EFFECT OF STREAM ACIDIFICATION AND INORGANIC ALUMINUM ON MORTALITY OFBROOK TROUT (SALVELINUS-FONTINALIS) IN THE CATSKILL MOUNTAINS, NEW-YORK

Juvenile brook trout (Salvelinus fontinalis) were exposed in cages to fluctuating chemical conditions in four Catskill Mountain streams duri ng the spring and fall of 1989 and the spring of 1990. Specific chemic al constituents and characteristics of acidic episodes that correlated with increased fish mortality were identified. Mortality increased du ring acidic episodes in one poorly buffered stream when inorganic mono meric aluminum (Al-im) concentrations increased; mortality was low in three other streams during acidic episodes of shorter duration and sma ller magnitude than measured in the poorly buffered stream. Variation in mortality was attributed primarily to differences in concentrations of both Al-im and dissolved organic carbon. Linear and logistic regre ssion analyses indicate that either mean or median Al-im concentration s could account for 73-99% of the variability in mortality. Regression analyses suggest that mortality was highly related (in order of impor tance) to Al-im pH, dissolved organic carbon, calcium, and chloride co ncentration. Brook trout mortality was also highly related to duration s of exposure above 0.225 and 0.250 mg/L Al-im during test periods. Ch aracteristics of acidic-Al-im episodes that are critical to mortality of caged brook trout appear to be (i) Al-im concentrations of at least 0.225 +/- 0.025 mg/L and (ii) exposure to these toxic Al-im concentra tions for at least 2 days.