Localized acidification near sour gas processing plants:: are forest floor macro-invertebrates affected?

The diversity and activity of forest floor invertebrates, particularly carabid beetles, were studied along a sharp acidification gradient in pine and aspen forests close to a sulfur block near a sour gas processing plant in SW central Alberta, Canada. Invertebrates were sampled by continuous unfenced pitfall traps at all sites, and fenced pitfall traps and core samples at selected sites. High sulfur contamination and subsequent acidification had a clear negative effect on earthworms, snails, and on several carabid species. Carabid beetles along the sharp acidification gradient in the pine forest were classified as vulnerable (Scaphinotus marginatus, Platynus decentis, Calathus ingratus, Stereocerus haematopus and Pterostichus riparius), resistant (Pterostichus adstrictus, Calathus advena and Agonum placidum) or favored (Amara hyperhorea). Ecological specialists were those most vulnerable to acidification, whereas ecological generalists were resistant. Few species dominated the assemblage at the acidified pine site. Fenced and unfenced pitfall samples produced similar results for carabid beetles and manual devegetation did not affect overall seasonal carabid catches. High levels of sulfur contamination at the aspen site substantially reduced ground plant cover but not pH and catches of most carabids were similar to the non-polluted aspen site. It is concluded that faunal structure at the acidified pine sites is severely affected negatively and further studies are warranted to study the consequences of reduced diversity for ecosystem processes such as organic matter decomposition. (C) 2001 Elsevier Science B.V. All rights reserved.