The drought that devastated crops and forced water restrictions throughout the region has resulted in a bumper crop of Bay grasses, one of the most important habitats in the Chesapeake.
Aerial surveys of the Bay last year have revealed the greatest amount of “submerged aquatic vegetation” — and the strongest single-year increase — measured since the surveys began in 1983.
Because of the terrorist attacks of Sept. 11, 2001, pilots were blocked from flying over and photographing roughly 15 percent of the Chesapeake. Nonetheless, recently produced figures documented 77,805 acres of the underwater meadows in the areas that could be surveyed.
That surpassed the previous high mark of 73,000 acres measured in 1993.
Scientists believe thousands of additional acres of grasses were thriving in areas they couldn’t observe, potentially putting the Baywide total over the 85,000 acre mark.
They credited the drought for much of the increase. Dry conditions that have persisted for the past several years have reduced the amount of nutrients and sediment-laden runoff from the watershed that fouls water quality and blocks critical sunlight from reaching the grasses.
“When you look at these numbers, they basically say that if you clean up the Bay, and you keep it clean, the Chesapeake is very resilient,” said Bob Orth, a researcher with the Virginia Institute of Marine Science who oversees the annual survey. “We’ve got to keep the pressure on getting the Bay cleaned up.”
He and others believe that when figures from 2002 become available, they will show a continued increase because of the drought. “Almost every place that we have looked, there was more this year than the year before,” Orth said. “We will probably see a general increase.”
Complete comparisons between 2001 and 2000 are not possible because the entire Bay could not be surveyed last year. In areas that were examined in both years, the amount of underwater grasses expanded by 27 percent.
If 2001 had the same amount of grasses in unmapped areas as were observed in those areas the year before, the Baywide total would grow by another 7,447 acres to 85,252 acres.
Even that number may be low, because scientists working in boats observed especially robust beds in areas that could not be mapped from the air, including parts of the Upper Bay near Aberdeen Proving Grounds.
“I think the number was better than we were able to show,” said Mike Naylor, of the Maryland Department of Natural Resources and the chair of the Bay Programs SAV Workgroup. “Some systems that were particularly good didn’t even get photographed because of the flight restrictions.”
Expanding grass beds has long been a major Bay Program objective because they are considered crucial habitat for many Bay species. They provide food and shelter for juvenile fish, clams and crabs — densities of young blue crabs can be 30 times greater in grass beds than in unvegetated areas. Grasses are also important food for waterfowl.
Some believe that as much as 600,000 acres of grasses may have once blanketed the Chesapeake, growing at water depths of more than 6 feet in places. But in recent decades, degraded water quality, largely caused by increased nutrient runoff, has caused huge declines in the historic grass acreage. They hit a low of about 37,000 acres in 1983. Excess nutrients increase the growth of algae that block the sunlight needed by the underwater grasses.
After underwater grass acreages climbed steadily in the late 1980s, peaking in 1993, grass coverage fluctuated between 60,000 and 70,000 acres through 2000, showing no Baywide trend, although beds tended to show improvement in the upper and lower Chesapeake.
Last year’s number was driven by a huge increase in the middle part of the Chesapeake, and upper and lower parts of the Bay showed significant gains as well.
By region, the 2001 figures show:
- In surveyed areas of the Upper Bay, which extends from the Susquehanna River to the Bay Bridge, grass coverage increased 10 percent over 2000.
- In the Middle Bay, which stretches from the Bay Bridge to the Rappahannock River and Pocomoke Sound (including the Potomac River), acreage surged 49 percent.
- In the Lower Bay, grass acreage grew 7 percent.
The huge increase in the Middle Bay reflected a rebound from 2000, when an unusually dense mahogany tide persisted for weeks during the spring, totally blocking the light to many mid-Bay grass beds.
Some areas lost all of their grasses, including hundreds of acres that vanished in the lower Chester River and thousands of acres in the Eastern Bay. Overall, the grasses in mid-Bay had declined by 9 percent from 1999 to 2000.
“It is interesting how rapidly the plants can come back when the conditions are right,” Orth said. “It shows there is hope that if keep the Bay on track to be cleaned up, I think we can get our grass beds back to reasonable levels within a relatively short period of time.”
But he and others cautioned that much of the mid-Bay gain consisted primarily of widgeon grass, a species notorious for widely fluctuating from year to year. Should rainfall return to normal levels and nutrients increase, it is likely the area could see a die-back in the future.
“I won’t be surprised at all if we have a decrease next year,” Naylor said. “Middle Bay is the area that is the least predictable.”
Nonetheless, he and others note that as grass beds become larger, and denser, they will become more stable over time and more able to resist adverse conditions than smaller, more sparse grass beds.
Bigger, denser beds also produce more seeds and reproductive tubers which not only help to maintain the beds, but also create surpluses that can be moved around by currents or animals, helping grasses to colonize unvegetated areas when suitable conditions occur.
“The more seeds and the more tubers you have out there, the better you are going to be able to respond to whatever happens,” Naylor said.
As part of its effort to develop new water quality standards for the Chesapeake, the Bay Program is developing the region’s first-ever water clarity standard aimed specifically at increasing the amount of light available for underwater grasses. The hope is to create conditions that will allow for the further expansion of the grass beds.
New nutrient and sediment reduction goals aimed at achieving that, and other new water quality standards, are expected to be unveiled by the end of April.
In the meantime, the Bay Program has an interim goal of achieving 114,000 acres of grasses by 2005.
The Bay Program is also producing a new strategy for increasing the abundance of grass beds around the Chesapeake.
In addition to calling for improved water clarity, the strategy will outline the need for protecting existing grass beds, accelerating restoration activities such as the planting of new beds, increasing funding for SAV-related activities, and enhancing research and public education activities.
The annual Baywide grass estimate, made for the Bay Program by the Virginia Institute of Marine Science, is derived from the analysis of more than 2,000 black-and-white aerial photographs taken between May and October.