Indicators of the statuses of amphibian populations and their potential for exposure to atrazine in four midwestern U.S. conservation areas.

Walt Sadinski,Alisa Gallant,Mark Roth,Tyrone Hayes,Perry Jones

doi:10.1371/journal.pone.0107018

Walt Sadinski, Alisa Gallant + Show 3 more

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https://doi.org/10.1371/journal.pone.0107018

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Abstract

Extensive corn production in the midwestern United States has physically eliminated or fragmented vast areas of historical amphibian habitat. Midwestern corn farmers also apply large quantities of fertilizers and herbicides, which can cause direct and indirect effects on amphibians. Limited field research regarding the statuses of midwestern amphibian populations near areas of corn production has left resource managers, conservation planners, and other stakeholders needing more information to improve conservation strategies and management plans. We repeatedly sampled amphibians in wetlands in four conservation areas along a gradient of proximity to corn production in Illinois, Iowa, Minnesota, and Wisconsin from 2002 to 2005 and estimated site occupancy. We measured frequencies of gross physical deformities in recent metamorphs and triazine concentrations in the water at breeding sites. We also measured trematode infection rates in kidneys of recently metamorphosed Lithobates pipiens collected from nine wetlands in 2003 and 2004. We detected all possible amphibian species in each study area. The amount of nearby row crops was limited in importance as a covariate for estimating site occupancy. We observed deformities in <5% of metamorphs sampled and proportions were not associated with triazine concentrations. Trematode infections were high in metamorphs from all sites we sampled, but not associated with site triazine concentrations, except perhaps for a subset of sites sampled in both years. We detected triazines more often and in higher concentrations in breeding wetlands closer to corn production. Triazine concentrations increased in floodplain wetlands as water levels rose after rainfall and were similar among lotic and lentic sites. Overall, our results suggest amphibian populations were not faring differently among these four conservation areas, regardless of their proximity to corn production, and that the ecological dynamics of atrazine exposure were complex.

Highlights

Large-scale agriculture is a principal driver of amphibian population declines [1,2,3] primarily for two reasons: historical and ongoing conversion of native land cover to agricultural production has caused the loss and fragmentation of amphibian habitat in many regions worldwide (e.g., [4,5,6,7]) and amphibians are susceptible to direct and indirect effects on fitness from potentially eutrophying or toxic agricultural chemicals released into the environment to enhance agricultural production (e.g., [4], [8,9,10])
Based on the results from the liquid chromatography/mass spectrometry (LCMS) analyses, atrazine and atrazine degradation products were present almost exclusively in samples from UMR sites, where we focused most of our site sampling for the enzyme-linked immunosorbent assay (ELISA)-LCMS comparisons (Tables S13–14)
Similar to results observed by McDaniel et al [69] and Byer et al [71], our results from the LCMS analyses indicated that atrazine accounted for less than the full concentration we measured via the ELISA, possibly due to the cross reactivity of the antibodies with the other triazines we described earlier

Summary

Introduction

Large-scale agriculture is a principal driver of amphibian population declines [1,2,3] primarily for two reasons: historical and ongoing conversion of native land cover to agricultural production has caused the loss and fragmentation of amphibian habitat in many regions worldwide (e.g., [4,5,6,7]) and amphibians are susceptible to direct and indirect effects on fitness from potentially eutrophying or toxic agricultural chemicals released into the environment to enhance agricultural production (e.g., [4], [8,9,10]). Midwestern farmers annually produce the majority of corn (Fig. S1) and soybeans in the United States, as well as lesser quantities of barley, oats, wheat, beans, hay, apples, pork, dairy products, beef, and other commodities [11]. As has been described for other areas [12], conversion of native land cover to agricultural production has caused broad-scale loss and fragmentation of midwestern wildlife habitat with direct ramifications for amphibians, in the corn belt across Minnesota, Iowa, Illinois, Indiana, and Ohio. Comparable changes in land cover and use occurred across areas of other midwestern states, resulting in the extensive loss and fragmentation of habitat for amphibians and other species since European settlers began farming the Midwest’s rich soils [4]

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