Maryland Marine Notes: May-August 2000 Spotlight - Restoring Bay Grasses to the Chesapeake: A Long Way Back

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Volume 18, Numbers 3-4 • May-August 2000

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Contents Restoring Bay Grasses to the Chesapeake: A Long Way Back Where Have All the Grasses Gone? Understanding Grass Habitat SAV Information on the Web From The Director
Water requirements to restore grasses baywide have probably become more stringent than before their initial declines Hydrilla verticillata		When Peter Bergstrom of the U.S. Fish and Wildlife Service recently visited the Severn River near Annapolis to check on the condition of what had been a large area of underwater grass, he was surprised at what he found. "There was almost nothing there," he says, "a few patches the size of a patio table." Since 1994, the grasses had been making a remarkable comeback. Mostly widgeon grass, along with redhead grass, sago pondweed and wild celery, their return was attributed by many to improved water quality conditions brought about in part by the Critical Areas law, which restricted clearance of trees near shorelines and presumably reduced runoff of sediment and nutrient pollution. Moreover, the Severn, unlike such rivers as the Choptank and Patuxent, does not have sewage plants discharging nutrient wastes, treated though they may be, into its waters. "We were patting ourselves on the back," Bergstrom says. Until this year, that is. What happened to the grasses? "It may have been some combination of drought and rain," he says. But precisely what "combination" remains open to speculation. Further down the Bay, in the higher salinity waters of Tangier Sound, the story is reversed. Between 1993 and 1998, underwater vegetation, largely eelgrass, had continued to decline until reaching a low of some 6,600 acres, down from 18,000 acres in years prior to 1993. This past year, however, grass acreage expanded dramatically: the 1999 aerial survey, conducted by researchers at the Virginia Institute of Marine Science (VIMS) since the 1980s, showed more than a 60 percent gain to some 10,600 acres. Though factors having to do with freshwater runoff might account for the turnaround, scientists and resource managers didn't predict it. The situations in the Severn River and Tangier Sound provide two examples of the challenges that bay grass restoration efforts in the Chesapeake have faced over the last 20 years. Vast meadows of underwater grasses, some 600,000 acres, once flourished throughout the Chesapeake system. Water stargrass, wild celery, southern naiad, redhead grass, coontail, waterweed and muskgrass, eelgrass, widgeon grass, sago and horned pondweed and a score of others. This lush vegetation provided important habitat and food for fish, other aquatic organisms and waterfowl. At the same time, it helped promote water clarity by absorbing nutrients, trapping sediments, slowing currents which can scour the bottom and resuspend sediments, and by producing oxygen. Except for scattered grass beds in various parts of the Bay – for instance, the Susquehanna Flats, areas of Eastern Bay and Mobjack Bay – much of that diversity is now gone. While restoration of submerged aquatic vegetation (SAV) has been a key goal of the Chesapeake Bay Program, its success has depended on stopping the immense volume of nutrient and sediment runoff throughout the Bay and its network of feeder streams, creeks and rivers. Nutrients stimulate the growth of algae, or phytoplankton, in spring and summer – with warming water temperatures and longer hours of sunlight, algal growth can become so extensive that thick blooms blanket vast stretches of water. This dense algae, combined with sediments in runoff and erosion, as well as resuspended sediments churned from the bottom, block the transmission of light, vital to the growth of SAV. While submerged grasses are self-sustaining in some areas, overall their recovery seems to have reached a plateau over this last decade, ranging between 60,000 and 75,000 acres a year; this is about a tenth of the former acreage and still far short of the Bay Program's first tier goal of restoring 114,000 acres by 2002 to nearshore areas that currently have only sparse or no vegetation. Longer-range goals call for eventual restoration to the 600,000 acres that once covered bottom grounds and in some areas helped make Bay water nearly transparent to depths as much as 10 to 12 feet. Ironically, baywide recovery of SAV seems stalled in a catch-22: healthy, sustainable bay grass communities require good water quality conditions, especially light; meanwhile, good water quality conditions require healthy, sustainable bay grass communities. This means that bringing SAV back on a baywide scale is even more difficult than it would be if water quality were not so poor and vegetation not so spotty. As Michael Kemp of the University of Maryland Center for Environmental Science (UMCES) Horn Point Laboratory and Chris Madden of South Florida Water Management District have written, water quality requirements to restore underwater grasses baywide have probably become "more stringent than before their initial declines."
