Status of zoobenthos and fish populations in subarctic rivers of the northernmost Finland: Possible effects of acid emissions from Russian Kola Peninsula

In 1990, a monitoring programme was initiated to survey the status of benth ic invertebrate communities and fish populations over a wide range of subar ctic rivers in northernmost Finnish Lapland (68 degrees 15'-70 degreesN). A special emphasis was placed on detecting possible effects of acidification through sulfur emissions from Russian Kola Peninsula. Sampling in 13 river s within four major river systems covered watercourses from small brooks to large 7(th) order rivers, and watersheds with different distances from the emission sources. The community structure of zoobenthos and the occurrence of acid-sensitive indicator species were assessed in 90 sampling sites. Se nsitive fluvial fish species, including Atlantic salmon (Salmo salar), brow n trout (Salmo trutta), European minnow (Phoxinus phoxinus) and burbot (Lot a Iota), were monitored by studying their occurrence, abundance and juvenil e recruitment. No signs of acid-induced failure in juvenile recruitment wer e detected in salmonid populations. The occurrence of minnow and burbot cov ered all the systems studied. In parallell, the structure of benthic commun ities with relatively high species diversity and wide distribution of a hig hly acid-sensitive caddisfly indicated no effects of acidification.