Urban expansion and the transformation of rural areas into suburban areas along with increasing human pressure can cause major changes in the environment. Typical effects of urbanization include degradation of aquatic ecosystems. However, urban expansion is often accompanied by an effort to provide residents with some contact with nature in the city. Natural waterbodies are the elements of the environment predestined to ensure appropriate conditions for recreation and other ecosystem services key to human well-being. In this study, the changes in the forms of development of a submontane stream catchment area (Carpathians, Poland) against the background of the gradual extension of city boundaries were analysed. In addition, the impact of urbanization on the ecological conditions of the urban stream, and therefore the potential ecosystem to provide ecosystem services, was assessed. Although the extension of the city entailed the development of settlements, it was accompanied by the expansion of the municipal sewage infrastructure, thus improving sewage management. The disappearance of arable lands from the stream catchment due to the decline in agricultural activities initiated the spontaneous process of buffer restoration along the stream. All the biotic indices such as Shannon diversity index, Margalef species richness index and BMWP-PL index, based on macroinvertebrate communities increased, and the fish were more numerous in the late stage of city development compared with the early (rural) stage. Surprisingly, the system has rehabilitated well with no revitalisation actions. It is necessary, however, to improve morphological in-stream conditions, and to make further efforts to improve water quality for the system to develop a semi-natural state. Only reaching full ecological potential can lead to an increase in the ecosystem capacity to provide ecosystem services. The studied ecosystem may provide many different services simultaneously, but their availability depends on the protection of the ecosystem's functioning as a whole.

The Eurasian beaver (Castor fiber) has been reintroduced into the Carpathian Mountains and has once again become an important factor for modifying streams. Forty-three sampling sites were compared with 10 reference sites in streams not settled by beavers. Models related to the impacts of beavers on various fish life history stages and a model presenting attributes influencing the ichthyofauna structure in streams with and without beavers were generated. Significant differences in the fish species composition were found between beaver ponds versus the running sections of streams. The changes associated with pond aging caused decrease of Siberian bullhead (Cottus poecilopus) density. For brown trout (Salmo trutta), beaver ponds were the only location where large individuals were found, while the upstream parts of the beaver complexes provided spawning habitat and an area for fry growth. Common minnow (Phoxinus phoxinus) and stone loach (Barbatula barbatula) had higher density in ponds than in streams. The decisive factors for the ichthyofauna in the mountain streams settled by beavers were local attributes related to beaver activity. Our results illustrate interactions among beaver, landscape context, and fish life history in influencing the response of the stream fish assemblages to beaver recolonization. It also helps answer the question of how Eurasian beaver influence stream fish assemblages, at a much larger scale than previous studies.

The increase in anthropogenic sediment has become the most significant factor responsible for degrading flowing waters, preventing them from attaining the good ecological state of rivers requested by Water Framework Directive. After agriculture and mining, forest exploitation is a major source of mineral suspension. The accumulation of fine sediments may reduce fish spawning effectiveness, inhibit migration, and interfere with feeding. Streams degraded by the influx of anthropogenic sediments may be recolonised provided that ecological continuity of the dendritic river network is maintained. The present study focused on mountain stream fish communities whose catchments have undergone natural and intensified soil erosion. We tested the hypothesis that forestry practices transforming the stream habitats combined with the discontinuities created by hydrotechnical structures have had negative impacts on the entire catchment and adversely altered fish communities. The research was carried out in two catchments: i) in the national park, and ii) outside the national park, in an area with forest exploitation. It was observed that the negative effects of the dramatic increases in mineral suspension loads were synergistically aggravated by the presence of objects disturbing fluvial system continuity. The consequences of the synergy between these two factors were evident in local brown trout populations. Sites formerly inhabited by brown trout lacked downstream barriers during our study. After eliminating this parameter, our analysis revealed that channel silting also reduced brown trout abundance downstream from the barrier. The weir in the Muczny Stream inhibited ichthyofaunal re-establishment in streams prone to enhanced mineral suspension input. Forest mountain streams must be preserved also as cold water refugia, hence our results are of significance for forest management. Based on our results, the complete removal of the barrier in Muczny Stream is planned for 2020, and a substantial reduction in the inflow of mineral suspension to stream channels is strongly recommended.