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A relative of hydrilla, Brazilian elodea grows in mats once it is established. It can clog rivers, but it helps capture
Friends of the Rappahannock Executive Director John Tippett shows patches of Brazilian elodea in the river.
BELOW: Native grasses mix with mats of elodea, providing a nursery and home for fish and other aquatic life. |
By RUSTY DENNEN
An invasive weed related to hydrilla has gained a foothold in the Rappahannock River above Fredericksburg.
"I was out last week and I was stunned at how rapidly it has covered large portions of the river," said John Tippett, executive director of Friends of the Rappahannock. "The [river] has changed dramatically in just one season."
He's talking about Brazilian elodea, a close relative of the hydrilla that has clogged waterways from Potomac Creek in Stafford County to Washington.
Once the plant gets established, it forms mats that can change the ecology of the river. But it's not all bad--it's a nursery and hiding place for fish and other aquatic creatures, and it encourages growth of native grasses.
"I'm conflicted about it," said Tippett, who first noticed some patches last year.
On one hand, weeds like hydrilla and Brazilian elodea tend to take over. But they also capture sediment, improving water clarity and quality.
"I am seeing several times more native wild celery between Motts [Run] and [FOR headquarters] than I ever have," Tippett said. "It will be fascinating to see what happens over time."
Tippett said that benefit has also been noted on the Potomac River.
He is familiar with hydrilla. "I used to run the harvester on the Potomac in the late 1980s," he said. Barges equipped with paddle wheels and cutters are used like lawn mowers to clip the hydrilla in areas that become too clogged for boat traffic.
Tippett also worked in a lab studying organisms that live within hydrilla beds.
One day last week at a spot along River Road in Spotsylvania County, he pointed out patches of native wild celery and sago pondweed among the green swaths of Brazilian elodea.
Tippett took some samples in for identification at FOR. Virginia Cooperative Extension also examined samples and confirmed the identification.
Hydrilla and Brazilian elodea "are so similar that the only way to tell the difference is with a magnifying glass," Tippett said.
Since there has been no comprehensive sampling on the Rappahannock, "We don't know yet if all of it is elodea, or if there may be hydrilla there, too."
He added: "That may be more of an academic interest than anything else, because they are both aggressive invasive species. I can attest to it being full of life."
How Brazilian elodea got into the river is unknown, but it is a common aquarium plant. It spreads when fragments break off and root.
John Odenkirk, a biologist with the Virginia Department of Game and Inland Fisheries, said the vegetation is a good sign for the Rappahannock.
"It's been a head-scratcher for a long time. We've never understood why there aren't more grasses in the Rappahannock," he said. "You look at other rivers like the Shenandoah, with star grass, and the Potomac, with hydrilla, and you say, 'What's up?'"
As a result, the Rappahannock is less productive than other rivers in terms of fish populations and their growth rates.
Odenkirk suspects that the amount of sediments running into the river might create less hospitable growing conditions for aquatic grasses.
Still, this is "a banner year" for submerged aquatic grasses, he said.
As for the invasiveness, "Overall the net impact on the ecosystem has been positive."
Odenkirk added: "Fishermen love it. It's always teeming with fish."
Rusty Dennen: 540/374-5431
Email: rdennen@freelancestar.com
| Brazilian elodea, native to South America, is a commonly used aquarium plant that has spread to waterways across the United States. Similar in appearance to hydrilla and to the native Elodea canadensis, or common waterweed, it can reach lengths of 6 feet and can grow in water depths of up to 20 feet. It spreads when shoots break off and root. |
