Microplastic pollution in small rivers along rural-urban gradients: Variations across catchments and between water column and sediments.

The aquatic ecosystems of the world are highly burdened with microplastics (MPs; particles <5 mm). There is a great need for better understanding of patterns of MP pollution across catchments and rivers of different sizes, anthropogenic pressures and hydrogeomorphological features. In this study, we investigated the MP concentrations including their characteristics (polymer type, shape, size and colour), and MP distribution in water and sediments of two hydrogeomorphologically different small-scale catchments (< 800 km2), namely Kamniska Bistrica (KB) and Ljubljanica (LJ), Slovenia. The main objective of this study was to gain a better understanding of how WWTP effluents and catchment urbanisation together with the diversity of natural hydrogeomorphology, affect the quantity and quality of MP pollutants in the rivers with smaller catchments. Significantly different mean MP concentrations were found in the water columns (KB: 59 ± 16 items m-3; LJ: 31 ± 14 items m-3), but not in the sediments (KB: 22 ± 20 items kg-1; LJ: 23 ± 25 items kg-1). A longitudinal gradient with increasing particle concentration was observed in both water and sediment samples and in both catchments. Polyethylene (PE) and polypropylene (PP) particles dominated in all samples. Fibres were predominant in the water column samples, while fragments were more common in the sediment samples. MP particles were mostly coloured, and most of them were smaller than 2 mm in both water and sediment samples. The critical evaluation of the results and previous studies suggest that the characteristics of the catchment (anthropogenic pressures, size, climate, etc.), the hydrogeomorphology of the river (sediment type, discharge, flow velocity etc.), the sampling location along the river, the sampled compartment (water, sediment), the sampling method, and the hydrometeorological characteristics at the time of sampling, are important factors for observed MP concentrations and other characteristics.

Presence of polyethylene terephthalate (PET) fibers in hyporheic zone alters colonization patterns and seasonal dynamics of biofilm metabolic functioning.

Worldwide, the production of plastics is increasing, and plastic pollution in aquatic environments is a major global concern. Under natural conditions, plastic weathers to smaller pieces called microplastics (MP), which come in various shapes, with fibers often being the most common in freshwater sediments. The hyporheic zone, an ecotone between surface and groundwater, is important for the transport and fate of all MP particles. The main metabolic pathways in rivers take place in the hyporheic zone and are driven by a diverse microbial community. The objective of this study was to investigate in situ whether the presence of PET fibers in riverbed sediments affects patterns of colonization and the seasonal dynamics of microbial metabolic activities in the hyporheic zone. The effects of the presence of PET on microbial metabolism were evaluated in situ over a month (colonization study) and over a year (seasonal study) by measuring total protein content (TPC), and microbial respiration as respiratory electron transport system activity (ETSA) and by community-level physiological profiling (CLPP). Additionally, PET fibers were examined under a scanning electron microscope (SEM), and isotopic analysis (δ13C) of PET was performed after one year of exposure to field conditions. The findings demonstrated that during colonization and biofilm formation, and also over the seasons, the date had a large and significant impact on biofilm growth and activity, while PET presence slightly suppressed microbial biomass (TPC) and respiratory activity (ETSA). Overall microbial activity was repressed in the presence of PET fibers but there was a higher capacity for the utilization of complex synthetic polymer substrates (i.e., Tween 40) which have previously been linked to polluted environments. SEM micrographs showed diverse microbial communities adhering to PET fibers but little surface deterioration. Similarly, isotopic analysis suggested little deterioration of PET fibers after one year of in situ conditions. The study indicated that PET fibers present in riverbed sediments could have impacts on the metabolic functioning in rivers and thus affect their self-cleaning ability.

Critical evaluation of biodegradation studies on synthetic plastics through a systematic literature review.

