About Water Quality

Error message

  • Deprecated function: Methods with the same name as their class will not be constructors in a future version of PHP; ctools_context has a deprecated constructor in require_once() (line 113 of /var/www/mililani/sites/all/modules/ctools/ctools.module).
  • Deprecated function: Methods with the same name as their class will not be constructors in a future version of PHP; ctools_context_required has a deprecated constructor in require_once() (line 113 of /var/www/mililani/sites/all/modules/ctools/ctools.module).
  • Deprecated function: Methods with the same name as their class will not be constructors in a future version of PHP; ctools_context_optional has a deprecated constructor in require_once() (line 113 of /var/www/mililani/sites/all/modules/ctools/ctools.module).
  • Deprecated function: Methods with the same name as their class will not be constructors in a future version of PHP; panels_cache_object has a deprecated constructor in require_once() (line 113 of /var/www/mililani/sites/all/modules/ctools/ctools.module).

Clean water is important to human and ecosystem health, and measuring chemical data (e.g. Oxygen, Nitrogen, pH) is one method to determine water quality in a given area. Comparing parameters between sites and over long periods of time are very useful, but comparing them to water quality standards provided by the State of Hawaii Department of Health may help us understand how clean the water we are measuring is.

What does water chemistry tell us about water quality?

Dissolved Oxygen: 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. The lower the concentration, the greater the stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills. Oxygen enters the water by direct absorption from the atmosphere or by plant photosynthesis. The oxygen is used by plants and animals for respiration and by the aerobic bacteria, which consume oxygen during the process of decomposition. When organic matter such as animal waste or improperly treated wastewater enters a body of water, algae growth increases and the dissolved oxygen levels decrease as the plant material dies off and is decomposed through the action of the aerobic bacteria. Thus, a decrease in the dissolved oxygen levels is usually an indication of some type of organic pollutant. These decreases in the dissolved oxygen levels can cause changes in the types and numbers of aquatic macroinvertebrates, which live in a water ecosystem. Species which cannot tolerate decreases in dissolved oxygen levels include several species aquatic insect larvae. As the dissolved oxygen levels decrease, these pollution-intolerant organisms are replaced by the pollution-tolerant worms and fly larvae. Dissolved oxygen levels change and vary according to the time of day, the weather and the temperature. For more information, visit the EPA website section about the importance of monitoring dissolved oxygen (Click Here).

Turbidity: Turbidity is a measure of the degree to which the water loses its transparency due to the presence of suspended particulates and is measured in Nephelometric Turbidity Units (NTU). The instrument used for measuring turbidity is called nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample. The more total suspended solids in the water, the murkier it seems and the higher the turbidity. Turbidity is considered as a good measure of the quality of water. There are various parameters that influence the cloudiness of the water, e.g., phytoplankton, sediments from erosion, resuspended sediments from the bottom (potentially by animals), waste discharge, algae growth, and urban runoff. These suspended particles can also absorb heat from the sunlight, making turbid waters become warmer, and reducing the concentration of oxygen in water (oxygen dissolves better in colder water). Many native stream organisms cannot not tolerate warmer water, whereas many non-native, aquarium introduced species can. The suspended particles can also scatter the light, thus decreasing the photosynthetic activity of plants and algae, which contributes to lowering the oxygen concentration even more. As a consequence of the particles settling to the bottom, causing stream channels fill in faster, fish eggs and insect larvae are covered and suffocated, gill structures get clogged or damaged. The suspended particles also aid the attachment of heavy metals and many other toxic organic compounds and pesticides. For more info, visit the EPA website about the importance of turbidity (Click here).

Conductivity: Conductivity is a measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge). Organic compounds like oil, phenol, alcohol, and sugar do not conduct electrical current very well and therefore have a low conductivity when in water. Conductivity is also affected by temperature: the warmer the water, the higher the conductivity. For this reason, conductivity is reported as conductivity at 25 degrees Celsius (25 C). Conductivity in streams and rivers is affected primarily by the geology of the area through which the water flows. Streams that run through areas with granite bedrock tend to have lower conductivity because granite is composed of more inert materials that do not ionize (dissolve into ionic components) when washed into the water. On the other hand, streams that run through areas with clay soils tend to have higher conductivity because of the presence of materials that ionize when washed into the water. Ground water inflows can have the same effects depending on the bedrock they flow through. Discharges to streams can change the conductivity depending on their make-up. A failing sewage system would raise the conductivity because of the presence of chloride, phosphate, and nitrate; an oil spill would lower the conductivity.

