The five following parameters are basic to life within aquatic systems.
- Dissolved oxygen
- Temperature
- Electrical conductivity
- PH
- Turbidity
Dissolved Oxygen
Dissolved oxygen is oxygen gas molecules (O2) present in the water. Plants and animals cannot directly use the oxygen that is part of the water molecule (H2O), instead of depending on dissolved oxygen for respiration.
Oxygen enters streams from the surrounding air and as a product of photosynthesis from aquatic plants. Consistently high levels of dissolved oxygen are best for a healthy ecosystem.
It is the amount of oxygen dissolved in water. Most aquatic organisms need oxygen to survive and grow.
Levels of dissolved oxygen vary depending on factors including water temperature, time of day, season, depth, altitude, and rate of flow. Water at higher temperatures and altitudes will have less dissolved oxygen. Dissolved oxygen reaches its peak during the day. At night, it decreases as photosynthesis has stopped while oxygen-consuming processes such as respiration, oxidation, and respiration continue, until shortly before dawn.
Human factors that affect dissolved oxygen in streams include the addition of oxygen-consuming organic wastes such as sewage, the addition of nutrients, changing the flow of water, raising the water temperature, and the addition of chemicals.
Dissolved oxygen is measured in mg/L.
0-2 mg/L: not enough oxygen to support life.
2-4 mg/L: only a few fish and aquatic insects can survive.
4-7 mg/L: good for many aquatic animals, low for cold water fish
7-11 mg/L: very good for most stream fish
2-4 mg/L: only a few fish and aquatic insects can survive.
4-7 mg/L: good for many aquatic animals, low for cold water fish
7-11 mg/L: very good for most stream fish
If there is not enough oxygen in the water, the following may happen:
- Death of adults and juveniles
- Reduction in growth
- Failure of eggs/larvae to survive
- Change of species present in a given water body is the amount of oxygen dissolved in water.
- Most aquatic organisms need oxygen to survive and grow.
Temperature
temperature is a measure of the average energy (kinetic) of water molecules. It is measured on a linear scale of degrees Celsius or degrees Fahrenheit.
It is one of the most important water quality parameters. Temperature affects water chemistry and the functions of aquatic organisms. It influences the:
- amount of oxygen that can be dissolved in water,
- the rate of photosynthesis by algae and other aquatic plants,
- metabolic rates of organisms,
- the sensitivity of organisms to toxic wastes, parasites and diseases, and timing of reproduction, migration, and aestivation of aquatic organisms.
Electrical Conductivity/Salinity
This is a measure of the capability of a solution such as water in a stream to pass an electric current. This is an indicator of the concentration of dissolved electrolyte ions in the water. It doesn't identify the specific ions in the water. However, significant increases in conductivity may be an indicator that polluting discharges have entered the water.
Every creek will have a baseline conductivity depending on the local geology and soils. Higher conductivity will result from the presence of various ions including nitrate, phosphate, and sodium.
The basic unit of measurement for conductivity is micromhos per centimeter (µmhos/cm) or micro siemens per centimeter (µS/cm).
Either can be used, they are the same. It is a measure of the inverse of the amount of resistance an electric charge meets in traveling through the water.
Distilled water has a conductivity ranging from 0.5 to 3 µS/cm, while most streams range between 50 to 1500 µS/cm. Freshwater streams ideally should have a conductivity between 150 to 500 µS/cm to support diverse aquatic life.
Salinity is a measure of the number of salts in the water. Because dissolved ions increase salinity as well as conductivity, the two measures are related. The salts in seawater are primarily sodium chloride (NaCl). However, other saline waters, such as Mono Lake, owe their high salinity to a combination of dissolved ions including sodium, chloride, carbonate, and sulfate.
Conductivity will vary with water source: groundwater, water drained from agricultural fields, municipal wastewater, rainfall. Therefore, conductivity can indicate groundwater seepage or a sewage leak.
PH
pH is a measure of how acidic or basic (alkaline) the water is. It is defined as the negative log of the hydrogen ion concentration. The pH of pure water is 7. In general, water with a pH lower than 7 is considered acidic, and with a pH greater than 7 is considered basic.
The normal range for pH in surface water systems is 6.5 to 8.5, and the pH range for groundwater systems is between 6 to 8.5. The pH scale goes from 0 to 14. For each whole number increase (i.e. 1 to 2) the hydrogen ion concentration decreases and the water become less acidic.
As the pH decreases, water becomes more acidic. As water becomes more basic, the pH increases.
Measured on scale from 0 to 14
- 0= highly acidic (HCl)
- pH of natural water 6.5-8.5
- neutral (pure water): 7
- Sea water pH ranges from 7.5- 8.5
- Optimal range for life = 6.5 - 8.2
- 14=highly basic (bleach)
Turbidity
Turbidity is a measure of the number of suspended particles in the water. Algae suspended sediment, and organic particles can cloud the water making it more turbid Suspended particles diffuse sunlight and absorb heat. This can increase temperature and reduce light available for algal photosynthesis.
If the turbidity is caused by suspended sediment, it can be an indicator of erosion, either natural or man-made. Suspended sediments can clog the gills of fish. The sediment can also carry pathogens, pollutants, and nutrients.
Suspended particles diffuse sunlight and absorb heat. This can increase temperature and reduce light available for algal photosynthesis. If the turbidity is caused by suspended sediment, it can be an indicator of erosion, either natural or man-made. Suspended sediments can clog the gills of fish. Once the sediment settles, it can foul gravel beds and smother fish eggs and benthic insects. The sediment can also carry pathogens, pollutants, and nutrients.
Other Constituents of Concern
Nitrogen (NO3-N)
Nitrogen is a nutrient that occurs naturally in both fresh and salt water. It is essential for plant growth in an aquatic ecosystem. Problems occur when large amounts nitrogen are introduced into the stream ecosystem.
Total Coliform
Total coliform bacteria, fecal coliform bacteria, and E. coli are all considered indicators of water contaminated with fecal matter. Contaminated water may contain other pathogens (micro-organisms that cause illness) that are more difficult to test for. Therefore these indicator bacteria are useful in giving us a measure of contamination levels.
E-Coli
E. coli is a bacterial species found in the fecal matter of warm-blooded animals (humans, other mammals, and birds). Total coliform bacteria are an entire group of bacteria species that are generally similar to and include the species E. coli. There are certain forms of coliform bacteria that do not live in fecal matter but instead live in soils. Fecal coliform bacteria are coliform bacteria that do live in fecal matter, including, but not limited to, the species E. coli. Most of the fecal coliform cells found in fecal matter are E. coli.
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