Weather-related declines in Upper Bay overshadow Mid-Bay bay grass increases

April, 2012 - Maryland’s bay grasses declined for the second year in a row, a result of extreme weather conditions in both 2010 and 2011. Bay grass coverage fell 14% from 40,053 acres in 2010 to approximately 34,461 acres in 2011. However, muddy waters from Hurricane Irene and Tropical Storm Lee delayed, and in some cases prevented, complete mapping in several sections of the Bay.

After several years of increase, bay grasses in the upper Bay (above Chesapeake Bay bridge) dropped by 34% in 2011. About 13,287 acres were mapped in Maryland’s portion of the upper Bay compared to the 21,353 acres in 2010. Most of the losses occurred on the Susquehanna Flats and the Elk and Sassafras Rivers on the Eastern Shore. Bay grasses in this area were affected by heavy early spring rains which created poor early season growing conditions. In late summer, both Hurricane Irene and Tropical Storm Lee again muddied the water again for over two months. While total acreage was lower in 2011 than 2010, the mapping in that portion of the Bay was conducted later in the season than usual (early November) when the plants naturally die-back. Some of the bay grass declines may have resulted from poor growing conditions resulting from very muddy water, but later than usual mapping also played a major factor.

Bay grasses in Maryland portion of the Middle Bay Zone, from the Chesapeake Bay Bridge south to the state line, increased by about 12%, from 18,700 to 21,174 acres offsetting the declines in the upper Bay. These numbers are estimates, however. Due to extremely poor water clarity in 2011, portions of the Patuxent and Potomac Rivers, were either not mapped during the aerial survey, or only partially mapped. In such cases, 2010 acreage values were used to estimate total bay grass acreages for the mid Bay.

Grass beds in Eastern Bay, Choptank, Little Choptank and Honga Rivers, increased by over 4,400 acres (139 %) in 2011. These areas are home to widgeon grass, a type of bay grass known for large annual fluctuations. The expansion of widgeon grass in the mid-Bay most likely resulted from lower than normal salinities, which allowed many more seeds to germinate, and also good mid-summer growing conditions as confirmed by State of Maryland monitoring.

Despite the widgeon grass increases, there was some bay grass loss in the mid-Bay (Tangier and Pocomoke Sounds and in the Manokin and Big Annemessex Rivers). These areas are dominated by eelgrass, a type of bay grass still recovering from a heat-related die-off in 2005. These declines resulted from higher than normal water temperatures in summer of 2010 and 2011, along with long-term declining water clarity.

The full impact of Hurricane Irene and Tropical Storm Lee on Maryland’s bay grasses will not be seen until the 2012 mapping is completed. As always, Maryland DNR biologists will continue to monitor the health of Maryland’s waters and underwater grasses since they are an important habitat in the Chesapeake Bay and provide food and shelter for many animals, including blue crabs, largemouth bass and canvasback ducks. Healthy bay grass beds also protect shorelines from erosion, produce oxygen and filter polluted water.

Restoring bay grasses and the Chesapeake Bay
Because bay grasses are sensitive to even small changes in water pollution, they serve as a key indicator of Chesapeake Bay health. Polluted runoff entering the Bay contains nutrients that can fuel algal blooms and sediments that block sunlight needed for bay grass growth. Further reductions in the amount of polluted runoff and sediment entering Maryland’s waterways are necessary for providing a clean and healthy Chesapeake Bay for all Marylanders, young and old.

Programs to plant cover crops, upgrade sewage treatment plants and septic systems, restore natural filters, conserve high priority lands, restore habitats and foster smarter, greener growth and living in Maryland will benefit bay grasses and the Bay’s other natural resources. Beneficial individual actions we can take include maintaining your septic system, sensible lawn care and planting trees and shrubs.

For more information, visit:
Bay Grasses: identification, importance and status www.dnr.maryland.gov/bay/sav
Restoring the Chesapeake Bay: Maryland’s Actions and Progress: www.baystat.maryland.gov
What can you do to help the Bay: http://www.dnr.state.md.us/bay/education/programs.html