Mediterranean Streams Research Articles

Response of macroinvertebrate communities to hydrological and hydrochemical alterations in Mediterranean streams

Mediterranean rivers are affected by natural disturbances and human pressures, which may alter their hydrology, water quality and habitat structure. In this study an analysis of macroinvertebrates community structure has been used to determine how distinct human pressures, such as point and non-point sources of pollution, together with groundwater withdrawal, may affect these ecosystems. A total of 4 sampling campaigns were conducted in the middle reach of the Onyar River (NE Spain), which was affected by agricultural and urban uses. Stream discharge and physicochemical parameters were measured in situ, and water samples and macroinvertebrates assemblages were taken and properly preserved for subsequent analysis and identification. Variation partitioning showed that macroinvertebrate community structure was particularly dependent on hydrochemical characteristics, but also on hydrological variations. In addition, results indicated that groundwater withdrawal altered stream hydrology, and the main reach of the Onyar River became intermittent and even completely dry in downstream positions. This reduction on stream discharge caused changes in habitat characteristics, as well as in the proportion of wastewater. Some wastewater dilution occurred, linked to groundwater with high nitrate concentrations inputs to the stream, and even though the macroinvertebrate community recovered its quality in some sampling campaigns, it presented a different structure than in sampling points not affected by any of these pressures. Therefore, the approach here used to analyze the hydrological effects on macroinvertebrate communities allowed us to determine their influence on hydrochemical and habitat characteristics.

Resilience of benthic diatom communities in Mediterranean streams: role of endangered species

The extent of drought in Mediterranean streams has been intensifying recently, and the mean annual discharge is expected to experience a decreasing trend in coming years, with significant effects on aquatic ecosystems. The aim of this study was to analyse colonisation patterns of diatom communities that differed in terms of taxonomic composition and percentage of endangered taxa exploring the possible development of resistance mechanisms. To this end, we selected three Mediterranean streams comparable in terms of water quality, but different in terms of surrounding land use, and we performed two experimental treatments. The first treatment consisted in artificially drying and cleaning of substrates (cobbles) to analyse the post-drought recolonisation process that is only driven by drift and immigration. In the second treatment cobbles coming from a site experiencing a seasonal drought were transplanted upstream in a perennial stretch to explore the possible development of resistance mechanisms within diatom communities periodically exposed to droughts. We observed that stream identity played an important role in determining diatom assemblage composition. Highly natural stretches had a high abundance of endangered species, which were less resilient to drought than assemblages composed of general and widespread taxa. Moreover, according to our results, resistance mechanisms did not play a significant role in recovery patterns. Improving our knowledge of diatom resilience mechanisms is very important in a global climate change scenario, especially in Mediterranean streams.

A Framework for Dry Period Low Flow Forecasting in Mediterranean Streams

The objective of this article is to provide a simple and effective tool for low flow forecasting up to six months ahead, with minimal data requirements, i.e. flow observations retrieved at the end of wet period (first half of April, for the Mediterranean region). The core of the methodological framework is the exponential decay function, while the typical split-sample approach for model calibration, which is known to suffer from the dependence on the selection of the calibration data set, is enhanced by introducing the so-called Randomly Selected Multiple Subsets (RSMS) calibration procedure. Moreover, we introduce and employ a modified efficiency metric, since in this modelling context the classical Nash-Sutcliffe efficiency yields unrealistically high performance. The proposed framework is evaluated at 25 Mediterranean rivers of different scales and flow dynamics, including streams with intermittent regime. Initially, signal processing and data smoothing techniques are applied to the raw hydrograph, in order to cut-off high flows that are due to flood events occurring in dry periods, and allow for keeping the decaying form of the baseflow component. We then employ the linear reservoir model to extract the annually varying recession coefficient, and, then, attempt to explain its median value (over a number of years) on the basis of typical hydrological indices and the catchment area. Next, we run the model in forecasting mode, by considering that the recession coefficient of each dry period ahead is a linear function of the observed flow at the end of the wet period. In most of the examined catchments, the model exhibits very satisfactory predictive capacity and is also robust, as indicated by the limited variability of the optimized model parameters across randomly selected calibration sets.

