The amount of underwater grasses in the Chesapeake plunged 44 percent over the last three years, leaving the Bay with its lowest coverage of the crucial plants since 1986 — about the time cleanup efforts began.
Aerial survey data from 2012 show that submerged aquatic vegetation, or SAV, acreage dropped 21 percent from the previous year, to 48,191 acres. It was first time Baywide underwater grass coverage declined for three consecutive years since the annual survey began in 1984.
More worrisome is that no single factor is driving the downward trend. Instead, scientists blamed multiple causes, including lingering effects from Tropical Storm Lee, which buried the Upper Bay with sediment in 2011; warm temperatures; and worsening overall water clarity.
"It's a pretty abysmal story," summed up Bob Orth, a scientist with the Virginia Institute of Marine Science who oversees the annual survey. "There were very few bright spots."
Just four years ago the Bay had 85,914 acres of grasses, the second highest amount reported in recent decades.
Underwater grasses need clear water to get the sunlight they, like all plants, need to survive. Because of that tight link to water clarity, the annual SAV survey is one of the most closely watched indicators of how the Bay is doing.
Grass beds are also one of the most critical components of the Bay ecosystem. They pump oxygen into the water, trap sediments, provide food for waterfowl and shelter for fish and blue crabs.
By studying old aerial photographs taken of the Bay, scientists believe the Chesapeake contained about 185,000 acres of grasses during the first half of the last century.
With rapid increases in population, development and nutrient pollution in the decades after World War II, the amount of grasses dramatically declined. Sediment washing in from cleared land clouded the water, as did the algae blooms fed by huge increases in nitrogen and phosphorus running off farms or discharged from wastewater treatment plants.
Tropical Storm Agnes in 1972 wiped out much of what was left, leaving just 38,228 acres when the aerial survey began in 1984.
Nutrient and sediment reductions required by the Chesapeake Bay Total Maximum Daily Load, or pollution diet, are intended in part to create water clear enough to again support 185,000 acres of grasses.
Lee Karrh, a biologist with the Maryland Department of Natural Resources and chair of the Bay Program's SAV Workgroup, cautioned against reading too much into the Baywide trend, noting that grass beds in some areas have shown an ability to bounce back rapidly.
"We probably shouldn't make too much out of it just yet," Karrh said. "It is worth being concerned about. But the sky hasn't fallen."
Less than two decades ago, the Upper Bay's Susquehanna Flats were mostly barren and scientists held out little chance for recovery. Now, lush beds occupy the area. Even after three years of decline, these beds remain the largest and healthiest in the Chesapeake.
While greatly reduced in size by a torrent of sediment washed in by Tropical Storm Lee in September 2011, Susquehanna Flats still covers thousands of acres and is capable of pumping out large amounts of seeds and plant parts, known as propagules, which can help the bed expand as well as provide a seed source to revegetate nearby rivers where grass beds were buried in the aftermath of Topical Storm Lee.
"There was a lot of seed production last year," Karrh said. "My gut feeling is that there is plenty of capacity to rebound."
But in looking at the Baywide data, he acknowledged, "It's going to be challenging to hit 185,000 acres."
Scientists monitoring Bay grasses divide the Chesapeake into three regions, the Upper, Lower and Mid Bay, each of which has its own unique characteristics. Things such as salinity changes sometimes harm species in one area but benefit those in another. Karrh noted that it is unusual for all three zones to decline in the same year.
But the Upper and Mid Bay regions have declined for three consecutive years while the Lower Bay has declined for two. Last year:
- In the Upper Bay, which stretches from the head of the Chesapeake to the Bay Bridge, underwater grasses decreased 32 percent from 13,287 acres in 2011 to 9,087 acres last year. Since 2009, grass coverage in the upper Bay has decreased 61 percent.
- In the Middle Bay, which stretches from the Bay Bridge to the Rappahannock River and Pocomoke Sound, acreage fell 28 percent, from an estimated 34,142 in 2011 to 24,522 acres. Since 2009, grass coverage in the Middle Bay has declined by 38 percent.
- In the Lower Bay, which is south of the Rappahannock River and Pocomoke Sound, acreage decreased 7 percent, from 15,654 acres in 2011 to 14,582 acres last year. Over the last two years, underwater grass acreage in the Lower Bay has decreased 36 percent, after being largely unchanged from 2009 to 2010.
