Riparian ground beetles in gravel bed rivers: validation of Invertebrate Bankfull Assessment method

Abstract

Bankfull Assessment Method (IBA method) applies riverine invertebrate community of ground beetles as a biotic indicator of bankfull variation in a dynamic river. IBA index is calculated as a proportion of small sized individuals (1–6 mm) to large size individuals (18–24 mm) of ground beetles in given sample site. The aim of the study was to validate the IBA bankfull discharge method with 135 carabid assemblages collected in gravel-bed rivers of various modifications of channel morphology in the Polish Carpathians. Constrained canonical correspondence analysis revealed that biotic factors such as IBA, plant cover and plant height described most of the variation of small and large sized species abundance. The IBA index variation confirmed earlier expectation of the mean IBA values. Mean value of the index for the lowest bench is about 5, for the middle bench about 2 and it never exceeds 1 for the highest bench. The bankfull calculated using morphometric methods (Wolmann) was located between the first and second bench on each river. Values of the IBA for the lowest bench depend significantly on channel incision whereas modifications of vegetation affect the values for all three benches. The study presents high value of IBA method in estimating bankfull discharge which is considered to be important supporting flow predicting morphological changes responsible for river channel shape with direct connection to living organisms occupying river banks as well as to river environmental quality. Proposed simple method could be important for local watershed managers for prediction of bank embankments level (e.g. maximum level of rip-rap or gabions) or for maximum level of low head hydraulic structures when they are necessary in terms of river engineering works but when they are still built as environmental friendly hydraulic structures.