Common Chemical Water Quality Indicators

Variable	Description	Example of Cause/Impact
Available Oxygen	The amount of molecular oxygen dissolved in water is an important measure of habitat availability for aquatic organisms. Low levels of oxygen result from the introduction of organic waste pollution which increases the rate of eutrophication and decreases the suitability for aquatic animal life. Sources include: agricultural runoff, urban runoff, and wastewater treatment plants.
pH	pH is a unit that expresses the strength of a solution based on its acidic or basic properties. Aquatic organisms can only function in a particular range of pH, and become forced to relocate when the surrounding water changes. Pollution from burning fossil fuels increases the amounts of sulfur and nitrogen oxides introduced into the water, thereby increasing the overall acidity.
Turbidity	The amount of suspended material in water can be measured by collecting the solids or assessing the relative light transmission of the suspension. The increased opaqueness is caused by increased sediment which negatively affect many aquatic organisms. Both algal production and fish reproduction and feeding can become diminished and some organisms, like shell-fish (continual filter-feeders) can become choked by sediment and eventually die in heavily turbid waters.
Toxic Organic Compounds	There are many chemicals that have the capacity to travel throughout a waterway. Many of these are pollutants and can cause significant distress to the surrounding habitat. Solutions such as oil or antifreeze enter a watershed from nearby runoff sources and directly poison the surrounding aquatic environment. With appropriate riparian vegetation, large surge concentrations of these chemicals can be prevented from directly entering the water.
Heavy Metals	Industrial effluents are major sources of heavy metals, and aquatic environments are extremely sensitive to even the smallest concentrations of these materials. Serious abnormalities have been reported in many aquatic organisms. Arsenic and mercury are two common examples of heavy metals, but other similar substances and compounds can also have significant effects on an aquatic community.
Nutrients	Additional nutrients, such as phosphorus and nitrogen, are added to streams by many avenues, but primarily through human sewage, animal waste, fertilizers and erosion. This area of water quality monitoring is greatly affected by both urban and agricultural human practices. Runoff from any inadequately covered lands can increase these nutrient loads and result in eutrophication of the nearby aquatic habitat.