The overall trends — especially in the Mid and Upper Bay — suggest the difficulty in meeting the 185,000-acre goal. "Not in my lifetime," Orth said, "unless a miracle happens."
Prior to the dieback over the last three years, grasses in the Upper Bay had largely occupied their potential habitat, leaving little room for further expansion.
In the Mid Bay, there has been no trend the last two decades, and grass beds in the Lower Bay have been trending downward since the mid-1990s. Most of the potential underwater grass habitat is in the Mid and Lower Bay. Reaching the Baywide goal means those areas would need dramatic rebounds; but both face challenges.
Unlike the Upper Bay, where many low-salinity plant species thrive — 13 are found in the Susquehanna Flats alone — the Mid and Lower Bay have much less diversity.
Prior to Tropical Storm Agnes, many Mid Bay beds contained three or four grass species, which helped make them resilient. Each species tolerates a slightly different set of conditions, so when one was knocked back another was available to take its place. Now, Mid Bay beds are dominated by widgeon grass, a species notorious for its year-to-year fluctuations. Without other species to provide stability, the beds come and go based on the boom-and-bust nature of widgeon grass.
Unfortunately, other species present in those areas were so completely removed by Agnes that there are few seed sources to spur their comeback. In the rare cases where other types of grass have shown up, they have quickly died back because of poor water quality. Efforts to bring those species back have, in many instances, had little success.
The outlook in the high-salinity areas of the Lower Bay is the most worrisome. Eelgrass is the dominant species in that area, but it likes cool temperatures. As Bay water has warmed over the last decade, the large, stable eelgrass beds that once dominated the region have been dying back.
Poor water clarity has increasingly forced eelgrass out of the deeper, cooler water where it once thrived and into water less than a meter deep near the shore, which also tends to be warmer, Orth said. "It's a double whammy," he said. "This Bay warming is going to be a challenge for eelgrass."
He also noted that the aerial survey may underestimate the severity of eelgrass loss in the Bay. Surveys done last year in grass beds that had been examined over a period of years revealed that some beds that historically consisted primarily of eelgrass were increasingly dominated by widgeon grass, the only other species in the Bay that tolerates high salinities.
"We were shocked in 2012 at how much eelgrass we've lost in these areas where it is mixed with widgeon grass," Orth said. That means the Lower Chesapeake is becoming increasingly dependent on a species that widely fluctuates in abundance.
"When you have widgeon grass, which is boom or bust, you are going to have whole systems where all of a sudden there is nothing, and next year it is everywhere," he said. "To rely on the presence of that species for a very large portion of the Bay as an indicator of water quality is going to be challenging."
Improving water clarity could help grasses, especially eelgrass. Clearer water means it's easier for plants to get the sunlight they need for photosynthesis so they can conserve more energy and better withstand other stresses, such as heat.
But water clarity has been worsening in much of the Bay, and scientists are uncertain exactly why. Nutrient reductions are aimed at improving clarity by controlling algal growth. Yet scientists said that clarity was worsening even in some places where monitoring shows levels of chlorophyll a — a measure of algae in the water — seem to be improving. They said that highlighted the need for stepped-up monitoring to better understand factors impacting grass beds.
Nonetheless, Orth noted that in small coastal bays on the seaside of Virginia, where temperatures are slightly cooler and the water is clearer, eelgrass is thriving. "They are not declining the way the Bay is," he said.
Nick DiPasquale, director of the EPA Chesapeake Bay Program Office, echoed the call for improved water quality, saying in a statement that "this year's data is a sobering reminder of how imperative it is to continue our restoration efforts."
DiPasquale said the latest SAV data showed "both cause for concern and encouragement; while the declines are worrisome, there are still some signs of resilience in the Bay. It is good to see the Susquehanna Flats underwater grasses remaining hardy and exciting to see emerging beds in the James River."
Indeed, despite the strong downward Baywide trend, the aerial survey data did provide good news in a handful of places. Perhaps most notably, was the mainstem of the James from Richmond to the mouth of the Chickahominy River.
After being mostly devoid of grasses for decades, the survey showed beds in that area had more than doubled, from 32 acres to 67 acres.
"The James has been dominated by point source pollution for many years, and that is the place where we've made the most progress," said Bill Street, executive director of the James River Association. "I think it shows that if we are able to make some progress, we can continue to see those improvements."
