Milan Lehotský

Influence of morphohydraulic habitat structure on invertebrate communities (Ephemeroptera, Plecoptera and Trichoptera)

Fluvial geomorphology proposes the methodology of cognition and assessment of the riverine landscape and points to the possibilities of exploitation of its results in hydrobiological research. Habitat structure of two reaches of the Drietomica brook (Biele Karpaty Mts, Slovakia) was assesed at level of morphological and morphohydraulic units in the sense of the River Morphology Hierarchical Classification (RMHC)). Physical habitats were described by flow hydraulics and substrate properties as directly measured variables (current velocity, depth, substrate size) and related variables (flow type, Froude and Reynolds numbers). According to the shear stress (expressed by Fr and Re), the morphological units were divided into two main groups — with low shear stress — pools, glides, edgewaters, bar nooks and bars; with high shear stress — riffles, runs, rapids and scours; characterized also by different Ephemeroptera, Plecoptera and Trichoptera (EPT) communities. The EPT communities were analyzed in relation to the morphological, hydraulic and substrate characteristics of the stream channel. The main environmental gradient responsible for the variation in EPT fauna was found using Principal Component Analysis and was related to gradient of flow in term of current velocity and other hydraulic attributes covered by Fr and Re numbers. The EPT communities (by means of abundance, feeding types, current, microhabitat and zonation preferences) showed preferences for different morphological units, flow type and current velocity. Depth and substrate grain size showed only weak relation to EPT communities.

Response of the Danube River Floodplain to Flood Events During 2002-2007 Period

Response of the Danube River Floodplain to Flood Events During 2002-2007 Period The relationship between floods and their geomorphic effect is discussed in this article. Almost every flood event is registered in overbank alluvia. We investigated sediment structures and textures as a response to three flood events occurred during 2002-2007 period on the Danube River floodplain in Bratislava. The change in sedimentation is the effect of floodwater flow energy changeability in the channel and floodplain. Generally, three main phases of energy flow changes of floods are recognised and thus the complete flood record can be expressed as the set of three layers. We also analysed conditions of the overbank sedimentation based on the shape and size of sedimented particles. Results show a relatively high variability of sedimentation processes during floods. The total amount of new overbank sediment accumulated in the 2002-2007 period, its texture characteristics and spatial distribution do not depend only on flood discharge, but also on the drainage basin sources of floodwater and sediment.

Geomorphic/Sedimentary Responses of Rivers to Floods: Case Studies from Slovakia

The aim of this study is to outline the geomorphic/sedimentary responses of three Slovak river systems of different character (a non-channelized meandering gravel-bed river, a mixed-bedrock headwater river, and a channelized section of a large alluvial river) to extreme flood events. Lateral channel shifts and the spatial variability of channel landforms as responses of a non-channelized gravel-bed stream to flood events were studied on a 13.2 km long reach of the Ondava River in two time horizons, 2002 and 2009 (reference year: 1987). Two different methods were used to quantify the geomorphic effect of floods on the Topl’a River. First is the analysis of the remotely sensed imagery before (September 2006) and after (October 2009) the July 2008 flood. Second is the analysis of representative cross sections measured on each of the 78 delimited channel reaches. Lithofacies studies of the Danube River overbank deposits were conducted on the right-bank inter-dike inundation area (active floodplain) of 300–600 m width. Case studies prove that the responses of different river systems to floods are governed by a combination of ‘global’ laws and ‘local’ spatial and/or temporal factors (different settings and scales).

Channel migration inferred from aerial photographs, its timing and environmental consequences as responses to floods: A case study of the meandering Topľa River, Slovak Carpathians

Abstract The bank erosion area, rate of bank retreat and overall geomorphological and financial effects of channel migration due to recent flood events (over the time span 1987–2009) are identified using remotely sensed data and GIS. A 39 km-long reach of the meandering, gravel bed Topľa River (Flysch Slovak Carpathians) was selected as the study area. Based on the analysis of culmination discharges, two different flood periods are identified. The first one (1987–2002) is characterised by the dominance of low magnitude flood events, compared to the second one (2002–2009) with higher magnitude floods. Aerial photographs from 2002 and 2009 were chosen as a way to capture the morphological changes that occurred after the flood periods, while those from 1987 served as the reference point. In total, an area of 85.2 ha was eroded and 60.1 ha were deposited. The average channel shift per year doubled from 0.8 m/year (1987–2002) to 1.6 m/year (2002–2009). The most eroded land cover category in the riparian zone is floodplain forest, followed by arable land, grasslands and pastures and shrubs. From an economic point of view, the eroded floodplain with arable land and grassland (€ 29,924.02 in total) is a negative consequence of channel migration.

Testing for longitudinal zonation of macroinvertebrate fauna along a small upland headwater stream in two seasons

Abstract The effect of longitudinal zonation patterns and macroinvertebrate responses to changes in habitat characteristics have been given a lot of attention. But studies of changes in macroinvertebrate assemblages along small upland undisturbed watercourses are still lacking. The aim of the study is to analyse variability in macroinvertebrate communities between two different habitats/morphological sequences – shallow (riffle/run/step/) and deeper (pool) channel-bed morphological units on the background of the environmental parameters (local relief, slope, channel confinement ratio, channel-valley walls connectivity, floodplain continuity and channel abut, channel sinuosity and predominant land cover of riparian zone) of seven valley segments (functional process zones) in two seasons of the year (spring and autumn). The longitudinal-downstream gradient research was conducted on the semi-natural upland headwater brook in the Little Carpathians (9,330 m long, average gradient 2.8%) at 15 morphological sequences (30 sampling points). Each sampling point in spring as well as in autumn was characterised by mean flow velocity, discharge, water depth, channel width, channel bottom particle size, and flow types. Selected physico-chemical variables: pH, dissolved oxygen content (DO), oxygen saturation (DO %), temperature (t) conductivity and total dissolved solids (TDS) were measured directly in the field using the multisonde measuring device. Organisms were identified into the family level. The results showed that differences in zonation of benthic invertebrates between seasons are more apparent than seasonal variability between pools and riffles. Spring samples followed the increasing gradient of total dissolved solids downstream with characteristic families for upper and lower stretch. The disruption of macroinvertebrates zonation was more evident in autumn samples with greatest effects in pools. Based on RDA, the distribution of families was driven by three significant variables in riffles and four in pools. Alike environmental factors of pool sequences in the middle and upper reaches were responsible for similarity in macroinvertebrate structure. In conclusion, the distribution pattern of benthic invertebrates of the natural part of the small headwater stream in terms of abundance of macroinvertebrate families followed the longitudinal zonation in spring, but in autumn were the local habitat conditions more important.