Abstract
Biomass quantification techniques are widely used in research on aquatic vegetation, but less often applied to monitor aquatic vegetation or assess specific control techniques. The application of these techniques to both assessing nuisance problems, and evaluating control tactics is discussed using case histories. The proper methods for developing a sampling regime, locating sample points, collecting samples, and analyzing data are reviewed. Critical factors such as quadrat size and sample frequency and number are discussed in depth. The purpose of biomass sampling programs within the context of management plans is to tailor the level of effort to the scale of the management effort, and to appropriately assess or predict the effects of the management tactics utilized.
.
Introduction
Aquatic vegetation is a key element in aquatic ecosystems, both lakes and streams. Aquatic plants produce food for aquatic organisms, serving as a base of the aquatic food chain. Larger vascular plants, whether rooted or free-floating, submersed or emergent, provide habitat areas for aquatic insects, young fish, adult fish, and other resident aquatic and semiaquatic organisms. Littoral zone vegetation is also a prime area for the spawning of many important fish species. Aquatic vegetation is extensively used as food by mammals, birds, reptiles, and amphibians that frequent aquatic environments. In addition, aquatic vegetation serves to anchor soft sediments, stabilize underwater slopes, and remove suspended particles from the overlying water. All these factors indicate the importance of a healthy, natural aquatic plant community.
However, through eutrophication or invasion of exotic species, aquatic plant communities may grow to excessive proportions. In these instances, both the development of plant growth up to the surface, and excessive amounts of plant material, contribute to a plant nuisance problem. Nuisance plant problems include flooding, impairment of commercial and recreational boat traffic, impairment of other recreational activities (e.g., swimming and fishing), and a decrease in aesthetic qualities. Other problems associated with nuisance plant growths, which are less obvious, include alterations in fish or other biotic communities (Crowder and Cooper 1982), suppression of native vegetation (Madsen et al. 1990), and increased eutrophication of lakes (Carpenter 1983).
The basic problem is essentially that too much plant material has grown in a given area, in a form that impairs human activity or appreciation. The term used to describe the amount of plant matter per unit area is biomass. Since overabundant plant biomass is the nuisance problem, it too should be the parameter measured to objectively assess the extent of the problem or to examine effectiveness of management strategies.
Recommendations
Biomass study techniques are not applicable for every situation, nor should they necessarily be used in every aquatic vegetation management program. However, they are well suited to evaluating effects of many control tactics that are designed to reduce the amount of plant material; particularly harvesting and biological control.
A biomass sampling program should be designed to utilize the smallest practicable quadrat and gather the fewest samples necessary to adequately characterize the target plant population. Sampling frequency should follow the same rule, with sampling repeated only so often as to obtain measurable change in plant biomass. Samples should be distributed using a stratified-random design within the study area, and samples carefully processed and oven-dried before weighing. Data should be examined carefully to determine if the values fit a normal distribution as required by many parametric statistical tests, and statistical analysis of data should include nonparametric statistics. Appropriate transformations may be required as part of data analysis.
The purpose of all sampling programs is to appropriately assess suitability and success of management tactics utilized. Just as monitoring should not cost more than the control effort, likewise sampling programs should be more intensive and rigorous in evaluating more expensive or potentially harmful tactics.
Acknowledgments
This study was supported by the Finger Lakes Water Resources Board by a grant administered through the New York Natural Heritage Trust to the Rensselaer Fresh Water Institute. The Finger Lakes Water Resources Board also supported the symposium at which this topic was presented. I would also like to thank Dr. Jay Bloomfield for his role in coordinating this effort, and for his comments on this manuscript. Contribution number 538 of the Rensselaer Fresh Water Institute and contribution number 25 of the New York State Fresh Water Institute.
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