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Water Quality: Management, Sanitation and Investigation

Limnological Fundamentals


Algae are photosynthetic plants that contain chlorophyll and have a simple reproductive structure but do not have tissues that differentiate into true roots, stems, or leaves. They do, however, grow in many forms. Some species are microscopic single cells; others grow as mass aggregates of cells (colonies) or in strands (filaments). Some even resemble plants growing on the lake bottom.

The algae are an important living component of lakes. They:

Factors that Affect Algal Growth

There are a number of environmental factors that influence algal growth. The major factors include:

It is a combination of these and other environmental factors that determines the type and quantity of algae found in a lake. It is important to note, however, that these factors are always in a state of flux. This is because a multitude of events, including the change of seasons, develop ment in the watershed, and rainstorms constantly create "new environments" in a lake.

These environmental changes may or may not present optimal habitats for growth or even survival for any particular species of algae. Consequently, there is usually a succession of different species in a lake over the course of a year and from year to year.

The Overgrowth of Algae

Excessive growth of one or more species of algae is termed a bloom. Algal blooms, usually occurring in response to an increased supply of nutrients, are often a disturbing symptom of cultural eutrophication.

Blooms of algae can give the water an unpleasant taste or odor, reduce clarity, and color the lake a vivid green, brown, yellow, or even red, depending on the species. Filamentous and colonial algae are especially troublesome because they can mass together to form scums or mats on the lake surface. These mats can drift and clog water intakes, foul beaches, and ruin many recreational opportunities.

Monitoring programs designed to monitor the algal condition of a lake usually require the volunteers to measure: