Water Quality and Human Impacts

Why is water quality important? How is water quality measured?
The US EPA has set water quality standards in accordance with the Clean Water Act: Water quality standards are important because they help to protect and restore the quality of the Nation's surface waters, consistent with the requirements of the Clean Water Act. Standards help to identify water quality problems caused by, for example, improperly treated wastewater discharges, runoff or discharges from active or abandoned mining sites, sediment, fertilizers, and chemicals from agricultural areas, and erosion of stream banks caused by improper grazing practices.* The impacts of nitrates and phosphates on water have been gaining increased press. But, from the list above, one can see that these are not the only impacts that need attention.


Next gen standards

Science and engineering practices

  • Planning and carrying out investigations
  • Analyzing and interpreting data

Crosscutting concepts

  • Patterns
  • Cause and effect
  • Stability and change

Disciplinary core ideas/content

  • ESS3C Human impacts on Earth systems
  • LS1D Information processing
  • LS2A Interdependent relationships in ecosystems
  • LS2C Ecosystem dynamics, functioning and resilience
  • ETS2A Interdependence of science, engineering and technology

Teacher background

Pollutants can enter water to change water quality through various routes. Both point source and non point source pollutants cause problems. Point source pollutants come from known outlets (sewage pipe or effluent from industry) while non point source pollutants include run off from multiple places and the amounts that come from each area are not clear. For example: salt from roads, fertilizer from fields. Fertilizer contains nutrients such as nitrates and phosphates.

  • Nutrients from fertilizers, human or animal wastes play a role in polluting waterways, as well. Here are the levels at which these nutrients may cause problems in waterways.
  • Nitrate-nitrogen Levels exceeding 50 mg/L (ppm) are considered unhealthy for lakes. It is recommended 0–1 ppm and 1–5 ppm for optimum growth in freshwater systems.
  • Phosphorous Discharge Standards: Total Phosphorous for discharge < 100 micrograms/L; Where stream enters lake < 50 micrograms/L; Discharge into a lake < 25 micrograms/L. (Note: microgram/L are equivalent to parts per billion)

Other factors affecting wildlife in water ecosystems include: Dissolved oxygen which is the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets in the water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. Recommended minimum levels for fresh water fish are as follows: warm water fish: 5.0 mg/L (ppm) and cold water fish: 6.0 mg/L (ppm). Temperature is another abiotic factor that affects ecosystems in many ways. The higher the temperature of water, the lower the amount of dissolved oxygen water can hold. The opposite is also true: the lower the temperature, higher amounts of oxygen can be dissolved in the water. Biochemical/biological oxygen demand (BOD) is the amount of dissolved oxygen that must be present in water in order for microorganisms to decompose the organic matter in the water. It is used as a measure of the degree of pollution. pH is a measure of how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH greater than 7 is basic. The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value (For example, a pH of 4 is 10 times more acidic than 5, and 100 times more acidic than 6) and each whole pH value above 7 is ten times more basic than the next lower value. Recommended values for pH in aquatic ecosystems range from 6–8.

* water.epa.gov

Curriculum author

Jane Hunt

Education Consultant at Education Projects & Partnerships LLC at Education Projects & Partnerships LLC.




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