Physical, Chemical and Biological Parameters

Physical Parameters

Physical Parameter

Ecology is the study of the complex system of interrelationships existing among living organisms and their abiotic (physical and chemical) and biotic (living) environments and themselves. The abiotic factors in the environment determine the ability of organisms to live and reproduce. We will measure the physical parameters of our waterway, which determine the types of organisms that can live there.

The physical parameters also have strong effects on the chemical and biological measurements. Factors such as flow velocity, volume of water, bottom contour, currents, depth, light penetration, and temperature govern the ability of a system to receive and assimilate pollution. To evaluate these data, you need to know the physical status of your waterway in terms of temperature, weather, stream flow, etc. You also should know whether physical conditions are similar to compare data from different field trips.

Chemical Parameters

The following parameters are just a few that can be measured:

  • pH
  • Alkalinity
  • Dissolved Oxygen
  • Nitrate
  • Phosphate
  • Chloride
  • Biochemical oxygen demand (BOD)
ph Graph

pH is an important factor in the chemical and biological systems of natural waters. The toxicity of many compounds is affected by pH. One example is hydrogen cyanide (HCN). Cyanide toxicity to fish increases as the pH is lowered. Similar results have been shown for hydrogen sulfide (H2S).

The solubility of metal compounds contained in bottom sediments or as suspended material also is affected by pH. As pH decreases, certain metals such as aluminum copper, and lead are more easily dissolved and are leached from soil and sediments into runoff and groundwater entering surface water. These metals can accumulate on fish gills or cause deformities in fish fry, reducing their chance to survive.

Any precipitation with a low pH is called acid rain. Acid rain is formed when sulfur and nitrogen oxides, primarily from automobile and coal-powered plant emissions, combine with precipitation to form sulfuric and nitric acids in the atmosphere. Acid precipitation has acidified some lakes and streams in eastern Canada, Northeastern United States, and Scandinavia. Water over rocks containing high calcium and magnesium carbonate levels are better able to neutralize acid (such as limestone or dolomite).

The following pH scale shows relative pH ranges that support aquatic life. At either very high or low pH, the water cannot support most organisms. Serious problems occur in lakes with pH below 5, and in streams that get a massive acid dose in spring when the acid snows melt (Stapp, 1995).

The alkalinity

of water expresses its' capacity to neutralize acid; in other words, its' buffering capacity. Alkalinity is commonly expressed as milligrams per liter (mg/L) of calcium carbonate.

Examples of commonly occurring materials in natural waters that increase the alkalinity are carbonates, bicarbonates, phosphates and hydroxides (EPA, 1972).


Since pH has a direct affect on organisms and an indirect effect on the toxicity of certain other pollutants in the water, the buffering capacity is important to water quality (EPA, 1972). The buffering capacity of natural water is also important because it determines the effect of acid precipitation. The lower the alkalinity, the greater the sensitivity of surface water to acid precipitation.

Fish and many other organisms are unable to survive large drops in pH. Trout are especially sensitive to decreases in pH; sudden acid inputs to pH below 4.5 - 5.0 can kill fish (such as spring runoff from melting snow). Fish eggs and fry are sensitive to changes in pH, and may not develop.

Species diversity generally decreases with increased acidity.

Dissolved oxygen

is essential for the survival of nearly all aquatic life. Its concentration in water is very low compared with that in air. Temperature, the types and concentrations of dissolved and suspended solids affect the amount of oxygen dissolved in a lake or stream, agitation of the water, and biotic activity (especially algae).


Low dissolved oxygen concentration is damaging to aquatic life --- only the hardiest organisms survive. Critical conditions can occur during the summer when temperatures are high for two reasons:

  • The solubility of oxygen is lower at higher temperatures,
  • Oxygen demand is higher when temperatures rise, because the metabolic rates of the organisms increase.

Oxygen supersaturation can also be harmful.

Nitrate Cartoon

is a required nutrient for plants. Excess nitrates into waterways may lead to eutrophication by aiding algae and plant growth. This "bloom" of algae growth also contributes to lower oxygen levels, high turbidity (see Activity 5.6 for more information on turbidity), and decreases the aesthetic value of the waterway. Large amounts of nitrates in drinking water supplies (public and wells) can cause a disease in infants less than six months of age called methamoglobinemia ("blue babies").

Major point sources of nitrogen pollution include organic wastes from some sewage treatment plants, municipal wastewater, septic tanks, and feed lot discharges. Non-point sources include fertilizers from lawns and farms which leach out of soil and enter water through runoff, animal wastes, leachate from waste disposal in dumps or sanitary landfills, atmospheric fallout (nitric acid deposition), and discharges from automobile exhausts and other combustion processes.


present as an element is toxic and can bioaccumulate up the food web in much the same way as mercury and other toxic chemicals. Phosphorus present as phosphate is an essential nutrient to plant growth (second only to nitrogen), and is also essential to life.

Chloride ion

Is a component of living things and of many naturally occurring salts. It enters waterways through erosion and leaching from soil. Other sources of chloride include seawater intrusion, human and animal wastes, industrial wastes, fertilizers, and winter highway deicing. Salt spread on streets in winter can soak into adjacent soils and continue to leach into nearby waterways throughout the year.

Biochemical oxygen demand, or BOD

Estimates the total organic matter in a water sample available for oxidation. The measurement of oxygen demand is an easy way to detect the degree of pollution by organic matter. BOD is the difference in oxygen concentration in a water sample before and after incubation for a length of time under specific conditions. During this time, microorganisms in the sample oxidize the organic matter, using the dissolved oxygen present in the water.

The organic material comes from natural sources and from pollution with sewage, animal wastes, or any kind of organic refuse.

Biological Parameters

The chemical and physical sampling and analyses provide a broad picture of the parameters that define the aquatic environment. Now we will examine the living components of the system. Biological investigation of an aquatic community can determine the extent it has been affected by human activity.

Biological parameters detect water quality problems that other methods may miss or underestimate. Organisms in their environments are continual monitors of environmental quality, increasing the detection of events such as spills, dumping, treatment plant malfunctions, nutrient enrichment, non-point source pollution (such as agricultural pesticides), cumulative pollution (multiple events over time or continuous low level inputs) or other impacts that chemical sampling is unlikely to detect. Impacts on the physical habitat such as sedimentation from storm water runoff and the effects of physical or structural habitat changes such as dredging, filling, or channelization can also be detected.

"Resident biota are continual monitors of environmental quality, increasing the detection of episodic events (spills, dumping, treatment plant malfunctions, nutrient enrichment), nonpoint source pollution (agricultural pesticides), cumulative pollution (multiple impacts over time or continuous low-level stress) or other impacts that chemical sampling is unlikely to detect. Impacts on the physical habitat such as sedimentation from storm water runoff and the effects of physical or structural habitat changes (dredging, filling, channelization) can also be detected." (EPA 1994).

Plankton (phytoplankton and zooplankton), benthic macroinvertebrates, aquatic plants, and fish are the most commonly used in assessing biological integrity. The selection you make will depend on the type of waterway you study. For example, benthic macroinvertebrates are most often studied for wadeable riffles in streams and rivers. Algae are often used in lakes to examine eutrophication.

Delta Laboratories, Inc
410 White Spruce Blvd.
Rochester, NY 14623
P 585.234.1726
F 585.424.2485

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