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NAUGATUCK RIVER WATERSHED ASSOCIATION

 

Aquatic Life in Summer

Aquatic Life Threatened—Historically, the flowing waters in rivers, streams and brooks experience oxygen depletion in the summer. Typically each summer there are several heat waves and little rain that produce life threatening environments for aquatic life. High water temperatures and low water can result in fish becoming stressed. They have difficulty breathing when the dissolved oxygen is low. If they don’t suffocate, they become weak and more vulnerable to disease. It is more difficult to resuscitate a stressed fish when little dissolved oxygen is available. Cool, clean water with a sufficient amount of dissolved oxygen is what most aquatic life need to survive. Aeration puts oxygen into water. Water blown by wind which contains oxygen, and water tumbled over rocks and dams are natural ways in which oxygen enters water.

Organic compounds in lakes and rivers degrade water quality for aquatic life by reducing dissolved oxygen. Biological Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present water. Most natural waters contain small quantities of organic compounds. Aquatic microorganisms have evolved to use some of these compounds as food. Microorganisms living in oxygenated waters use dissolved oxygen to oxidatively degrade the organic compounds, releasing energy which is used for growth and reproduction. Fish and aquatic insects may die when oxygen is depleted by microbial metabolism.

Populations of these microorganisms tend to increase in proportion to the amount of food available. This microbial metabolism creates an oxygen demand proportional to the amount of organic compounds useful as food. Under some circumstances, microbial metabolism can consume dissolved oxygen faster than atmospheric oxygen can dissolve into the water or the autotrophic community (algae, cyanobacteria and macrophytes) can produce. The amount of oxygen required to completely oxidize the organic compounds to carbon dioxide and water through generations of microbial growth, death, decay and cannibalism is total BOD.

Fish are cold-blooded (poikilothermous). Which means that they do not generate their body heat. Their body temperature varies with their external environment. They adjust to the water temperature; they eat and move accordingly. Moving less slows down their digestion and need for food. The oxygen levels vary greatly during the year. Cold water holds more dissolved oxygen than warm water, but there is less oxygen. Winter and summer are the two seasons when riverine fish mortality are highest due to insufficient amounts of dissolved oxygen in the water and inappropriate water temperatures. Low water levels and high temperatures raise water temperatures into the 80’s which can kill aquatic life-thermal pollution.

The efforts by conservationists to removing organic matter from water is valuable for promoting aquatic life. Here are examples of the Outdoor Life Span of some types of litter: cotton rags and paper (four weeks), wooden stakes (four years), wax paper cup (five years), cigarette filters (15 years), styrofoam cup (10 - 20), plastic (50-70), tin or steel cans (100 years), glass containers (forever), rubber products (forever).

The river bank and in-river clean ups done by conservationists address four types of pollution: Chemical – a variety of chemicals and decaying metal objects; Biological – human and animal waste products and decayed matter; Visual – paper, Styrofoam and plastic bags, cups and containers, tin and steel products, glass bottles, shopping carts, furniture, newspapers, car parts, etc.; Siltation – sand and soil run-off into waterways can build up in river bottoms and kill plant and aquatic