Reference conditions of German stream types analysed and revised with macro invertebrate

This study investigates reference conditions of Gentian stream types using the top-down stream typology developed by POTTGIESSER & SOMMERHAUSER (2004) and 264 macrozoobenthos samples selected as representing reference status. With the aid of discriminant and correlation analyses, the use of typological parameters is investigated as regards their relevancy and the study alms to show whether the metrics used in the newly developed type-specific indices (BOHMER et al. 2004b) reflect the reference conditions. The data cover 15 of the 24 German stream types. The use of stream size, of ecoregions as an indirect parameter for geographical altitude, and of the bottom substrate for the lowland stream types as typological factors can be confirmed, as can six stream types as separate and independent. As bottom substrate is an essential factor for the lowland stream types, their independency is at least probable. For the stream types of the lower mountain regions, a separation of siliceous and calcareous types seems not to be crucial for the bioassessment on metric level, while a new approach for and a possible splitting of the small streams in floodplains is recommended.