Dissolved Oxygen

May 26, 2006

One of the best indicators of the health of a water ecosystem is the dissolved oxygen parameter. . Dissolved oxygen can range from 0-18 parts per million (ppm). Most natural water systems require 5-6 parts per million to support a diverse population.

Oxygen enters the water either by direct absorption from the atmosphere or by plant photosynthesis. The oxygen is used by plants and animals for respiration and by the aerobic bacteria which consume oxygen during the process of decomposition. When organic matter such as animal waste or improperly treated wastewater enters a body of water, Algae growth increases when organic matter such as animal waste or improperly treated wastewater enters a body of water causing the dissolved oxygen levels to decrease as the plant material dies off and is decomposed through the action of the aerobic bacteria.

When the dissolved oxygen levels decreases it effects the number and types of aquatic macroinvertebrates which live in a water ecosystem. Species which cannot tolerate decreases in dissolved oxygen levels include mayfly nymphs, stonefly nymphs, caddisfly larvae and beetle larvae. As the dissolved oxygen levels decrease, these pollution-intolerant organisms are replaced by the pollution-tolerant worms and fly larvae.

Dissolved oxygen levels change and vary according to the time of day, the weather and the temperature, which is why we took the time and the temperature at each sampling point.

A decrease in the dissolved oxygen levels is usually an indication of an influx of some type of organic pollutant.

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