Effects of urban wastewater on hyporheic habitat and invertebrates in Mediterranean streams

Wastewater discharges into fluvial ecosystems represent a significant and continuous source of fine particles and nutrients that can severely modify stream community composition and functionality. Depending on both wastewater and stream features (e.g., nutrient removal treatments and stream dilution capacity), the ecological effects can be more or less severe. To determine how hyporheic habitat and hyporheos are affected, we analysed eight Mediterranean streams both upstream and downstream of a wastewater effluent. The results demonstrated that environmental factors associated with clogging, such as the quantity of fine particulate and organic matter in sediment, were magnified downstream of the wastewater inputs. Likewise, dissolved nutrients also increased but depended to a greater extent on the presence of a wastewater treatment plant and on the nitrogen and phosphorus removal treatments. The hyporheic invertebrates were more affected by clogging than by eutrophication. Both richness and diversity parameters were negatively correlated with clogging features but were not correlated with eutrophication. The most affected taxa were Macrocrustaceans, Hydrachnidia and several insect species, which decreased or were not detected downstream of the effluents. On the contrary, other taxa such as Naididae (Oligochaeta), Orthocladiinae (Chironomidae) and Potamopyrgus antipodarum (Gastropoda) benefited from the wastewater inputs.

Longevity and population age structure of the arroyo southwestern toad (Anaxyrus californicus) with drought implications.

The arroyo southwestern toad is a specialized and federally endangered amphibian endemic to the coastal plains and mountains of central and southern California and northwestern Baja California. It is largely unknown how long these toads live in natural systems, how their population demographics vary across occupied drainages, and how hydrology affects age structure. We used skeletochronology to estimate the ages of adult arroyo toads in seven occupied drainages with varying surface water hydrology in southern California. We processed 179 adult toads with age estimates between 1 and 6 years. Comparisons between skeletochronological ages and known ages of PIT tagged toads showed that skeletochronology likely underestimated toad age by up to 2 years, indicating they may live to 7 or 8 years, but nonetheless major patterns were evident. Arroyo toads showed sexual size dimorphism with adult females reaching a maximum size of 12 mm greater than males. Population age structure varied among the sites. Age structure at sites with seasonally predictable surface water was biased toward younger individuals, which indicated stable recruitment for these populations. Age structures at the ephemeral sites were biased toward older individuals with cohorts roughly corresponding to higher rainfall years. These populations are driven by surface water availability, a stochastic process, and thus more unstable. Based on our estimates of toad ages, climate predictions of extreme and prolonged drought events could mean that the number of consecutive dry years could surpass the maximum life span of toads making them vulnerable to extirpation, especially in ephemeral freshwater systems. Understanding the relationship between population demographics and hydrology is essential for predicting species resilience to projected changes in weather and rainfall patterns. The arroyo toad serves as a model for understanding potential responses to climatic and hydrologic changes in Mediterranean stream systems. We recommend development of adaptive management strategies to address these threats.

Short, medium and long-term effects of density on the demographic traits of a threatened newt

Mediterranean streams undergo seasonal reductions in water availability that may affect amphibian demography due to habitat loss and the concentration of individuals in the shrinking aquatic habitats. However, there are few empirical examples of how increased population density experienced by larval stages produces long-term effects on growth and fitness at postmetamorphic stages. We tested the effect of four different larval densities on the demography and growth of the endangered stream-dwelling newt Euproctus platycephalus. By manipulating larval populations in experimental aquaria, we analyzed the short-term effects of density in terms of growth and mortality rates as well as of social behavior. To assess medium- and long-term effects we tested the metamorph individuals after 1 and 3 years, respectively, and adults for maternal effect by assessing the relationship between mean larval size and fecundity. Larval body size and growth rate appeared inversely proportional to larval density. Density affected the incidence of aggressive behavior by increasing the rate of mutilation to arms and tail. One-year-old salamanders raised at the highest larval density grew significantly less. All 3-year-old individuals reached comparable body size and body condition irrespective of initial larval density. Salamanders presented a positive relationship between maternal size and (1) fecundity and (2) larval size. In natural conditions, increased density may cause slower growth and a reduction in the percentage of individuals reaching metamorphosis. Prolonged dry periods and increased water withdrawals for agricultural and industrial practices have almost certainly affected the population dynamics of Sardinian newt populations in the long term.

