis.
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Photo 3
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Remote Sensing
Remote sensing-- whether from satellite, balloon, helicopter or airplane-- has shown
great promise for quantifying aquatic vegetation, although early results from satellite
imagery proved disappointing. Remote sensing is a relatively low impact, low effort
method that provides detailed information on distribution of all aquatic plants
that grow near the surface in relatively dense formations. It is less successful
in detecting diffuse plant beds or those growing near the bottom. Although some
progress has been made distinguishing between species, to date this technology is
inadequate to be reliable for most applications. Despite technological advances,
ground-truthing is still required and remote sensing will not replace more labor-intensive
methods. Modern digitizing and data analysis techniques can fully utilize the data
produced by remote sensing to produce vegetation maps, and analyze seasonal and
interannual changes in plant distribution.
Remote sensing information can be used directly in Geographic Information System
(GIS) technologies to provide another layer of information in examining whole-lake
management approaches.
Geographical Information Systems (GIS)
GIS has become the new tool of the 1990's. Data of all types can be combined to
examine land management options and effects. Output can more directly be utilized
to effect precise management objectives. The full potential of GIS for riparian
and vegetation management has yet to be realized. Drawbacks to GIS are that all
data has to be coded to make it effective, and the costs of the system and trained
operators make them beyond the reach of most lake associations. However, most local,
regional, state, and federal governmental agencies are already using GIS for other
applications, and these systems will be applied to aquatic vegetation management.
Computer Simulation Modeling
Many governmental agencies are developing simulation models for aquatic vegetation
management applications, but few working models that successfully perform their
designed function are currently available. One working model allows aquatic plant
managers to explore effects of various white amur (grass carp) stocking rates on
aquatic plant community composition and biomass levels over several years (Boyd
and Stewart 1990). Problems with developing these models are the lack of mechanistic,
deterministic relationships of plant distribution and abundance, and the ability
to generalize models to be applicable beyond a given waterbody. Also, model development
typically requires additional data collection for model algorithms, verification,
and operation. However, the potential remains for simulation models to provide the
ability to examine the outcomes of various management scenarios, or predict the
potential for nuisance aquatic vegetation problems.
Acknowledgments
The organization, presentation, and publication of this symposium was funded by
grants to the Rensselaer Polytechnic Institute's Fresh Water Institute and New York
Natural Heritage Trust from the Finger Lakes Water Resources Board. Contribution
number 594 of the Rensselaer Fresh Water Institute and number 22 of the New York
Fresh Water Institute.
Literature Cited
Boyd, W. A. and R. M. Stewart. 1990. Preliminary simulation results of triploid
white amur stocking rates for Guntersville Reservoir using AMUR/STOCK (Version 1.5),
pages 247-259 in Proc. 24th annual meeting, Aquatic Plant Control Research Prog.,
Misc. Paper A-90-3, US Army Engineer Waterways Experiment Station, Vicksburg, MS..
Madsen, J. D. and J. A. Bloomfield. 1992. Aquatic vegetation monitoring and assessment
protocol manual. New York Fresh Water Institute, Albany, NY. 42pp.