The role of macroinvertebrate taxonomic resolution in bioassessment of urban streams: A case study from the City of Lodz, Poland

Benthic macroinvertebrates were sampled at 28 sites situated on ten urban streams (Łódź, Poland) representative of a wide range of anthropogenic modifications of water chemistry and bed structure. A total of 5,043 individuals, comprising 121 species belonging to 37 families and 15 orders, were collected. Diptera (35.8 %) and Ephemeroptera (31.8 %) were dominant.

The studied sites were grouped into clusters based on separately-analyzed environmental parameters, various levels of taxonomic diversity, and bioassessment variables. All analyses demonstrated similar trends of anthropogenic modification, intensifying concentrically from the suburbs towards the city centre. The first cluster included the upper section of streams; less polluted, richer in ecotone zones and natural stream bed substrate. The second cluster comprised streams demonstrating the influence of moderate human pressure. The third cluster included streams flowing through the city center in concreted beds and which were connected to a combined sewage system in which sewage and rain water are transported through a single canal system and enters the nearest stream. Modification of stream beds was significantly negatively correlated with the number of species, families and orders, but not with total abundance.

The number of species, the number of families and the number of orders were highly mutually correlated. Moreover, they were similarly correlated with biodiversity and biotic indices, which are used to assess the ecological status of the aquatic environment. Hence, different levels of taxonomic identification demonstrate similar effectiveness in assessment, i.e. higher taxa of aquatic macroinvertebrates may be suitable for simplified ecological monitoring of urban watercourses.