Influence of pH, Aluminum, and Organic Matter on Stream Invertebrates

Abstract

The interactive effects of low pH, aluminum, and organic matter on five species of invertebrates collected from low-alkalinity (160–300 μeq/L) Michigan streams were measured using five 28-d experiments during 1982 and 1983. Such interactive effects had not been tested previously for these species. Each experiment consisted of a control channel (pH 7.0), a pH modified (4.0 or 5.0), and pH plus Al (250 or 500 μg Al/L) modified channel. Three experiments were conducted using natural stream water (dissolved organic carbon of 42–47 mg C/L), while two were conducted using simulated stream water with no dissolved organic carbon added. The invertebrates included Asellus intermedius Forbes, Pycnopsyche guttifer (Walker), Lepidostoma liba (Ross), Nemoura sp., and Physella heterostropha (Say). Survival of all species was significantly decreased at pH 4 compared with controls but not at pH 5 except for Asellus (15–20% mortality). Adding 500 μg Al/L caused significant additional mortality under some conditions for all species except Physella. Removal of organic matter from the water caused complete mortality at pH 4 for Nemoura and Asellus when 500 μg Al/L was added and decreased survival for Pycnopsyche to less than 20%. Addition of citrate as an organic ligand reduced susceptibility to Al in the low-organic streamwater treatment.