Sources of major elements and nutrients in the water cycle of an undisturbed river basin - Samothraki Island, Greece.

We studied the origin of elements of an undisturbed stream basin during the dry season as derived by atmospheric inputs and lithological processes. Α mass balance model was applied taking into account atmospheric (rain and vapor) inputs and their origin from marine aerosol and dust, as well as the contribution of rock mineral weathering and dissolution of soluble salts. The model results were enhanced using element enrichment factors, element ratios and water stable isotopes. Weathering and dissolution of bedrock and soil minerals contributed the main element portions, besides sodium and sulfate that chiefly derived from wet deposition. Vapor was shown to contribute water to inland waters of the basin. However, rain was the main source of elements compared to vapor, with marine aerosol being the only atmospheric chloride source, contributing also over 60 % of atmospheric sodium and magnesium. Silicate derived from mineral weathering (mainly plagioclase and amorphous silica), while soluble salt dissolution contributed the main portions of the rest of major elements. In headwater springs and streams, element concentrations were more affected by atmospheric inputs and silicate mineral weathering was more intense, contrary to lowland waters that were more affected by soluble salt dissolution. Effective self-purification processes were mirrored in low nutrient levels, despite the significant inputs from wet deposition, with rain being more important contributor than vapor for the majority of nutrient species. Relatively high nitrate concentrations in headwaters were attributed to increased mineralization and nitrification, while the downstream nitrate diminishing was due to prevailing denitrification processes. The ultimate goal of this study is to contribute in establishing stream elements' reference conditions using mass balance modeling approaches.

REVIVE: A feasibility assessment tool for freshwater fish conservation translocations in Mediterranean rivers.

Conservation translocation is a management action applied for population recovery of threatened freshwater fishes, often however with partially successful outcome, mainly due to inadequate feasibility assessment prior to the translocation. Up to date, feasibility assessments have been mainly focused on economically important species (e.g., salmonids) inhabiting perennial rivers, while little attention has been given to fish translocations in rivers in Mediterranean climate areas. In this study, we developed a robust feasibility assessment tool for freshwater fish translocations in Mediterranean-type riverine ecosystems within an interdisciplinary, multispecies approach. The REVIVE tool integrates quantitative and semi-quantitative data, incorporates uncertainty and consists of two main components. The first component is the evaluation of the potential release water bodies (R-WBs) for their suitability for the planned translocation, incorporating a number of essential criteria for Mediterranean rivers, with emphasis on flow regime and habitat quantity. Additional criteria include the current and historical presence of the target species, water and biological quality, habitat suitability in terms of the ecological requirements of the target species, alien invasive species' pressure, and hydromorphological pressures, including their mitigation potential. The second component is the evaluation of the potential source water bodies (S-WBs) in terms of genetic compatibility and provision of a sufficient number of propagules. A trial application in a Mediterranean basin (Vassilopotamos River, Southern Greece) for the potential translocation of two threatened cyprinids in five R-WBs indicated the robustness of the tool. This integrative, flexible tool combines several elements identified as essential in reintroduction biology and can have wider applications, for a multitude of freshwater fish taxa and riverine systems, maximizing the success of planned translocation actions by natural resources' managers. Modifications to enable its transferability to other river types or fish taxa are also discussed.

Effects of olive mill wastewater discharge on benthic biota in Mediterranean streams.

Olive mill wastewaters (OMW) discharging in river ecosystems cause significant adverse effects on their water chemistry and biological communities. We here examined the effects of OMW loads in four streams of a Mediterranean basin characterized by changing flow. The diatom and macroinvertebrate community structures were compared between upstream (control) and downstream (impacted) sites receiving OMW discharge. We also tested if effects occurred at the organism level, i.e. the occurrence of deformities in diatom valves, and the sediment toxicity on the midge Chironomus riparius. We evaluated these effects through a two-year analysis, at various levels of chemical pollution and dilution capacity. The impacted sites had high phenol concentrations and organic carbon loads during and after olive mill (OM) operation, and were characterized by higher abundances of pollution-tolerant diatom and macroinvertebrate taxa. Diatom valve deformities occurred more frequently at the impacted sites. The development of C. riparius was affected by phenolic compounds and organic carbon concentrations in the sediments. The similarity in the diatom and macroinvertebrate assemblages between control and impacted sites decreased at lower flows. Diatoms were more sensitive in detecting deterioration in the biological status of OMW receiving waterways than macroinvertebrates. Our results indicate that the negative effects of OMW extended to the whole benthic community, at both assemblage and organism level.

Acute and sub-chronic toxicity bioassays of Olive Mill Wastewater on the Eastern mosquitofish Gambusia holbrooki.

Olive oil production generates large volumes of wastewaters mostly in peri-Mediterranean countries with adverse impacts on the biota of the receiving aquatic systems. Few studies have however documented its toxicity on aquatic species, with an almost total lack of relative studies on fish. We assessed the acute and sub-chronic OMW toxicity, as well as the acute and sub-chronic behavioural, morphological and biochemical effects of OMW exposure on the mosquitofish Gambusia holbrooki. LC50 values of the acute bioassays ranged from 7.31% (24 h) to 6.38% (96 h). Behavioural symptoms of toxicity included hypoactivity and a shift away from the water surface, coupled with a range of morphological alterations, such as skin damage, excessive mucus secretion, hemorrhages, fin rot and exophhalmia, with indications also of gill swelling and anemia. Biochemical assays showed that OMW toxicity resulted in induction of catalase (CAT) and inhibition of acetylcholinesterase (AChE) activities. The implications of our results at the level of environmental policy for the sustainable management of the olive mill industry, i.e. the effective restriction of untreated OMW disposal of in adjacent waterways, as well as the implementation of new technologies that reduce their impact (detoxification and/or revalorization of its residues) are discussed.

Multiple stressor effects on biodiversity and ecosystem functioning in a Mediterranean temporary river.

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.

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.

Combined effects of water stress and pollution on macroinvertebrate and fish assemblages in a Mediterranean intermittent river.

Water stress is a key stressor in Mediterranean intermittent rivers exacerbating the negative effects of other stressors, such as pollutants, with multiple effects on different river biota. The current study aimed to determine the response of macroinvertebrate and fish assemblages to instream habitat and water chemistry, at the microhabitat scale and at different levels of water stress and pollution, in an intermittent Mediterranean river. Sampling was conducted at high and low summer discharge, at two consecutive years, and included four reaches that were targeted for their different levels of water stress and pollution. Overall, the macroinvertebrate fauna of Evrotas River indicated high resilience to intermittency, however, variation in community structure and composition occurred under acute water stress, due to habitat alteration and change in water physico-chemistry, i.e. water temperature increase. The combined effects of pollution and high water stress had, however, pronounced effects on species richness, abundance and community structure in the pollution impacted reach, where pollution sensitive taxa were almost extirpated. Fish response to drought, in reaches free of pollution, consisted of an increase in the abundance of the two small limnophilic species, coupled with their shift to faster flowing riffle habitats, and a reduction in the abundance of the larger, rheophilic species. In the pollution impacted reach, however, the combination of pollution and high water stress led to hypoxic conditions assumed to be the leading cause of the almost complete elimination of the fish assemblage. In contrast, the perennial Evrotas reaches with relatively stable physicochemical conditions, though affected hydrologically by drought, appear to function as refugia for fish during high water stress. When comparing the response of the two biotic groups to combined acute water stress and pollution, it is evident that macroinvertebrates were negatively impacted, but fish were virtually eliminated under the two combined stressors.