RELATIVE IMPORTANCE OF SEASONAL, SHORT-TERM PH DISTURBANCES DURING DISCHARGE VARIATION ON A STREAM ECOSYSTEM

In a S-central Ontario stream during spring and fall, with increased acidity, inorganic monomeric Al and Ca concentrations were significantly increased in stream water during spring and fall, whereas Fe, Mn, and Zn concentrations did not change. Total Al and DOC concentrations in stream water showed no constant pattern. Benthic density and generic richness during spring decreased in mineral, but not organic sediments. Total drift density did not change, but mayflies increased in the drift. In the fall, benthic density and generic richness fluctuations were not correlated with pH disturbance, whereas drift density increased significantly during elevated acidity. Diversity and evenness of benthic invertebrates did not change above or below pH disturbance in either season. Discharge was the primary correlate of spring drift, whereas pH played a secondary role. In autumn, Ca and DOC were predominant factors associated with increased drift but were related to hydrology. -from Author