Enhancing the Ecological Quality Assessment of River Floodplains Based on Benthic Invertebrates

ABSTRACT Floodplains are crucial components of river landscape, essential for the biodiversity and ecological integrity of large rivers. However, they are often overlooked and underestimated when assessing the ecological status of the main river channel. The main objective of this study was to identify the most relevant scheme for assessing the ecological status of side arms in the Danube floodplain (Slovakia) based on benthic invertebrates. The calculation of ecological status for the Danube main channel was adapted to the environmental conditions of the floodplain as a measure of the evaluation accuracy of six taxonomically different floodplain indexes. The study was based on a comprehensive survey of benthic invertebrate diversity conducted at 19 sampling sites, covering eupotamal and parapotamal side arms. Three floodplain indexes that significantly correlated with ecological status were categorised based on predicted values in relation to status class thresholds. The floodplain index based on Polychaeta, Oligochaeta, Mysida, Isopoda and Amphipoda (FI_P) showed the best result, aligning closely with the commonly used classification of lateral habitats. Although it divides the eupotamon into two subclasses, a main channel and a side arm, the inclusion of two different eupotamal habitats in the classification supports the geomorphological variability of side arms and their degree of ecological succession. The shortcomings of the assessment based on the lateral habitat classification scheme are discussed, emphasising the importance of applying this method for the assessment of floodplain waters and their conservation management.