The effect of hypoxia and flow decrease in macroinvertebrate functional responses: A trait-based approach to multiple-stressors in mesocosms

River ecosystems are most often subject to multiple co-occurring anthropogenic stressors. Mediterranean streams are particularly affected by water scarcity and organic loads that commonly lead to a simultaneous reduction in flow and increasing depletion of dissolved oxygen.In the present study, the single and combined effects of water scarcity (flow velocity reduction) and dissolved oxygen depletion were used to evaluate alterations of drifting macroinvertebrates on a channel mesocosm system, by employing a multiple trait-based approach.Our main findings confirmed that the impact of the two combined stressors can be implicated in alterations of ecosystem functions as result of the changes in proportions of biological traits. Overall, our results showed that, individually, flow velocity reduction and a severe oxygen depletion promoted a shift in community traits. In more detail, biological traits describing the dispersal of organisms and their respiration showed the strongest responses. The respiration mode responded to low flow with drift increase of gill breathers and decrease of individuals with tegument, whereas dispersal was clearly affected by the combination of stressors. Resistance through eggs was higher with the single effect of flow reduction, while swimmers´ relative abundance increased in individuals that drift after exposure to the combination of stressors. Thus, while flow reduction alone is expected to specifically filter out the gill breathers and the egg producers, the combination of stressors will impact more drastically organism's dispersal and swimmers. Such changes in biological traits can result in variations in ecosystem functioning through, for example, local changes in biomass, secondary production, stream metabolism as well as resulting in biodiversity losses or alterations of its distribution patterns.

A benthic macroinvertebrate multimetric index for Chilean Mediterranean streams

Increased anthropogenic disturbances affecting streams worldwide have resulted in declines of freshwater biodiversity. Mediterranean ecoregions are very sensitive to such disturbances because of their high levels of natural hydrological variability and increasing trends in human population growth. The use of aquatic macroinvertebrate assemblages as bioindicators is a commonly applied approach for evaluating water body condition. However, extensive use of macroinvertebrates across similar ecoregions may be limited because of natural local differences in biodiversity and differing anthropogenic disturbances. Here, we present a multi-metric index (MMI) based on macroinvertebrate assemblages from Chilean Mediterranean streams. To evaluate the relative level of disturbance among sampling sites with respect to multiple anthropogenic perturbations, we used an integrated disturbance index based on catchment and local scale disturbances. We sampled 95 sites from streams and rivers during the 2016 austral summer including 26 least-disturbed reference sites, 13 highly disturbed sites, and 56 intermediately disturbed sites. In addition, we re-sampled 14 sites during winter and spring to validate our findings. Using a set of screening criteria, we evaluated 74 candidate macroinvertebrate metrics, representing diversity, composition, trophic structure, and tolerance to pollution. The resulting MMI included Diptera taxa richness, total macroinvertebrate density, number of Ephemeroptera-Plecoptera-Trichoptera individuals, and predator taxa richness. The final MMI scores classified the 95 sampling sites into three categories of biotic condition, including good (n = 46), fair (n = 18), and poor (n = 31). Our approach is transferable to other rivers in the region and is a sufficient tool to evaluate the condition of sites affected by several human perturbations at both local and catchment scales in Chilean Mediterranean streams.

Understanding the effects of predictability, duration, and spatial pattern of drying on benthic invertebrate assemblages in two contrasting intermittent streams.

