As scientists study more about the Chesapeake Bay ecosystem, they discover more evidence that links air and water. It’s now known that air pollution can contribute nitrogen and toxic chemicals to land and to water. That pollution is carried in the form of rain or snow, which eventually becomes groundwater.

Fluctuations in climate patterns influence the amount of precipitation that falls. But even a small amount of precipitation can have a great impact in the Bay watershed. Drops of rain carry air pollution as they hit city streets, picking up sediment pollution as they trickle into a storm drain. Other drops hit farmland, absorbing fertilizers. Eventually, these nutrient-rich drops find their way into the Bay’s tributaries.

It’s estimated that the Bay’s nine largest tributaries contribute 93% of the total freshwater that enters the Bay. However, drops of rain that fall today may not make it into those tributaries or the Bay for five years or more. This natural, slow process by which water travels on land is called groundwater lag time. For example, runoff from storm events can infiltrate the ground before reaching a stream, can move with groundwater, then can eventually seep back into streams, rivers and the Bay.

Nutrients from urban and agricultural sources enter the ground water and streamflow that discharge into the Chesapeake Bay. Once in the Bay, the overabundance of nutrients causes algal blooms, which block sunlight and lower dissolved oxygen levels. Image courtesy S. Phillips / USGS

Lag time can have an impact even when there’s no precipitation. In the Bay watershed, several cities and towns use groundwater as a source for their public water supplies. During times of drought, a lack of precipitation eventually disrupts supplies of groundwater.

Though it’s impossible for humans to control the climate, we can make the precipitation she gives us a little "cleaner" before it seeps into the Bay’s tributaries. Any actions to reduce the amount of nutrients in the air and on land will help. And, once water is in the ground, grasses, vegetation, trees and roots (buffers) next to waterways can trap sediment pollution before the water reaches streams and rivers. This is another reason to help protect and restore streamside forest buffers in the Bay region.

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For more information, contact the Chesapeake Bay Program Office:
410 Severn Avenue, Suite 109, Annapolis, MD 21403 / Tel: (800) YOUR-BAY / Fax: (410) 267-5777.

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Last modified: 02/04/02