BROWN TROUT (SALMO-TRUTTA) STATUS AND CHEMISTRY FROM THE NORWEGIAN 1000 LAKE SURVEY - STATISTICAL-ANALYSIS

Substantial negative impacts of acidic precipitation on freshwater fis hes have been recorded over the last 50 yr in Norway. We analyzed the present status and historical trends of brown trout (Salmo trutta) pop ulations in relation to water chemistry in 584 Norwegian lakes. Since the 1940s, 39% of the lakes have lost their trout populations, and ano ther 17% of the lakes have declining trout populations; thus, 56% of t he populations have been adversely affected, The results of analysis o f variance, principal components analysis, and discriminant analyses c onverge on the variables pH, monomeric inorganic aluminum, and alkalin ity as most strongly related to trout status. Lakes whose trout popula tions are extinct have an average aluminum concentration of 133 mug/L, an alkalinity of - 34 mueq/L, and a pH of 4.8 versus 11 mug Al/L, + 2 7 mueq/L, and 6.0 for lakes with healthy populations. Also, nitrate an d sulfate levels are significantly higher in affected versus unaffecte d lakes. Calcium and sulfate appear to influence trout status moderate ly as individual variables, but strongly in combination, since they ar e the major determinants of alkalinity in these lakes. Models based on discriminant analyses showed good success (up to 89%) in predicting t rout population status categories from water chemistry.