What’s the Point and Non-Point in Water Quality?

Michigan has nearly 3,300 miles of shoreline – second only to Alaska. Understanding sources of water pollution is important to our quality of life, recreation and economy.

Nearly half of Michigan is comprised of water. The Great Lakes, connecting rivers, inland lakes, ponds and streams all provide water to be used and enjoyed by residents. Because water above and below ground is connected it is easy to pollute an area and have it spread for many miles throughout the water system. Understanding basic concepts about sources of pollution can help improve overall water quality.

There are two categories of water pollution:

  1. Point source pollution is pollution where the source of the pollution can be identified, such as a spill or discharge
  2. Non-point source pollution is when the source of pollution either cannot be identified or may come from many sources

Point source types of pollution are usually individual occurrences, such as a sewer overflow during a heavy rain event or the recent oil spill into the Kalamazoo River. The source can be identified and responsible parties held accountable for cleanup and correction.

Non-point sources of pollution are much harder to identify and correct because they may be intermittent or from many sources at the same time. Most non-point source pollution is caused by either sediment or nutrients.

Sediment could include soil particles that have eroded from construction sites, stream banks, cropland or residential renovation. Sediment can be a point or non-point type of pollution.

Impacts of sediment on aquatic life

Sediment turns the water cloudy or “turbid.” This makes it difficult for fish to see and feed. It can damage gills, which makes it harder for fish to breathe. Soil particles can also cover spawning habitats limiting reproduction of fish populations.

Sediment can destroy a stream’s natural “riffle and pool” pattern by settling into the crevices of these areas and flattening out the river bottom. Sediment also inhibits photosynthesis by clouding water and covering aquatic plant leaves

Impacts of sediment on humans

 Sediment causes streams to become shallower and wider by filling in the riffle and pool areas, increasing potential flooding. The shallow water causes warmer temperatures that can reduce some fish populations.

 Sediment also impacts boating activity. Shallower water can increase the risk of damage to equipment and make some areas un-navigable. It can reduce recreational swimming in areas where silt has built up due to increased sediment deposition. Silted areas can be dangerous if deep holes become filled with loose sediment.

 Nutrients are usually non-point source pollution and are primarily phosphorus and nitrogen. Sources of nutrients are primarily from manure, pet waste, failed septic systems and overuse of fertilizer. Nutrients increase aquatic plant (weeds and algae) growth in lakes and rivers.

 Nutrient impacts on aquatic life

Nutrients contribute to eutrophication (excessive nutrients) in lakes, streams, rivers. This overloading of nutrients causes aquatic plants to grow faster than the ecosystem can handle. When these plants die, the bacteria used in the decomposition process uses up oxygen in the water. This lowers the oxygen levels and makes it difficult for aquatic animals and fish to breathe.

Excessive algal blooms block sunlight and can reduce bottom-rooted plants which are habitat and oxygen producers for aquatic organisms and fish.

Nutrient Impacts on humans

Increased aquatic plant growth can affect boating activity. Plants can get tangled in propellers and cause damage.

Some types of algae, called cyanobacteria or “blue-green” algae, are harmful to humans if they come in contact with it when swimming or wading.

By protecting water sources from sediment and nutrient pollution, Michigan’s water resources will remain an attraction for recreational and economic activity.

For more information on water pollution, visit the Environmental Protection Agency.

For information on watersheds, read Michigan State University Extension educator Christina Curell’s article on watersheds or MSU Extension educator Bindu Bhakta’s article on the water cycle and water quality protection.

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