Rivers In Croatia Research Articles

Discharge regimes of the Bregana and Breganica rivers in Croatia

Discharge regimes of the Bregana and Breganica rivers in Croatia

One new species of Aneumastus D.G. Mann et Stickle (Bacillariophyceae) from Krka River, Croatia

Karst rivers in Croatia are common phenomena and known biodiversity hotspots for many different groups of organisms. Due their importance from a natural, cultural and socio-economic point of view, most of them are protected as National Parks. Diatoms in these habitats are not well known, and recently detailed study has been started. During observations of samples from Lake Visovac on Krka River, one <i>Aneumastus</i> species with specific morphological features, has been recorded. The species is characterized by linear valves with almost parallel margins in the mid-valve, rostrate apices and striae that are partly biseriate, coarsely punctate and distantly spaced. In this study, it is described as a new species <i>Aneumastus </i><i>visovacensis</i> sp. nov. Its morphology is documented with light and scanning electron microscopy, described in detail, and compared with the most similar species from <i>A. tusculus </i>species complex.

Contribution of alien peracarid crustaceans to the biocontamination of benthic macroinvertebrate assemblages in Croatian large rivers

Peracarid crustaceans (orders Amphipoda, Isopoda and Mysida) are one of the most important groups of invaders in fresh and brackish waters. Although large rivers in Croatia have been heavily invaded by peracarid crustaceans, little is known about their impact on local benthic macroinvertebrate assemblages. The main aim of this study was to investigate the contribution of alien Peracarida to the biocontamination of macroinvertebrate assemblages in Croatian large rivers as a proxy measure of their impact. Quantitative sampling was conducted twice (2015 and 2016/2017), at 48 sites on four large rivers (Danube-4, Sava-21, Drava-20, Mura-3). Physicochemical parameters were measured eight times during 2015 and 2016. In total, 16 species were recorded, five native and 11 alien species. The highest number (10 alien species, most from genus Dikerogammarus and Chelicorophium) were found in the Danube River, while subsets of alien species were found in the Sava (5 spp.) and Drava Rivers (6 spp.), and no alien species were found in the Mura River. The most upstream reaches of the Mura, Drava, and Sava Rivers in Croatia have not yet been colonized by invasive peracarids and the native peracarids are still abundant there. In the Drava River, alien Peracarida had the highest densities. Significant negative correlations were established between the number of native taxa and alien Peracarida species. Proportions of alien peracarids in the total density of benthic macroinvertebrates were spatially variable, the highest average values in the Drava River (24.4 %), and lower in the Danube (20 %) and the Sava (17.7 %) Rivers. Alien Peracarida had the most important contribution to the richness and abundance contamination of macro¬invertebrate assemblages. The upstream spread of invasive peracarids will increase biocontamination and could cause a decline of native species richness and abundance in the most upstream reaches of the Sava and Drava Rivers. To prevent further up¬stream spread of alien Peracarida, “check, clean and dry” protocols should be included in the national regulations.

Dinaric karst intermittent rivers harbour some rare mayflies (Insecta, Ephemeroptera)

While investigating the aquatic macroinvertebrate fauna of four intermittent Dinaric karst rivers in Croatia, we confirmed or recorded new distribution data and ecological features for several mayfly species rare in Croatian freshwater habitats: Nigrobaetis niger (Linnaeus, 1761), Procloeon pennulatum (Eaton, 1870) and Paraleptophlebia werneri Ulmer, 1920. To our knowledge, this is the first record of N. niger in intermittent lotic habitats. We discuss their substrate preferences in the studied habitats as well as their relationships with measured physico-chemical water parameters. The newly obtained results confirm that our knowledge about Croatian mayfly fauna and species ecological requirements in intermittent Mediterranean rivers is still incomplete and is increasing with systematic studies.

Can Ephemeroptera, Plecoptera, Trichoptera (EPT) assemblage reflect nitrogen and phosphorus load in the riverine ecosystem?

