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Underwater Hydrilla Plant Not as Harmful as Thought
When it was discovered in the Potomac River in the early 1980s, the exotic plant Hydrilla verticillata was seen as the ecological equivalent of suburban sprawl. Environmentalists feared that the fast-growing Asian import would crowd out less aggressive native plants that are important sources of food for waterfowl.
But a new study by the U.S. Geological Survey has found that hydrilla is not such a bad neighbor after all. The submerged plant, which can grow to the surface and form dense mats, did not impair the reemergence of native species at a time when officials were working to reduce nitrogen concentrations in the river from sewage-treatment facilities, the study found. Cutting nitrogen levels reduces algae blooms and allows more light to get to the bottom of the river, which in turn permits aquatic plants to grow.
Hydrologists Nancy B. Rybicki and Jurate M. Landwehr of the USGS examined data between 1985 and 2001 in aquatic plant beds in the Potomac.
"As hydrilla increased, the other plants increased," Rybicki said. "In a particular year, if the water quality was good and the plants increased, not only did one species increase, the others increased as well."
The hydrilla also has been a boon to waterfowl, which eat the plant's tubers, a kind of underground stem, in the winter, Rybicki said. The research appears in the May issue of the journal Limnology and Oceanography.
-- Christopher Lee
Ring of Dark Matter Found Around a Galaxy
Scientists believe they have found a ring of mysterious dark matter surrounding a distant galaxy -- a potential breakthrough in identifying the most widely distributed but least understood particles in the universe.
Using the Hubble Space Telescope, astronomers identified the ghostly ring that they said was created by the long-ago collision of two galaxy clusters. The dark matter itself was not visible -- it does not shine or reflect light -- but it left a distinct "footprint" in the shapes of background galaxies. Although the presence of dark matter has been detected before, it has always been far more interspersed among the hot gases and galaxies that make up galaxy clusters.
"This is the strongest evidence so far for the existence of dark matter," said astronomer M. James Jee of Johns Hopkins University. He likened dark matter to the wind -- which we cannot see except through its effects on other objects.