Increasing amounts of plastic waste in the environment and their fragmentation into smaller particles known as microplastics (particles, <5mm) have raised global concerns due to their persistency in the environment and their potential to act as vectors for harmful substances or pathogenic microorganisms. One possible solution to this problem is biodegradation of plastics by microorganisms. However, the scientific information on plastic-degrading microorganisms is scattered across different scientific publications. We conducted a systematic literature review (SLR) with predefined criteria using the online databases of Scopus and Web of Science to find papers on bacterial biodegradation of synthetic petroleum-based polymers. The aims of this SLR were to provide an updated list of all of the currently known bacteria claimed to biodegrade synthetic plastics, to determine and define the best methods to assess biodegradation, to critically evaluate the existing studies, and to propose directions for future research on polymer biodegradation in support of more rapid development of biodegradation technologies. Most of the bacteria identified here from the 145 reviewed papers belong to the phyla Proteobacteria, Firmicutes and Actinobacteria, and most were isolated from contaminated sites, such as landfill sites. Just under a half of the studies (44%) investigated the biodegradability of polyethylenes and derivates, particularly low-density polyethylenes. The methods used to monitor the biodegradation were mainly scanning electron microscopy and Fourier-transform infrared spectroscopy. We propose that: (1) future research should focus on biodegradation of microplastics arising from the most common pollutants (e.g. polyethylenes); (2) bacteria should be isolated from environments that are permanently contaminated with plastics; and (3) a combination of different observational methods should be used to confirm bacterial biodegradation of these plastics. Finally, when reporting, researchers need to follow standard protocols and include all essential information needed for repetition of the experiments by other research groups.

Modelling the effects of multiple stressors on respiration and microbial biomass in the hyporheic zone using decision trees.

Integrity of freshwater surface- and groundwater ecosystems and their ecological and qualitative status greatly depends on ecological processes taking place in streambed sediments overgrown by biofilm, in the hyporheic zone (HZ). Little is known about the interactions and effects of multiple stressors on biologically driven processes in the HZ. In this study, machine learning (ML) tools were used to provide evidence-based information on how stressors and ecologically important environmental factors interact and drive ecological processes and microbial biomass. The ML technique of decision trees using the J48 algorithm was applied to build models from a data set of 342 samples collected over three seasons at 24 sites within the catchments of five gravel-bed rivers in north-central Slovenia. Catchment-scale land use data and reach-scale environmental features indicating the HZ morphology and physical and chemical characteristics of water were used as predictive variables, while respiration (R) and microbial respiratory electron transport system activity (ETSA) were used as response variables indicating ecological processes and total protein content (TPC) indicating microbial biomass. Separate models were built for two HZ depths: 5-15 cm and 20-40 cm. The models with R as a response variable have the highest predictive performance (67-89%) showing that R is a good indicator of complex environmental gradients. The ETSA and TPC models were less accurate (42-67%) but still provide valuable ecological information. The best model show that temperature when combined with selected water quality elements is an important predictor of R at depth of 5-15 cm. The ETSA and TPC models show the combined effects of temperature, catchment land use and selected water quality elements on both response variables. Overall, this study provides new knowledge on how ecological processes occurring in the HZ respond to catchment and reach-scale variables, and provides evidence-based information about complex interactions between temperature, catchment land use and water quality. These interactions are highly dependent on the selection of the response variable, i.e., each response variable is influenced by a specific combination of predictive environmental variables.

Uncertainty of modelled flow regime for flow-ecological assessment in Southern Europe.

Sustainable water basin management requires characterization of flow regime in river networks impacted by anthropogenic pressures. Flow regime in ungauged catchments under current, future, or natural conditions can be assessed with hydrological models. Developing hydrological models is, however, resource demanding such that decision makers might revert to models that have been developed for other purposes and are made available to them ('off-the-shelf' models). In this study, the impact of epistemic uncertainty of flow regime indicators on flow-ecological assessment was assessed at selected stations with drainage areas ranging from about 400 to almost 90,000km2 in four South European basins (Adige, Ebro, Evrotas and Sava). For each basin, at least two models were employed. Models differed in structure, data input, spatio-temporal resolution, and calibration strategy, reflecting the variety of conditions and purposes for which they were initially developed. The uncertainty of modelled flow regime was assessed by comparing the modelled hydrologic indicators of magnitude, timing, duration, frequency and rate of change to those obtained from observed flow. The results showed that modelled flow magnitude indicators at medium and high flows were generally reliable, whereas indicators for flow timing, duration, and rate of change were affected by large uncertainties, with correlation coefficients mostly below 0.50. These findings mirror uncertainty in flow regime indicators assessed with other methods, including from measured streamflow. The large indicator uncertainty may significantly affect assessment of ecological status in freshwater systems, particularly in ungauged catchments. Finally, flow-ecological assessments proved very sensitive to reference flow regime (i.e., without anthropogenic pressures). Model simulations could not adequately capture flow regime in the reference sites comprised in this study. The lack of reliable reference conditions may seriously hamper flow-ecological assessments. This study shows the pressing need for improving assessment of natural flow regime at pan-European scale.

