Summary
In lake ecosystems, changes in eukaryotic and prokaryotic microbes and the concentration and availability of dissolved organic matter (DOM) produced within or supplied to the system by ...allochthonous sources are components that characterize complex processes in the microbial loop. We address seasonal changes of microbial communities and DOM in the largest Croatian lake, Vrana. This shallow lake is connected to the Adriatic Sea and is impacted by agricultural activity. Microbial community and DOM structure were driven by several environmental stressors, including drought, seawater intrusion and heavy precipitation events. Bacterial composition of different lifestyles (free‐living and particle‐associated) differed and only a part of the particle‐associated bacteria correlated with microbial eukaryotes. Oscillations of cyanobacterial relative abundance along with chlorophyll a revealed a high primary production season characterized by increased levels of autochthonous DOM that promoted bacterial processes of organic matter degradation. From our results, we infer that in coastal freshwater lakes dependent on precipitation‐evaporation balance, prolonged dry season coupled with heavy irrigation impact microbial communities at different trophic levels even if salinity increases only slightly and allochthonous DOM inputs decrease. These pressures, if applied more frequently or at higher concentrations, could have the potential to overturn the trophic state of the lake.
Phytoplankton is a polyphyletic group of organisms that responds rapidly to environmental conditions and provides a reliable response to changes, making it a good ecological indicator for water ...quality monitoring. However, a gradient is almost essential for a reliable relationship between pressure and impact. In a low-gradient environment, ingenuity is required to outsmart the limitations of the commonly used linear relationship. Here, we examine changes in biomass and functional biodiversity by analysing larger data sets (2013–2022) in six ecologically diverse, natural, deep Croatian karst lakes with low nutrient gradients using nonlinear correlation coefficients and multivariate analyses in 209 samples. We found that phytoplankton biomass was most strongly influenced by nutrients, salinity and alkalinity, while light availability and total nitrogen strongly influenced phytoplankton functional biodiversity. An additional analysis of the TN:TP ratio revealed that the oligotrophic Lake Vransko is nitrogen-limited, and lakes Kozjak and Prošće are phosphorus-limited. This further clarified the relationship of phytoplankton to nutrients despite the low gradient. The complex analysis in this study provides a new perspective for predicting changes in the structure and succession of phytoplankton in deep karst lakes for successful management under apparent anthropogenic pressure and climate change.
Phytoplankton is a well-studied group of organisms that can change rapidly with environmental conditions, providing a reliable response to these changes. We analysed phytoplankton biomass, diversity, ...and its response to environmental conditions in the shallow brackish Mediterranean Lake Vransko. Although protected as Nature Park, the Lake's succession is enhanced by intensive agricultural activity and an artificial connection to the sea. Analysis of phytoplankton reveals a specific community composition strongly influenced not only by nutrients but also by salinity gradient, with species composition shifting from freshwater to brackish. Conditions of higher salinity support the dominance of brackish species, often with low biomass, while periods of low salinity are characterised by dominance of cyanobacteria or other freshwater species capable of rapidly taking up nutrients and forming algal blooms. Changes in water transparency caused by phytoplankton dynamics strongly influence the overall lake system through the availability of macrophyte growth and sediment fixation. These findings are critical for the future lake management, particularly its hydrological regime and maintenance of natural oligohaline and mesotrophic conditions. Understanding the response of phytoplankton to environmental conditions, exacerbated by anthropogenic influence and recent climate change, contributes to the protection of Mediterranean shallow lakes at local and global scales.
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•A comparison of morphology and eDNA-based phytoplankton analysis was performed.•The Croatian natural karst lakes were classified in Good or High ecological status.•The comparable ...ecological status between both approaches was presented.•Most of the differences in HLPI values were caused by the biomass metric.•The 18S rRNA V9 could be suitable for assessing the ecological status of phytoplankton.
Phytoplankton is one of the key Biological Quality Elements within the Water Framework Directive, used to assess the ecological status of surface water bodies. Water samples for phytoplankton identification were collected from April to September at a total of eight sampling sites in all six Croatian natural karstic lakes with an area greater than 0.5 km2. The main objective was to show the comparability of environmental DNA metabarcoding (Illumina sequencing using the hypervariable V9 region of the eukaryotic SSU rRNA gene) with morphologically based assessment and its applicability in assessing the ecological status of lakes. The value of Hungarian lake phytoplankton index (HLPI) indicating the final ecological status was calculated for both datasets using biomass and composition metrics. Chlorophyll a concentration measured using Ultra-High-Performance Liquid Chromatography and Spectrophotometer giving two biomass metrics along with the functional group approach (FG) as the composition metric for the complete taxa/operational taxonomic units (OTUs) lists as well as for the taxa/OTUs that contributed more than 5% to the total biomass/number of amplicons gave four to four HLPI values per sample. HLPI values from both approaches were highly correlated (Pearson's r > 0.92) and classified into good or high ecological status, although different compositions and proportions of FGs were recorded, thus giving the important role to the equal or similar factors assignment to different FGs with similar ecological demands and favourable habitats. In 89% of the samples, HLPI values indicate an equal range of ecological status and most differences were found due to different methods of Chlorophyll a measurement. Different composition metrics between approaches showed significant differences (p < 0.05) only in lakes Prošće and Crniševo. This study showed the applicability of the V9 region of 18S rRNA in ecological status assessment for oligotrophic and mesotrophic lakes due to the comparable results between approaches, but further development and standardization of eDNA metabarcoding are needed for the implementation in routine monitoring programs.
