Effect of stream acidification and inorganic aluminum on mortality of brook trout (Salvelinus fontinalis

Abstract: Juvenile brook trout (Salvelinus fontinalis) were exposed in cages to fluctuating chemical conditions in four Catskill Mountain streams during the spring and fall of 1989 and the spring of 1990. Specific chemical constituents and characteristics of acidic episodes that correlated with increased fish mortality were identified. Mortality increased during acidic episodes in one poorly buffered stream when inorganic monomeric aluminum (Alim) concentrations increased; mortality was low in three other streams during acidic episodes of shorter duration and smaller magnitude than measured in the poorly buffered stream. Variation in mortality was attributed primarily to differences in concentrations of both Alim and dissolved organic carbon. Linear and logistic regression analyses indicate that either mean or median Alim concentrations could account for 7399 % of the variability in mortality. Regression analyses suggest that mortality was highly related (in order of importance) to Alim, pH, dissolved organic carbon, calcium, and chloride concentration. Brook trout mortality was also highly related to durations of exposure above 0.225 and 0.250 mg/L Alim during test periods. Characteristics of acidicAlim episodes that are critical to mortality of caged brook trout appear to be (i) Alim concentrations of at least 0.225 ± 0.025 mg/L and (ii) exposure to these toxic Alim concentrations for at least 2 days. Résumé: Des juvØniles dombles de fontaine (Salvelinus fontinalis) ont ØtØ exposØs dans des cages à des conditions chimiques fluctuantes dans quatre cours deau des monts Catskill pendant le printemps et lautomne de 1989 et le printemps de 1990. Les constituants chimiques spØcifiques et les caractØristiques des Øpisodes acides qui Øtaient corrØlØs à une hausse d