COASTAL wetlands can actually increase the amount of pollution reaching
beaches.
Stanley Grant, a researcher at the University of California at Irvine, has
found that artificial wetlands can collect bacteria from birds and animals and
then release the potentially harmful organisms into the sea.
Wetlands are an important habitat for wildlife. They can also help remove
harmful metals, excess nutrients and bacteria from the environment. Talbert
Marsh in the Los Angeles metropolitan area was drained over the last century.
But in 1992 it was restored with the opening of a drainage channel. As well as
providing a wildlife habitat, the artificial saltwater marsh takes storm water
from the city streets and, after 40 minutes, passes cleaned-up water out to
sea.
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To find out how well Talbert Marsh is doing its job, Grant compared the
amount of enterococcal bacteria鈥攁n indicator of faecal
contamination鈥攅ntering the wetland with the amount flowing out to a nearby
beach. He was surprised to find the marsh discharged more enterococci than
flowed in from city streets. 鈥淲e discovered that the marsh was generating
bacteria rather than removing them,鈥� he says. Bacteria levels were so high that
the beach had to be closed, he reports in a future issue of Environmental
Science and Technology.
By setting up cameras to monitor wildlife, he discovered the elevated levels
of bacteria were down to a large flock of gulls that routinely defecate in the
marsh.
Jack Fancher, a coastal biologist with the US Fish and Wildlife Service,
cautions against extending Talbert鈥檚 faecal problem to artificial wetlands in
general. He says the bacterial overload is due to a sandbar at the mouth of
Talbert Marsh that attracts large numbers of gulls. Knocking out the sandbar
would solve the problem, Fancher says.
But wetland scientists say monitoring should be done to guard against similar
situations elsewhere.