Comparison of amphibian habitat suitability in USDA CREP and reference wetlands in the Des Moines lobe of Iowa


Principal Investigator:

Clay L. Pierce

Student Investigator:

Rebecca Reeves (M.S.)


Erin Muths, USGS Fort Collins Science Center

Mark Vandever, USGS Fort Collins Science Center


September 2011 to December 2014

Funding Source(s):

Iowa Department of Natural Resources (IDNR)

Goals and Objectives:

  • Compare amphibian species richness in restored CREP and reference wetlands in central Iowa
  • Estimate lethal and sub-lethal impacts to adult leopard frogs (Lithobates pipiens) in CREP and reference wetlands in central Iowa by estimating  survival rates and population sizes and characterizing developmental stress exhibited by frogs (via fluctuating asymmetry and body condition)
  • Estimate and compare chorus frog (Pseudacris maculata) population sizes in reference and restored wetlands in central Iowa
  • Characterize abiotic factors (e.g., depth, hydroperiod, water pH, turbidity, nutrient concentrations, and conductivity) and environmental stressors (e.g., predators, emergent diseases, as well as parasite and pesticide exposure) experienced by amphibians in restored and reference wetlands in central Iowa



All project objectives were completed, a final report will be submitted in July, and three manuscripts are being prepared for publication.

Conclusions and Recommendations:

We sampled environmental characteristics and amphibian populations in six wetlands (3 CREP and 3 reference) between 2011 and 2013. As anticipated, given their purpose, water samples from CREP wetlands had higher concentrations of nitrogen. Additionally, we tested water, frog tissue, and sediment samples for nearly 100 agricultural contaminants, including fungicides, insecticides, herbicides and degradation products. While we found contaminants in all samples, there were no differences in concentrations between CREP and reference wetlands. Compounds detected in amphibian tissue were similar to those detected in water and sediment samples, so it is likely that frogs are picking up contaminants from their habitat. We found no differences in amphibian species richness or adult leopard frog survival rates between wetland types. Reductions in leopard and chorus frog population size correlated with extended hydroperiods and the presence of fish and non-native bullfrogs (Lithobates catesbieana) in wetlands. The amphibian chytrid fungus was detected in all wetlands, but was found in higher concentrations in water samples from reference wetlands. Exposure to the amphibian chytrid fungus is known to increase hind limb asymmetry in frogs. In line with this, leopard frogs from reference wetlands exhibited higher levels of developmental stress (i.e., reduced body condition and increased size differences between paired limbs) than frogs from CREP wetlands. Overall, our findings suggest that CREP and reference wetlands are valuable components of the amphibian habitat available in central Iowa. Maintaining a complex of fish-free wetlands with variable hydroperiods may reduce the impacts of drought and variable rainfall on amphibians in central Iowa. 


09/01/2011 to 12/31/2014