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Algae and Bacteria Influence Herbicide Fate

By Tara Weaver-Missick
June 4, 1999

Species of green algae that help break down soil-applied herbicides could lead to improved soil and water quality, Agricultural Research Service scientists report.

Microbiologist Robert M. Zablotowicz, with ARS’ Southern Weed Science Research Unit in Stoneville, Miss., discovered the one-celled organisms while studying microbial populations in three Mississippi watershed lakes--Beasley, Deep Hollow and Thighman.

The study is part of the USDA-ARS Mississippi Delta Management Systems Evaluation Area (MSEA) project, which is evaluating farming practices in the 7,320-acre area surrounding the three lakes. The project’s goal is to improve farming techniques and ultimately enhance soil and water quality in the area.

Studies conducted by Zablotowicz and his colleagues indicate that management practices influence lake microbial populations and their impact on water quality. Deep Hollow watershed, where intensive conservation practices such as winter cover crops and reduced tillage are employed, had the lowest sediment and highest algal populations. These algae, Selenastrum and Ankistrodesmus, can absorb and break down herbicides, such as atrazine and fluometuron, commonly used in corn and cotton production.

Another major finding, according to Zablotowicz, is that a specific group of bacteria, called fluorescent pseudomonads, can degrade metolachlor, propanil and trifluralin--three commonly used herbicides in the MSEA area. These bacteria and algae can reduce herbicide longevity in Mississippi Delta lakes.

Zablotowicz and other ARS scientists will continue to study how microbes, like algae and bacteria, help improve soil and water quality. Knowledge gained from the MSEA study will ultimately be used to develop management techniques that help maintain diverse aquatic microbial populations that can degrade agrochemical pollutants.

ARS is the U.S. Department of Agriculture’s (USDA) chief scientific research agency.

Scientific contact: Robert M. Zablotowicz, ARS Southern Weed Science Research Unit, Stoneville, Miss., (phone) 601-686-5260, (fax), (601) 686-5422,