Combined use of the hydraulic and hydrological methods to calculate the environmental flow: Wisloka river, Poland: case study.

The scarcity of water can result in a direct conflict between the protection of aquatic resources and water use. For many agencies, environmental flow (EF) methods are essential in environmental impact assessments and in the protection of important fisheries resources. The objective of this paper is to compare selected hydrological and hydraulic methods and determine the scientifically acceptable and cost-effective way to environmental flow within a section of a mountain river with high naturalness, on the example of the Wisloka. In this paper, environmental flow was calculated using conventional hydrological methods: Tennant's, Tessman's, flow duration curve and hydraulic methods, wetted perimeter method (WPM) and method based directly on ichthyofauna habitat requirements (spawn and migration). The novelty is the combined use of the hydraulic and hydrological methods which relates to flow hydraulics based directly on ichthyofauna habitat conditions. The hydraulic methods provide lower values of environmental flow in comparison with the hydrological methods. The key issue in the use of the hydraulic methods is the choice of criteria. The development of the required set of parameters while taking into account their seasonal nature shifts the method toward habitat modeling methods. However, the scope of habitat requirements of ecosystems must be defined, including the set of aquatic organisms and watercourse type before a hydraulic method may be widely used. Being generally low-cost and simple, the methods presented in this paper can be applied in the water management legislative process.

On the reintroduction of the endangered thick-shelled river mussel Unio crassus: The importance of the river's longitudinal profile.

Freshwater mussels of the order Unionida provide important ecosystem functions and services. Unfortunately, some previously widespread species are now seriously endangered. To restore the historical range of the population of Unio crassus in the Biala River, southern Poland, the species was reintroduced into a series of 'stepping stones' joining two remnant populations. During the first phase of the study, the relationships between the abundance of U. crassus, physical habitat, and water quality were studied to assess reintroduction potential. In general, chemical water quality improved upstream from the existing population, favouring the decision for reintroduction, whereas morphological variables worsened. Mussel abundance was correlated negatively with the elevation and slope of channel, organic matter contents, and pH (exceeding 8.0), but positively with silt presence, water conductivity, and concentrations of HCO3-, Ca2+, and NO3-. During the second phase, adult individuals were introduced into one type of functional habitat-marginal channel sectors with still water and fine sediment. Despite the initial very high rate of reproduction in some parts of the upper reach of the river, the juveniles were ultimately recruited only in the lower part of the restored range, resulting in a very rapid change in recruitment at a channel slope of 1.8‰. Recruitment was positively related to silt content, conductivity, and Ca2+ and HCO3- ions, negatively to channel elevation and slope, and water pH. The host fish species showed no correlation with abiotic habitat features within the studied reach. These results imply that most of the habitat traits related to U. crassus occurrence depended on the river's longitudinal profile, not on the chemical water quality, and that final success of introduction should be evaluated after several years.