The basic unit of measurement of conductivity is the mho or siemens. Conductivity is measured in micromhos per centimeter (µmhos/cm) or microsiemens per centimeter (µs/cm). Distilled water has a conductivity in the range of 0.5 to 3 µmhos/cm. The conductivity of rivers in the United States generally ranges from 50 to 1500 µmhos/cm. Studies of inland fresh waters indicate that streams supporting good mixed fisheries have a range between 150 and 500 µhos/cm. Conductivity outside this range could indicate that the water is not suitable for certain species of fish or macroinvertebrates. Industrial waters can range as high as 10,000 µmhos/cm. For more info visit the EPA website about the importance of Conductivity (Click Here).

Temperature:The rates of biological and chemical processes depend on temperature. Aquatic organisms from microbes to fish are dependent on certain temperature ranges for their optimal health. Optimal temperatures for fish depend on the species: some survive best in colder water, whereas others prefer warmer water. Benthic macroinvertebrates are also sensitive to temperature and will move in the stream to find their optimal temperature. If temperatures are outside this optimal range for a prolonged period of time, organisms are stressed and can die. Temperature is measured in de-grees Fahrenheit (F) or degrees Celsius (C). For fish, there are two kinds of limiting temperatures the maximum temperature for short exposures and a weekly average temperature that varies according to the time of year and the life cycle stage of the fish species. Reproductive stages (spawning and embryo development) are the most sensitive stages. Temperature affects the oxygen content of the water (oxygen levels become lower as temperature increases); the rate of photosynthesis by aquatic plants; the metabolic rates of aquatic organisms; and the sensitivity of organisms to toxic wastes, parasites, and diseases. Causes of temperature change include weather, removal of shading streambank vegetation, impoundments (a body of water confined by a barrier, such as a dam), dis-charge of cooling water, urban storm water, and groundwater inflows to the stream. For more info visit the EPA website about the importance of temperature (Click here).

Nitrate: Nitrates are a form of nitrogen, which is found in several different forms in terrestrial and aquatic ecosystems. These forms of nitrogen include ammonia (NH3), nitrates (NO3), and nitrites (NO2). Nitrates are essential plant nutrients, but in excess amounts they can cause significant water quality problems. Together with phosphorus, nitrates in excess amounts can accelerate eutrophication, causing dramatic increases in aquatic plant growth and changes in the types of plants and animals that live in the stream. This, in turn, affects dissolved oxygen, temperature, and other indicators. Excess nitrates can cause hypoxia (low levels of dissolved oxygen) and can become toxic to warm-blooded animals at higher concentrations (10 mg/L) or higher) under certain conditions. The natural level of ammonia or nitrate in surface water is typically low (less than 1 mg/L); in the effluent of wastewater treatment plants, it can range up to 30 mg/L. Sources of nitrates include wastewater treatment plants, runoff from fertilized lawns and cropland, failing on-site septic systems, runoff from animal manure storage areas, and industrial discharges that contain corrosion inhibitors. For more info visit the EPA website about the importance of Nitrates (Click here).

Total Dissolved Solids: In stream water, dissolved solids consist of calcium, chlorides, nitrate, phosphorus, iron, sulfur, and other ions particles that will pass through a filter with pores of around 2 microns (0.002 cm) in size. The concentration of total dissolved solids affects the water balance in the cells of aquatic organisms. An organism placed in water with a very low level of solids, such as distilled water, will swell up because water will tend to move into its cells, which have a higher concentration of solids. An organism placed in water with a high concentration of solids will shrink somewhat because the water in its cells will tend to move out. This will in turn affect the organism's ability to maintain the proper cell density, making it difficult to keep its position in the water column. It might float up or sink down to a depth to which it is not adapted, and it might not survive. For more info visit the EPA website about the importance of Total Solids (Dissolved and Suspended) (Click here).

pH: pH affects many chemical and biological processes in the water. For example, different organisms flourish within different ranges of pH. The largest variety of aquatic animals prefer a range of 6.5-8.0. pH outside this range reduces the diversity in the stream because it stresses the physiological systems of most organisms and can reduce reproduction. Low pH can also allow toxic elements and compounds to become mobile and "available" for uptake by aquatic plants and animals. This can produce conditions that are toxic to aquatic life, particularly to sensitive species like rainbow trout. Changes in acidity can be caused by atmospheric deposition (acid rain), surrounding rock, and certain wastewater discharges. For more info, visit the EPA website about the importance of pH measurements (Click here).

More to come, stay tuned!