Ecological integrity of river-floodplain systems-assessment by dragonfly surveys (Insecta : Odonata)

Dragonflies are reliable indicators of the ecological quality of land-water ecotones, habitat heterogeneity and the hydrological dynamics of water bod ies. In recent years, surveys of dragonfly communities have become a powerf ul tool for the ecological assessment of floodplain areas. The goal of this paper is to present a new approach towards assessing the ecological integr ity of river-floodplain systems by analysing resident breeding dragonfly sp ecies. The methodology is based on experiences with existing approaches usi ng macroinvertebrates as bioindicators, in particular, calculations of sapr obic indices, longitudinal zonation and functional feeding group patterns. In addition to the total number of species and the number of sensitive spec ies, the 'Odonate Habitat Index' (OHI) is a key element of the assessment m ethod. It indicates characteristic features of a river-floodplain system, s uch as connectivity aspects, flow dynamics and terrestrialization processes . The OHI is calculated from the species-specific habitat values (expressin g habitat preferences), abundances and the species-specific indication weig ht, which distinguishes eurytopic from stenotopic species. The comparison o f the status quo with a reference condition allows an assessment of individ ual water bodies and/or of a whole area in a five-tiered classification sch eme. The approach presented may also be used for the evaluation of restorat ion measures (e.g. reconnection of side arms) and for the definition of man agement objectives. Apart from the methodological framework, the results of a first application of this approach are presented in the paper as well. T he study areas were selected floodplain systems of the Austrian section of the Danube and man-made inshore structures of the impounded Danube section in Vienna. Copyright (C) 2001 John Wiley & Sons, Ltd.