Maryland Marine Notes: May-August 2000 Sidebar - Where Have All the Grasses Gone?

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

Where Have All the Grasses Gone?

^* Note: Total acreage mapped in 1999 was 64,689. More than 3,000 acres of bay grass beds mapped in 1998 were not fully mapped in 1999 due to extreme weather events. To account for those areas, the hatched area of the bar indicates the estimated additional acreage, for a total of 68,125.

Adapted from The Chesapeake Bay: How is it Doing?
(Maryland Department of Natural Resources)

The Chesapeake's underwater grasses reached their low point in the early and middle 1970s after Tropical Storm Agnes deluged the Bay in 1972, sending torrents of sediment down its rivers and main stem. With the immense volumes of fresh water and sediments came heavy concentrations of nitrogen compounds, in some cases two to three times normal levels. A report by the Chesapeake Research Consortium in 1974 inventoried the impact and concluded that next to oysters and soft clams, "the ecological group most depressed was submerged aquatic plants." Moreover, this storm of the century arrived at the worst possible time, says Bob Orth of VIMS, in June, at the height of the grasses' growing season.

But Agnes only magnified declines that had already begun more than a decade before in many areas, particularly the upper Bay, says Mike Naylor of the Maryland Department of Natural Resources and chair of the Chesapeake Bay Program's SAV Workgroup. "In the 60s and 70s, there were massive changes in farming practices," he says, "with heavy use of chemical fertilizers and pesticides." At the same time, he adds, "waste treatment flows doubled and tripled." In the Patuxent River, for instance, where vast grass beds had begun to die off in the 1960s, researchers began tracking immense amounts of nutrients coming in from runoff and from groundwater seepage, along with poorly treated wastes in sewage discharges, as major causes. Research in recent years has been detailing unexpectedly high amounts of nitrogen from airborne deposits, as much as 25 percent or more of the nitrogen entering estuarine waters like the Bay.

There are indications of grasses returning to some areas of the Chesapeake since the late 1970s, particularly in the upper Bay and western shore. How much of that return is due to natural recovery and how much to better controls on runoff and nutrient discharges remains an open question. A unique database may begin providing some answers over the next few years.

For two decades, VIMS has been using aerial photography, taking more than 2,000 photographs annually, to track the comings and goings of grassbeds, from the Conowingo Dam on the Susquehanna River to the mouth of the Bay. Each year, a cadre of researchers and citizen volunteers tromps through some 2,300 miles of shorelines to identify and ground truth species of grasses. With these data now in geographical information systems, VIMS has a rich lode of information that may help scientists and managers clarify just what effect restoration efforts are actually having.

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