Environmental status of the NE Adriatic Sea, Istria, Croatia: Insights from mussel Mytilus galloprovincialis condition indices, stable isotopes and metal(loid)s.

The environmental status of the marine environment in the NE Adriatic Sea was assessed, using as a bioindicator species the Mediterranean mussel Mytilus galloprovincialis Lamarck, 1819. Samples were collected seasonally from mariculture sites and from major Istrian ports between the years 2010 and 2013. The condition indices of mussels ranged from 13.3 to 20.9% at mariculture sites and from 14.3 to 23.3% at port locations. The seasonally δ13CDIC values of seawater varied between -10.9 to 0.7‰. Pollution by sewage sludge (based on δ15N values) was confirmed only in two ports. Tissue concentrations of Mn, Co, Ni, Cu, Zn, Se, Cd, and Pb were significantly higher in the tissue of the mussels collected from the ports (polluted sites). Arsenobetaine was the major As compound present in the samples and there was no significant difference in the levels of total As in mussel tissues from mariculture and port sites.

Groundwater drift as a tracer for identifying sources of spring discharge.

Groundwater invertebrate drift, collected from the spring outlets at the interface of vadose and phreatic zones, has been examined for its potential for identifying sources of discharge from a karst aquifer. Concurrently, major ion geochemistry, dissolved inorganic carbon (δ13CDIC), particulate organic carbon (δ13CPOC), and naturally occurring stable isotopes of oxygen and tritium (δ18O, 3H) were investigated over a period of 1 year in two outlets, a temporary (TS) and a perennial (PS) spring. A few differences in major ion geochemistry and stable isotope composition were found between the two springs together with moderate seasonal variability. In contrast, invertebrate drift showed clear differences between TS and PS springs in density and composition. Canonical correspondence analysis showed the presence of two distinct groups of samples from TS and PS, with Ca2+ as the only significant explanatory variable for differences in drift composition. Finally, certain species from the drift were found to be useful tracers for distinguishing between the phreatic and the epikarst and vadose zones as the origin of spring water.

Redefinition of the Genus Typhlocypris Vejdovský, 1882 (Ostracoda, Candonidae).

The taxonomy of the genus Typhlocypris Vejdovský, 1882 is reviewed. New morphological information on Typhlocypris eremita (Vejdovský, 1882), the type species of the genus, is provided, and a new reference material is presented. The generic diagnosis is emended with details derived from the developmental trajectory of the valves, from the juvenile stage A-3 to the adult. Those criteria clearly differentiate Typhlocypris from the related genus Pseudocandona Kaufmann, 1900. As here redefined, Typhlocypris is a phylogentic lineage of the subfamily Candoninae containing extant species presently living in aquatic subterranean habitats and fossil species recovered from non-marine Late Palaeogene to Neogene and Quaternary deposits in Europe and western Asia. The type species of Typhlocypris is considered a metaspecies, taxonomically treated as T. eremita (sensu lato), which includes populations resembling the newly designated reference material. The homeomorphic triangular valve shape of the Candoninae is discussed. Careful examination of the valve morphology of Typhlocypris combined with the analysis of limb traits helps to distinguish representatives of this genus from unrelated phylogenetic groups presenting similar triangularly shaped valves. It is emphasised that for a useful description of Typhlocypris taxa both transmitted light and scanning electron microscopy are necessary.