Sediment in stormwater is a common pollutant which negatively impacts water quality

Recognizing point and nonpoint source pollution is the first step to helping to protect Michigan’s water resources.

Water pollution can generally be divided into two general types: point source pollution and nonpoint source pollution.

Point source pollution is a pollution source that enters the environment from a single point and which can be clearly identified. Examples of point source pollution include discharges from factories and wastewater treatment plants. One recent and well-known example of point source pollution is the Enbridge oil pipeline spill that occurred near Marshall, Mich. in July 2010.

Nonpoint source (NPS) pollution is one that cannot be traced back to one single source or property. It may be discharged over a wide land area and does not come from a single pipe. Small amounts of contaminants accumulate from many sources and properties and can eventually reach concentrations that can impair surface water quality. Nonpoint source pollutants include animal waste, metals, nitrogen, organic matter, pathogens (specifically human disease-causing bacteria and viruses), pesticides, petroleum and petroleum by-products, salts and sediment. One recent example of nonpoint source pollution is phosphorus-containing lawn fertilizers which led to new amendments to the Michigan Fertilizer Law which led to restrictions on its use.

Consider the route you travel to and from home, work or school. What do you notice in and around roadways? You will likely see various pollutants that can easily be washed by stormwater into nearby waterways. This article will take a closer look at sediment as a source of nonpoint source pollution. Sediment is earth material or soil particles (such as sand, gravel and clay).

In the United States, sediment is the most significant nonpoint source leading to impaired surface water quality. Sediment sources include particles that have washed into a body of water from farm fields, forestlands, bare spots in the home landscape, inland lakes shorelines, stream banks, improperly managed construction sites and other locations. Nutrients like phosphorus can also be tightly bound to sediment that washes into waterways introducing an often unwanted supply of nutrients into bodies of water.

It is often overlooked as a water contaminant because it is everywhere in the natural and built environment. In surface water, sediment can become a water quality concern when it washes into waterways by:

  • changing water clarity (ability of water to transmit light)
  • reducing oxygen levels in the water and degrading habitat for fish and wildlife species
  • increasing sedimentation (the process by which sediment is carried into a water body and either deposited or suspended in the water) which can fill in waterways and lead to flooding and reduced navigability
  • damaging or destroying waterfront property

For additional information on how sediment impacts aquatic and human life and what you can do to recognize and prevent water pollution, read the Michigan State University Extension article, “What’s the Point and Non-Point in Water Quality?”

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