Ecosystem impacts of acidity

Posted on December 15, 2011


In shaded headwater streams photosynthesis is limited and aquatic production is based largely on nutrients derived from falling leaves. In these systems food webs tend to be dominated by decomposers, shredders and their predators. Because acid environments suppress the microbial breakdown of organic detritus and may be toxic to invertebrates, low-pH conditions have the potential to influence the productivity, food web structure and functioning of headwater ecosystems. This possibility has been explored through studies of an acid stream in southern England. Broadstone Stream is spring-fed and has a pH of 5.3 at its source, but this value is increased by about 1 pH unit over the first kilometre as its waters pick up buffering compounds. Surveys and rearing experiments revealed that rising pH is paralleled by an increase in the diversity and protein content of dominant shredder species (stoneflies), and previous work showed that stoneflies grew slower on acid-conditioned leaves. These results suggest that in low-pH conditions shredders experience higher energy demands and /or a lower energy supply. It’s likely that freshwater ecosystems are moulded, at least in part, by biochemical constraints on key taxa, and such limitations may slow the speed at which polluted streams recover from acidification.

Reference: Aga, A.L., Layer, K., Basaguren, A., Pozo, J. & Woodward, G. 2010. Consumer body composition and community structure in a stream is altered by pH. Freshwater Biology 55, 670–680.

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