Phytoplankton is one of the five biological quality elements used to assess the ecological status of lakes within the Water Framework Directive. Classical morphological Utermöhl method and eDNA ...metabarcoding by Ilumina sequencing the hypervariable V9 region of the eukaryotic SSU rRNA gene were used to analyse the qualitative and quantitative composition of the phytoplankton and compared at the taxonomic and FG level to highlight advantages and disadvantages of eDNA metabarcoding method over classical microscopy. Samples were collected from April to September in seven Croatian natural karst lakes. Cluster analysis based on the Bray–Curtis similarity of taxa biomass (microscopy) and number of sequences (eDNA metabarcoding) clearly separated lakes showing that eDNA metabarcoding is sensitive to species change. Overlap at the species level between methods was found primarily in the taxa of Cryptophyta, Miozoa, and Ochrophyta, while some very common taxa of Bacillariophyta, Charophyta, and Chlorophyta identified by microscopy were not detected by eDNA metabarcoding, possibly due to incompleteness of the reference databases. At a higher organizational level, the results showed poor overlap of taxonomic and functional group composition and poor comparability of relative biomass to relative number of sequences, indicating the need to complete reference databases and standardize quantification to further develop eDNA metabarcoding for ecological status assessment.
In 2019, phytoplankton and environmental parameters were analysed monthly during the growing season from April to September at 26 sampling sites in the Danube and 10 additional sampling sites in the ...main tributaries as part of the Joint Danube Survey 4, organised by the ICPDR. Our results showed that both phytoplankton biomass and composition follow the River Continuum Concept on free-flowing sections, but also responds to hydromorphological changes where the largest dam Iron Gate represents the largest interruption of the river and the phytoplankton continuum. Besides longitudinal interruption, water residence time was the most important factor for phytoplankton composition, while nutrients were less relevant. The low phytoplankton biomass and its composition in the Danube support the oligotrophication trend, but this one-year study could not confirm it with certainty. Phytoplankton is the most important autotrophic component in the Upper and Middle Danube, where environmental conditions do not support the optimal growth of other river flora. The predominant FGs coda were A, C and D as a typical potamoplankton component, while the codon TB occurs throughout the Danube but is more prominent in the Upper reach and other river sections with higher discharge events.
Typology systems are frequently used in applied and fundamental ecology and are relevant for environmental monitoring and conservation. They aggregate ecosystems into discrete types based on biotic ...and abiotic variables, assuming that ecosystems of the same type are more alike than ecosystems of different types with regard to a specific property of interest. We evaluated whether this assumption is met by the Broad River Types (BRT), a recently proposed European river typology system, that classifies river segments based on abiotic variables, when it is used to group biological communities. We compiled data on the community composition of diatoms, fishes, and aquatic macrophytes throughout Europe and evaluated whether the composition is more similar in site groups with the same river type than in site groups of different river types using analysis of similarities, classification strength, typical species analysis, and the area under zeta diversity decline curves. We compared the performance of the BRT with those of four region-based typology systems, namely, Illies Freshwater Ecoregions, the Biogeographic Regions, the Freshwater Ecoregions of the World, and the Environmental Zones, as well as spatial autocorrelation (SA) classifications.
All typology systems received low scores from most evaluation methods, relative to predefined thresholds and the SA classifications. The BRT often scored lowest of all typology systems. Within each typology system, community composition overlapped considerably between site groups defined by the types of the systems. The overlap tended to be the lowest for fishes and between Illies Freshwater Ecoregions.
In conclusion, we found that existing broad-scale river typology systems fail to delineate site groups with distinct and compositionally homogeneous communities of diatoms, fishes, and macrophytes. A way to improve the fit between typology systems and biological communities might be to combine segment-based and region-based typology systems to simultaneously account for local environmental variation and historical distribution patterns, thus potentially improving the utility of broad-scale typology systems for freshwater biota.
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•River typologies are commonly used in applied and fundamental ecology.•Several river typologies exist at a European scale.•Typologies don't capture patterns in community composition of freshwater taxa.•Combining existing typologies might improve fit to biota.•Data on biota could be used to weight type descriptors.