In the present study, we examined the effects of different drying conditions on the composition, structure and function of benthic invertebrate assemblages. We approached this objective by comparing invertebrate assemblages in perennial and intermittent sites along two intermittent Mediterranean streams with contrasting predictability, duration, and spatial patterns of drying: Fuirosos (high predictability, short duration, downstream drying pattern) and Rogativa (low predictability, long duration, patchy drying pattern). Specifically, we quantified the contribution of individual taxa to those differences, the degree of nestedness, and shifts in the composition, structure and function of benthic invertebrate assemblages along flow intermittence gradients. We observed greater effects of drying on the benthic invertebrate composition in Fuirosos than in Rogativa, resulting in a higher dissimilarity of assemblages between perennial and intermittent sites, as well as a lower degree of nestedness. Furthermore, a higher number of biotic metrics related to richness, abundance and biological traits were significantly different between perennial and intermittent sites in Fuirosos, despite a shorter dry period compared to Rogativa. At the same time, slightly different responses were detected during post-drying (autumn) than pre-drying (spring) conditions in this stream. In Rogativa, shifts in benthic invertebrate assemblages along increasing gradients of flow intermittence were found for three metrics (Ephemeroptera, Plecoptera and Trichoptera (EPT) and Odonata, Coleoptera and Heteroptera (OCH) abundances and aerial active dispersal. Furthermore, we demonstrated that combined gradients of dry period duration and distance to nearest perennial reach can generate complex, and different, responses of benthic invertebrate assemblages, depending on the flow intermittence metric. Our study advances the notion that special attention should be paid to the predictability, duration and spatial patterns of drying in intermittent streams in order to disentangle the effects of drying on benthic invertebrate assemblages, in particular in areas subject to high spatial heterogeneity and temporal variability in drying conditions.

Diatom responses to sewage inputs and hydrological alteration in Mediterranean streams

We analyzed the conjoint effects of sewage inputs and hydrological alteration on the occurrence of teratological forms and on the assemblage composition of stream benthic diatoms. The study was performed in 11 Mediterranean streams which received treated or untreated urban sewage (Impact sites, I), whose composition and morphological anomalies were compared to upstream unaffected (Control, C) sites. The impact sites had high concentrations of ammonium, phosphorus, and pharmaceutical compounds (antibiotics, analgesics, and anti-inflammatories), particularly in those receiving untreated sewage. Impact sites had a higher proportion of teratological forms as well as a prevalence of diatom taxa tolerant to pollution. The differences in the diatom assemblage composition between the paired C and I sites were the largest in the impacted sites that received untreated sewage inputs as well as in the systems with lower dilution capacity. In these sites, the diatom assemblage was composed by a few pollution-tolerant species. Mediterranean river systems facing hydrological stress are highly sensitive to chemical contamination, leading to the homogenization of their diatom assemblages.

Population status of the native Cottus gobio after removal of the alien Salmo trutta: a case-study in two Mediterranean streams (Italy)

In the Mediterranean area, one of the major threats to freshwater fish fauna is represented by the introduction of alien species. The bullhead, Cottus gobio, is a species of great conservation interest threatened by the massive introduction of hatchery-reared brown trout, Salmo trutta, for angling purposes. The aims of this research were: i) to present a case-study of interspecific and intraspecific competition in dwelling fish from two Mediterranean streams (central Italy); ii) to evaluate the bullhead population status before and after the alien brown trout removal, and iii) to investigate the influence of the environmental parameters on the abundance of both species. For the bullhead populations the abundances and the young-of-the-year percentage significantly increased after the removal activities. The growth analysis showed that, after the trout removal, bullhead were distinguished by greater performance and larger sizes in all age classes in comparison to the pre-removal period, while the condition factor (Kn) showed no differences, suggesting that the effects of trout population control acted mainly through predator-prey dynamics. An inverse correlation between the abundance of bullhead and its body condition suggested that the beneficial effects due to the reduction of predation could be compensated by the intraspecific competition due to the increase of the bullhead population density.

