Assessment of sediment connectivity using modelling and field-based approaches in the Slavíč River catchment(MoravskoslezskéBeskydy Mts,Czech Republic)

Mountain streams act as conveyors of sediments within the river continuum,where the physical transport of sediments between river reaches through the catchment or between individual parts(e.g.,between hillslopes and channels)of the catchment is assumed.This study focused on sediment connectivity analysis in the SlavíčRiver catchment in the MoravskoslezskéBeskydy Mts in the eastern part of the Czech Republic.The connectivity index and connectivity index target modelling were combined with an analysis of anthropogenic interventions.Additionally,field mapping,grain size of bed sediments and stream power analysis were used to obtain information about connectivity in the catchment.Based on the analysis and obtained results,terrain topography is the current main driving factor affecting the connectivity of sediment movement in the SlavíčRiver catchment.However,the modelling provided valuable information about high sediment connectivity despite different recent land use conditions(highly forested area of the catchment)than those in historical times from the 16th to 19th centuries when the SlavíčRiver catchment was highly deforested and sediment connectivity was probably higher.The analysis of anthropogenic interventions,field mapping,grain size of bed sediments and stream power analysis revealed more deceleration of sediment movement through the catchment,decreased sediment connectivity with bed erosion,and gradual river channel process transformation in some reaches.Field mapping has identified various natural formations and human-induced changes impacting the longitudinal and lateral connectivity in the SlavíčRiver.For instance,embankments along 48%of the river's length,both on the right and left banks,significantly hinder lateral sediment supply to the channel.Stream power index analysis indicates increased energy levels in the flowing water in the river's upper reaches(up to 404.8 W m^(-2)).This high energy is also observed in certain downstream sections(up to 337.6 W m^(-2)),where it is influenced by human activities.These conditions lead to intensified erosion processes,playing a crucial role in sediment connectivity.Similar observations were described in recent studies that pointed out the long-term human interventions on many streams draining European mountains,where a decrease in sediment connectivity in these streams is linked with sediment deficits and the transformation of processes forming channels.

Effect of repeated spring drought and summer heavy rain on managed grassland biomass production and CO_(2) efflux

Aims Ecosystem respiration represents an important component of the carbon cycle.The response of respiration to climate change can have a significant effect on carbon sequestration in terrestrial ecosystems in the future when,according to climate scenarios,spring drought and consequent summer heavy rains are expected.Aims of our study were to determine the effect of repeated spring drought on biomass production and CO_(2) efflux from a mountain grassland in Beskydy Mountains in the Czech Republic and to evaluate factors driving the differences among the study years.Methods CO_(2) efflux was measured on plots with ambient precipitation con-ditions(AMB)and on plots where drought conditions(DRY)in the first half of the growing seasons and consequent heavy rain were simulated in 2011-14.Important Findings The spring drought significantly decreased the amount of above-ground biomass sampled just after the simulated drought in all years except for 2014.On the contrary,the spring drought stimulated root production.The drought also resulted in a rapid decrease in CO_(2) efflux.It was lower by up to 46%for the DRY treatment compared to AMB treatment.After the sim-ulated drought period,differences in CO_(2) efflux between the treatments gradually decreased.Simulated heavy rains in DRY resulted in fast but temporary increase in CO_(2) efflux.We can assume that the future spring drought will have a significant effect on carbon balance of grassland eco-systems.The impact will depend on the length of the dry period and the time between the beginning of the growing season and the dry period.