Hydromorphological conditions, potential fish habitats and the fish community in a mountain river subjected to variable human impacts, the Czarny Dunajec, Polish Carpathians

Abstract

The Czarny Dunajec River, Polish Carpathians, has been considerably modified by channelization and gravel mining-induced channel incision and it varies in morphology from a single-thread, incised or regulated channel to an unmanaged, multi-thread channel. For twelve cross-sections with between 1 and 4 flow threads, the abundance and diversity of fish fauna were determined by electrofishing and compared with an assessment of hydromorphological river quality and the variation in flow depth, velocity and bed material size. Hydromorphological quality of the river varied between high-status conditions (Class 1) in unmanaged, multi-thread cross-sections with varying proportions of islands and Class 4 in channelized cross-sections. The increased number of low-flow channels in a cross-section was associated with a larger aggregated width of low-flow channels and greater variation in flow depth, velocity and bed material size. Single-thread cross-sections hosted only 2 fish species and 13 individuals on average, whereas 3-4 species and 82 individuals on average were recorded in cross-sections with four low-flow channels. Regression analysis indicated that both the number of fish species and individuals increased linearly with increasing variation in depth within a cross-section and exponentially with improving hydromorphological river quality, while they were unrelated to flow width, suggesting that it is the increase in variability of habitat conditions rather than simple habitat enlargement, that supported the increased abundance and diversity of fish fauna in the multi-thread cross-sections. This study shows that the simplification of flow pattern and the resultant degradation of hydromorphological river quality, caused by human impacts, is reflected in remarkable impoverishment of fish communities and that recovery of these communities will require an increase in morphological complexity of the river. Figure 3. Scores given by four evaluators for the hydromorphological river quality in the investigated cross-sections of the Czarny Dunajec and the average of the four estimates. The number of flow threads in each cross-section is also indicated Figure 5. Scatter plots of physical characteristics of the Czarny Dunajec versus the number of flow threads in the investigated cross-sections.The significance of the difference of the parameter means between the cross-sections with one and four low-flow channels were determined by Mann-Whitney test. The dashed lines link the parameter means between the two groups of cross-sections

The impact of wildfire on stream fishes in an Atlantic-Mediterranean climate: evidence from an 18-year chronosequence

“…It is, however, notable that the apparent ecological impact was significantly related to the degree of management intervention, increasing with the incidence of bank management and associated channelization. Again, the likely mechanistic process, increased erosive power, has been well-documented in geomorphological studies (Barker et al, 2009) and corroborates with evidence from previous ecological studies (Oscoz et al, 2005;Wyzga et al, 2009). By exacerbating ecological disturbance and impeding recovery, the combined stress of habitat modification and wildfire can provoke a synergistic disturbance interaction.…”

Assessment of river hydromorphological quality for restoration purposes: an example of the application of RHQ method to a Polish Carpathian river

“…Notably, the difference in scores given to both types of river crosssections was greater at the sites where no channel incision is observed in unmanaged river reaches, but smaller where the Biała is deeply incised in such reaches. A similar pattern of hydromorphological quality was found with the RHQ method for the Czarny Dunajec River, in which channelized cross-sections differed by three quality classes from cross-sections in the unmanaged reach with a multithread, vertically stable channel and by two classes from those in the unmanaged reach with a single-thread, deeply incised channel (Wy_ zga et al 2009(Wy_ zga et al , 2010b. Also in this river, the spectacular disparity in hydromorphological quality scores between different types of cross-sections was reflected in marked differences in the richness of riverine communities: fish (Wy_ zga et al 2009) and benthic macroinvertebrates (Wy_ zga et al 2012a).…”

“…This resembles the manner of evaluation typical of RHS method, based on the diversity of habitat features rather than on the degree of deviation from the conditions that would be natural for a particular river (surface water body). With a lack of relevant assessment procedure that would provide insight into both river state and active fluvial processes in Poland, a new method of assessment-River Hydromorphological Quality, RHQ, was developed (Wy_ zga et al 2009(Wy_ zga et al , 2010b to enable evaluation of hydromorphological river conditions in the context of its contemporary dynamics. This method is described in detail below.…”

“…These methods involve evaluation of the entire river corridor and both present and recent river change analysed on maps, aerial photos and orthophotos (Rinaldi et al 2013a;Belletti et al 2015). This group of methods includes, among others, the Australian River Styles Framework (Brierley and Fryirs 2005); IHG method in Spain (Ollero et al 2011), MQI in Italy (Rinaldi et al 2013b) and Polish method of river hydromorphological quality assessment RHQ (Wy_ zga et al 2009(Wy_ zga et al , 2010b(Wy_ zga et al , 2012b. Consideration of ongoing processes and field recognition of the river state make these methods most suitable for river restoration purposes.…”

“…Hydromorphological evaluation of rivers in the country has been performed with a few methods (Lewandowski 2012). The lack of a versatile, suitable method of assessment led to the development of River Hydromorphological Quality (RHQ) method (Wy_ zga et al 2009(Wy_ zga et al , 2010b designed also for the purpose of planning and evaluation of restoration measures. This paper aims to provide:…”