Large wood recruitment and mobility in steep mountain streams of contrast European landscapes

We present a comparative study of large wood (LW) mobility in two steep channels (0.06<S<0.20) of contrast European landscapes during major hydro-geomorphic events of similar magnitude. We investigated a headwater perennial stream draining Central European medium-high mountain relief (the Klepáčský, Hrubý Jeseník Mts, Czech Republic; A≤2.5 km2) and an ephemeral Mediterranean steep stream (the Sfakiano Gorge, Crete, Greece; A≤52 km2). Both studied hydro-geomorphic events were partially accompanied by debris-flood or debris-flow character of sediment transport including significant content of LW. The minimal estimations of transported LW volume were 71.3 m3 along 1.7 km long reach in the Klepáčský and 49.4 m3 along 4 km long reach in the Sfakiano Gorge. Despite completely different characters of hydrologic regimes, riparian zones and valley confinement settings, living trees in the valley floor played crucial role in wood deposition and development of large jams in both environments. The trees living in the valley floor were the main source of LW in the studied Mediterranean channel, whereas long-term LW recruitment from very steep hillslopes or rock cliffs was quite negligible. On the other hand, previous windstorms in the Klepáčsky caused notable delivery of LW from adjacent hillslopes and LW recruitment by bank erosion occurred only at spatially-limited semi-confined parts of the valley.

Restoration of native Mediterranean brown trout Salmo cettii Rafinesque, 1810 (Actinopterygii: Salmonidae) populations using an electric barrier as a mitigation tool

This study assessed the effectiveness of a novel conservation strategy for the native brown trout populations in Sardinia (Italy). The conservation measures included: (i) installation of an electric fish barrier; (ii) removal of all the resident introgressed brown trout upstream from the barrier; (iii) restocking of the upstream region with native Sardinian trout genetically characterised; and (iv) estimation of native trout population size with prediction of future growth. Introgressed brown trout were removed using multiple-pass electrofishing methods in a 2-km region upstream from the barrier. In two eradication campaigns, conducted in 2010 and 2012, a total of 1801 trout were captured, comprising a total biomass of 55,501 g. The capture efficiency analysis showed total capture rates of over 99% were achieved for parr (0+ age cohort), and 100% for adult trout. After the eradication campaigns we restocked this area with native brown trout (Adriatic lineage, AD, according to the mitochondrial DNA control region nomenclature). The monitoring campaigns showed good survival (S = 60%) and reproduction of 3.1 recruits/adult trout. Successful breeding was recorded starting from the summer of 2015 and a self-sustaining population resulted after only two restocking events. The results of this restoration project allow recommendations to be made for future conservation eradication and repopulation projects for restoration of typical Mediterranean streams.

Linking the recruitment and survivorship of a freshwater stream-specialist fish species to flow metrics in Mediterranean climate temporary streams

ABSTRACTNovel modelling was utilised in the present study to reveal significant relationships between the abundance of the Australian freshwater stream-specialist fish Galaxias olidus and metrics defining flow regimes across a region dominated by temporary streams. It was revealed that increases in total abundance were linked to metrics (both 1- and 3-year periods) that indicate greater water availability and the persistence of water in pools across the year, namely the average duration of zero-flow days over the low-flow season (negatively) and total duration of bankfull flows across the year (positively). The analysis identified 3-year metrics as being more important to the abundance of 0+ fish rather than annual ones. Taken together, these findings describing the flow requirements of a stream specialist will help to guide implementation of environmental flows, but will also highlight the need for continued exploration of flow–ecology relationships.

Assessing hydro-morphological changes in Mediterranean stream using curvilinear grid modeling approach - climate change impacts

