BackgroundBackground

o Pesticides are broadly used by humans to control and eliminate unwanted species of insects and plants.

o More than one billion pounds of pesticides are used in the US each year, especially in agricultural areas such as Pennsylvania.

o Aquatic communities are at great risk due to the widespread use of pesticides and concern has risen over the beginning global decline of amphibians (Houlahan et al. 2000).

o Directly, the physiology, behavior, or health of the aquatic organism may be influenced by the chemical composition of the contaminant.

o The indirect effects of pesticide contamination alter the food web of tadpoles by affecting the availability of periphyton, which is attached algae that is the main food source of tadpoles.

o Herbicides are known to decrease algae as a food source (Rohr and Crumrine 2005, Boone et. al 2004, 2003,Gustavson et. al 2003).

o Insecticides are known to decrease zooplankton that competitively feed on algae, therefore increasing algae as a food source (Rohr and Crumrine 2000, Havens 1995).

Indirect effects of coapplication of pesticide and herbicide on tadpoles

Bethany Rhoads Department of Biological Sciences, York College of Pennsylvania

ResultsResults

ConclusionsConclusions

o Insecticide showed higher levels of chlorophyll in this experiment supporting the hypotheses but was only significantly higher than the herbicide and both pesticides treatment at weeks 6 and 10.

o Mesocosms treated with herbicide showed lower levels of chlorophyll in this experiment as predicted in the hypotheses but was only significantly lower than the insecticide at weeks 6 and 10.

o Treatment with both pesticides showed the lowest amount of chlorophyll a throughout the experiment.

o In this experiment, the insecticide treatment showed greatest mass of tadpoles at the end which supports the hypotheses, although this was not significant.

o Mesocosms treated with both pesticides showed lowest mass and greatest mortality at the end in this experiment although this was not significant.

Take home messageTake home message

o It is not known how chemicals will react with one another and the effect they will have on organisms through the mechanism alone.

o The addition of more chemicals, both an herbicide and an insecticide, seemed to have the most negative impact on the tadpoles, influencing availability of food, growth of the tadpoles, and the rate of survival.

o Farmers should consider the interaction of chemicals and the negative effects that may be seen on nearby organisms when choosing how to treat their crops.

o More research is needed using more replicates and more tadpoles in the experiment for better statistical analysis.

The tadpoles were weighed and the chlorophyll concentration was measured each week for 4 weeks and then every other week for a total of 10 weeks.

HypothesesHypotheses

H1:Herbicide will directly kill algae resulting in less food availability and smaller sized tadpoles than the control tub.

H2: Insecticide will kill zooplankton resulting in an increase in algae concentration which will cause the tadpoles experience more growth than the control tubs.

H3: The effects of the mixture of the insecticide and herbicide will counteract one another and therefore not affect the algal food source of the tadpoles.

H4: There will be a small chemical effect on tadpole growth but not as large as indirect effects through modification of food web.

QuestionQuestion

What are the indirect effects of the coapplication of pesticides and herbicides on ecology of freshwater environment?

MethodsMethods

11 ½ liters of tap water ½ liter of pond water 8 grams of leaf material1 ½ grams rabbit chow

Literature Cited1. Boone, Michelle D. et. al 2004. Effects of an Insecticide on Amphibians in Large-Scale Experimental Ponds. Ecological Applications [serial online] 14: 685-691. Available from BioOne.2, Gustavson, K. et. Al 2003. Effects of Exposure Duration of Herbicides on Natural Stream Periphyton Communities and Recovery. Arch. Environ. Comtam. Toxicol. [serial online] 45: 48-58. Available from BioOne.3. Houlahan, Jeff E. 2000. Quantatative evidence for global amphibian population declines. Nature [serial online] 404: 752-754. Available from BioOne.4. Rohr, Jason R. and Crumrine, Patrick W. 2005. Effects of an Herbicide and an Insecticide on Pond Community Structures and Processes. Ecological Applications [serial online] 15: 1135-1147. Available from BioOne.

Acknowlegements

I would like to thank Dr. Nolan for all her continued help and guidance.

Pond water control

2 replicates

Herbicide treatment

2 replicates

Insecticide treatment

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Both herbicide and insecticide treatment

2 replicates

Mass of Tadpoles

Chlorophyll Concentration

Mesocosm:

Figure 2. Chlorophyll concentration vs. Time. Statistical analyses of chlorophyll a conc. of periphyton of mesocosms exposed to different variables of pesticides. A two-way ANOVA with the Bonferroni post test was applied to the data to determine significance of difference. * indicates p < 0.05

Figure 1. Mean mass of tadpoles vs. time. Statistical analyses of mass of tadpoles of mesocosms exposed to different variables of pesticides performed using a two-way ANOVA with the Bonferroni post test to determine significance of difference. No significant difference was found.

Figure 3. Percent of tadpoles alive vs. Time. Statistical analyses performed of transformed data using a two-way ANOVA with the Bonferroni post test to determine significance of difference. No significant difference was found.

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