Blue crab in widgeon grass. Photo copyright 2010 Jay Fleming/iLCPPhoto © 2010 Jay Fleming/iLCP

Underwater Grasses

There are more than a dozen varieties of underwater grasses, also called submerged aquatic vegetation or SAV, that grow in shallow water regions of the Bay and its rivers. At its most pristine, the Bay may have supported several hundred thousand acres of underwater grasses. Since the 1950s, there has been a tremendous decline of grass beds due to degraded water quality. CBF is working to help meet the Bay-wide goal of 185,000 acres of underwater grasses covering the bottom of the Bay and its tidal tributaries. 

Importance of Underwater Grasses

  • Underwater grasses filter polluted runoff, provide food for waterfowl, and provide essential habitat for blue crabs, juvenile rockfish (striped bass), and other aquatic species. 
  • Underwater grasses are one of the best barometers of the Bay's water quality because they are associated with clear water, and their presence helps improve water quality. Their leaves and stems baffle wave energy and help settle out sediments. Their roots and rhizomes bind the substrate. 
  • Underwater grasses also take up nitrogen and phosphorus that, in overabundance, lead to algae blooms that can degrade water quality. Decomposing underwater grasses provide food for benthic (bottom-dwelling) aquatic life. 
  • Migrating waterfowl, such as ducks and geese, rely on underwater grasses for food. 

Threats

Like most grasses on land, underwater grasses require sunlight to grow and thrive. When the Bay's waters become clouded with sediment from stormwater runoff and algal blooms resulting from excess nutrients in the water, grasses find it harder to survive.

Restoration Status: Mixed

  • 1972—Huge amounts of rainfall and runoff caused by Tropical Storm Agnes dealt a devasting blow to many grass beds. Underwater grasses continued to decline to a documented low of 38,000 acres in 1984. 
  • 1984 to 1993Underwater grasses increased to 73,000 acres.
  • Early 2000sUnderwater grasses were on the rise due to prolonged drought, which kept pollutants from the land locked in the soil. In 2001-2002, grasses increased to 90,000 acres in the Chesapeake Bay and its tributaries.
  • Mid 2000sData collected in 2008 showed Bay grasses covering 73,063 acres, or 39.5 percent of the 2010 185,000-acre Bay restoration goal. The 2008 data show an 18 percent increase in underwater grasses from 2007.
  • 2010 to 2012 Extreme heat in 2010 led to a significant decline in grasses in the lower Bay in 2011 and coverage dropped to an estimated 63,074 acres. High spring rains, Hurricane Irene, and Tropical Storm Lee all created poor conditions for growth in 2012 and coverage dropped again to an extimated 48,191 acres.

Solutions

In Bay restoration we don't often see straight-line progress, and the recent decline in underwater grasses in the Bay is a sobering reminder that extreme weather can set back recovery. It also reminds us that we need to focus on the elements we can control, especially reducing pollution to the Bay and its rivers and streams.

Though we can't control Mother Nature, reducing pollution—including better managing stormwater runoff before it gets into rivers and streams—will help mitigate weather extremes, improve water quality, and contribute to Bay grass revival. Virginia, Maryland, Pennsylvania, the other Bay states, and the District of Columbia all committed to reducing pollution from all sources as their part of their Clean Water Blueprint.

All of CBF's activities—from land-use planning and stormwater management to wetland protection and riparian buffer planting—contribute to Bay grass revival.
Where water quality is good enough to support underwater grass survival, hands-on restoration efforts can help establish, expand, or diversify grass communities.
CBF's Grasses for the Masses program engages volunteers in Virginia in growing wild celery in homes, schools, and businesses to transplant at appropriate restoration sites. CBF hopes its simultaneous efforts to improve water quality and restore and protect underwater grasses will start an "ecological chain reaction" in which improved water quality promotes grass growth.

Bay grass abundance 1984-2012 / Chesapeake Bay Program Chesapeake Bay Program

Progress is being made, but many local waterways and the Chesapeake are still polluted. If we don't keep making progress, we will see more signs declining grasses numbers, and we will continue to have polluted water, human health hazards, and lost jobs—at a huge cost to society.

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