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The distribution patterns of fish assemblages within streams can provide insights for river type classifications and may warrant specific conservation actions. However, there is limited knowledge of how fish assemblages assort along a longitudinal axis in Mediterranean intermittent streams. Patterns in spatial and temporal distribution of fish communities were analysed in a Mediterranean intermittent river (Evrotas River) located in Southern Greece, hosting three endemic range restricted species of high conservation concern, during the period 2007−2009, with 80% of the river’s total length desiccating in the 2007 and 2008 droughts. The general trend was an increase in fish density and species richness along an upstream-downstream gradient. Fish assemblages from upstream to downstream were characterized by a decrease of the most rheophilic species (Squalius keadicus) and an increase of the most stagnophilic species (Tropidophoxinellus spartiaticus). Three river segments, characterized by a high degree of homogeneity were delineated. Habitat and environmental preferences for the studied fish species were identified, with elevation and low flowing habitats being the most important environmental factors affecting fish distribution patterns. The current study provides evidence that even in an intermittent river an assemblage pattern following a longitudinal gradient can be identified, mainly due to the lack of instream barriers that allows recolonization after flow resumption.

Abstract: Despite the long‐term research on the use of hydraulic‐hydrodynamic habitat models (HHMs) for predicting the response of aquatic biota to habitat alteration, their practical application in model‐based environmental flow assessments (EFAs) has been limited due to reasons mainly associated with cost‐effectiveness, time‐efficiency, required expertise, and availability of hydroecological information. In this study, we demonstrate a cost‐effective and time‐efficient application of a benthic‐invertebrate, two‐dimensional, fuzzy rule‐based EFA in a 277‐m long reach in the downstream route of a regulated river in western Greece. Apart from developing ecosystem‐based environmental flow (eflow) scenarios, we highlight the valuable features of HHMs, comment on their disadvantages, and propose working solutions to overcome them. The results of the study show that the hydrology‐based eflow of 0.2 m3/s, initially proposed by the managing authorities, is not sufficient to ensure the long‐term functionality of the downstream benthic communities, as the ecosystem‐based eflow ranged between 0.6 and 2 m3/s. As social resilience relies heavily on ecological resilience, ecosystem‐based approaches can ensure the sustainability of aquatic ecosystems. This study demonstrates, inter alia, that HHMs‐based EFAs can be implemented cost‐effectively and time‐efficiently to serve as an accurate scientific basis for water managers and stakeholders, in search of the fine balance between anthropogenic water demand and long‐term ecosystem integrity and functionality. [ABSTRACT FROM AUTHOR]

The dominant factor regulating Greek riverine dissolved inorganic solid concentrations is chemical weathering, which depends on catchmentclimate and petrography. The majority of Greek rivers are moderatelypolluted and only a few of them show significant human impact and anincrease in pollutant concentrations over time. Due to droughts in recent years and anthropogenic influence, the mean annual riverine dissolved solid concentrations exhibit a general interannual increase and significant long-term variations in their intra-annual hydrochemical fluctuations. The shallow Greek lakes are eutrophic, while the deepones are oligo-mesotrophic. The majority of the lakes are monomicticand show summer thermal stratification, while the shallow ones are characterized by anoxic hypolimnetic conditions. Catchment petrographyis not a dominant factor in the composition of lake waters since biochemical processes prevail. The majority of Greek lakes are also moderately polluted and are characterized by phosphorous-limited photosynthesis. [ABSTRACT FROM AUTHOR]

Heavy metal contamination of the aquatic environment is of worldwide concern, due to the toxicity of metals and their lethal effects on aquatic organisms. The investigation of heavy metal concentrations in freshwater bodies has increased over the last decades in Greece; however, most studies have been sporadic and spatially limited. An overall assessment of the heavy metal contamination status in Greek surface water bodies is lacking. In this review, all available published data from 1999 to 2019 were collected and analysed to assess the heavy metal contamination status of the surface water bodies of Greece. Data were available for 68 water bodies and several pollution indices (e.g. Heavy Metal Pollution index, Geoaccumulation index, Moderated Pollution Index) were calculated to evaluate their surface water quality. Overall, heavy metal concentrations in water samples were below the Environmental Quality Standards (EQS) and the vast majority of water bodies were classified as good quality based on surface water pollution indices. Sediment heavy metal concentrations exceeding the Sediment Quality Guidelines (SQGs) were detected in most water bodies. Rivers Axios, Evros, Louros, Gallikos, Greveniotikos, Palea Kavala, Kompsatos, Alfeios and Evrotas, and lakes Pamvotis, Doirani and Koumoundourou were either moderately or highly contaminated. Up to date, heavy metal pollution indices used worldwide for surface waters refer to potable water. Thus, pollution indices must be developed for assessing primarily the ecological consequences of heavy metal pollution and surface water pollution status. Finally, sediment pollution guidelines must be suggested at a European or regional level., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

