Comparison of stream macroinvertebrate assemblages in canyon ecosystems of the Blue Mountains (Australia) with and without recreational traffic: A pilot study in impossible terrain

In Australia, the adventure sport of canyoning occurs predominantly in the protected areas of the Greater Blue Mountains World Heritage Area, 50 km west of Sydney. It involves travelling through narrow, deep gorges using a combination of walking, abseiling, wading, rock scrambling and/or swimming through the canyon streams. The sport's popularity is reported to have increased substantially over time, causing concern for the sustainability of these fragile ecosystems. To investigate visitor impacts, benthic macroinvertebrate assemblages and water quality were compared among four canyons subject to high visitation (average 20-100 visits per week) with those in four unvisited/low visitation canyons (0-5 visits per week). Comparison was also made between impacted and nonimpacted areas within two of the high visitation canyons. Sampling was undertaken over two canyoning seasons (early spring to late autumn). No significant relationship between macroinvertebrate assemblage composition or water quality was observed due to visitation level within and among canyons, although there were inherent differences among canyons. Water quality was consistent with pristine conditions in all locations. Macroinvertebrate assemblages included a range of pollution sensitive taxa (e.g., Ephemeroptera represented by 42.3% of all animals). Although family richness was concentrated within a few orders (84.2% of families were represented by 50% of orders), most families were represented by 2 Recognisable Taxonomic Units, 47.4% of these were represented by a single taxon. We concluded that, at current visitation levels, there is no measurable impact on the predominant animal component of these ecosystems. This finding was contrary to the expectations of the land managers of this area.