Impact of acidification and eutrophication on the distribution of fish species in shallow and lentic soft waters of The Netherlands: an historical perspective

Abstract

The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983–1984 Esox lucius, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH≥5) Rutilus rutilus, Scardinius erythrophthalmus, Perca fluviatilis, Ictalurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra pygmaea was extremely acid‐tolerant. The percentage of waters which harboured fish as well as the average number offish species per water decreased steeply between pH 6 and 4.The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification, six groups of waters could be distinquished with respect to their fish fauna. The site groups are defined and characterized physico‐chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.