Abstract
We describe two artificial stream experiments that exposed aquatic insect communities to Zn, Cu, and Cd (year 2014) and to Zn, Cu, and Ni (year 2015). The testing strategy was to concurrently expose insect communities to single metals and mixtures. Single metals tests were repeated to evaluate reproducibility of the methods and year‐to‐year variability. Metals were strongly accumulated in sediments, periphyton, and insect (caddisfly) tissues, with the highest concentrations occurring in periphyton. Sensitive mayflies declined in metals treatments and effects concentrations could be predicted effectively from metals concentrations in either periphyton or in water. Most responses were similar in the replicated tests, but EC50 values for the mayfly Rhithrogena sp. varied 20‐fold between the tests, emphasizing the difficulty comparing sensitivities across studies and the value of repeated testing. Relative to the single metal responses, the toxicity of the mixtures was either approximately additive or less than additive when calculated as the product of individual responses (response addition). However, even less‐than‐additive relative responses were sometimes greater than responses to similar concentrations tested singly. The ternary mixtures resulted in mayfly declines at concentrations that caused no declines in the concurrent single‐metal tests. When updating species‐sensitivity distributions (SSDs) with these results, the mayfly responses were among the most sensitive 10th percentile of available data for all 4 metals, refuting older literature placing mayflies in the insensitive portion of metals SSDs. The approach of testing translocated aquatic insect communities in 30‐day artificial streams is an efficient approach to generate multiple species effects values under quasi‐natural conditions that are relevant to natural streams.This article is protected by copyright. All rights reserved.
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