A May 23 Metro article incorrectly identified the organization that issued a report on underwater grasses in the Chesapeake Bay. The report was issued by the Chesapeake Bay Program, a partnership of state governments and the U.S. Environmental Protection Agency, not by the Chesapeake Bay Foundation. (Published 5/25/04)

The Chesapeake Bay Foundation released a study last week showing that underwater grasses in the bay had declined by about 30 percent between 2002 and 2003. This was the sharpest one-year drop since scientists started tracking the grasses in the early 1980s. Maryland's section of the bay suffered even more, losing 41 percent of its grasses.

Scientists said the biggest reason for the drop was extraordinarily high rainfall. This washed pollutants from farms, cities and sewage plants into the bay, where they fed algae blooms that cut off sunlight for the plants.

W. Michael Kemp, a professor at the Horn Point Laboratory of the University of Maryland Center for Environmental Science, answered questions from staff writer David A. Fahrenthold. Kemp referred to the grasses by the acronym SAV, for submerged aquatic vegetation.

QWhy are these grasses so important to the Chesapeake Bay?

AThere are many reasons why these underwater grasses are important to the bay:

* They provide habitat for many fish and invertebrates, including commercially valuable species such as the blue crab. Juvenile fish and molting crabs use the grasses as a refuge from predation to increase their survival rate to adulthood.

* The grasses help to buffer nutrient levels, helping to keep them from stimulating excessive algal blooms, and the bacterial communities that live in association with the grass roots actually help to convert nutrients into unusable forms. These processes help to minimize the negative effects of over-fertilizing the bay.

* The canopy of the bay grasses enhances the sinking of suspended particles from the water to the sediments. This tends to make the water clearer. In areas where dense grass beds exist, you can often see a dramatic improvement in water clarity over the beds compared to adjacent areas without these plants. Clearer water makes everyone happy (except maybe the fish that are trying to hide from their predators), especially the grasses themselves because it ensures that they will receive more sunlight for photosynthesis.

What's the prognosis for this year?

So far, river flow has been relatively low this year, and the water appears to be clearer. Therefore, I am optimistic that there will be substantial recovery of widgeon grass this year. . . . As far as we know, many of the widgeon grass beds in our area (Choptank River, Eastern Bay, Honga River) did go to flower and produce seeds last year. So we assume and hope that there will be sufficient seeds for the beds to be re-established this summer.

What can be done to remedy the situation in the future?

The existing SAV beds in the bay are a mere fraction of what was here prior to 1960. At the top of the list of factors that led to the decline throughout the bay is poor water quality resulting from inputs of [algae-feeding pollutants] and other materials from human activities in the watershed. There will be no significant recovery of SAV until we do something to improve these conditions. There will continue to be year-to-year variations in SAV abundance resulting from changes in rainfall and river flow. . . . The occurrence of wet years like 2003 should serve as wake-up calls for us to be reminded that we are a long way from achieving the lofty goals that are outlined in the Chesapeake Bay 2000 agreement.

W. MICHAEL KEMP