HOW MANY FISH POPULATIONS IN FINLAND ARE AFFECTED BY ACID PRECIPITATION

The number of fish populations affected or lost from small lakes in so uthern and central Finland due to acid precipitation is estimated. Tol erance limits (pH and labile aluminum) of common fish species were obt ained from a fish status survey of 80 lakes. These tolerance values we re used to estimate the proportion of affected lakes from the water ch emistry data of 783 statistically selected lakes. The proportion of an thropogenically acidified lakes was estimated by calculating pre-acidi fication pH and aluminum concentrations of the lakes, using a steady-s tate model based on water chemistry. The number of fish populations fo r which acidification has affected growth or population structure was estimated at between 2200 and 4400. Out of these, the number of fish p opulations that have disappeared due to acid precipitation would be ab out 1000-2000. Almost 60% of the affected or lost populations are roac h, Rutilus rutilus, the most sensitive of the common fish species in s mall lakes in southern and central Finland. Less than 15% of the damag ed population is European perch, Perca fluviatilis, the most common sp ecies. This is due to the substantially higher tolerance of perch to a cidified water in comparison with roach.