"Water quality constituents alone are not sufficient to describe SAV coverage."		Setting Water Quality Goals To develop realistic strategies for curtailing runoff for SAV restoration, resource management agencies need specific water quality goals that they can aim for. In 1992, the Chesapeake Bay Program released Submerged Aquatic Vegetation Habitat Requirements and Restoration Targets, a report that took the first steps in detailing conditions that would promote SAV growth. The technical synthesis, as it was called, aimed at determining minimum water quality conditions necessary for survival and propagation of underwater grasses in the Chesapeake. With these conditions as the goal, state and federal agencies could then develop management policies – particularly in targeting limits on runoff. The synthesis drew on 15 years of research data such as extensive monitoring of grass beds and water quality conditions in the Bay system where SAV was flourishing. Grasses in lower salinity areas of the Potomac, for example, saw a resurgence during the 1980s – while not extensive, their recovery was strong, and accompanied by an increase in plant diversity as well. In part, this recovery resulted from the inadvertent introduction of Hydrilla verticillata, a fast-growing, non-indigenous species often considered a nuisance and referred to by some as aquatic kudzu. "Hydrilla started modifying shallow water environments," says Bob Orth of VIMS, "and that made it possible for other species to survive." Those positive conditions, according to the synthesis, relied on minimum water quality requirements for (1) inorganic nitrogen, (2) inorganic phosphorus, (3) water column light attenuation coefficient (a gauge of water clarity), (4) chlorophyll (an index of algal biomass) and (5) total suspended solids. In other words, the technical synthesis set the standards that sediment and nutrient reduction efforts would need to meet. "This synthesis was a great step forward," says Richard Batiuk of the U.S. Environmental Protection Agency. "It gave management agencies scientifically defensible numbers to aim for," he says, "numbers that we wouldn't have had otherwise – it is the only reason these standards were adopted by the Chesapeake Bay Program." It was also an example, he adds, of how the relationship between management and science can really pay off. Still, there were a number of factors that the synthesis did not account for – while it highlighted the requirements for salinity zones, it did not take into account differences among grasses adapted to low salinity waters and those that grow in higher salinities. It is not possible to generalize about such requirements for all grass species and all habitats, says Bob Orth. "You're dealing with different species and each is adapted to different needs of light, salinity and nutrients. Think about all the varieties of grass growing on your lawn," he says. "Some want more shade, others more sun; some require more fertilizer, others less." In other words, Orth says, "there are species-specific differences." And these are important differences, he adds, that we need to consider in developing plans for SAV restoration. There were also limitations to the water quality measures themselves. For instance, they were unable to predict the recovery of vegetation, what Nancy Rybicki of the U.S. Geological Survey (USGS) calls, "the variation in SAV coverage." How many of the five requirements had to be met? Why did some areas consistently have grass but fail the water quality requirements? Studies in the Potomac River by Rybicki and colleagues at USGS showed that "water quality constituents alone are not sufficient to describe SAV coverage." In analyzing data in the Potomac River between 1983 and 1996, they have since found that coverage of SAV for the previous year is an important factor in explaining the extent of coverage in any given year. Nor did the five water quality conditions account for light that actually reaches leaves. In many regions, even if enough light penetrates the Bay's dark waters, grasses may still not "see" that light because of the microscopic plant growth (epiphytes) and sediment grains that can cover their leaves. Epiphytes cling to leaves and compete for nutrients and light – unless grazed by other organisms, they can sheathe leaves and further block available light, preventing photosynthesis. Researchers have long known that epiphytic growth was a key factor in limiting light that leaves actually absorb. Studies have shown that in tidal fresh and low salinity regions, they can diminish light 20 to 60 percent more than what is lost when light passes through water. It is only in the last few years, however, that scientists have been developing the ability to relate epiphytic growth to water quality conditions.
