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Chesapeake Bay News

Archives: November 2006


Cover Crops: One Key to Reducing Nutrients to Bay

It's no secret that agricultural runoff in the Bay watershed contributes a significant amount of nitrogen and phosphorous to Bay waters. Excessive amounts of these nutrients spur harmful algal blooms that deplete dissolved oxygen levels, block out sunlight needed for bay grasses and, in some cases, produce toxic chemicals that can cause fish kills.

Farmers have been using cover crops as one way to reduce the amount of nutrients that end up in the Bay. Cover crops, which are planted in the fall after the autumn harvest, usually consist of cereal grains like wheat, rye and barley that continue to grow during the winter.

Once established, cover crops absorb excess nutrients in the soil and reduce erosion from rain, snow and wind. For every acre of farmland planted with cover crops, an estimated 6.2 pounds of nitrogen and nearly one-quarter of a pound of phosphorous is prevented from reaching our waterways, according to Bay scientists.

Enrollment in cover crop programs has risen steadily over the past several years, showing farmers' support of the initiative. Besides for the notable benefits to Bay health, cover crops also help farmers by retaining nutrients and increasing organic matter in the soil. They also help block out noxious weeds and can inhibit weed seeds from germinating.

State and federal Bay Program partners have recognized the importance of making cover crop programs available for farmers and are expanding existing programs and developing new ones to meet the increased demand. For example, Maryland has more than doubled its funding for cover crop programs to a record $8 million and 290,000 acres.

Runoff from farmland is one of many factors that contribute to high amounts of nutrients and low dissolved oxygen levels in the Bay. Increased use of cover crops each winter is one way to lessen the human environmental footprint on the Bay and support the restoration of a healthy, balanced Bay ecosystem.


Too Much of a Good Thing

Nutrients are generally considered to be a good thing for humans because they are necessary for our health and strength. But just like anything else, too many nutrients can be too much of a good thing. In fact, excess nutrients are the main cause of the Bay's degraded water quality and aquatic habitat loss.

Nutrients occur naturally in air, water and soil. However, in addition to these natural sources, vehicle exhaust, treated sewage and runoff from urban, residential and agricultural areas all contribute nutrients to the Bay and its tributaries.

Together, these sources send too many nutrients to the water, causing serious problems:

  • Excess phosphorus and nitrogen cause rapid growth of phytoplankton, causing algal blooms that reduce sunlight to bay grasses.
  • Algae eventually sink and decompose, which depletes bottom waters of dissolved oxygen (DO). Without enough oxygen, fish and other underwater species die.

This summer, high nutrient levels were responsible for harmful algal blooms and low DO levels that led to fish kills in several Bay tributaries, including:

  • in the Potomac River, where more than 8,000 fish died due to a combination of algal toxins and anoxic waters that sloshed into shallow areas due to a high wind event.
  • in the Corsica River, where a similar fish kill occurred for the second year in a row. High nutrient levels to the river caused a harmful algal bloom to form. As the algae decomposed, DO levels dropped and 2,000 fish died. In comparison, 30,000-50,000 fish were killed after last year's bloom.

Bay scientists have found that reducing nutrient loads to the Bay in spring is critical to improving water quality conditions. The majority of nutrients are washed into the Bay in spring as snow melts and larger amounts of rain fall on the watershed. Planting cover crops in the fall and skipping spring fertilizer are two important ways people can reduce the amount of nutrients that enter the Bay.

Keywords: fish kill
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