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Mississippi Delta MSEA Volume 2, Issue 3, Page 4
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Volume 2, Issue 3, Page 4, Third Quarter 1996

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MSEA Reporter Archive

Microbial Populations of MSEA Lakes

Researchers at the SWSL collaborating with ecologists from the National Sedimentation Laboratory have been monitoring populations of various bacteria and algae as well as total solids and an enzymatic indicator of microbial activity. Variations in these parameters were dependent upon site and sampling time; however, it is too early in the study to correlate these parameters with specific BMPs established at these lakes. Fluorescent pseudomonads were one of the more dominant groups of bacteria observed representing about 10 to 45% of the total bacterial population.

Since pseudomonads have been known to have an extensive potential for biodegradation of a wide range of pollutants, the metabolism of six herbicides was studied in cell suspensions of fluorescent pseudomonads isolated from these lakes. All isolates metabolized trifluralin (Treflan) indicating that the enzyme nitroreductase is prevalent among these bacteria. Metolachlor (Dual) was detoxified via dechlorination in 66% of the isolates. Propanil (Stam) was rapidly hydrolyzed in about 50%of the isolates. No fluometuron (Cotoran), 2,4-D, or cyanazine (Blazer) metabolism was observed by any of the pseudomonas isolates. These studies indicate that aquatic fluorescent pseudomonads are capable of transforming certain herbicides that are widely used in the Mississippi Delta. Future studies will consider herbicide transformations by other aquatic microorganisms, especially to identify groups of organisims that are responsible for the metabolism of herbicides such as Cotoran and Blazer. Preliminary studies indicate that certain green algae can metabolize fluometuron (Cotoran). This research may contribute to our understanding of the relationships between microbial population dynamics, microbial activity, and herbicide persistence in Mississippi lakes.

Dr. Robert Zablotowicz, Research Leader
USDA-ARS-MSA, Southern Weed Science Laboratory
Stoneville, MS 38776
Phone: 662-686-5272
Fax: 662-686-5422

Dr. Martin Locke,  Research Leader
USDA-ARS-MSA, Water Quality and Ecology Research Unit
Oxford, MS 38655
Phone: 662-232-2908
Fax: 662-232-2988


All nine surface water quality sampling sites have been installed in the three watersheds. Flumes were installed at four of the nine sampling sites. Stage discharge relationships have been established at two of the flume sites and partially established at the other two flume sites. Automated sampling began in June 1996 at the four flume sites. Most of the "bugs" have been worked out at these four sites since installation. Since June 1996, about 10 water quality samples and about 50 sediment samples were collected by the automatic samplers (prior to June 1996, about 25 samples were collected manually at these and other sites in the three watersheds). Sample analyses include sediment concentration; herbicide concentration, namely fluometuron (Cotoran) and norflurazon (Zorial); and nutrients (nitrate, nitrite, phosphorus, total organic carbon, and so forth).

Area-velocity meters were installed at two of the nine sampling sites. The area-velocity meters were installed to aid in measuring streamflow during backwater conditions, which are prevalent at these two sites. Stream discharge measurements have not been made at either site due to extremely dry conditions this summer. Typically, a large storm event is required to calibrate the area velocity meters so that streamflow measurements can be made over a wide range of stage. Automatic sampling at these two sites has not yet begun. These instruments were not installed until the mid-summer of 1996, and monitoring of streamflow data and storm duration is required before the automatic samplers can be programmed.

Three sampling sites were recently (Sept.-Oct., 1996) installed in the riparian zone of the Beasley Lake watershed. These sites were outfitted with devices to measure stage, which in turn activates an automated sampler. Only stage data will be recorded at these sites. Two sites were installed to the east of the riparian zone at the entrance, and one site was installed to the west at the exit. The site installed at the exit of the riparian zone required a 90-ft. walkway. Automatic samplers were installed, but not programmed, in October of 1996 at the riparian zone sites.

In FY97, the USGS plans to finish establishing stage discharge relationships at the two flume sites and complete streamflow and velocity measurements at the area velocity meter sites before the 1997 growing season. Manual samples will continue to be collected as necessary to correlate with samples collected by automated samplers. Automatic sampling at the four flume sites will continue, and automatic sampling at the two area velocity meter sites and the three riparian zone sites will begin. The sampling schedule for FY97 is as follows:

  • Composite samples will be collected at all nine sites for nearly every event; samples will be analyzed for both sediment and chemical concentrations.
  • Discrete sediment samples will be collected for every storm event.
  • Discrete chemical samples will be collected during the period mid-March through mid-June, 1997.

Other efforts in FY97 include a presentation at the 1997 Water Resources Conference explaining the sampling network. The Mississippi District will also participate in the development of an immunoassay for fluometuron analyses with the USGS Kansas District. The immunoassay technique will lower analyses costs for fluometuron from about $100 per sample to about $25 per sample.

Mr. Richard A. Rebich
U.S. Geological Survey, WRD
Jackson, MS 39208-6649
Phone: 601-965-4600, ext. 5583
Fax: 601-965-5782

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