BALTIMORE — From Turkey Point to the Bay Bridge, water clarity in the Chesapeake Bay improved suddenly in June and July, a summertime mystery the reasons for which are as unclear as the rest of the Bay.
In some rivers, including the Magothy and South on the western side of the Bay and the Chester and Corsica on the Eastern Shore, the water also has cleared. Bay scientists are pondering the few clues they have — blooms of long strands of macroalgae in the Bay and an explosion of a type of small mussel in some rivers.
“I think that’s something we’ll be sorting through here for a while,” said Peter Tango, chief of quantitative ecological assessment for the Maryland Department of Natural Resources (DNR).
For the first half of the year, water clarity was average or below average at Turkey Point, across from the Aberdeen Proving Ground. In June, it was about 100 percent better and by July, about 200 percent better, setting a record of 1.9 meters, or about 6 feet, Mr. Tango said.
Seeking an explanation, researchers talked to watermen, who said the macroalgae are so thick in some places that it is preventing them from crabbing, Mr. Tango said.
The macroalgae may be helping improve the water quality by trapping sediment, Mr. Tango said, but Bay scientists haven’t figured out why they appeared this year.
While an abundance of rain is being credited for lowering salinity and spurring the growth of the mussels, the macroalgae grow in varieties that can tolerate a range of salt levels.
“It’s a tough one to call,” Mr. Tango said.
State officials also have been receiving several calls about increases in Bay grasses and vegetation, all good signs for the health of the Bay. Whether the reports are actually good news or another sign of ecological distress has not been determined, he said.
“It’s nice to see these changes in the water quality. Definitely it’s benefiting grasses in some regions, but we need to better understand … how all this is interacting before we can say how good it is,” Mr. Tango said.
The mussels are helping water quality because they are filter feeders.
They consume the microalgae that are spurred by pollutants such as nitrogen and phosphorous that find their way into the Bay from farms, lawns, power plant exhausts and other sources. Blooms of microalgae cloud the water and rob oxygen from the Bay when they die and decompose.
Chris Judy, DNR’s shellfish program director, said he recently jumped into the South River near the Riva Road bridge in Anne Arundel County below Annapolis and found the mussels covering the pebble bottom “like a thick, crunchy carpet.”
In the Magothy, above the Bay Bridge, the mussels weren’t able to attach to the sandy bottom, but instead coat man-made structures such as bridge pilings. The explosion of dark false mussels, however, is being found only in areas where lower salinity and other conditions favor their growth, Mr. Judy said.
Although water clarity was very good near the Riva Road bridge, the water was cloudy just downstream. The explosion of mussels also may be short-lived, but it does show the benefit of such filter feeders to the Bay, he said.
“It’s important to keep it in perspective,” Mr. Judy said. “We see that they’re doing a good job, and what it says is the Bay needs an abundant bivalve population.”