Effects of environmentally realistic daily temperature fluctuations on contaminant toxicity in aquatic ecosystems
Willming, Morgan M
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Temperature is one of the most critical environmental factors that can influence an organism’s metabolism as well as impact toxicokinetics and toxicodynamics. Most studies investigating the effects of temperature on toxicity do not incorporate realistic daily temperature fluctuations. These fluctuations may be important for high elevation/arid aquatic ecosystems, which experience large changes in daily temperatures. Temperature and contaminants can also affect important ecosystem processes like organic matter decomposition via impacts on microbial communities and the shredding invertebrates responsible for breakdown of this material. The objectives of this research were to: 1) assess how realistic daily temperature fluctuations, based on field collected playa wetland temperatures, impact toxicity of pesticides to aquatic invertebrates, 2) determine how pharmaceutical-fungicide mixtures and temperature regimes affect leaf decomposition processes, 3) examine toxicity of the fungicide pyraclostrobin to the shredding amphipod Hyalella azteca and effects on leaf processing and the microbial community, and 4) assess how daily temperature regimes impact growth and development of larval Mexican spadefoot toads (Spea multiplicata). Results indicated that toxicity of pesticides under fluctuating daily temperature cycles can differ compared to a constant temperature or a temperature regime altered based on climate change predictions. There was no clear trend of mixture effects for triclosan, ciprofloxacin, or chlorothalonil, on H. azteca or leaf processing, but ciprofloxacin may have the greatest effect. Pyraclostrobin was toxic to H. azteca and caused reductions in leaf processing, and some effects also depended on temperature regime. However, at environmentally relevant concentrations of pyraclostrobin there were limited effects on H. azteca, fungal biomass and microbial community function. In general growth of S. multiplicata did not differ between temperature regimes, and this may indicate natural adaptation to thermally heterogeneous environments. Therefore, effects of realistic daily temperature fluctuations on ecologically relevant responses may be complex, but are important for assessing how risk of contaminants may be altered under future climate change scenarios, especially for organisms that inhabit thermally variable environments.