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Underwater grasses show some improvement in Chesapeake Bay

Underwater grasses show some improvement in Chesapeake Bay

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In 2021, an estimated 67,470 acres of underwater grasses were mapped in the Chesapeake Bay and its tidal tributaries, achieving 37 percent of the ultimate restoration goal of 185,000 acres, according to new data from the Chesapeake Bay Program.

And it is likely that more underwater grasses grew in the Bay in 2021 than the mapped acreage suggests. Adverse weather conditions, such as frequent rain and cloudy water, prevented researchers from successfully collecting imagery over the Mattaponi and Pamunkey rivers.

While underwater grass abundance did increase by almost 9 percent from 2020 to 2021, the preliminary acreage observed in 2021 is still a slight decrease from the long-term average of 69,623 acres, and approximately a 38-percent decline from 2018, when it was estimated that the Bay might have supported up to 108,078 acres.

“The last few years have been difficult in so many ways – and no less so for our underwater grasses and the animals that rely on them for habitat.

It’s a testament to our management actions and the resilience of the Chesapeake that our underwater grass acreage began to increase again in 2021,” said Brooke Landry, who chairs the Chesapeake Bay Program SAV Workgroup and is a natural-resource biologist at the Maryland Department of Natural Resources.

Although the overall gain in acreage “wasn’t extraordinary,” Landry said there were remarkable increases in some very important areas and provide “inspiration and hope that we can and will – one day – achieve our ultimate underwater grass goals and outcomes and get our Bay back to where it needs to be.”

Underwater grasses in the Chesapeake Bay are measured and calculated each year by an aerial survey conducted by the Virginia Institute of Marine Science. In some instances, satellite imagery may be used to complement the results from the aerial survey.

The Chesapeake is grouped into four different salinity zones to better reflect the various communities of underwater grasses that are found in the Bay. All of the salinity zones experienced increases in underwater grass acreage from 2020 to 2021, but the largest was observed in the very salty waters at the mouth of the Bay.

These gains are largely due to widgeon grass, which fluctuates year-to-year depending on the weather and changes in water quality. Widgeon grass experienced a heavy decline in this portion of the Bay in 2019, and while we are observing its active recovery in this region, it continues to decrease in other portions of the Bay, such as the moderately salty waters of the mid Chesapeake.

Underwater grass abundance can vary from species to species and river to river. In 2021 data, local highlights included:

• Northern Maryland: Underwater grass abundance in and around the Susquehanna Flats region increased from 9,200 acres in 2020 to 10,331 acres in 2021. However, the Elk River decreased from 613 acres in 2020 to 190 acres in 2021.

• Middle and Eastern Chesapeake Bay: Underwater grass acreage in the Little Choptank River continued to decline, dropping from 551 acres in 2020 to 175 acres in 2021. Likewise, the Choptank River to its north decreased its acreage from 4,562 acres in 2020 to 4,132 acres in 2021. The Eastern Bay did not fare much better, declining from 840 acres in 2020 to 507 acres in 2021. On the middle Western shore of the Bay, the Severn and Magothy rivers both saw significant decreases in underwater grass acreage. The Severn declined from 294 acres in 2020 to 227 acres in 2021, while the Magothy decreased from 124 acres in 2020 to 59 acres in 2021.

• Mid-to-Lower Chesapeake Bay: In the Virginia portion of the mid-to-lower Bay, underwater grasses did particularly well in the Corrotoman and Rappahannock rivers, as well as in Mobjack Bay. The Rappahannock, which includes the Corrotoman, increased from 2,204 acres in 2020 to 3,235 acres in 2021. In Mobjack Bay, underwater grass acreage increased from 7,440 acres in 2020 to 8,355 acres in 2021.

Like grasses on land, underwater grasses need sunlight to survive. When the waters of the Chesapeake Bay become clouded with algae blooms or suspended sediment, sunlight cannot reach the bottom habitat where these grasses grow.

While healthy grass beds can trap and absorb some nutrient and sediment pollution – thus improving water clarity where they grow – too much pollution can cause grass beds to die off. High water temperatures, turbulence from strong storms and drought can also affect the growth and survival of underwater grass beds.

“The importance of underwater grasses is undeniable, both for the health of the Bay and for the 18 million people who live within the Chesapeake Bay watershed .”said Meredith Maloney, Environmental Center director and citizen-science program director at the Havre de Grace Maritime Museum.

“The health and longevity of bay grasses begins with all of us – goals cannot be met without the help of volunteer monitors, advocates and environmentally conscious residents of the watershed.”

The Chesapeake Bay Program is a regional partnership that has coordinated and conducted the restoration of the Chesapeake Bay since its formation in 1983. Partners include the U.S. Environmental Protection Agency, representing the federal government; the U.S. Department of Agriculture; the states of Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia; the District of Columbia; the Chesapeake Bay Commission; and advisory groups of the public, scientists and local government officials.

For information, see the Website at chesapeakebay.net.

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