The aim of this paper is to make a comparative analysis of benthic macroinvertebrate compositions in streams and rivers in Croatia with relation to different physical-chemical factors, especially nutrients. Samples were collected according to the AQEM method. At all the sites, 20 taxa were recorded of which Turbellaria, Gastropoda, Bivalvia, Oligochaeta, Hirudinea, Crustacea, Ephemeroptera, Odonata, Plecoptera, Heteroptera, Trichoptera, Coleoptera and Diptera were included in the present study. Water temperature mostly affected the composition of benthic macroinvertebrates to which it was inversely proportional. Nutrient enrichment, i.e., higher concentrations of ammonium, nitrates, nitrites, total nitrogen, orthophosphates and total phosphorus mostly affected Ephemeroptera, Plecoptera, Trichoptera and Diptera, by decreasing their diversity.

Plasticity, Mineralogy, and WRB Classification of Some Typical Clay Soils along the Two Major Rivers in Croatia

Quantification of soil plasticity is usually based on Atterberg limits or indices, which are then used for engineering and agricultural purposes on clay soils. Because these limits/indices are seldom analyzed during routine soil surveys, they are sometimes estimated from available soil properties using pedotransfer functions (PTFs). Main aim of this study was to test if two robust PTFs, previously created by other authors for other soils/areas, may be used for predicting plasticity of typical clay soils on fluvial deposits in Croatia. We analyzed mineralogy, plasticity, and related physicochemical properties of four representative soil profiles along Sava and Drava, two longest Croatian rivers. Particle size distribution patterns pointed to more uniform sedimentation along Sava, compared to Drava. Also, more clay was found within Sava profiles. Soil texture was finer farther away from the sources of both rivers. Soil cation exchange capacity (CEC) was almost fully positively correlated to clay content. On the other hand, Corg content showed no correlation to CEC. This is attributed to the significant presence of smectite across all studied soils. Clay was recognized as the main factor influencing soil plasticity. When compared to the measured values, the predicted values of plasticity index and liquid limit were heavily underestimated. Hence, region-specific PTFs should be developed for more accurate prediction of plasticity in these soils. According to the WRB-2015, the soils were classified as Eutric Reductigleyic Stagnic Gleysols (Clayic, Humic, Protovertic). Because soils were not dry during field description, shrink-swell cracks were not prominent, and therefore soils were not classified as Vertisols. We suggest that field criteria for classification of Vertisols should not depend on actual soil moisture. Instead, plastic limits/indices could be used.

Microbiological Quality Assessment of Water and Fish from Karst Rivers of the Southeast Black Sea Basin (Croatia), and Antimicrobial Susceptibility of Aeromonas Isolates.

Karst rivers are of great interest for commercial fishing and aquaculture, yet they are quite vulnerable aquatic environments because the permeable karst rocks do not effectively filter out contaminants. To understand the current state of karst rivers water quality, we analysed the physico-chemical and microbiological parameters, focusing on antibiotic pollution and the emergence of antibiotic-resistant microbes of three such rivers in Croatia. Water quality varied between classes I and II across sampling sites, and the numbers of total coliforms, enterococci and heterotrophic bacteria varied substantially among sites. Swabs from fish gills, spleen, liver and kidneys were cultured and 94 isolates identified by MALDI-TOF mass spectrometry. The predominant genus was Aeromonas (42.5% of all identified isolates), known for its adaptability to polluted environments and its frequent association with antibiotic resistance. Of the selected Aeromonas isolates known as most pathogenic, half were resistant to at least three antibiotic categories. The Enterobacteriaceae family was represented by the greatest number of genera, most of which are pathogenic for humans and animals and are spoilage bacteria for fish. The results of this study highlight the extent of antibiotic contamination in aquatic environments and the increasing threat of pathogenic and spoilage bacteria in traditionally high-quality karst rivers.

Analysis of Basic Physical-Chemical Parameters, Nutrients and Heavy Metals Content in Surface Water of Small Catchment Area of Karašica and Vučica Rivers in Croatia

This paper deals with the surface water quality of a small catchment area of the Karašica and Vučica rivers based on the analysis of water physical and chemical parameters according to the national Decree on Water Quality Standards (2013). Water samples were collected and analysed monthly at five sampling stations situated along the watercourses in the period between 1998 and 2015. Analysed parameters were pH, chemical oxygen demand (COD-Mn), five-day biochemical oxygen demand (BOD5), nutrients: nitrate compounds (nitrates and total nitrogen), phosphorus compounds (orthophosphates and total phosphorus), and the content of heavy metals. The obtained results indicate a water quality status between moderate and good, depending on the parameter and sampling station.

