Ecotoxicological analysis of the influence of an industrial effluent on fish populations in a regulated stream

Abstract

Abstract. The influence of an industrial effluent on the spatial distribution of fish populations in the regulated Río Duratón (northern Spain) was examined by field and laboratory studies. The effluent caused an increase in the fluoride ion concentration at three downstream sampling sites (mean values 6·8, 2·7 and 1·3mg/l) compared with reference stations (0·1 mg/l). The suspended inorganic matter (SIM) only increased immediately below the effluent, settling on the stream bottom of this sampling station. In addition, hypolimnial waters with low concentrations of dissolved oxygen (<5 mg/l) were released daily by the dam. Rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., disappeared downstream of the impoundment. The 72 and 96h LC50s (mgF-/1) calculated from fluoride toxicity tests in soft water were 138·5 and 107·5 for rainbow trout, and 223·0 and 164·5 for brown trout. Fish (Barbus bocagei Steindachner, Rutilus arcasii (Steindachner) and Gobio gobio (L.)) were collected at all sampling stations. The benthic fish species Cobitis maroccana Pellegrin was also collected downstream of the impoundment but was absent just below the industrial effluent. It is concluded that the main physicochemical factors responsible for the spatial distribution of fish populations were low concentrations of dissolved oxygen for trout and the siltation of SIM for cobitids, the increased fluoride concentration being a minor factor.