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Mapping the Distribution of Rooted Plants
In healthy lakes, several different species of rooted aquatic plants usually occupy the littoral (shallow) zone. Submergent, rooted floating- leaved, free-floating, and emergent plants are all important for the overall ecology of a lake. Traveling around the shoreline with a lake map, volun teers can draw in the location of significant aquatic plant beds and note where growth has reached the surface. This effort will serve as an historical record for studying changes in vegetative location. In addition, t hese maps can be useful for planning the application of aquatic plant control methods, such as harvesting.
Determining the Relative Density of Rooted Plant Types
It is often useful to take a closer look at the types of rooted aquatic plants in the littoral zone. A healthy lake usually has many different kinds aquatic plants. Many lakes, however, have littoral zones that have been disturbed, fertilized, and/or inva ded by more aggressive plant species. In these instances, the least tolerant species are often eliminated and one or two more-tolerant species begin to take over the zone. In fact, in the majority of lakes where aquatic plant overgrowths occur, it is the result of a population explosion of only one or two species.
Several exotic plant species (originally from other continents) are notorious for displacing native plants and dominating the littoral zone. They can become major nuisance problems primarily because no natural check and balance system controls their growt h. A lack of predators and pathogenic organisms allows exotics to out-compete native species for growing space, light, and nutrients.
The relative density of different plants growing in the littoral zone can be examined by the personnel. The method described in this chapter has personnel collect plants at specific intervals along a transect line. Addi tionally, the personnel are directed to measure the length and depth of the littoral zone along the line.
Identification of Rooted Aquatic Plants
Eurasian watermilfoil (Myriophyllum spicatum ) and water hyacinth (Eichhornia crassipes) are examples of exotic (non-native) species that can flourish and cause problems in waters of the United States. One purpose of a citizen program focuse d on monitoring rooted aquatic plant conditions on lakes should be to inventory locations where there are significant amounts of plants.
The identification of plant species is important because the effectiveness of lake management techniques differ according to plant type. In many instances, the early detection (and elimination) of aggressive exotic species can save a lake from severe infe station problems later.
The Vermont Department of Environmental Conservation, for example, has
established a Milfoil Watchers Program to train the personnel to identify
Eurasian watermilfoil. Then, at least once or twice a summer, citizens
survey lakes where the plant has not been seen.
The location of sample collection and transect sites in a lake are defined on a lake-by-lake basis from an initial site visit by the program manager. Some lakes have extensive weed growth throughout the lake, others have small, well-defined problem areas.
In general, it is best to assign a team of two worker no more than four hours of sampling work. What can be accomplished in this period depends on the size of the lake, the length of the littoral zone, and the extent of the rooted plants.
In some lakes, the aquatic plant population is relatively stable through out the growing season. In other lakes, there is a definite pattern of succession. If the lake is small, personnel may need to examine plant growth only once or twice a year (in spr ing and late summer). The pro gram manager may wish to break a large lake with a significant weed problem into segments and send personnel out every two weeks to sample different areas.
The density, diversity, and growth patterns of aquatic plants are unique
to each lake. Therefore, many of the details concerning sample site loca
tions and other program aspects must be worked out by the program man ager
on a lake-by-lake basis.
Basically, these sampling activities are divided into four main segments.
The program manager should provide personnel with a sampling schedule
and a sampling protocol sheet.