Abstract
Flow variability determines the conditions of river ecosystem and river ecological functioning. The variability of ecological processes in river ecosystems gradually decreases. Prediction of the environmental flow allowing to keep biological diversity and river health develops as a response to the degradation of aquatic ecosystems overexploited by humen. The goal of the study was to test the influence of river incision on environmental flow estimation based on the macroinvertebrate BMWP_PL index. The 240 macroinvertebrate assemblages of 12 waterbodies varying in the bed substrate, amplitude of discharge were surveyed in southern Poland. The variations in the distribution of 151 466 macroinvertebrates belonging to 92 families were analysed. The similarity of benthic macroinvertebrates reflects the typological division of the rivers into three classes: mountain Tatra streams, mountain flysch rivers, and upland carbonate and silicate rivers (NMDS, ANOSIM, p < 0.001). As a response variable reflecting the macroinvertebrate distribution in the river, environmental parameters, BMWP_PL index was chosen. Our results show that the BMWP_PL index reached its highest values in shallower zones (by the shores) and at high water velocity in the Tatra Rivers or low velocity in most lowland rivers. The river incision significantly increased the values of e-flow calculations in relation to redeposited channels. The area of habitat suitability decreased with the bed incision intensity. In highly incised rivers, the environmental flow values are close to the mean annual flow, suggesting that a high volume of water is needed to obtain good macroinvertebrate conditions. As a consequence, the river downcutting processes and impoverishment of suitable habitats will proceed.
Highlights
Prediction of the environmental flow allowing to keep biological 17 diversity and river health develops as a response to the degradation of aquatic ecosystems overexploited by humen
206 3.1 Environmental flow based on benthic invertebrates distribution in relation to river hydromorphology
The present study showed that river bed transformation, disturbing sedimentation processes and increasing the incision of the river bed vastly increases the environmental flow values for macroinvertebrates habitat suitability
Summary
Human water demand, including irrigation to increase crop productivity, dams, and reservoirs to control the timing of stream flow, and water withdrawal from rivers, has increased dramatically over the last 100 years (Vörösmarty et al, 2010; Veldkamp et al, 2019). Maintenance of a suitable water flow in an active river channel should secure human needs, but above all ensure the proper functioning of aquatic ecosystems (Anderson et al, 2006). This has become important since river beds began to be perceived as channels filled with water, but as complex ecological systems, in which biological elements play a key role (Poff et al, 1997; Bunn and Arthington, 2002; White et al, 2016). Water flow intensity is one of the most important factors influencing multispecies communities of aquatic and water-dependent organisms (Tharme, 2003; Arthington et al, 2006; Higgisson et al, 2019).
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