the algae population), and Secchi disk transparency (a measure of water clarity). The use of these three indicators is based on the fact that changes in nutrient levels cause changes in chlorophyll a, which in turn produces a change in water clarity.
Plant nutrients are necessary for the growth and maintenance of plants. The proper level of nutrients is important in limiting growth of algae and other aquatic vegetation. High nutrient levels often trigger algae blooms. Algae blooms result in increased turbidity, lower oxygen levels, and decreased water clarity. The effects of nutrients on the aquatic environment are discussed in the “Plant Nutrients” section in Chapter 3.
Chlorophyll a is the dominant green pigment found in algae and plants; it allows plants to convert solar energy into chemical energy through photosynthesis. Chemical energy is used to change carbon dioxide and water into the carbohydrates needed for the growth and maintenance of plants. Elevated chlorophyll a levels indicate an increase in productivity.
Water clarity gives an idea of how far light will penetrate into the water column or how much light is available to algae, phytoplankton, and other aquatic plants. The limit of light penetration is the limit of plant growth. Reduction in water clarity is often the result of large algae populations in the water column. The effects of water clarity on water quality are discussed in the “Suspended Solids” section in Chapter 3.