Effect of key water quality variables on macroinvertebrate and fish communities within naturally acidic wallum streams

Adverse impacts of acidification on aquatic biota have been observed worldwide, however, most reports are based on freshwaters acidified from anthropogenic means. By contrast, naturally low pH values may not affect biota within naturally acidic freshwaters. This field study provides information on the water quality, macroinvertebrate and fish communities in little-studied, naturally acidic wallum streams, in Central Queensland, Australia. Mid-range pH sites (pH 5–6) were compared with low pH sites (pH 5–3.8) to investigate the effect of pH and other key water quality variables on these communities. Field data indicated that pH had less of an effect in these systems in terms of biotic changes compared with other water quality variables, with dissolved oxygen (% saturation) identified as the key driver for changes in macroinvertebrate composition. Fish were present at all sites, including those with pH ,4. Several possible explanations for this lack of pH effect are discussed. These results provide support for the reduced importance of acidity, relative to other water quality parameters, in naturally acidic waters. The work also provides baseline data on the biota of little-studied wallum streams.