Chesapeake Bay grasses are rebounding
CAMBRIDGE — A key indicator of the health of the Chesapeake Bay is prompting optimism from area researchers.
Since September 2017, underwater grasses began appearing near the University of Maryland Center for Environmental Science (UMCES) Chesapeake Biological Laboratory in southern Mar yland.
Their comeback after 45 years signals a major positive shift in the health of the Chesapeake Bay, according to a statement from UMCES.
“The Chesapeake Bay has turned the corner,” Peter Goodwin, president of UMCES, said. “In fact, it’s one of the large ecosystems in the world that has probably made the most progress.”
Since 1925, UMCES’s Chesapeake Biological Laboratory has occupied the peninsula in Solomons, where the Patuxent River flows into the Chesapeake Bay. The grasses haven’t been seen there since 1972.
“We’re very glad to report the largest resurgence of (Bay) aquatic grasses, due to management actions, ever recorded,” Bill Dennison said. He is vice president for science applications at UMCES.
According to a new study co-authored by Dennison, the resurgence of grasses here — and similar recent comebacks seen throughout the estuary in recent years — are the direct result of decades of efforts to reduce nutrient pollution in the Chesapeake Bay.
An analysis of more than 30 years of data shows that sustained management actions over the past two decades have reduced nutrient pollution in the Chesapeake by 23 percent since 1984 and have led to a resurgence of ecologically and economically important aquatic grasses.
Underwater grasses, also known as submerged aquatic vegetation (SAV), have regained 17,000 hectares to achieve the highest cover in almost half a century. A hectare equals 100 acres.
“What emerged from that analysis is that this nutrient diet is starting to pay real dividends in the resurgence of grasses around the Bay,” Dennison said. “We’re been calling these grasses our coastal canaries, the things that are most sensitive to water quality degradation, and the things we have to watch as long-term indicators of these water quality situations.”
Aquatic grasses are known as a sentinel species, an indicator of broader ecological function or an early warning of ecological impairment.
They are important ecologically, providing habitat for baby crabs and other creatures while protecting shorelines and stabilizing sediments so that erosion is minimized. They are also important economically since they are home for commercial species such as blue crab, silver perch, and striped bass.
Since 1950, the human population around the Chesapeake Bay has doubled, leading to changes in land use and adding to the substantial nutrient and sediment runoff from both urban and agricultural lands.
Increasing nutrient inputs fueled algal growth in the water that prevented light from reaching the Bay grasses, which grow along the bottom. These conditions also favored the growth of algae that grow on the leaves of the bay grasses themselves, further shading them from light. Tens of thousands of hectares of SAV were lost, the largest decline documented in more than 400 years.
Researchers from 10 institutions across the country analyzed 30 years of data to predict the impacts of people living near the Bay on submerged aquatic vegetation, an ecologically and economically viable habitat.
The study used aerial surveys from 1984 to 2015, monitoring data, historical information on land use and fertilizer application and watershed model estimates for the loads of nutrients and sediments from land runoff and point sources such as wastewater treatment plants.
The study confirmed that nutrients play a dominant role in reducing SAV cover.
Long-term nutrient trends show that water column nitrogen concentrations have declined on average by 23 percent, and phosphorus concentrations by eight percent since 1984, the biggest reductions occurring in the mid-1990s.
Declining nutrient levels coincided with a 316 percent, or fourfold, increase in SAV cover during the same period, from 7,878 hectares in 1984 to 24,874 hectares in 2015, based on aerial surveys.
“Concern for the overall health and economy of the Bay led to unparalleled cooperation among federal, state, local and scientific agencies whose joint efforts identified nutrient pollution and subsequent loss of SAV as the two most critical issues facing Chesapeake Bay,” according to a UMCES statement.
These agencies instituted measures to reduce nutrient inputs as well as longterm monitoring programs to gauge their effectiveness, established the Chesapeake Bay as one of the few places on Earth where comprehensive long-term data exist to link impacts and ecological restoration at broad scales, according to UMCES.
“This comeback of underwater grasses reaffirms that government and stakeholders can come together to set goals and implement management actions to make an impact on a large and complex coastal ecosystem,” Goodwin said. “These are sensitive indicators of the health of Chesapeake Bay, and it is important that these successful management strategies are continued.”
The study, “Long-term nutrient reductions lead to the unpredecented recovery of a temperate coastal region” was published in the March 5 Proceedings of the National Academy of Sciences by researchers from the Bigelow Laboratory for Environmental Science, Virginia Institute of Marine Science, University of Maryland Center for Environmental Science, Environmental Protection Agency Chesapeake Bay Program, U.S. Geological Survey, National SocioEnvironmental Synthesis Center, St. Mary’s College of Maryland, Smithsonian Environmental Research Center, Maryland Department of Natural Resources, and Texas A&M University Corpus Christi.
“UMCES leads the way toward better management of Maryland’s natural resources and the protection and restoration of the Chesapeake Bay,” according to www.umces.edu. “From a network of laboratories located across the state, UMCES scientists provide sound advice to help state and national leaders manage the environment, and prepare future scientists to meet the global challenges of the 21st century.”
Submerged aquatic grasses are making a comeback in the Chesapeake Bay, according to researchers at the University of Maryland Center for Environmental Science.