Changes in discharge regimes of rivers in Croatia

This paper presents the results of the first comprehensive national analysis of changes in discharge regimes of rivers in Croatia. Seven types of discharge regimes have been defined for rivers in Croatia. We analyzed the changes in discharge regimes of all types, comparing the standard period from 1961 to 1990 with the most recent period from 1990 to 2009. We found evidence of a redistribution of discharge throughout the year, an increase in autumn and winter discharges (especially for rivers dominantly fed by snowmelt), and a decrease in summer discharge values. Furthermore, we detected a change in the month of the appearance of mean discharge maxima and minima. In most cases, the changes can be explained by changes in the regime of climate elements (temperature, precipitation, and evapotranspiration). The results are consistent with those from upstream countries; that is, Slovenia, Austria, and Bosnia and Herzegovina.

Monitoring of selected pharmaceuticals in surface waters of Croatia.

Sulfonamides, macrolides, torasemide, fumagillin, and chloramphenicol were simultaneously analyzed in surface water samples by using solid-phase extraction (SPE) and reversed-phase (RP) liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS). In the pre-concentration and clean-up process, the pH value of samples and volume of the solvent for extraction of analytes from cartridge were optimized. Extraction recoveries were high with values in the range from 62 to 115%. Limits of quantification (LoQ) were in the range from 0.02 to 0.2μgL-1. Repeatability of the method was evaluated at LoQ and expressed as relative standard deviation (RSD). Calculated RSDs were low with values in the range from 2.4 to 14.5%. The method was successfully applied for analysis of surface water real samples. Samples were collected along the rivers in Croatia on four sampling sites in 2012 in Danube catchment areas, 19 sampling sites in Danube and Adriatic catchment areas in 2013, and another 19 places in 2014. Altogether, 20 target compounds were analyzed in 148 water samples and detected in 31 samples in range (0.1-5.3)μg L-1 or in 20.1% of samples. The most frequent and highest concentrations were detected for macrolide antibiotics. This is the first attempt of such monitoring in surface waters in Croatia.

Mayfly (Insecta: Ephemeroptera) assemblages of a regulated perennial Mediterranean river system in the Western Balkans

AbstractThe influences of river regulations on aquatic biota are insufficiently investigated. We assessed the level of ecological disturbance of the mayfly assemblages through the damming and flow alterations at two highly regulated Mediterranean rivers in Croatia: the Cetina River and its tributary, the Ruda. Contrary to our hypotheses, species richness, abundance and diversity of mayflies increased along the river’s course. At the sites directly influenced by the river regulations, mayfly assemblage changed: it was less diverse and less abundant. However, no obvious influence of the river regulation on the mayfly assemblages was detected for the sites that were indirectly influenced by these alterations. This was most likely due to specific karst hydrology, i.e., the presence of lateral springs along the course of the river. Multidimensional scaling analysis (MDS) revealed grouping of sites according to the similarity in physico-chemical water properties. The pH and water temperature were the most important environmental variables influencing mayfly assemblages. The data on ecology and distribution of mayflies presented in the current study represent a valuable background for further research and conservation practices in the Mediterranean region.

Year cycle and morphometrical characteristics of Austropotamobius torrentium from two karstic rivers in Croatia

Year cycle and morphometrical characteristics of Austropotamobius torrentium from two karstic rivers in Croatia

Leaf Morphology Variation of Populus nigra L. in Natural Populations along the Rivers in Croatia and Bosnia and Herzegovina

