February 15-18, 2009 Washington State Convention Center Seattle ...

RISK EVALUATION TO AQUACULTURE PONDS FROM COMMON AERIALLY-APPLIED
HERBICIDES IN THE MISSISSIPPI ALLUVIAL PLAIN (DELTA)
Peter W. Perschbacher,* Gerald M. Ludwig and Regina Edziyie
Department Aquaculture/Fisheries
University of Arkansas at Pine Bluff
Pine Bluff, AR 71601
pperschbacher@uaex.edu
Common row crop herbicides were tested for possible adverse effects from drift to aquaculture production pond plankton and
water quality in triplicate 500-L outdoor, pool mesocosms.
Production pond systems greater than 7 ha. Forty aerially-applied herbicides were tested, including 11 soybean, 13 rice, 10
cotton, 5 corn and 1 winter wheat at low (1% of field rates) and high (10%) drift estimates for ponds 7ha and greater (ie channel
catfish). Diuron (cotton) affected phytoplankton and oxygen production in relation to dose. Morning oxygen levels fell to
critical levels of 3 ppm and below after one week in the high drift treatment. Zooplankton were also reduced relative to control
levels at both drift levels. Atrazine (corn) reduced zooplankton numbers. Carfentrazone (soybean) also reduced zooplankton,
but slightly
Positive impacts. Diuron, propanil and atrazine reduced larger cyanobacteria (bluegreen algae), pH and thus unionized ammonia
(UIA). Propanil and atrazine stimulated green algae and diatoms, as well as chlorophyll a, after initial reductions.
Other species pond systems. Greater impact was noted from propanil on systems with midlevel algal levels (50-200 ug/l as in
hybrid striped bass and catfish ponds) than in low and high chlorophyll a levels (below 20 and above 300 ug/l as in freshwater
shrimp and goldfish ponds, respectively). Drift levels were estimated up to 20% due to pond sizes typically less than 7 ha.
Algal scum conditions. Scums were more susceptible to propanil than populations mixed in the water column and impacts
approximated direct application levels (ie. overspray). Bloom instability and greater contact were assumed responsible.
Fry and fingerling pond systems. Smaller fry ponds were found to have potential drift levels of up to 3 times larger production
ponds. Greater effects were found accordingly, however chlorophyll a was low and reduced the impacts of atrazine and propanil.
Ph and UIA were also reduced. Thus, little impact was expected on fry production. Diuron however reduced DO below
3 ppm for on the second and third days. Recovery in DO was noted after two weeks. Thus, additional aeration may be needed
following diuron drift. Cladocerans were also reduced and may affect production.
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