River restoration with the use of in-stream structures has been widely implemented to maintain/improve physical habitats. However, the response of aquatic biota has often been too weak to justify the high costs of restoration projects. The ecological effectiveness of river restoration has thus been much debated over claims that large-scale environmental drivers often overshadow the potential positive ecological effects of locally placed in-stream structures. In this study, we used a two-dimensional hydrodynamic-habitat model to evaluate the ecological effectiveness of habitat restoration with the use of in-stream structures in various water discharges, ranging from near-dry to environmental flows. The habitat suitability of benthic macroinvertebrates and of three cyprinid fish species was simulated for six restoration schemes and at four discharge scenarios, and was compared with a reference model, without in-stream structures. We found that the ecological response to habitat restoration varied by species and life stages, it strongly depended on the reach-scale flow conditions, it was often negative at near-environmental flows, and when positive, mostly at near-dry flows, it was too low to justify the high costs of river restoration. Flow variation was the major environmental driver that our local habitat restoration schemes attempted -but mostly failed-to fine-tune. We conclude that traditional river restoration, based on trial and error, will likely fail and should be ecologically pre-optimized before field implementation. Widespread use of in-stream structures for ecological restoration is not recommended. However, at near-dry flows, the response of all biotic elements except for macroinvertebrates, was positive. In combination with the small habitat-suitability differences observed among structure types and densities, we suggest that sparse/moderate in-stream structure placement can be used for cost-effective river restoration, but it will only be ecologically effective -thus justifying the high implementation costs-when linked to very specific purposes: (i) to conserve endangered species and (ii) to increase/improve habitat availability/suitability during dry periods, thus proactively preventing/reducing the current and future ecological impacts of climate change., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Benthic macroinvertebrates are often used in ecological quality monitoring. However, due to the large number of samples and specimens, sample processing (sorting/identification) is a labor-intensive task that is susceptible to errors. These errors can consequently lead to biased assessment results. We conducted the first audit of the Greek National Water Monitoring program. Totally, 444 samples were sorted at the laboratory by primary sorters and macroinvertebrate identification was conducted mainly at family level by primary taxonomists, having different taxonomic expertise. The Percentage Sorting Efficiency (PSE), Percentage of Taxonomic Disagreement (PTD), and the Relative Percentage Difference (RPD) were calculated to determine differences between auditing stages. Control charts were used to determine the process changes of the personnel (sorting: PSE index and identification: PTD index) as a calibration check. Additionally, national ecological indices/metrics were calculated to identify how they are affected by errors. All samples except from one had PSE values higher than 90%. The most common overlooked families were Chironomidae, followed by Baetidae and Gammaridae due to their high abundances. Average values of the PTD index for the total number of samples was 5.75% and 1.86% in each phase, respectively. The PTD values decreased between the two phases due to the gained experience of primary taxonomists during the 1st phase. The average action control limit was 95% for the PSE values and 14% for the PTD values. Overall, our ecological quality results indicated that the sorting error was less important than the identification one as the latter may lead to different ecological quality classifications. Our results show that our auditing procedure is effective and increases the quality and accuracy of the sample analysis procedure. It also highlights that human error should not be neglected since it may affect the ecological quality results and especially the good/moderate boundary which leads to rehabilitation measures., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The Mediterranean region is anticipated to be (or, already is) one of the hot spots for climate change, where freshwater ecosystems are under threat from the effects of multiple stressors. Climate change is impacting natural resources and on the functioning of Ecosystem Services. The challenges about modelling climate change impact on water cycle in general and specifically on socio-economic dynamics of the society leads to an exponential amount of results that restrain interpretation and added value of forecasting at local level. One of the main challenges when dealing with climate change projections is the quantification of uncertainties. Modellers might have limited information or understanding from local river catchment management practices and from other disciplines with relevant insights on socio-economic and environmental complex relationship between biosphere and human based activities. Current General Circulation Models cannot fulfil the requirements of high spatial detail required for water management policy. This article reports an innovative transdisciplinary methodology to down scale Climate Change scenarii to river basin level with a special focus on the development of climate change narrative under SSP5-RCP8.5 combination called Myopic scenario and SSP1-RCP4.5 combination called Sustainable scenario. Local Stakeholder participative workshop in the Evrotas river basin provide perception of expected changes on water demand under to two developed scenario narratives., (Copyright © 2018. Published by Elsevier B.V.)

