Ecotoxicological study of the influence of an industrial effluent on a net-spinning caddisfly assemblage in a regulated river

Abstract

The influence of an industrial effluent on the spatial distribution of net-spinning caddisflies (Trichoptera, Insecta) in the regulated Rio Duraton (northern Spain) was studied using field and laboratory methods. The effluent caused an increase in the fluoride concentration at three downstream sampling sites (mean values 6.8, 2.7 and 1.3 mg F-L−1 at S-3, S-4 and S-5) compared with control stations (0.1 mg F-L−1 at S-1 and S-2). The suspended inorganic matter (SIM) only increased just below the effluent (S-3), settling on the stream bottom at this sampling station. In addition, discharge fluctuations of hypolimnial waters with a significant OZ deficit, < 5 mg L−1 just below the reservoir (S-2), were produced daily by the dam, causing an hourly variation of fluoride concentrations at S-3, S-4 and S-5. The 48 and 72 hr LC50s (mg F-L−1) calculated from fluoride toxicity bioassays in soft water were 79.2 and 44.9 for Hydropsyche bulbifera, 86.6 and 43.7 for H. exocellata, 112 and 59.1 for H. pellucidula, 78.2 (72 hr) for H. lobata, and 120 and 79.7 for Chimarra marginata. H. siltalai, H. bulbifera, H. exocellata and Polycentropus flavomaculatus increased their abundances at S-4 and S-5 with regard to the upstream control station (S-1). Densities of Hydropsyche sp., H. lobata, H. pellucidula, Chimarra marginata and Cheumatopsyche lepida decreased or were absent downstream from the dam. No caddisfly species was collected at S-3 during sampling surveys. It is concluded that the main physicochemical factors responsible for changes in structure and composition of the net-spinning caddisfly assemblage along the study area were short-term flow fluctuations, dissolved O2 deficit and siltation of SIM. The increased fluoride concentration was a minor factor.