Dissolved Oxygen (DO) - Virtually all living organisms (with the exception of a few anaerobic bacteria, for example) need oxygen. Our atmosphere typically y contains about 21% oxygen so obtaining oxygen is usually not a problem for air-breathing organisms. However, oxygen can be limited in aquatic situations. The amount of oxygen in water is influenced by flow and turbulence as well as temperature and pressure. For example, cold water will hold more oxygen than warm water. For aquatic organisms, the percent saturation (the amount of oxygen in the water relative to the maximum it can contain at a given temperature and pressure) is more important than the actual amount. The percent saturation determines how readily the oxygen will cross gill or other respiratory surfaces and therefore how available it is to aquatic organisms. Organisms vary tremendously in there requirements for oxygen. Some stream organisms that live in still water or wetlands may be adapted to much lower levels.

 

pH - pH, potential Hydrogen, is a measure of hydrogen irons in water. All aquatic organisms have a range of pH within which they can exist. Changes in pH, for example, by acid precipitation can lead to the changes in the community structure of an aquatic system.

 

Temperature - Aquatic organisms may be found over a wide range of temperatures from hot springs where some bacteria exist in water that is close to the boiling point to water that is always ice covered. Different organisms are adapted to particular ranges of temperature. Increasing temperature by addition of hot water to natural systems may cause native species to be eliminated. Warm water contains less oxygen and the increased temperature will increase the metabolic activities of many of the organisms in this water.

 

Other potential tests to consider:

Hardness - Water hardness tends to measure calcium and magnesium ions in water. Hard water is often slightly basic (above pH 7) and because it contains carbonate and bicarbonate ions, it is more likely to have a higher buffering capacity. It is more able to withstand inputs of acid without the pH dropping. Many organisms seem to be restricted to water within some range of hardness. Many invertebrate, for example, require calcium for their shells or exoskeletons.

 

Chloride - Chloride occurs naturally in low concentrations in natural water. It will tend to be higher in precipitation in areas near the ocean. Increased chloride levels may come from domestic sewage, food processing or other activity, and road salt.

 

Nitrate and Phosphate - These two nutrients are important for the growth of algae and other organisms. They are often limiting nutrients. The levels of these nutrients may be increased by domestic sewage, agricultural activity and industrial processes. An increase in the concentration of these nutrients leads to eutrophication, rapid growth of algae or other plants, which can become harmful. When these plants die, their rapid decay can deplete the water of oxygen.

 

Alkalinity - Alkalinity is a measure of the carbonate and bicarbonate ions in water. It can be used to determine the amount of carbon potentially available for photosynthesis.

 

Bacteria - (Has to be done in lab) - Bacteria will be present in almost all natural waters. High levels of bacteria are associated with high nutrient levels or large amounts of organic compounds. High level of bacteria lead to high biological Oxygen Demand (BOD) Activity of these bacteria can deplete water of oxygen. Coliform bacteria may indicate sewage or other fecal contamination. Water containing high levels of coliforms is unsafe for recreational activity.