Background and Purpose: The aim was to determine the morphological differences between the hairy type of European black poplar (Populus nigra subsp. caudina) and the typical type from the riparian forests populations as well as between the river systems. Hairy black poplar spreads in a mosaic pattern across the Submediterranean climatic type along the River Neretva and the typical European black poplar is growing on alluvial soils along large rivers in the territory of Croatia and Bosnia and Herzegovina. Material and Methods: Samples for leaf morphometric analysis were collected in 17 natural populations of European black poplar along six rivers in Croatia and Bosnia and Herzegovina. Results: Discriminant analyses have determined that in the differentiation of population groups largely contribute some characters such as the distance between the leaf widest part and the leaf base (DBW) and the petiole length (PL). The differences between populations and analysed groups, as well as the differences between populations belonging to a particular river system, were confirmed for all studied characteristics. Conclusions: Significant differences have been determined between the typical and the hairy type of European black poplar in the studied morphological traits and these dissimilarities are in accordance with the climatic differences in respective habitats of continental riparian forests and the Submediterranean type of climate. Populations sampled in the lower course of the River Neretva, which correspond to the hairy type of the European black poplar, have smaller leaves and a greater angle between the first lower lateral vein and the midrib.

THREATENED FISHES OF THE WORLD: Telestes turskyi (Heckel, 1843) (Cyprinidae)

Tursky dace, Telestes turskyi , is a freshwater species endemic to the Adriatic drainage. This species is found only in two rivers in Croatia, the River Krka and River Cikola, and is protected by Croatian law. Major threats for this species are extremely limited distribution, river regulation, water extraction and pollution. Suggested conservation actions for this species are: habitat protection, bans on regulation and alteration of watercourse and restriction of introduction of alien fish species.

LENGTH WEIGHT RELATIONSHIPS OF THE EUROPEAN EEL Anguilla anguilla (Linnaeus, 1758) FROM SIX KARST CATCHMENTS OF THE ADRIATIC BASIN, CROATIA

This study presents the first references available for the length–weight relationships (LWRs) of eels from six karstic rivers in Croatia. A total of 380 European eels 13.0–76.0 cm long were collected by electro-fishing from six karst catchments of the Adriatic basin between 2004 and 2007. Eels of 34.0 cm in length dominated (over 50%) the catches, while abundance of eel smaller than 15.0 cm was very low. Value b of LWRs remained within the range between 2.5957 and 2.8155 , which indicates a negative allometric growth. CPUE (g 100 m -1 ) rapidly declined during the period of sampling, probably due to environmental changes, but also due to global disappearance of this species.

Typology of Discharge Regimes of Rivers in Croatia

Typology of Discharge Regimes of Rivers in Croatia

The effects of water diversion and climate change on hydrological alteration and temperature regime of karst rivers in central Croatia

Karst rivers in Croatia have been heavily dammed in the past. However, long-term impacts of dams, water diversion and climate change on karst rivers in Croatia have rarely been examined. This study analyzes long-term trends of hydrological and temperature conditions, prior to closure of new large dam, in five connected karst rivers of central Croatia: the sinking rivers Gornja Dobra and Zagorska Mrežnica that have underground connections with the Gojačka Dobra, Tounjčica and Mrežnica Rivers. It was established that hydrological conditions of these rivers have been greatly changed after the Gojak HPP, located at spring of Gojačka Dobra, became operational in 1959. Water diversion from the reservoirs on Zagorska Mrežnica and Gornja Dobra to the Gojak HPP has increased mean annual discharge (52-106%), causing great subdaily fluctuations and overall modification of natural flow regime along the whole course of Gojačka Dobra. By cutting the connection between Zagorska Mrežnica and Tounjčica, water diversion has caused a reduction of mean annual discharges of the Tounjčica (-60%) and Mrežnica (-29%) Rivers. Analyses of long-term trends in water temperature over the last 50 years have revealed significant positive trends in average annual temperature at three gauging stations on three rivers with increase of 0.17, 0.44 and 0.48°C per decade and climate change as the primary cause. The highest significant increasing trend was established at the lower course of Mrežnica where discharge was reduced by water diversion. Mitigation measures for the improvement of hydrological conditions of affected rivers and underground systems are proposed and discussed.

Rotifer fauna in the periphyton of Karst rivers in Croatia, Yugoslavia

Rotifer fauna in the periphyton of Karst rivers in Croatia, Yugoslavia