LIGHT REDUCTION TECHNIQUES FOR AQUATIC PLANT CONTROL

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Abstract
Moderation of aquatic plant growth by changing the primary growth control factor, light, is an economically viable and ecologically acceptable technique for many lake and stream habitats. In open unshaded waters, great potential exists for plant growth either by large plants (macrophytes) or algae. Although other factors such as nutrients affect growth, without light no plant growth would occur. Attempts to eradicate macrophytes are likely to be unsuccessful and may lead to unstable or extreme situations such as dense algal blooms or monotypic plant stands. The absence of macrophytes, particularly in streams, also can lead to a poor aquatic community. Techniques for moderating plant growth include (1) intercepting light above the water by bank vegetation or at the water's surface by opaque materials, or by redesigned lake or stream margins; (2) reducing light penetration of the water by the action of bottom-feeding fish or of boats, the addition of dyes, or the redesign of waterbodies to maintain materials in suspension; (3) confining macrophytes to deeper water (redesigning margins, protecting marginal plants, and using netting); and (4) combining the detrimental effects of environmental factors on plants with their physiological responses (differential cutting to maintain very dense and very sparse plant stands). Surveys to identify the extent of the problem and potential solutions must be emphasized. No universal solution exists and apparently similar sites may vary subtly but significantly.