In this study, the quality of the aquatic habitats of mountain and piedmont streams was evaluated using the ‘Instream Flow Incremental Methodology (IFIM)’ decision-making tool. The quality of habitats was interpreted from the behaviour of bioindicators in the form of habitat suitability curves (HSCs). From 1995 until the present, 59 different reaches of 43 mountain streams in Slovakia and 3 validation reaches were evaluated, and the results analysed. The aim of this study was to generalize the parameters of the HSCs for the brown trout. The generalized curves will be useful for water management planning. It is difficult and time-consuming to take hydrometrical and ichthyological measurements at different water levels. Therefore, we developed a methodology for modifying suitability curves based on an ichthyological survey during a low flow and a flow at which fish lose the ability to resist the flow velocity. The study provides the information how such curves can be modified for a wider flow range. In summary, this study shows that generalized HSCs provide representative data that can be used to support both the design of river restoration and the assessment of the impacts of the water use or of climate change on stream habitat quality.

The study is focused on the objectification of an assessment of the quality of an in-stream habitat in mountain and piedmont streams by the decision-making Instream Flow Incremental Methodology (IFIM) due to climate change. The quality of the habitat was assessed on the basis of a bioindication, represented by ichthyofauna. Sixty-four reaches of 47 watercourses in five river basins in Slovakia, in which ichthyologic, topographic, and hydraulic measurements were performed, were evaluated. The effect of the physical characteristics of the stream channel on the quality of the in-stream habitat has been verified on a number of reference reaches in which the measurements were performed at different water levels. From the set of the data measured, an analysis aimed at determining the impact of individual characteristics on the quality of an in-stream habitat has been carried out. The results show the optimum ratio of the weights of the flow velocity and water depth for an assessment of the quality of an in-stream habitat due to climate change.

The article aims at assessing the impact of hydraulic characteristics on the habitat quality of mountain and piedmont watercourses. The solution results from the Riverine Habitat Simulation model, where the quality of the aquatic habitat is represented by the weighted usable area (WUA), which is determined using brown trout as the bioindicator. Flow velocity and water depth are basic abiotic characteristics that determine the ratio of suitability of the instream habitat represented by the weighted usable area. The influence of these parameters on the objective evaluation of the habitat quality is the essence of the paper. The measurements were carried out during the summer period at minimum discharges for 17 mountain and piedmont streams in Slovakia. Three methods for assessing the habitat quality were tested, and differences in the results were found to be significant. The evaluation shows the optimum design methods for calculating the weighted usable area.

This study evaluated the relationship between abiotic flow characteristics and habitat quality. Habitat quality was assessed using the Instream Flow Incremental Methodology (IFIM), which uses bioindication. Brown trout was selected as a bioindicator because of its sensitivity to morphological changes and its occurrence in sufficient reference reaches. The correlation between the morphological characteristics of the stream and the area-weighted suitability (AWS), which represents habitat quality, was evaluated. Fifty-nine reference reaches of fifty-two mountain and piedmont streams in Slovakia were analysed. The correlation analysis demonstrated the strongest relationship between the AWS and the stream depth and width. The relationship between the water surface area and the AWS indicated that, for mountain streams, there is a significantly increasing trend of the AWS value with increasing surface area. Considering piedmont streams, the AWS variation with a change in the water-surface area was minimal. These results can form the basis for deriving regression equations to determine habitat quality. Such a procedure can significantly simplify the evaluation of the quality of aquatic habitat, making it much more accessible for design practice.