Chemical compounds in water and their effect on the health of a stream

This is a supplemental discussion on chemical compounds in water and their effect on the health of a stream, To learn more about the 2013 Water Quality Survey of the Little Manistee River,  LMWCC-Newsletter-FW-2013

Chemicals and Compounds in Trout Stream Ecosystems

Dissolved oxygen — there is a direct relationship between dissolved oxygen (ppm) and water temperature… higher water temperatures hold less oxygen

Solubility of oxygen at sea-level/air-pressure of 760mm 29.92in. (29.38) at 500’ above sea-level

Air temperature                     Oxygen PPM

32°                         14.6

41°                         12.8

50°                         11.3

59°                         10.2

68°                         9.2

77°                         8.4

83°                         7.6

A minimum of 4 ppm of dissolved oxygen is necessary for a viable aquatic ecosystem

 

The following chemicals/compounds in excess contribute to eutrophication — excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen. High quantities of nutrients (sources: agricultural run-off, raw sewage, and products high in phosphates, i.e. fertilizers and cleaning products) create explosive growth in aquatic plants, exceeding the BOD — biological oxygen demand — the amount of oxygen required to decompose organic material. Increasing the abundance of nutrients in the water leads to an increase in the demand for oxygen to decompose the organic material. A BOD that exceeds the available oxygen produces dangerous levels of carbon dioxide.

E. coli — elevates water temperatures as oxygen is depleted to break down the various compounds; increases growth of aquatic plants adversely  affecting the ecosystem.

pH  — Alkalinity (pH above 7) is important for fish and aquatic life because it protects or buffers against pH changes.

Ammonia — Ammonia is toxic to fish and aquatic organisms, even in very low concentrations. When levels reach 0.06 mg/L, fish can suffer gill damage. When levels reach 0.2 mg/L, sensitive fish like trout and salmon begin to die. As levels near 2.0 mg/L, even ammonia-tolerant fish like carp begin to die. Ammonia levels greater than approximately 0.1 mg/L usually indicate polluted waters.

Ammonia is quickly assimilated in moving water.

Nitrate — Nitrates stimulate the growth of plankton and water weeds that provide food for fish. This may increase the fish population. However, if algae grow too wildly, oxygen levels will be reduced and fish will die.

Like ammonia most forms of aquatic nitrogen break down in moving water and the nitrogen is  released into the atmosphere.

Phosphates — indispensable for plant growth – insufficiencies limit biological productivity. In high  concentrations can lead to the rupture of blood vessels in aquatic organisms as well as oxygen depletion in the water chemistry — see BOD above.

Phosphates stimulate the growth of plankton and water plants that provide food for fish. This may increase the fish population and improve the waterway’s quality of life. If too much phosphate is present, algae and water weeds grow wildly, choke the waterway, and use up large amounts of oxygen.

 Dissolved Oxygen — If water is too warm, there may not be enough oxygen in it. When there are too many bacteria or aquatic animal in the area, they may overpopulate, using DO in great amounts.  Oxygen levels also can be reduced through overfertilization of water plants by run-off from farm  fields containing phosphates and nitrates (the ingredients in fertilizers). Under these conditions, the numbers and size of water plants increase a great deal. Then, if the weather becomes cloudy for     several days, respiring plants will use much of the available DO. When these plants die, they  become food for bacteria, which in turn multiply and use large amounts of oxygen.

Numerous scientific studies suggest that 4-5 parts per million (ppm) of DO is the minimum amount that will support a large, diverse fish population. The DO level in good fishing waters generally averages about 9.0 parts per million (ppm).

 Chlorides — Free chlorine (chlorine gas dissolved in water) is toxic to fish and aquatic organisms,  even in very small amounts. However, its dangers are relatively short-lived compared to the dangers of most other highly poisonous substances. That is because chlorine reacts quickly with other substances in water (and forms combined chlorine) or dissipates as a gas into the atmosphere.

Nitrite — relatively short-lived because they’re quickly converted to nitrates by bacteria. Like ammonia most forms of aquatic nitrogen break down in moving water and the nitrogen is released into the atmosphere.