Different sensitivity of mayflies (Insecta, Ephemeroptera) to ammonia, nitrite and nitrate: linkage between experimental and observational data

Complex toxic effects of ammonia, nitrite and nitrate to aquatic animals are not well investigated. In rivers of southwestern Siberia, Russia, elevated ammonia and nitrite concentrations corresponded to significant reduction in species diversity of mayflies. The objectives of the study were to evaluate the sensitivity of six mayfly species to the mixture of ammonia, nitrite and nitrate in acute laboratory tests and to compare the sensitivity found with results of the first river bioassessment in the region considered and with species saprobic indexes. The rank of the species sensitivity was: Baetis vernus < Potamanthus luteus < B. fuscatus = Cloeon bifidum < Ephemerella lenoki < Heptagenia sulphurea (p < 0.05). The experiments revealed variation in sensitivity among the species by a factor of 7.5. Comparison of the tests results and the available field data shows that species which exhibit higher tolerance in the tests inhabit comparatively greater amount of sites include contaminated places. Final conclusion is addressed in comparison of the results found with more spatially and temporally extensive observations. Saprobic indexes of the species and their acute tolerances (LC50s) tend to be positively correlated (r = 0.93, p = 0.02).