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Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks., Earth-Science Reviews, 188, ISSN:0012-8252, ISSN:1872-6828

Methane (CH4) emissions from temperate freshwater reservoirs have only been evaluated for the last several decades. Freshwater ecosystems (including water reservoirs) release crucial quantities of this important greenhouse gas. Ebullition that releases methane into the atmosphere from bubbles originating from sediment is important source of methane. Regardless of the importance of these emissions, a very limited number of scientific research papers monitoring this flux into the atmosphere are available. Estimated values of methane emissions from freshwater temperate reservoirs vary considerably. There are many different methods for monitoring methane emissions. It seems that the freshwater reservoir stimulates methane formation in increasing scales. The size of the sum of methane emitted from freshwater reservoirs is also difficult to say.

This thesis follows previous works of our group (Rieger T. et al., 2008; Cepl J. et al., 2010 and Patkova I. et al., 2012), where we focused on the morphology of the bacterial colonies Serratia marcescens and its variety caused by changing of the inoculation conditions on nutrient agar. When bacterial colonies S. marcescens are grown on nutrient agar enriched with glucose isolated enough from other colonies in its living space, it can form coloured structured colonies, which we named morphotype "fountain" (F). This morpotype becomes ideal for following studies of mutual influencing of the bacterial colonies, because of its ability of pigmentation change or structure loss caused by altering surrounding inoculation conditions. We noticed in normal sowed agar plates, that bacterial colonies, which grows in the close distance with other colonies develop their pigmentation sooner, than colonies, that grows more isolated. We studied how is this influencing happening and what are the necessary conditions for it. We proved, that different species of bacterial macrocolonies (S. marcescens - morphotype (M), S. rubidea and E. coli) emits into the nutrient agar informative signal, which makes the recipient colonies S. marcescens reacts on this signal with the same manner (X structure). It looks, that this is...

Mayfly emergence patterns and microhabitat preferences were studied in the Plitvice Lakes NP (Croatia) during a nine-year period in two types of karst freshwater habitats: a spring and two tufa barriers, using pyramid-type emergence traps. A total of nine mayfly species were recorded. Highest proportion of collected individuals belonged to the genus Baetis which was recorded at all three study sites, but we were unable to distinguish between two included species (B. rhodani and B. cf. nubecularis). Other numerous recorded species were Paraleptophlebia submarginata, Ephemera danica and Rhithrogena braaschi. Tufa barriers had higher species richness and diversity than the spring but significantly lower population densities. In NMDS analysis, the spring separated from tufa barriers. Mayfly assemblages were at all sites dominated by species typical for the rhithral zone, while in tufa barriers, potamal and littoral elements also appeared. In the studied spring, emergence mainly occurred between March and November, where the main trigger for emergence was photoperiod. In tufa barriers, emergence mainly occurred between April and July and was related to the elevated water temperature. Generally, higher abundance of emerging individuals was recorded during the years with higher water discharge. Emergence patterns of some species were in accordance with their typical Central European emergence patterns (e.g. E. danica) while some other showed certain discrepancies (e.g. Rh. braaschi). The highest species richness was recorded on moss, and the highest number of individuals on gravel/tufa. Baetis sp. preferably emerged from gravel/tufa and moss, and Rh. braaschi from vegetation (moss and macrophytes).

Reservoirs are man-made water-bodies predominantly created by using a dam or a lock to store water that may be used for irrigation, flood control or production of electric en- ergy. Reservoirs could provide important habitats for birds, fish and other aquatic organ- isms. Macroinvertebrate communities were studied at nine reservoirs located in the Dinaric ecoregion of Croatia during July and September 2016. At each reservoir, one study site, with the lowest anthropogenic influence was selected. The littoral zone was sampled, on a surface area of 250 m2 or less, depending on the incline of the bank. At each sampling site, four levels of depth were defined in 25 cm segments to 1 m total depth (0 to 0.25 m, 0.25 m to 0.5 m, 0.5 m to 0.75 m and 0.75 m to 1 m). Ten samples were collected at each site using benthos hand net (25 cm × 25 cm ; 500 μ m). Physico-chemical water properties were measured: dissolved oxygen concentration, oxygen saturation, electrical conductiv - ity, pH and alkalinity. Significantly higher population densities of Oligochaeta (p < 0.05), found in deeper littoral reaches of all reservoirs, were most probably related to substrate characteristics and their tolerance in terms of oxygen demands. On the contrary, Odonata and Ephemeroptera were significantly more abundant (p < 0.05) in shallower littoral parts of the reservoirs, due to higher variability of microhabitats and higher demands for oxygen concentrations. Results of this study provide new information about the ecology of benthic macroinvertebrates in reservoirs of the Dinaric karst

This study investigates water quality and hazardous substances toxic to aquatic life in a small lowland stream under different hydrological conditions. The objective was to explore links among hydrology, water chemistry and microbial contamination in a stream predominantly impacted by structural degradation of stream morphology (channelization and straightening), agricultural land use in the catchment, and by a high load of treated wastewater. Sampling was carried out during spring high (HWL, > 200 cm), summer low (LWL