Date of Award

Fall 9-5-2025

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Joseph Milanovich

Abstract

Since European settlement, vast areas of U.S. land have been modified by humans. In the Midwest, an estimated 99% of native grasslands have been replaced by agriculture and urban development. Such alternations have replaced native habitat, redefined hydrology and introduced a wide array of chemicals into aquatic ecosystems. Modern agricultural practices utilize fertilizers and pesticides to maximize crop production. These chemicals frequently runoff into surrounding waters, potentially effecting aquatic organisms. One group of organism thought to be susceptible to agricultural contaminants are amphibians. Amphibians are vulnerable to pollution due, in part, to their permeable skin and biphasic life history. Global amphibian declines are well documented with over 40% of populations either in decline or facing extinction. To evaluate the short-term and long-term (legacy) effects of agricultural chemicals on amphibians, we utilized aquatic and terrestrial mesocosms and exposed American toads to three common contaminants (nitrogen, phosphorus, fungicide: azoxystrobin) in a fully crossed multi-factorial experimental design. We found that environmentally relevant concentrations of nitrogen and phosphorus decreased time to metamorphosis and increased size at metamorphosis. Azoxystrobin exposure had no effect on the metamorphic endpoint metrics. Toad mortality was very high (97%) in our terrestrial mesocosms across all treatments. We recommend further study into the short-term and long-term effects of common chemical combinations and their potential interactions with environmental conditions.

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