The objective of this work was the estimation of time-space hydraulic (water depth, flow velocity) and morphological (sediment transport and bank erosion) characteristics in the downstream part of a Mediterranean stream under current and future climatic conditions. The two-dimensional hydraulic model MIKE 21C was used, which has been developed specifically to simulate 2D flow and morphological changes in rivers. The model is based on an orthogonal curvilinear grid and comprises two parts: (a) the hydrodynamic part and (b) the morphological changes part. The curvilinear grid and the bathymetry file were generated using a very high-resolution DEM (1 m × 1 m). Time series discharge data from a hydrometric station introduced in the hydrodynamic part of the model. Regarding the morphological part of the model, field measurements of suspended sediment concentration and of bank erosion were used. The model was calibrated and verified using field data that were collected during high and low flow discharges. Model simulation was in good agreement with field observations as indicated by a variety of statistical measures. Next, for predicting the riverbank change, future meteorological data and river flow data for the next 10 years (2017–2027) were employed. These data series were created according to a lower and a higher emission climate change scenario. Based on the results, an increase in rainfall intensity may cause significant changes in river banks after 10 years (more than 5 m of soil loss in river meanders). Using the obtained simulation results, extreme hydrological events such as floods transporting large sediment loads and changes in river morphology can be monitored. The proposed methodology was applied to the downstream part of the Koiliaris River Basin in Crete, Greece.

Impact of urban chemical pollution on water quality in small, rural and effluent-dominated Mediterranean streams and rivers

The impact and occurrence of wastewater (treated and untreated) derived pharmaceutically active compounds (PhACs) have been investigated in small, rural and effluent-dominated tributaries of the lower Ebro River located in the North-Eastern Spain (Catalonia). We have observed the predominant effect of stream flow and consequently dilution factor on the concentration levels of detected PhACs that combined with the absence of wastewater treatment plants (WWTP) resulted in 12 times higher concentrations in streams with direct discharge of untreated wastewater. Non-steroidal anti-inflammatory drugs (NSAIDs) were the most ubiquitous compounds, in terms of both individual concentration and frequency of detection. In the sites impacted by raw wastewater, acetaminophen and ibuprofen showed the highest concentrations among all analyzed PhACs, reaching concentrations up to 7.78μgL−1 and 2.66μgL−1, respectively. However, PhACs detected in the sites impacted by treated wastewater showed generally lower concentration levels and frequencies of detection. Also, effluent-dominated streams showed higher concentration levels of PhACs due to a generally lower stream flows and small dilution factors. However, concentration levels of detected PhACs were dependent on the hydraulic travel time and distance from the discharge point and related with the in-stream attenuation. As a result, this study highlights the combined impact of hydrological and chemical stressors on the water quality of the rural Mediterranean aquatic ecosystems.

Bed disturbance below dams: observations from two Mediterranean rivers

AbstractRiver‐bed disturbance and associated sedimentary processes such as particle mobility are central elements to assess river ecosystem functioning. Dams change river dynamics affecting the magnitude and frequency of biophysical elements that depend on them. This paper examines the effects of two dams different in size, management, and location, on the flow regime, flood competence, and bed disturbance in two contrasting Mediterranean rivers, the Ésera and the Siurana. For this purpose, two reaches on each river were monitored upstream and downstream from reservoirs. Several monitoring and modeling techniques were used to characterize flow competence, particle entrainment, and the volumes of sediments eroded and deposited after floods. The flow regime of the Ésera has been modified from nivo‐pluvial regime, typical of humid mountainous environments, to that observed in dry semiarid regions, in which high magnitude but low frequency floods are the dominant processes. Conversely, the flow regime of the Siurana has changed from a typical Mediterranean stream to a regime observed in more temperate environments, with more permanent and stable flows. Both rivers show notably physical changes, with channels clearly less dynamic below the dams. The lack of competent flows together with the sediment deficit associated with the dams has led to less active fluvial environments (reduced particle mobility and bed scour dynamics), a fact that affects instream habitat structure (more uniform grain size distribution, less physical heterogeneity, more stable flows), overall contributing to the degradation of the stream corridor and the subsequent environmental deterioration of the whole fluvial landscape. Copyright © 2017 John Wiley & Sons, Ltd.

