The Chesapeake Bay’s grass beds, once devastated, are making a comeback.
A study published this week in the Proceedings of the National Academy has documented a three-fold increase in the amount of bay bottom and its tributaries covered by the beds.
It’s gone from 7,000 hectares of grass in 1984 to about 25,000 hectares now, said Jonathan Lefcheck, the lead author of the study. That’s enough grass to cover New York City’s Central Park three times over.
Lefcheck, from the Bigelow Laboratory for Ocean Science in Maine, said the 14 scientists involved linked together data sets on water quality, development, farming practices and other activity within the bay’s 64,000 square mile watershed.
And what the data shows, he said, is "that the thing that really dives the cover of underwater grass in the Chesapeake Bay is nutrients. Too much nutrients is a bad thing for grasses."
The nutrients come in many forms, most prominently in the discharges from sewer plants and the run-off from farm fields.
Fortunately, Lefcheck said, upgrades to sewage treatment plants and the bay’s pollution diet have reduced the amount of nutrients flowing into the bay and its tributaries.
The nutrients lead to algae blooms that suck the oxygen from the water, show up as scum on the surface and keep light from getting to the grasses.
The grasses are important because they capture sediment, help clean the water and provide nurseries for many of the bay’s most important species, crabs for example.
J.J. Orth, from the Virginia Institute for Marine Science, says people may not understand about the life cycle of crabs. They hatch off the coasts of North Carolina and Virginia as creatures so small you can barely see them, then swim into the lower bay and settle in the grass beds to mature before they eventually wind up on somebody’s plate.
The grass beds are "the iconic place for an iconic species," said Orth, another author of the study.
Jennifer Keisman, from the U.S. Geological Survey and another author, says the study clearly demonstrates that reducing nutrients in the bay works.
"When we reduce those nutrient concentrations in the water, then the bay does respond, and it gets healthier," she said. "But we’re not there yet."
Bill Dennison from the University of Maryland’s Center for Environmental Science and another one of the authors, said they call the grasses "our coastal canaries" because they’re most sensitive to changes in the environment.
The resurgence of the grass beds, he says, shows "we have gotten the right trajectory and we can point the finger to the fact that his has happened as a result of nutrient reductions."
But that doesn’t mean the mission has been accomplished, he added. "Just because we’ve lost a little weight, as we would with a human diet, we don’t just go and binge eat. We have to continue the diet."
But that progress could be threatened, he and the others say, by President Trump’s plan to write the federal Chesapeake Bay Program out of his budget. The Bay program’s $73 million budget helps creates partnerships with state and local governments and NGOs, Dennison says. It provides the support "for people on the ground to get on with the business of cleaning up the bay."