Quantifying neonicotinoid concentrations in Missouri wetlands, their driving factors, and the potential effects on the reliant avian community
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Neonicotinoid insecticides became available for commercial use in North America in the late 20th Century. Since their introduction, studies of surface waters where neonicotinoids are available for use have measured neonicotinoid concentrations at levels considered harmful for non-target organisms. Among non-target organisms, aquatic invertebrates have been highlighted as a group that may be especially susceptible to neonicotinoids. In addition to aquatic insects, avian aerial insectivores have been proposed as indicator taxa as they are reliant on insect food reserves and have recently experienced population declines. Thus, we developed two studies in floodplain wetlands to quantify neonicotinoids in Missouri wetlands and potential effects on non-target taxa. First, we sampled 40 wetlands across four sampling periods to quantify neonicotinoid concentrations in Missouri wetlands as well as potential factors influencing these concentrations. Second, we selected 22 additional study wetlands in a paired study design to measure the biotic response to neonicotinoid treatment using emergent insects and nesting tree swallows (Tachycineta bicolor). Overall, we found neonicotinoids were frequently detected in wetland water and sediment, however sediment concentrations were an order of magnitude greater. Wetland sediment neonicotinoid concentrations were partially related to management decisions including the amount of agriculture planted within wetlands and Conservation Areas during the study year and water depth within study wetlands. Through the monitoring of emergent insects and nesting tree swallows we found no link between neonicotinoid concentrations or treatment and wetland food-web function. However, we caution that neonicotinoid levels detected in Missouri wetlands may be detrimental to aquatic insects and wetland dependent taxa at different spatial and temporal scales. Managers should consider taking reasonable measures to limit the potential contamination of wetlands by neonicotinoid insecticides.
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