Testing mechanical characteristics of chestnut stakes used in bed sills for stream restoration

Using of wood elements for constructing bed sills in Mediterranean streams, where the banks are not protected by tree vegetation, needs an evaluation of biological and mechanical characteristics for evaluating both the wood durability and the effectiveness of the stream restoration project. Very few studies have dealt both with the decay of mechanical characteristics of wood elements employed for stream restoration works and with the changes over time of physical and chemical wood characters. In this paper, for a wood and stone bed sill located in a stream having no shaded banks, the changes of physical and chemical characters detected after 12, 18, 24, 30, 36, 42 and 48 months on chestnut stakes are preliminarily recalled. Then, using three chestnut stakes extracted after 96 and 108 months and two unaltered stakes, as reference condition, the mechanical compression tests were carried out. The results of the compression tests for both runs (altered and unaltered stake) allowed to establish the influence of the ageing process on the compressive strength and stiffness of the chestnut wood. Finally, using two chestnut stake extracted after 108 and 120 months and two unaltered stakes, the flexural tests were carried out by a four points scheme (two supporting points and two loading points) according to UNI EN 408-2012 standard. The results of the flexural tests for both runs (altered and unaltered stake) allowed to establish that the wood ageing process determines the decay of mechanical strength of the material and reduces the bending strength of the chestnut wood. From an applicative point of view, the obtained results showed that after 10 years the mechanical resistance characteristics of the wood stakes are less than those corresponding to the undisturbed reference condition.

Interbasin water transfer for the rehabilitation of a transboundary Mediterranean stream: An economic analysis

Global demand for freshwater is increasing as human population grows, climate changes and water resources are being overexploited. Consequently, many freshwater ecosystems, particularly in water-stressed regions, are severely degraded. Here we present a unique case of an Interbasin Water Transfer (IWT) project aiming at ecosystem rehabilitation and recreation enhancement of an intermittent transboundary stream (Ayun, Israel). For the past century, water diversion at the Lebanese side had led to flow secession in the Israeli Ayun Nature Reserve during the dry season (May–November). To restore flow continuum, a sum of 0.5 million cubic meters of high quality freshwaters have been allocated annually during the dry months. The aim of this study is to evaluate the IWT project by: (1) examining the correlation between water flow in the Ayun and recreational visitation, and (2) performing a cost-benefit analysis of the IWT scheme, including non-market benefits. A time-series regression (Adj. R2 = 0.688, n = 125) shows that a 10% increase in water flow corresponds to a 2.1% increase in monthly visitors. An estimated 18.8% of the visitation rate between 2009 and 2015 can be attributed to the water reallocation project. Through a single-site travel cost model, we estimate the visitor's willingness to pay in US$ 37.8 per person per trip. When non-market benefits for recreation are included, the total benefits of the IWT project substantially exceed its costs. Our results suggest that IWT can be applied to restore water flow and enhance ecosystem services also in water-stressed regions.

Combined effects of hydrologic alteration and cyprinid fish in mediating biogeochemical processes in a Mediterranean stream

Flow regimes are important drivers of both stream community and biogeochemical processes. However, the interplay between community and biogeochemical responses under different flow regimes in streams is less understood. In this study, we investigated the structural and functional responses of periphyton and macroinvertebrates to different densities of the Mediterranean barbel (Barbus meridionalis, Cyprinidae) in two stream reaches differing in flow regime. The study was conducted in Llémena Stream, a small calcareous Mediterranean stream with high nutrient levels. We selected a reach with permanent flow (permanent reach) and another subjected to flow regulation (regulated reach) with periods of flow intermittency. At each reach, we used in situ cages to generate 3 levels of fish density. Cages with 10 barbels were used to simulate high fish density (>7indm−2); cages with open sides were used as controls (i.e. exposed to actual fish densities of each stream reach) thus having low fish density; and those with no fish were used to simulate the disappearance of fish that occurs with stream drying. Differences in fish density did not cause significant changes in periphyton biomass and macroinvertebrate density. However, phosphate uptake by periphyton was enhanced in treatments lacking fish in the regulated reach with intermittent flow but not in the permanent reach, suggesting that hydrologic alteration hampers the ability of biotic communities to compensate for the absence of fish. This study indicates that fish density can mediate the effects of anthropogenic alterations such as flow intermittence derived from hydrologic regulation on stream benthic communities and associated biogeochemical processes, at least in eutrophic streams.