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Thermal Pollution: Sources and Impacts
Town of Waynesville -- Press Release: The Town of Waynesville Government: Thermal pollution is a type of pollution often overlooked.
Thermal pollution is caused when
there is an influx of heated water into a stream that causes the stream’s temperature to increase. Heated water inputs can come from a variety of sources. For example, on a typical summer afternoon, the temperature of asphalt can reach 120 - 150 °F! When rain-water flows across the hot asphalt it heats up on its way to the storm drain where it is dumped, untreated, into a nearby waterway. Rainfall coming into contact with a dark roof-top can also heat up stormwater before it’s dumped into a waterway. Some industries have permits allowing for warm water releases as part of their cooling system. A lack of streamside shade trees and shrubs, which can block the heat of the afternoon sun, can lead to increased stream water temperatures. Thermal pollution can become more severe during times of drought when there is less groundwater influence to offset the input of increased water temperatures.
Nearly all Haywood County streams are considered “cold-water” streams, meaning trout, mayflies, and other organisms thrive when temperatures are below 70°F. When warmed rain water or too much sunlight hits the stream on a regular basis, the higher than normal temperatures can lead to disease, reduced reproductive success, starvation, or even death. When one organism is negatively affected, it also affects the entire ecosystem. For example, trout eat insects. If insects die, then trout starve or leave the area in search of food. Haywood Waterways Association monitors water temperatures in a few streams in Haywood County. Several years ago, when there was a severe drought, they reported afternoon water temperatures in lower Richland Creek at 80°F.
Thermal pollution can be reduced by trapping stormwater and allowing it to cool down before it flows into streams or filters into groundwater. Examples of stormwater entrapment devices are retention ponds, rain gardens, underground cisterns, and rain barrels. Planting native trees and shrubs along stream banks can help shade the stream and slow runoff before entering streams. Diverting downspouts into the lawn instead of the storm drain will allow rooftop water to cool before it enters the storm drain or groundwater. Easy tips at home can help reduce thermal pollution in our cool mountain streams.
Image: WNCTimes
