Nonparametric evaluation of environmental parameters determining the occurrence of stonefly larvae (Plecoptera) in streams

Abstract

This study explored the relationship between the occurrence of stonefly species, stream type and basic environmental conditions. Only 13 taxa, out of 115 species occurring in catchments investigated in the Czech Republic (Soldan, Zahradkova, Helessic, Dusek and Landa, 1998), were selected for this study. The environmental parameters chosen were those that characterized the hydraulic and physical environments of almost all the streams: slope, current velocity, discharge regime, bottom roughness, current type (Reynolds number and Froude number). Organic water pollution, characterized as BOD5 and saprobity, was intentionally not embodied in the evaluation, because the chosen sampling sites were in streams which proved to have minimal or almost no organic pollution. The relationships between the occurrence of stoneflies and the stream types (as set out by Illies and Botosaneanu, 1963) were evaluated on the basis of chi-square tests. For two species (Nemurella pictetii - crenal and Perla burmeisteriana - epipotamal) there was strong evidence of affinity to the stream type. The following parameters were shown to have a statistically significant influence on stonefly communities: slope, substrate roughness, current velocity and current type (Reynolds number and Froude number). For the most abundant individual species, Perla burmeisteriana, Isoperla grammatica, Leuctra albida, Leuctra nigra and Isoperla sudetica the influence of the investigated factors on occurrence and species abundance was assessed.