Prepared by the Western U.P. Center for Science, Math and Environmental Education at Michigan Technological University

WATER CHEMISTRY – Data Interpretation and Standards

 

Dissolved Oxygen

Aquatic animals need dissolved oxygen (DO) to live.  Fish, invertebrates, plants and aerobic bacteria all require oxygen for respiration.  The amount of oxygen that can be dissolved in the water is reduced with increased temperature.  The temperature effect is compounded by the fact that living organisms increase their activity in warm water, requiring more oxygen to support their metabolism. Fish and invertebrates that can move will leave areas with low DO.

            DO levels < 3 ppm are stressful to most aquatic organisms.

            DO levels < 2 ppm will not support fish.

            DO = 5-6 ppm is required for growth and activity of most aquatic organisms.

 

Biological Oxygen Demand (BOD)

Oxygen is not only required for survival of most living organisms, but is needed to decompose organic (plant) material and human/animal wastes (sewage).  BOD is determined by measuring the DO of a freshly collected sample and comparing it to the DO level in a sample that was collected at the same time but incubated in complete darkness, at 20°C, for 5 days.  Unpolluted natural waters £ 5 mg/L BOD.

 

Nitrate-Nitrogen

Nitrogen is essential for plant growth, but the presence of excessive amounts in water supplies presents a major pollution problem.  Nitrogen compounds may enter water from agricultural fertilizers, human sewage, industrial wastes, livestock wastes, and farm manure.  Nitrate in drinking water must be £ 10 ppm.

 

pH

A pH of 6.5 to 8.2 is optimal for most organisms.  Rapidly growing algae or submerged aquatic vegetation remove CO2 from the water during photosynthesis, significantly increasing pH levels.     pH levels > 9.0 begin to be harmful to salmonids (trout) and perch.   Rainwater naturally has a pH of 5.5; pH < 5.5 is harmful to freshwater shrimp, snails, and clams; metals normally trapped in sediments may be released into the acidified water.

Acidic <  6.5 pH                      Basic > 7.5 pH

 

Turbidity

Turbidity, or cloudiness in water, is caused by suspended materials that scatter light passing through the water.  There are many possible sources of turbidity, including sediments from disturbed or eroded soil and high numbers of microscopic plankton due to excess nutrients and sunlight.  Microscopic examination and streamwalk observations can help determine the sources of turbidity. In addition to blocking out the light needed by submerged aquatic vegetation and burying fish eggs and benthic (bottom dwelling) creatures, suspended sediment can carry nutrients and pesticides throughout the water system, damage gills, and interfere with the ability of fish to find food.  Suspended particles near the water surface can absorb extra heat from sunlight, raising surface water temperatures.      Drinking water < 0.5 NTUs or JTUs                  Typical groundwater < 1.0 NTUs or JTUs

 

Iron    Iron in water stains fixtures and may have an odor or taste. Values of 0-0.5 are acceptable. High values in streams may indicate contamination from landfills.

 

Phosphates

Phosphate test kits measure the form of phosphate applied as fertilizer to agricultural fields, grass lawns, or golf courses.  Phosphates accelerate the growth of algae and aquatic plants.  Total P > 0.03 ppm will increase plant growth and eutrophication.

 

Copper    Copper in water is from stamp sands or waste rock from copper mines.  The national standard for aquatic life is .018 mg/l and for drinking water is 1.3 mg/l.  (mg/l = ppm)

Alkalinity

Alkalinity is the amount of buffering material in the water.  If a body of water has an abundance of buffering materials (high alkalinity), it is more stable and resistant to changes in pH.  If a body of water has very little buffering material (low alkalinity), it is very susceptible to changes in pH. As increasing amounts of acid (acid rain) are added to ponds and lakes, their buffering capacity is consumed.  If surrounding soils and rocks supply additional buffering materials, the alkalinity may eventually be restored.  Even a temporary loss of buffering capacity can permit pH levels to drop to levels harmful to aquatic life.

 

Odor

Odor affects the acceptability of drinking water, the aesthetics of recreational water, and the taste of fish.  Sewage and industrial chemical waste discharges or natural sources such as decomposing vegetation and microbial activity can cause odor. The human nose can accurately detect a wide variety of smells, making it the best odor-testing device available!  To measure odor, put sample in wide-mouth container.  Use your hand to wave the air above the water sample toward you.  Record your observations.

 

Carbon Dioxide

Aquatic plants depend on CO2 in water for growth and respiration.  CO2 increases when organic wastes reduce the oxygen available, making it difficult for fish to use the limited amount of oxygen present.  Surface waters normally contain < 10 ppm of free CO2.

 

Water Temperatures

Temperature is one factor in determining which species may or may not be present.  Temperature affects the feeding, reproduction, and metabolism of aquatic animals.  A week or two of high temperature each year may make a stream unsuitable for sensitive aquatic organisms, even though temperatures are within tolerable levels throughout the rest of the year.  Not only do different species have different temperature requirements, but the optimal temperature may change for different stages of life.  Fish eggs and larvae usually have a narrower temperature require-ment than adult fish.  Therefore, it is important to consider the life stage of species present when analyzing temperature data.

 

Water Color

Verbal descriptions of color are unreliable and subjective.  Use a system of color comparison that is reproducible and can be compared to systems used by other groups.  Below is a list of possible colors and what they may be caused by:

Blue = transparent water with a low accumulation of dissolved materials and particulate matter,

indicates low productivity. 

Yellow/Brown = dissolved organic materials, humic substances from soil, peat, or decaying plant material. 

Red = can be produced by some algae. 

Green = water rich in phytoplankton and other algae. 

Mix of colors = may be caused by soil runoff.