Abstract
To identify the mechanism(s) by which acidity alters the composition and richness of chironomid communities and to determine the acid tolerance of chironomid taxa inhabiting a large river, pH was manipulated in three stream channels. The chironomid community that developed after a 10-wk exposure to pH 4.5 was poorer in species and lower in abundance than those exposed to pH 5.9 or 7.4 (reference pH). The reduced density of chironomids at pH 4.5 was not a result of differential egg deposition, behavioural drift, or emergence. Acid-enhanced larval mortality appeared to be the primary mechanism accounting for reduced density. Tribelos predomined in the channel acidified to pH 4.5, while Ablabesmyia was predominant in the other channels. Tanytarsus, Microtendipes, and Nilothauma were the most acid-sensitive taxa. When pH was returned to 7.4 from 4.5, the composition and density of the community changed rapidly; acid-sensitive species invaded quickly, and within 6 wk the community resembled that in the other channels. These results suggest that acidity is important in structuring and maintaining lotic communities and that reduction in acidic emissions should lead to rapid biological recovery of acidified lotic systems, provided that acid-sensitive species have survived in nearby refuges.
Published Version
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