Variation in riparian consumer diet composition and differential bioaccumulation by prey influence the risk of exposure to elements from a recently remediated fly ash spill

Abstract

Emerging aquatic insects play a key role in transporting aquatic nutrients and contaminants to riparian consumers. However, little is known about how within- and between-year variation in the diet or patterns of element bioaccumulation in emerging insect taxa may influence the risk of exposure to wildlife. During 2 breeding seasons, the composition of the diet of tree swallows (Tachycineta bicolor) was examined at several colonies that were exposed to element contamination from a remediated coal fly ash spill to determine how variation in the diet influenced the risk of exposure to elements. The proportion of the diet that consisted of insects with an aquatic larval stage was positively related to concentrations of As, Fe, Se, and Tl in the samples. The proportion of the diet that consisted of Chironomidae (midges) was positively related to exposure to these elements at most colonies within and between years. Ephemeroptera (mayflies) contained higher concentrations of Se than midges, including 17 samples with concentrations of Se above 5 µg/g dry mass, the threshold of toxicological concern for birds. This was even the case at colonies several kilometers downstream from the spill. The results indicate that greater consideration should be given to the pattern of element bioaccumulation among different prey taxa and their relative importance in the diet to better assess the risk of contaminant exposure.

Spatial and temporal trends in contaminant concentrations in Hexagenia nymphs following a coal ash spill at the Tennessee Valley Authority's Kingston Fossil Plant

“…Dietary studies of nestling and adult tree swallows (Tachycineta bicolor) around the spill site suggest some trophic transfer through insects that have an aquatic stage (mostly chironomids, but mayflies also were found in the diet). However, the concentrations of contaminants were not associated with any lethal or sublethal physiological effects [57,58]. Downstream of the ash spill redear sunfish (Lepomis microlophus), a species likely to have a diet predominantly of aquatic organisms, were found to have elevated levels of Se [59] and evidence of possible sublethal physiological changes [60].…”

Temperature and land use influence tree swallow individual health

“…(2016 , 2018 ) provides strong evidence that aquatic insects provide critical nutritional benefits to aerial insectivorous birds; accordingly, other studies of aerial insectivore diets have demonstrated a reliance on aquatic insect subsidies (e.g. Beck et al , 2014 ; Michelson et al , 2018 ).…”

Monitoring Cadmium Concentrations in Sediments and Aquatic Insects (Hydropsychidae: Trichoptera) in a Stream near a Zinc Mining Area

“…Adult aquatic insects, which form a significant portion of the diet of some terrestrial organisms [7], inevitably emerge from contaminated sediments and transfer body burden to the terrestrial environment either directly as prey items to insectivores, or indirectly through the detritus food chain [8]. A number of studies [9][10] have shown that both immature and emerging insects play a crucial role in determining metal contaminants in the environment. Currie et al [11] collected emerging insects (Diptera, Odonata, Ephemeroptera, and Trichoptera) from lake water in order to quantitatively estimate the export of cadmium by aquatic insects from a natural system having elevated cadmium concentrations in the water and sediment.…”