Forget the lawn. The grasses are growing in the Rappahannock River — and that’s a good thing.
According to an annual survey released by the Chesapeake Bay Program, the area of the Bay covered by underwater grasses increased by 7%, to 82,937 acres. In the lower Rappahannock, beyond Fredericksburg, the grasses increased 43% between 2022 and 2023, achieving 90% of the program’s previous restoration target of 1,700 acres. The state’s new goal approved by the EPA is 5,500 acres.
Underwater grasses, or submerged aquatic vegetation (SAV), are a key barometer of the health of the Chesapeake Bay.
SAV is “absolutely a critical habitat for many of the creatures that you know are critical to the Chesapeake Bay and the Rappahannock River,” said Joe Woods, Virginia senior scientist at the Chesapeake Bay Foundation.
The Virginia Institute of Marine Science (VIMS) has been monitoring SAV since the 1970s using techniques like aerial imagery. The data collected is broken down by river and segments. For the Rappahannock, segments are based on salinity: the tidal fresh; the oligohaline (somewhat salty); the mesohaline (more salty); and polyhaline (the saltiest), at the mouth of the Bay.
“The most dramatic growth in SAV has been in that tidal fresh portion,” Wood said. “We went from seeing very little grasses, pre-2000 and now there’s a pretty substantial amount.”
In 2023, the polyhaline (very salty) zone experienced the largest amount of underwater grasses since 1997. Experts think a La Nina climate cycle is responsible for the growth since it brings below-average rainfall and cooler temperatures. Some species of underwater grasses — like eelgrass — cannot grow in waters that are too warm. The positive effects of water quality improvements are also a possible cause of the meadow expansions.
Over 180 volunteers in the Grasses for the Masses program brought out underwater bay grasses they had been growing in their homes for 10 weeks. The plantings were held on the James River at Westover Plantation and on the Potomac River at Mason Neck State Park in late April and early May 2008. Libby Norris led the planting demonstration. (Photo courtesy CBF).
“It’s been exciting to observe some tremendous expansion in some areas of the polyhaline with eelgrass growing at depths we haven’t seen in decades.” said Christopher J. Patrick, director of the SAV Monitoring and Restoration Program at VIMS. “We often call these plants ‘the canary in the coal mine for the Chesapeake,’ as they tell us a lot about how the Bay is doing.”
Wood said that although scientists can’t point to specific reasons why the SAV is returning to the tidal fresh portions of the Rappahannock, there are factors that contribute to any growth of underwater grasses.
“In general, we think addressing nutrients is going to drive SAV improvements,” he said. “And what gives me hesitance about saying we’ve made progress in the Rappahannock is we’ve had a 50% increase in phosphorus in the Rappahannock in the last 20 years… and a 10% increase in sediment.
“I would just point out that the Rappahannock is in a place where nutrient loads are increasing. That’s what the water quality is telling us, and SAVs are still going up. And that’s a little bit confusing.”
Healthy rivers with flourishing vegetation improve water quality and provide critical shelter and food for species like blue crabs, migrating water birds, and fish. A river or stream with little to no underwater grasses indicates the presence of pollutants and sediment because not enough sunlight can reach the plants. Underwater grasses act like the “antacids” of the Bay, diminishing the acidity of the water caused by agricultural runoff and untreated waste.
“Historically, the Rappahannock River has been a little bit more pristine than some of the other watersheds,” Wood said. “The Rappahannock is still degraded in terms of grasses — we have a fraction of what used to live there, and we have oxygen issues in the river.
“We can think about Chesapeake Bay restoration as a global issue, or a regional issue where other states play a big role. Certainly, there are vibrant, healthy communities that still exist there, but it’s got a long way to go, and we could have a much healthier system.”
Preventing pollution is key to addressing the issues facing both the Rappahannock and the Bay overall. According to Wood, the largest pollutants in the Rappahannock River come as a result of agriculture and development, and environmental efforts can focus on those sources.
“Whether it’s incentivizing farmers and producers to do things in a slightly different way that’s better for water quality,” said Wood, “or helping local governments to implement measures that prevent runoff, or whether it’s for a homeowner not falling in love with the lawn that’s green 365 days a year, and converting to trees and native plants that don’t require so much toxic stuff for our waterways — any of those are all important.”
The overall increase in SAV wasn’t experienced evenly across the Bay. Slightly salty areas of the Bay saw a major decrease attributed to algal blooms and sediment, while cooler water stemming from La Niña fueled a significant increase in the saltier Lower Bay’s underwater grasses.
No underwater grasses at all were mapped in the Elk River despite the tributary meeting its grasses goals repeatedly since 2000.
This year’s survey still represents a major decline from the 2018 survey, which estimated approximately 108,000 acres of grasses. But it does get the Bay closer to the Chesapeake Bay Watershed Agreement target of 185,000 acres of underwater grasses covering the bottom of the Bay and its tidal tributaries. The Bay states won’t meet many of the outcomes by the 2025 deadline set by the agreement.
This story has been updated to reflect the report came from the Chesapeake Bay Program and cite the program’s new state goals.
