U.S. Department of the Interior
U.S. Geological Survey
News Release
May 18, 2007 Nancy Rybicki 703-648-5728 nrybicki@xxxxxxxx
Jurate Landwehr 703-648-5893 jmlandwe@xxxxxxxx
Exotic Hydrilla Benefits Chesapeake
Bay’s Ecosystem
Editors: “Long-term changes
in abundance and diversity of macrophyte and waterfowl populations in an
estuary with exotic macrophytes and improving water quality,” is available
online in the May issue of ASLO:
Limnology and Oceanography,
v 52, pages 1195-1207.
An exotic species of aquatic vegetation
that was deemed a severe nuisance when it began rapidly colonizing the
Potomac River, has instead benefited the watershed’s ecosystem, according
to a study by the U.S. Geological Survey (USGS) published in the journal
Limnology and Oceanography.
The robust exotic hydrilla first
appeared and began to flourish in the fresh water reaches of the tidal
Potomac River just as management investments to reduce nutrient loads from
sewage treatment plants were beginning to take effect. Submerged
aquatic vegetation is an important ecosystem resource for fish and waterfowl
and it was feared that the expansion of hydrilla would impair the reemergence
of native species, but this has not proven to be the case.
“Before and during the seventeen-year
period of the study, restoration of the Potomac has focused on reducing
nitrogen loads entering the river system and the Chesapeake Bay,” said
USGS scientist Nancy Rybicki, who with colleague Jurate Landwehr were curious
how the emergence of hydrilla would affect the benefits sought for by management
investments.
Shortly after it first appeared
in the Potomac in 1983, hydrilla produced dense vegetation masses and,
in some areas, impeded boat traffic and water sports." More significantly,
it was feared that hydrilla would interfere with native vegetation, which
is important for waterfowl, such as black duck, a signature species in
this area.
Using information from annual field
surveys and aerial photographs, Rybicki and Landwehr created a data base
to document bed-by-bed which species of vegetation were found in different
sections of the Potomac River system. They recorded the percentage
of total coverage and biomass each species attained annually. In
comparing species coverage with water quality composition, they discovered
that, with the reduction of nitrogen concentration in Potomac River, hydrilla
coverage expanded but so did the diversity of plant species found in the
River. Hydrilla did not crowd out native species; indeed, native species
increased. In addition, hydrilla is a good winter food source for
waterfowl communities, which have increased significantly over this period.
“This research is the only long-term,
quantitative study of aquatic plant biodiversity following the colonization
of an exotic species in an estuary where millions of dollars are spent
annually to reduce nutrient input and it demonstrates that exotics are
not always harmful to an ecosystem,” said Rybicki.
"Furthermore," Landwehr
pointed out, "the methods developed for this study are transferable
to any ecological assessments that need to merge remotely-sensed spatial
coverage with field observations."
The findings support current federal
and state management strategies to improve water clarity and reduce nutrient
loads to: enhance aquatic vegetation coverage; increase waterfowl habitat;
and protect biodiversity of the existing native community.
The study was conducted as part
of the USGS Chesapeake Bay studies, which is providing integrated science
to for effective conservation and restoration of the Bay ecosystem. The
USGS is a federal partner in the Chesapeake Bay Program, the federal-state
partnership to restore the Bay ecosystem. More information can be found
at http://chesapeake.usgs.gov
USGS provides science for a changing
world. For more information, visit www.usgs.gov.
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Diane Noserale
Media Relations, Eastern Region
U.S. Geological Survey
150 National Center
Reston, VA 20192
phone: 703-648-4333
fax: 703-648-4588