" A particular threat lies in the loss of plant biodiversity... Years ago, we had multiple species."		New Synthesis Refines Water Quality Goals Over the last decade, researchers have been tackling some of the difficult questions that the 1992 synthesis could not then deal with. How much light needs to reach leaves in order for them to grow? In waters where light is not penetrating to the bottom, how much of the dark water is due to suspended solids, how much to nutrients, how much to algae? To address these questions for the purposes of management, the Chesapeake Bay Program recently completed a second technical synthesis that consolidates much of the research of the last ten years (see SAV Information on the Web). For example, Charles Gallegos of the Smithsonian Environmental Research Center has summarized studies on distinguishing the different optical properties of suspended sediments, algae and nutrients in the water column by how they absorb or reflect light. He has developed a set of diagnostic equations that can provide management with different options for targeting reductions of chlorophyll and suspended solids. While these equations do not account for all factors that affect the availability of light, they offer an overall view of the magnitude of the reductions that are needed and some of the tradeoffs available. Meanwhile, from other research, including studies supported in part by EPA's Multiscale Experimental Ecosystem Research Center (MEERC) at the University of Maryland Center for Environmental Science (UMCES), Mike Kemp and Rick Bartleson of the UMCES Horn Point Laboratory have developed a mathematical model that predicts epiphytic growth, or how much light reaches a leaf based on measurements of depth of light, total suspended solids, and dissolved inorganic nitrogen and phosphorus. Studies have shown that in mid- and high-salinity waters, underwater vegetation like eelgrass needs at least 15 percent of surface sunlight to grow. If we see that we are only getting 10 percent sunlight, says Batiuk, we know we may have to reduce runoff. Is the main problem sediment, nutrients, algae? Though not foolproof, we can now provide some answers, Batiuk says. Gallegos' equations can tell us how much we have to reduce total suspended solids or chlorophyll. One strategy may fit the lower James River, for example, while another works for the lower Potomac. In the lower James, for instance, most of the darkness may be coming from suspended sediments – perhaps in runoff – in contrast to chlorophyll (or algae). In the lower Potomac the bigger problem may be algae. "We can use the tools we now have to make a diagnosis," says Batiuk, "and, like a doctor, write a prescription for what we need to do." It is such work that the technical synthesis has brought together. "We've taken a step we couldn't take in 1992," says Batiuk. If the standards in the new synthesis are adopted, they are likely to serve as a basis for states in the Bay watershed to develop regulations that, river by river, will place maximum discharge and runoff limits. The synthesis report will be printed and distributed after final editorial corrections have been made.
		Restoration May Be Slow As much of an advance as this second synthesis is, there are still other factors that can affect SAV growth, among them, waves and sediments, animal grazing and disturbance, and propagation patterns, whether by seed or propagules, says Michael Kemp. Moreover, as Bob Orth has said, this is a system still on the edge. A particular limiting factor, he points out, lies in the loss of plant biodiversity. It is likely, according to Orth, that before the widespread decline in grasses got underway in the 1960s, which was then followed by the devastating impact of Tropical Storm Agnes in 1972, the Bay enjoyed – and relied on – a much greater plant diversity. In years of heavy rains and greater runoff, plants more tolerant of suspended sediments or lower salinity or lower light conditions might outcompete other less-adapted species. "What makes things different now is that years ago we had many areas that had multiple species so that in a wet year, for example, one species might dominate and in another year, another species would. In the Honga River," says Orth, "the amount of eel and widgeon grass and sago pondweed were all abundant. What we see now is that many areas that had diverse beds no longer do." Added to the loss of diversity has been the continuing clearance of land for development, which has left many creeks and streams over the last 50 years more vulnerable to runoff surges that can overwhelm the most adaptable species. "There are so many conduits for putting water into the Bay system quickly," says Richard Batiuk. And with that water comes eroding land and a flood of sediments and nutrients. One thing is certain – in order to ensure healthy ecosystems in the Bay, we need to restore grasses, not only to the initial 114,000 acres by 2002 set as a goal by the Bay Program, but to levels approaching those that existed before the steep declines of the 70s began. The new synthesis will provide a better chart for guiding our efforts – but will it mean that we have turned the corner at last in our striving to restore the Bay? We can't be sure yet, but above all, we have to keep going, says Orth, who has been conducting research on SAVs since the 1970s. "Every little step we take makes a difference. Our job will never be over. We must not give up." The illustrations of SAV, by Karen Teramura, were published in the U.S. Army Corps of Engineers booklet Identification Guide to Submerged Aquatic Vegetation of the Chesapeake.

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