Plasticity in life history traits of a cyprinid fish in an intermittent river

The extreme seasonal environmental variation of intermittent rivers has a profound effect on freshwater fish communities. Yet, few studies have examined the consequences of the seasonal cycles of flooding and drying to fish condition and reproduction in these ecosystems. In this study, we compared the body condition, reproduction and diet of two chub populations from two adjacent sites (a perennial and an intermittent site) on the main stem of a Mediterranean river (Evrotas River, S. Greece). The study was conducted in spring 2017, three months after flow resumption and before the onset of chub reproductive period. Condition (net weight adjusted for length) of fish did not differ significantly between the two sites, despite lower aquatic macroinvertebrate availability at the intermittent site. Fish at the intermittent site compensated for the lower aquatic prey availability by increasing their feeding intensity and by shifting to higher terrestrial prey consumption. In addition, chub liver weight (adjusted for length) and gonadal weight (adjusted for length) were significantly higher at the intermittent site, indicating higher somatic and reproductive investment. These results highlight the resilience of fish populations inhabiting streams with extreme variation in flow, due to natural and/or anthropogenic drought

A Conceptual Framework for Understanding the Biogeochemistry of Dry Riverbeds Through the Lens of Soil Science

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

Particle bound pollutants in rivers: Results from suspended sediment sampling in Globaqua River Basins

Transport of hydrophobic pollutants in rivers such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metals is often facilitated by suspended sediment particles, which are typically mobilized during high discharge events. Suspended sediments thus represent a means of transport for particle related pollutants within river reaches and may represent a suitable proxy for average pollutant concentrations estimation in a river reach or catchment. In this study, multiple high discharge/turbidity events were sampled at high temporal resolution in the Globaqua River Basins Sava (Slovenia, Serbia), Adige (Italy), and Evrotas (Greece) and analysed for persistent organic pollutants such as PAHs (polycyclic aromatic hydrocarbons) or PCBs (polychlorinated biphenyls) and heavy metals. For comparison, river bed sediment samples were analysed as well. Further, results are compared to previous studies in contrasting catchments in Germany, Iran, Spain, and beyond. Overall results show that loadings of suspended sediments with pollutants are catchment-specific and relatively stable over time at a given location. For PAHs, loadings on suspended particles mainly correlate to urban pressures (potentially diluted by sediment mass fluxes) in the rivers, whereas metal concentrations mainly display a geogenic origin. By cross-comparison with known urban pressure/sediment yield relationships (e.g. for PAHs) or soil background values (for metals) anthropogenic impact – e.g. caused by industrial activities – may be identified. Sampling of suspended sediments gives much more reliable results compared to sediment grab samples which typically show a more heterogeneous contaminant distribution. Based on mean annual suspended sediment concentrations and distribution coefficients of pollutants the fraction of particle facilitated transport versus dissolved fluxes can be calculated

River ecosystem processes: A synthesis of approaches, criteria of use and sensitivity to environmental stressors

River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. Structure and functioning respond in contrasting and complementary ways to environmental stressors. Moreover, assessing the response of ecosystem functioning to stressors is critical to understand the effects on the ecosystem services that produce direct benefits to humans. Yet, there is more information on structural than on functional parameters, and despite the many approaches available to measure river ecosystem processes, structural approaches are more widely used, especially in management. One reason for this discrepancy is the lack of synthetic studies analyzing river ecosystem functioning in a way that is useful for both scientists and managers. Here, we present a synthesis of key river ecosystem processes, which provides a description of the main characteristics of each process, including criteria guiding their measurement as well as their respective sensitivity to stressors. We also discuss the current limitations, potential improvements and future steps that the use of functional measures in rivers needs to face.Science of The Total Environment (2017), 596-597: 465-48

Geology Can Drive the Diversity–Ecosystem Functioning Relationship in River Benthic Diatoms by Selecting for Species Functional Traits

The biodiversity–ecosystem functioning (BEF) relationship has been studied extensively for the past 30 years, mainly in terrestrial plant ecosystems using experimental approaches. Field studies in aquatic systems are scarce, and considering primary producers, they mainly focus on phytoplankton assemblages, whereas benthic diatoms in rivers are considerably understudied in this regard. We performed a field study across nine rivers in Greece, and we coupled the observed field results with model simulations. We tested the hypothesis that the diversity–biomass (as a surrogate of ecosystem functioning) relationship in benthic diatoms would be affected by abiotic factors and would be time-dependent due to the highly dynamic nature of rivers. Indeed, geology played an important role in the form of the BEF relationship that was positive in siliceous and absent in calcareous substrates. Geology was responsible for nutrient concentrations, which, in turn, were responsible for the dominance of specific functional traits. Furthermore, model simulations showed the time dependence of the BEF form, as less mature assemblages tend to present a positive BEF. This was the first large-scale field study on the BEF relationship of benthic diatom assemblages, offering useful insights into the function and diversity of these overlooked ecosystems and assemblages

