Mosquito Mayhem in the Marshes!
EverythingWestport.com
Sunday,
September 07, 2008
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The eastern salt marsh mosquito seems to have the coastal area residents
along either side of lower Horseneck Road in Dartmouth and Westport fit to be
tied as multiplying mosquito populations stalk area inhabitants, harshly biting
exposed and unprotected legs and arms. The pesky, thinner mosquito with the
silver streaks is a day feeder, adding to the misery of its hosts.
The eastern
salt marsh mosquito, Aedes sollicitans,
is a severe biter of man, and is found in grass salt marshes just like those at
Allens Pond. “An unfortunate combination of heavy rains in July and an inlet
blockage enhanced the breeding ground potential in Allens Pond,” said Gina Purtell, Director of the Allens Pond Sanctuary. “The
blockage prevented an important exchange of water between the pond and the
ocean, resulting in less salinity in Allens Pond, threatening a normally healthy
coastal salt pond ecosystem.”
Mosquitoes
can begin to multiply in any standing water that remains for more than four
days. Brackish water favors this particular mosquito’s development.
“Allens
Pond is a ‘coastal salt pond,’ supporting many unique plant and marine species
including bait fish,” said Ms. Purtell. “These fish
are largely responsible for controlling mosquito populations by eating the
mosquitoes’ larvae.”
According
to the Woods Hole Research Center, “A coastal salt pond is a shallow marine
embayment that receives freshwater inflow from groundwater entering the head of
the pond, and saltwater inflow through an inlet from the sea. The inlet is
periodically opened and closed by the shifting of barrier sands. Tidal and
groundwater inflows mix to form a salinity gradient in the pond. Much of the
pond's plant and animal life is segregated along this gradient, because
different organisms prefer different salinities. However, conditions will vary
greatly with the opening and closing of the inlet, and
some organisms will not survive the sudden changes in salinity.”
“When the inlet is closed for a long
period of time there will be large-scale die offs among the plant and animal
communities, and massive decay will give off unpleasant odors and make the pond
unsightly. When the pond is reopened by a breach in the barrier beach the
organisms adapted to the fresher water conditions will then die off due to the
increasing salinity levels.”
A stressful time for Allens Pond
“Allens pond is under stress,” said Lauren Miller-Donnelly Allens Pond
Sanctuary’s property manager. “The marsh grass is suffering. You can see its fall
colors (reddish-brown tinge) ahead of schedule (see photo above left).” Without an open inlet to the sea, the
flushing action by the ocean’s tides so vital to the health of the pond can’t
occur. “Allens Pond was becoming eutrophic, loosing
oxygen and creating a dead zone that would not be able to support marine life,”
said Ms. Miller-Donnelly. “Allens Pond has suffered channel blockage before and
local residents know the resulting stench can be horrible.”
Blocked
inlets on Little Beach (pictured left)
aren’t a recent problem as every four or five years the ocean’s tides will
shift enough sand to obstruct the channel. Summer tides carve sand from the
western edge of the channel and deposit it on the eastern edge, essentially
shifting the channel westward a bit more every year until it reaches a headland
that resists scouring. The combination of these two natural phenomena
periodically blocks the channel, at which point, humans step in and dig a fresh
channel back at the eastern-most point.
That’s when
the Allens Pond Association under permits from the Army Corp of Engineers (ACOE) contracts out to have the channel reopened.
An
ambivalent attitude toward the problem by the state and the Town of Dartmouth
forced the formation of the Allens Pond Association whose members, mostly
property owners around Allens Pond including the Audubon Society, had to
organize and periodically reopen the channel at their expense. “It seemed every
four to five years we were seeking permits to dredge a channel from the Army
Corp of Engineers,” said Bob Cunningham of the Allens Pond Association.
This year
there was a problem. “When we applied for a permit in late spring, we were told
some of the permitting conditions had changed,” said Mr. Cunningham. “Usually the
contractors deposit the dredged sand next to the dunes on the eastern edge of
Little Beach, extending the dune line. Now the ACOE
wants the sand deposited and spread out over the beach, in essence replenishing
the shoreline. No sand can be deposited below the high tide water mark.”
Unfortunately,
the new permitting process was lengthy, and many regulatory bodies were
involved in the process. The Audubon Society, although not involved in the
permitting process, helps facilitate communication between agencies and
applicants in this case. “Coordinating all the authorities is a rigorous task,”
said Mr. Cunningham. The necessary permit to reopen an inlet on the eastern
side of Little Beach has yet to be granted.
“A while
back we identified an endangered plant species, “sea beach knotweed”, on Little Beach,” said Ms. Purtell. “We quickly had volunteers go out and flag the
plants. None of them interfered with the dredging operation.”
Bristol County Mosquito Control
steps in.
Complaints
were poring in to the Dartmouth Conservation Commission, Dartmouth Board of
Health, and the Bristol County Mosquito Control. “We sent out an excavator in
July to extend an existing mosquito control channel through the shoreline on
the western edge of Little Beach,” said Wayne Andrews, Superintendent.
“Unfortunately it closed up in a few days.”
Left to
right: (1) The excavator opens a channel starting from inside the shoreline;
(2) the channel moves back to the ocean. A small dam is left in place; (3) the
dredging complete, the dam is removed and the pond water rushes to the sea!
Exacerbating
this whole problem was the fact that recent testing in North Westport by the
Massachusetts Arbovirus Surveillance program had
found a positive mosquito result for the West Nile Virus. The mosquito species
found is culiseta melanura,
which feeds primarily on birds not humans, and emerges from cedar swamps, not
salt marshes. “So far, the eastern salt marsh mosquito has not been found to
carry the virus,” said Ms. Purtell.
Under a
general ACOE permit, Bristol County Mosquito Control
is allowed to maintain and extend an existing mosquito control trench on the
western edge of Little Beach without seeking additional permits.
On August
29th the excavators were back on the job, this time with heavier
equipment to dig a larger inlet. “The trench has to be wide enough and deep
enough to sustain heavy exchanges of water without collapsing on itself,” said Steve Burns of Bristol County Mosquito Control.
“It’s always tricky to dredge a new channel.”
Left to
right: (1) Bridget Barkley (left) with friends; (2) BCMC
Superintendent Wayne Andrews speaking with a local resident; (3) Lauren
Miller-Donnelly of Allens Pond Sanctuary (left) with 50 year resident Joe Veiga and Association member (center), and Steve Burns of BCMC.
Bridget
Barkley, summer resident on Little Beach, and her friends were kayaking in the
pond. “I’m glad they’re doing the temporary dredging,” she said. “We certainly
look forward to their doing a more permanent job on the east end of Little
Beach.”
“We had to
close the inlet in 2003 to protect the pond due to the Buzzards Bay oil spill,”
Ms. Miller-Donnelly said. “It was nice to have that option when you need it.”
“We knew
there was a problem down here,” Ms. Purtell mused.
“The Least Terns, common and others, had left perhaps in part because of bad
fishing. Usually the Terns hang around the beach and even come in from other
beaches to gorge on the bait fish!”
Superintendent
Andrews thought for a moment. “Unfortunately, I believe we would have had
increase in mosquito population in spite of the channel issue. The heavy
thunderstorm activity this summer placed a lot of pressure, with heavy rains,
on Allens Pond. The phragmites, an
invasive large perennial grass, create a lot of decaying material,
forming a spongy mass which retains water, creating a breeding ground for
mosquitoes.”
Editor’s note: The inlet remains
open at the time of this writing, and appears to be performing up to
expectations.
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