Acidification Effects on Stream Biota and Organic Matter Processing

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Abstract
Experimental acidification effects on stream biota and organic matter decomposition rates in natural, low-alkalinity (7–15 mg CaCO3/L) Michigan streams were studied using paired, artificial, recirculating streams. Acidification to pH 4 with sulfuric acid from pH 7.0 to 7.4 resulted in significant decreased decomposition rates for 5-g leaf packs of white birch (Betula papyrifera) and sugar maple (Acer saccharum). Populations of total macroinvertebrates on leaf packs in the acid stream were substantially reduced over a 264-d exposure period, whereas populations remained unchanged in the control stream. Detailed studies were conducted on a caddisfly, Lepidostoma liba, and an isopod, Asellus intermedius. The Lepidostoma population was resistant to short-term exposure to acidification, but significant mortality occurred after 80 d at pH 4 at 2–4 °C. Late instars were not affected by acidification and emerged after more than 60 d at 15–20 °C. Asellus was very sensitive to acidification with up to 93% mortality after only 24 d and with inhibition of reproduction. Acidification also resulted in increased mortality for a snail, Physa heterosiropha, and another caddisfly, Pycnopsyche sp.