Podveležje je tipični krški plato na prisojnoj strani planine Velež, koja se proteže u pravcu SZ - JI u dužini od oko 21 km. Nalazi se u BiH, u sastavu Hercegovačko-neretvanskog kantona, na području ...grada Mostara. Kao dio jugoistočne Hercegovine pripada krškom području Dinarida, dok u strukturno - geološkom smislu prostor Podveležja pripada tektonskoj jedinici Velež. Na području Podveležja i padinama Veleži istraživan je ukupno 31 speleološki objekt, od čega 21 jama i 10 špilja. Uglavnom je riječ o jednostavnim objektima dubine i duljine do 30 m. Najdulja i najkompleksnija istražena špilja je Prosečenica (347 m), a najdublje jame su Golubinka na Svetigori/Jama na Svetoj gori II (149 m) i Željuškovača (90 m). Obje jame imaju velike perspektive za nastavak istraživanja, a također ne treba zanemariti niti pećinu Prosečenicu. S obzirom na konfiguraciju i morfologiju terena te geološku podlogu, uz velik broj pronađenih speleoloških objekata, na istraživanom području postoji mogućnost nailaska na još neotkrivene speleološke objekte. Za vrijeme istraživanja prikupljeni su podatci i o brojnim objektima na padinama Veleži, međutim oni nisu istraživani zbog teškog pristupa i zahtjevnije logistike.
Prilikom kretanja po terenu i istraživanju speleoloških objekata velika su poteškoća brojna minsko-eksplozivna sredstva zaostala i odbačena nakon rata.
Općina Dubrovačko Primorje pripadaDubrovačko-neretvanskoj županiji. Sličnih je prirodno-geografskih obilježja kao i drugi dijelovi Dalmacije, odnosno radi se o tipičnom krškom dinarskom prostoru s ...malo plodnih površina,oskudnim pašnjacima ikamenjarom.
Među istraživanim speleološkim objektima uglavnom je riječ o špiljama i jamama jednostavnog karaktera (dubine i duljine do 30 m). Od ukupno 15 istraženih speleoloških objekata na području dubrovačkog primorja njih 4 se nalazi na platou Lisačkih Rudina među kojima je i najdublji poznati objekt na tom području, jama Bezdan na Rudinama, duboka 68 metara. Ovdje su još istražene Jama kod Kazerne, Špijaturica (Đurašica) i Jama između gomila. Nedaleko od kuća u selu Točionik nalazi se Vranja peć, najdulji poznati speleološki objekt na području Dubrovačkog primorja. Duljine je 188 m, a dubine 50 m. Uz granični prijelaz u Čepikućama nalazi se Jama na Gomilama. Isto tako, u blizini Čepikuća, na brdu Štrbina nalazi se Zmajeva peć, a špilja u uvali Domaglina (Pod Njivicama) nalazi se u unutrašnjosti istoimene uvale. Istočno od uvale Domaglina nalazi se uvala Hodoblja gdje su istražene tri špilje: Špilja I, Špilja II i Špilja III u uvali Hodoblja. Na području sela Trnova istražena su dva speleološka objekta: Jama na groblju i Špilja u ogradama. U mjestu Đonta doli nalazi se Delova jama u Borima. Traverza kod Miljkovića staja nalazi se na području sela Trnovica u Dubrovačkom primorju. Po svojim karakteristikama Traverza kod Miljkovića staja je špilja s dva ulaza koji su međusobno udaljeni oko 50 m zračne udaljenosti.
Na području općine Dubrovačko primorje nalazi se veliki broj neistraženih područja te su potrebna daljna rekognosciranja terena te komunikacija s lokalnim stanovništvom u potrazi za novim, neistraženim speleološkim objektima.
Put ekspedicionizma 2017. - 2020. jedinstven je projekt u povijesti Hrvatskog planinarskog društva „Željezničar” (HPDŽ) s ciljem udruživanja članova svih sekcija i odsjeka kako bi se obilježila 70. ...godišnjica osnutka. Tijekom projekta organizirane su alpinističke ekspedicije u inozemstvo u cilju priprema za krajnji cilj, a to je bio uspon na neki od značajnih vrhova Himalaje. Međutim, 2020. godina biti će dobro upamćena po pandemiji, a unutar projekta po tome što se je daleki himalajski cilj zamijenio za bližim speleološkim, unutar granica Republike Hrvatske. Obzirom na intenzivna i uspješna speleološka istraživanja Crnopca te tradiciju Speleološkog odsjeka „Željezničar“ da organizira speleološke logore na tom perspektivnom području, oko odabira lokacije nije se puno dvojilo. Kao glavni ciljevi bili su nastavak istraživanja u dvama kapitalnim objektima Crnopca –Oazi (od kolovoza 2019. kao dijelu Jamskog Sustava Crnopac) te u Mudima labudovima. Pripremne akcije krenule su već u siječnju 2020., a glavna aktivnost bila je organizacija speleološkog logora na Jami vjetrova u periodu 25.7. – 2.08. Kao glavni rezultat logora ističe se ukupno 1262 m nacrtanih kanala te dostizanje novog dna Muda labudova na -720 m. U zadnjoj održanoj akciji u 2020. dostignut je cilj, koji je mnogim speleolozima godinama predstavljao san, a to je bilo spajanje Muda labudova s ostatkom crnopačkog sustava. Ulaskom iz Oaze u Muda labudova, ukupna duljina Jamskog Sustava Crnopac naglo je porasla za 7414 m na nestvarnih ukupnih 52 342 m. U nastavku je opisan tijek ovih istraživanja iz svih zornih kuteva.
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