Among different stressors like drought, hydro-morphological alterations, and pollution from agricultural activities, nutrients, organic compounds and discharges from wastewater treatment plants (WWTPs), potentially toxic elements (PTE) may also contribute to the overall pollution of the Evrotas River, Greece. Nevertheless, information on pollution of elements in water and sediments in this river is scarcely documented. There is also no information available on the impact of elemental pollution from the aquatic environmental compartments on biota. To fill these gaps, in this study, water, sediment and fish samples were collected from four sampling sites along the Evrotas River under variable flow regimes (July 2015, higher discharge; June 2016, low discharge and September 2016, minimum discharge). Total and dissolved element concentrations in water samples, total and acetic acid extractable contents in sediments, and element concentrations in fish samples were determined by inductively coupled plasma mass spectrometry and significant relationships between samples were established using correlation analysis. The concentrations of PTE (Ni, Cr, Cd, As, Pb, Zn and Cu) in water were generally low, while elevated Ni and Cr contents were found in sediments (up to 150 and 300 mg/kg, respectively), with total Cr concentration in water and sediment being positively correlated. The ecological risk posed by the simultaneous presence of PTE in sediments evaluated by calculating the Probable Effect Concentration Coefficient (PEC-Q), demonstrated that PEC-Qs, which were above the critical value of 0.34, derived mostly from Cr and Ni inputs. Since their mobile sediment fraction was extremely low, Cr and Ni origin is most probably geogenic. The analysis of elements in the target fish species, the Evrotas chub, showed low to moderate PTE concentrations, with Pb being positively correlated with total Pb concentration in water. Moderate Zn concentrations found in fish samples from the Evrotas are possibly derived from pesticides and fertilizers., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

The hydrological and biological complexity of temporary rivers as well as their importance in providing goods and services is increasingly recognized, as much as it is the vulnerability of the biotic communities in view of climate change and increased anthropogenic pressures. However, the effects of flow intermittency (resulting from both seasonal variations and rising hydrological pressure) and pollution on biodiversity and ecosystem functioning have been overlooked in these ecosystems. We explore the way multiple stressors affect biodiversity and ecosystem functioning, as well as the biodiversity-ecosystem functioning (B-EF) relationship in a Mediterranean temporary river. We measured diversity of benthic communities (i.e. diatoms and macroinvertebrates) and related ecosystem processes (i.e. resource use efficiency-RUE and organic matter breakdown-OMB) across a pollution and flow intermittency gradient. Our results showed decreases in macroinvertebrate diversity and the opposite trend in diatom assemblages, whereas ecosystem functioning was negatively affected by both pollution and flow intermittency. The explored B-EF relationships showed contrasting results: RUE decreased with higher diatom diversity, whereas OMB increased with increased macroinvertebrate diversity. The different responses suggest contrasting operating mechanisms, selection effects possibly driving the B-EF relationship in diatoms and complementarity effects driving the B-EF relationship in macroinvertebrates. The understanding of multiple stressor effects on diversity and ecosystem functioning, as well as the B-EF relationship in temporary rivers could provide insights on the risks affecting ecosystem functioning under global change., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

The contamination patterns and fate of pharmaceutically active compounds (PhACs) were investigated in the Evrotas River (Southern Greece). This is a temporary river with differing levels of water stress and water quality impairment in a number of its reaches. Three sampling campaigns were conducted in order to capture different levels of water stress and water quality. Four sampling sites located on the main channel of the Evrotas River were sampled in July 2015 (moderate stream flow), and June and September 2016 (low stream flow). Discharge of urban wastewater has been determined as the main source of pollution, with PhACs, nutrients and other physicochemical parameters considerably increasing downstream the wastewater treatment plant (WWTP) of Sparta city. Due to the pronounced hydrological variation of the Evrotas River, generally, the highest concentrations of PhACs have been detected during low flow conditions. Simultaneously, low flow resulted in an increased water travel time and consequently longer residence time that accounted for the higher attenuation of most PhACs. The average decrease in total concentration of PhACs within the studied waterbody segment (downstream of Sparta city) increased from 22% in July 2015 to 25% in June 2016 and 77% in September 2016. The PhACs with the highest average concentration decrease throughout the sampling campaigns were hydrochlorothiazide, followed by sotalol, carbamazepine, valsartan, and naproxen., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

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 90,000km 2 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., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)