Unraveling Aquatic Quality Controls of a Nearly Undisturbed Mediterranean Island (Samothraki, Greece)

Due to its rough, mountainous relief, Samothraki remains one of the last minimally disturbed islands in the Mediterranean. This paper examines the hydrogeochemical regime of the island’s surface waters as it results from geological, morphological, and hydro(geo)logical controls within a frame of minimally disturbed environmental conditions. Shallow, fractured groundwater aquifers, in combination with steep slopes and predominant weathering resistant rocks, bring about flashy stream regimes with remarkably low solute concentrations. Streams and springs revealed hydrochemical similarities. Contrary to streams chiefly draining sedimentary rocks, streams underlined by granite and ophiolite rocks do not respond hydrochemically to geochemical differences. Using ion proportions instead of concentrations, geochemical fingertips of magmatic stream basins were detected. Atmospheric inputs largely affect stream and spring composition, e.g., by 75% regarding sodium. Only 20% of dissolved oxygen and pH variance was assigned to biological activity, while nutrient levels were consistent with the undisturbed conditions of the island, except nitrate. Small mountainous springs and brooks fed by restricted, fractured groundwater aquifers with perennial flow, despite scarce summer rainfalls, may be fueled by cloud and fog condensation. High night-day stream flow differences, high atmospheric humidity predominately occurring during the night, and low stream water travel times point out toward this phenomenon

Spatiotemporal Variation in Benthic-Invertebrates-Based Physical Habitat Modelling: Can We Use Generic Instead of Local and Season-Specific Habitat Suitability Criteria?

Generic habitat suitability criteria (HC) are often developed from spatially and temporally variable hydroecological datasets to increase generality, cost-effectiveness, and time-efficiency of habitat models. For benthic macroinvertebrates (BMIs), however, there is no prior knowledge on the spatiotemporal variation in their habitat preferences and how this may be reflected in the final environmental flow (e-flow) predictions. In this study, we used a large, spatiotemporally variable BMI-hydroecological dataset and developed generic, local, and season-specific subsets of HC for three seasons and two river types within various data pre-treatment options. Each subset was used to train a fuzzy habitat model, predict the habitat suitability in two hydrodynamically-simulated river reaches, and develop/compare model-based e-flow scenarios. We found that BMIs shift their habitat preferences among seasons and river types; consequently, spatiotemporally variable e-flow predictions were developed, with the seasonal variation being greater than the typological one. Within this variation, however, we found that with proper data pre-treatment, the minimum-acceptable e-flows from the generic models mostly (65⁻90%) lay within the acceptable e-flows predicted by the local and season-specific models. We conclude that, within specific limitations, generic BMI-HC can be used for geographically extended, cost-effective e-flow assessments, compensating for the within-limits loss of predictive accuracy

Harmonization of the assessment method for classifying the ecological quality status of very large Greek rivers

The intercalibration exercise is required by the European Water Framework Directive (WFD) to harmonize the national ecological class boundaries across Member States. It is applied to individual types of water bodies, comparing WFD-compliant biological assessment methods using specific quality elements. This study addresses the harmonization of the STAR_ICMi index for the ecological status assessment of very large Greek rivers in compliance with the completed intercalibration exercise for European very large rivers. River sites were sampled biannually for benthic invertebrates (as biological quality element) and environmental data during different surveys. The water quality of the samples ranged from high to bad. STAR_ICMi was significantly correlated to the Combined Abiotic Pressure index (CAPi) and its component pressures channelization, riparian vegetation alteration, and to a lesser extent to organic pollution. During the intercalibration approach benchmark standardization was applied to the component metrics of the intercalibration index prior to boundary comparison to minimize typological differences. The Greek class boundaries of high/good and good/moderate ecological status were compared and harmonized with the “Global Mean View” defined in the completed European intercalibration exercise. Similarity percentage analysis of biological community variation was performed for sites in high, good, and less than good ecological status according to the intercalibrated Greek classification