Science Article

Dissolved Oxygen

Why dissolved oxygen is important: Dissolved oxygen analysis measures the amount of gaseous oxygen (O) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. When performing the dissolved oxygen test, only grab samples should be used, and the analysis should be performed immediately. Therefore, this is a field test that should be performed on site.

Environmental impact: Adequate dissolved oxygen is necessary for good water quality. Oxygen is a necessary element to all forms of life. Natural stream purification processes require adequate oxygen levels in order to provide for aerobic life-forms. As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life is put under stress.

Biochemical Oxygen Demand

Why BOD is important: Biochemical oxygen demand is important because it shows the amount of organic matter that is in the water. It is the measure of the amount of oxygen that would be consumed if bacteria and protozoa oxidized all of the organic matter in one liter of water. If the level is too low, it could put aquatic organisms at risk.

Nitrate

Why nitrate is important: Nitrogen is one of the most abundant elements. About 80% of the air we breathe is nitrogen. It is found in the cells of all living things and is a major component of proteins. Inorganic nitrogen may exist in the free state as a gas [N2], or as nitrate [NO3-], nitrite [NO2-], or ammonia [NH3+]. Organic nitrogen is found in proteins and is continually recycled by plants and animals.

Environmental impact: Nitrogen-containing compounds act as nutrients in streams and rivers. Nitrate reactions [NO3-] in freshwater can cause oxygen depletion. Thus aquatic organisms depending on the supply of oxygen in the stream will die. The major routes of entry of nitrogen into bodies of water are municipal and industrial wastewater, septic tanks, feedlot discharges, animal wastes (including birds and fish), and discharges from car exhausts. Bacteria in water quickly convert nitrites [NO2-] to nitrates [NO3-].

pH

Why pH is important: pH is a measure of the acidic or basic (alkaline) nature of a solution. The concentration of the hydrogen ion [H+] activity in a solution determines the pH. Mathematically this is expressed as: pH = - log [H+]. The pH value is the negative power to which 10 must be raised to equal the hydrogen ion concentration.

Environmental impact: A pH range of 6.0 to 9.0 appears to provide protection for the life of freshwater fish and bottom-dwelling invertebrates. The most significant environmental impact of pH involves synergistic effects. Synergy involves the combination of two or more substances that produce effects greater than their sum. This process is important in surface waters. Runoff from agricultural, domestic, and industrial areas may contain iron, aluminum, ammonia, mercury, or other elements. The pH of the water will determine the toxic effects, if any, of these substances.

Phosphate

Why phosphorus is important: Phosphorus is one of the key elements necessary for growth of plants and animals. Phosphorus in elemental form is very toxic. Phosphates [PO4---] are formed from this element. Their occurrence may result from the breakdown of organic pesticides that contain phosphates. They may exist in solution, as particles, as loose fragments, or in the bodies of aquatic organisms.

Environmental impact: Rainfall can cause varying amounts of phosphates to wash from farm soils into nearby waterways. Phosphate will stimulate the growth of plankton and aquatic plants that provide food for fish. This increased growth may cause an increase in the fish population and improve the overall water quality. However, if an excess of phosphate enters the waterway, algae and aquatic plants will grow wildly, choke up the waterway, and use up large amounts of oxygen.

Temperature

Why temperature is important: Human activities should not change water temperatures beyond natural seasonal fluctuations. To do so could disrupt aquatic ecosystems. Temperature affects the solubility of oxygen and therefore affects fish. Good temperatures are dependent on the type of stream you are monitoring. Lowland streams, known as "warmwater" streams, are different from mountain or spring-fed streams that are normally cool. In a warmwater stream, temperatures should not exceed 32°C (89°F). Cold-water streams should not exceed 20°C (68°F).

Turbidity

Why turbidity is important: Turbidity is a measure of the amount of suspended particles in the water. Algae, suspended sediment, and organic matter in the water increase turbidity to unhealthy levels for certain organisms. Turbidity is important because a high level of suspended particles in the river can diffuse sunlight and absorb heat, which increases temperature and reduces the light available for plants. Turbidity increases with bank erosion, excessive algal growth, and changes in the river's flow.

Coliform Bacteria

Why coliform bacteria are important: Coliform bacteria are a collection of relatively harmless microorganisms that live in large numbers in the intestines of humans and warm- and cold-blooded animals. They aid in the digestion of food. A specific subgroup of this collection is the fecal coliform bacteria, the most common member being Escherichia coli. These organisms may be separated from the coliform group by their ability to grow at elevated temperatures and are associated only with the fecal material of warm-blooded animals.

Environmental impact: The presence of fecal coliform bacteria indicates that the water has been contaminated with the fecal material of humans or other animals. At the time this occurred, the source water may have been contaminated by pathogens or disease-producing bacteria or viruses that can also exist in fecal material. Some waterborne pathogenic diseases include typhoid fever, viral and bacterial gastroenteritis, and hepatitis A. The presence of fecal contamination is an indicator that a potential health risk exists for individuals exposed to this water. Fecal coliform bacteria may occur in ambient water as a result of the overflow of domestic sewage or nonpoint sources of human and animal waste.