INFOTERRA: News: Wetlands Shown To Remove Selenium from Farm Runoff
[The journal from with the research is cited can be accessed at:
http://pubs.acs.org/journals/esthag/]
http://ens-news.com/ens/jan2003/2003-01-08-09.asp
Wetlands Clean Selenium From Farm Runoff
BERKELEY, California, January 8, 2003 (ENS) - Researchers from the
University of California have found a natural detoxification program for
selenium contaminated farm runoff: wetlands vegetation and microbes.
Results from a two year study by researchers at the University of
California - Berkeley show that manmade wetlands in the state's San
Joaquin Valley were able to remove an average of 69.2 percent of the
selenium in agricultural drainage water. Some plant populations showed
promise at converting selenium into a harmless gas, meaning less of the
selenium would end up in sediment or plant tissue.
The new study, published online last week in the journal "Environmental
Science and Technology," follows previous research at the Chevron oil
refinery in Richmond, California. The researchers found that wetland ponds
built in Richmond could take out as much as 89 percent of the selenium
from millions of gallons a day of refinery discharge, preventing it from
reaching San Francisco Bay.
"We thought that if wetlands could filter selenium from oil refinery
wastewater, then they could probably be used for agricultural runoff,"
said Norman Terry, professor of plant biology at UC Berkeley's College of
Natural Resources and principal investigator of the study. "We're
basically learning that some of the best, most efficient filters for
pollutants can be found in nature."
Terry said the entire wetland ecosystem is acting as a bio-geo-chemical
filter.
"Everything is working in concert to take the selenium out of the drainage
water," said Terry. "The extensive root system of the plants slows down
the water flow so the selenium gets trapped in the sediment. The plants
also provide a source of fixed carbon to fuel microbes, which metabolize
the selenium into non-toxic gas. It is truly an amazing process."
The toxic effects of selenium made headlines in 1983 when high levels from
polluted farm water were found at the Kesterson national wildlife refuge
in the San Joaquin Valley, part of the Central Valley. The soil on the
west side of the San Joaquin Valley is rich in natural selenium, which
leaches into the shallow groundwater of the region. Agricultural
irrigation accelerates this leaching process.
A large quantity of selenium-polluted agricultural drainage water was
being discharged into the reservoir in the early 1980s. The selenium was
linked to severe deformities suffered by birds and other wildlife at the
Kesterson refuge.
"Kesterson lacked proper environmental monitoring and management, so the
selenium continued to build up, becoming concentrated over time through
the food chain," said Zhi-Qing Lin, lead author of the study and former
post-graduate researcher with Terry at UC Berkeley.
Terry said wetland plants could become a major wastewater remediation tool
for both agriculture and industry.
"The upshot is that wetlands are a very efficient and affordable solution
to ridding polluted water of a toxic chemical," said Terry. "Plants grow
year after year, and while a constructed wetland system would need to be
monitored, it would be relatively easy to maintain."
* * *
Copyright Environment News Service (ENS) 2003. All Rights Reserved.
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