The Chesapeake Bay Program has created a new dynamic online mapping tool that anyone can use to see how the Bay's underwater grasses have changed in location, abundance and species over the last 30 years. Visit: www.chesapeakebay.net/visualization/baygrasses/.
Information about SAV in the Bay and 2012 survey results are also available on the VIMS website at http://web.vims.edu/bio/sav/index.html.
New SAV strategy to focus on smaller restoration projects
Scientists hope to learn more about what conditions are needed by grass beds to survive.
With underwater grass beds in a downward trend, a new strategy from the Bay Program outlines new research, protection and restoration efforts needed to revive these critical habitats.
In a sharp contrast to the last strategy, written a decade ago, it scales back calls for large plantings of new grass beds in favor of smaller projects where scientists hope they can learn more about conditions needed for underwater grasses to survive.
But the strategy's overriding goal remains the same — like the previous strategy, it says it is "essential" that jurisdictions achieve the Bay water clarity goals that produce the minimum light requirements necessary to achieve 185,000 acres of underwater grass beds.
Like all plants, submerged aquatic vegetation, or SAV, needs light to survive, and today's murky Bay makes many historic habitats off-limits. Achieving Baywide nutrient and sediment reduction goals is considered an overriding objective for the widespread recovery of underwater grass beds.
The strategy also says that regulatory programs need to protect existing grass beds from disturbances, including dredging, boating, fishing or other activities that directly affect grass beds. In addition, it said that particularly important beds should be identified and get extra protection. It also calls for efforts to minimize disturbances to grass beds from exotic species such as mute swans or water chestnuts.
In a significant change, the strategy also calls for regulatory programs to protect from disturbance potential SAV habitat — areas where underwater grass beds were once present but do not exist today.
"We have enough problems reaching 185,000 acres," said Lee Karrh, a biologist with the Maryland Department of Natural Resources and chair of the Bay Program SAV Workgroup, which wrote the strategy. "If we are reducing that footprint where that grass once occurred by building something over the top of it, it makes it that much more challenging. Now you have to find different areas to reach your goal."
The largest change in the strategy is the smaller SAV planting goal. The 2003 strategy had called for planting 1,000 acres of grasses by 2008, or 200 acres a year. Only about 150 acres ended up being planted, largely because of a lack of funding. Most of those planted in the Bay died, although large plantings in coastal bays on the seaside of Virginia thrived.
The new strategy calls for planting at least 20 acres a year Baywide, and sets forth rigorous monitoring requirements so scientists can better understand why plantings in the Chesapeake succeed or fail.
"The ultimate goal is to make a habitat difference locally, and also learn how to apply the lessons learned at a much larger scale in the future," Karrh said. "If you don't learn something from your activities and do it better in the future, you are just wasting your money."
Indeed, the strategy emphasizes the need for increased water quality monitoring and research to bolster underwater grass levels, which are now at a 26-year low. Much of the monitoring in the Bay and its tidal rivers is conducted in channels, far from the shallow water where underwater grasses grow, and studies suggest water clarity can be significantly different in those near-shore areas.
The strategy notes there has been "virtually no funding" for SAV restoration research in the last five years, but says ramped-up studies are needed to understand impediments to restoring SAV in unvegetated areas.
Bay water clarity goals are based on research that identified the extent of water quality needed to maintain existing beds. But restoring grasses in barren areas may require even better water quality. "Once we determine what those restoration requirements are, we will be in a much better position to know if it is possible, if it is practical, to try large-scale restoration again," Karrh said.
In addition, past projects have indicated that other factors, such as sediment type, waves, the condition of nearby shorelines and disturbances in the watershed may also affect the ability of grass beds to survive. Understanding how all of these factors influence grass bed regrowth is "not going to be easy, but it is going to be huge," Karrh said. "It will be a very big piece going forward."
The strategy also calls for research to better understand how climate change and sea level rise will affect underwater grass beds, and the extent to which grasses will be able to adapt to those changes. In particular, eelgrass in the Lower Bay has been shown to be sensitive to warmer water and scientists are worried about its ability to persist in the Chesapeake.
Because they are out of sight to many people, scientists often consider underwater grasses to be an unappreciated habitat — one author described them as the "ugly duckling" of coastal ecosystems. The strategy calls for increased efforts to improve public awareness and understanding of the importance of underwater grass beds.