Pesticides, nutrients and disease: Do restored wetlands provide quality amphibian habitat in an agricultural landscape?

Background/Question/Methods

Habitat loss, emergent disease and chemical contaminants are all factors in recent amphibian population declines. The impacts of anthropogenic activities such as urban development and agriculture may have exacerbated the role of these factors. The Conservation Reserve Enhancement Program (CREP) strategically restores wetlands in landscape locations where they primarily receive subsurface tile drainage, and aims to reduce nutrient (especially nitrogen) concentrations in surface waters. However, the benefits of this increased wetland area as amphibian habitat may be negated if the quality of the wetlands is insufficient to sustain viable amphibian populations. Other restored wetlands are prevalent across the Des Moines Lobe and generally receive surface water and to a lesser extent subsurface flow.  Similar to CREP wetlands, these “reference” wetlands were restored from agricultural use at one time but are not typically positioned to accept substantial amounts of tile drainage. This project examines these two wetland types (CREP and reference) in Central Iowa, and investigates their ability to support amphibian biodiversity. We measured contaminant occurrence in water, sediment and frog liver tissue; pathogen (Batrachochytrium dendrobatidis (Bd)) occurrence, and aquatic predator occurrence, and relate them to the population sizes of chorus and leopard frogs (Pseudacris maculata and Lithobates pipiens, respectively).

Results/Conclusions

Population sizes were estimated for four wetlands in 2012 and 2013. The chytrid fungus Bd was detected in all six wetlands in 2012. Additionally, predacious fish were detected in one reference and one CREP wetland in 2012. Water, sediment and liver samples were analyzed for 100 compounds, including 36 fungicides, 27 insecticides, 23 herbicides and 14 degradation products. In 2012, 14 compounds were detected in water samples, 8 compounds were detected in sediment, and 16 were detected in liver tissue samples. Detections were primarily fungicides, but atrazine, an endocrine disruptor in frogs, was detected in the water collected from all wetlands. The highest concentration of atrazine was found in a reference wetland, but in general, a greater diversity of chemical contaminants were detected in CREP wetlands. In 2012, reference wetlands tended to dry up more rapidly than CREP wetlands, which may indicate that CREP wetlands with a longer hydroperiod are an important habitat for amphibians, especially during droughts. However, for amphibians, the benefits of increased habitat area from these CREP wetlands could be negated by the risk of increased chemical and parasite exposure.