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Simulations of tracer experiments conducted with a three‐dimensional primitive‐equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are low—at most O(10−1) kg m−3difference among sources—and almost negligible from a dynamic point of view—compared with inertial forces—they are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients.

We investigated sediment-water heat flux estimation in relation to applications (hydrodynamics simulation, evaporation studies, or global change effects assessment) in which sediment temperatures are not available because of technical complications (difficulties in installing sensors, for example) or because of methodology used (remote sensing, for example). We used field sediment temperature data measured every 10min to 1m depth at Doñana National Park marshland to obtain sediment thermal properties and to calculate diel sediment-water heat exchange through Beck’s sequential function specification method. We compare four models for the simulation of sediment-water heat flux by using surface temperatures. Two models need initial estimated inside sediment temperatures; the other two do not. Influence of estimated initial temperature profiles depends on the temperature distribution assumption and is significant for three days or fewer at the daily timescale. A model that does not use initial sediment temperatures provides accurate estimations with low computation time.

espanol?Pueden ser las grandes masas de agua sensores de cambio global? Como acumuladoras de agua y calor, algunas de sus caracteristicas termicas podrian verse alteradas por cambios hidrometeorologicos a medio y largo plazo y asi ser utilizadas como indicadoras de los efectos del cambio global sobre los ecosistemas fluviales. Este trabajo se centra en el estudio de la incidencia de cambio global (cambio climatico mas cambio de usos de agua y suelo) en la organizacion interna del lago de Sanabria, concretamente en su ciclo anual termico. Se estudia la existencia de tendencias temporales en el comportamiento termico del lago, donde se dispone de perfiles de temperatura del agua desde el ano 1986. Los analisis de datos incluyen las tecnicas estadisticas no parametricas del test de tendencia de Man-Kendall y la estimacion de pendiente de Sen para evaluar patrones estacionales y a largo plazo de variables hidrometeorologicas y termicas del lago. Los resultados principales indican que, sorprendentemente, el lago de Sanabria se esta enfriando globalmente, lo cual podria explicarse por un fortalecimiento de la termoclina y un descenso de la transferencia de calor al hipolimnion durante el periodo de estratificacion. Estos resultados contribuyen a entender y cuantificar la susceptibilidad de las masas de agua ibericas al cambio global EnglishAre large water bodies able to act as sensors of global change? As accumulators of water and heat, some of their thermal characteristics might be altered by long term (decadal) hydrometeorological changes and thus may be used as indicators of the effects of global change on fluvial ecosystems. This work focuses on the effect of global change (climate change plus water quantity and land use changes) in the internal organization of Sanabria Lake, specifically in its thermal annual cycle. The existence of temporal trends in the thermal behaviour of the lake was investigated based on the water temperature profiles that are available since 1986. Data analyses include the non-parametric Mann-Kendall trend test and the Sen slope estimate to evaluate long term and seasonal patterns of hydrometeorological and in-lake thermal variables. The main results surprisingly point to a net lake cooling that could be explained by a stronger thermocline and a weaker vertical transfer of heat to the hypolimnion during the stratification period. These results contribute to understand and quantify the effects of global change on Iberian freshwater bodies

IntroductionThe increase in elderly population has led to an associated increase in multiple pathologies, frailty, polypharmacy, healthcare costs, decreased quality of life and mortality. We designed an intervention based on person-centred care model. This article outlines a study protocol, which aims to explore the effects of the intervention to improve therapeutic adequacy in polymedicated elderly patients.Methods and analysisAn open, randomised, multicentre, controlled clinical trial. The study population includes polymedicated (≥8 prescription medications) patients ≥75 years old. In the intervention group, the multidisciplinary team (primary care pharmacist, family doctor and nurse) will meet to carry out multidimensional reviews (frailty, clinical complexity, morbidity and therapeutic adequacy) of the study subjects. If changes are proposed to the treatment plan, a clinical interview will be conducted with the patient to agree on changes in accordance with their preferences. Follow-up visits will be scheduled at 6 and 12 months. In the control group, where the usual clinical practice will be followed, the necessary data will be collected to compare the results.The key variables are the variation in the mean number of incidents (potentially inappropriate prescription) per patient, the number of medications, the number of changes implemented to the treatment plan and the variation in the number of hospital admissions.Ethics and disseminationThis study was approved by the Ethics Committee of the IDIAPJGol and by the University of Barcelona’s Bioethics Commission. The results are expected to be published in peer reviewed open-access journals, and as part of a doctoral thesis.Trial registration numberNCT04188470. Pre-results.

Department of Environmental Engineering Sao Paulo State University UNESP, Av. Tres de Marco 511

13 páginas, 4 figuras, 5 tablas., The Water Framework Directive EU2000/60/EC (WFD) was implemented for reservoirs at a regional scale (northeastern Spain). Twenty-one reservoirs were monitored quarterly over the course of a year. Using principal component analysis, the reservoirs were classified into types according to their geological and morphometric features. The Ecological Quality (EQ) of the reservoirs was assessed by integrating values of total chlorophyll a, cyanophyta chlorophyll a concentration, fish metrics, Secchi depth, averaged hypolimnetic oxygen concentration and total phosphorus. For each reservoir type, a reference condition of quality was selected. When possible, this reference was the reservoir displaying the best EQ; otherwise expert judgment was used. To allow comparison of quality among reservoirs belonging to different types, thus identifying intrinsic differences, an Ecological Quality Ratio (EQR) was calculated by dividing the EQ value of each reservoir by that of its reference. According to EQR, the majority of the reservoirs accomplished the quality criteria of the WFD. This study identified a number of useful indicators for EQ assessment. Moreover, because the references were chosen among similar reservoirs, low EQR values are indicative of specific problems, such as untreated or wastewater spills or droughts. The results also demonstrate that expert judgment is a reasonable compromise when the low number of water bodies available for the study prevents statistical approaches., This research was funded by Catalan Water Agency (ACA), which also provided historical data for the reservoirs. Additional financial support was provided by the Spanish Ministry of Education and Science (projects CGL2004-05503- CO2-O1, and CGL2008-06377-C02-01).

Carbon dioxide emissions from lakes contribute to the continental carbon balance. Water chemistry analyses of reservoirs in Spain suggest that carbonate weathering causes CO2 supersaturation in lakes above a threshold alkalinity.

[1] A field data set collected under different conditions is analyzed to characterize the spatial arrangement of two large inflows (Ebro and Segre) with distinct physical-chemical characteristics as they join at the upstream end of Ribarroja reservoir in northern Spain. Given the short average residence time of water in the reservoir, the spatial arrangement of the rivers at their confluence and their mixing rates are likely the drivers of the stratification patterns observed near the dam. In winter, inflows have similar densities—Δρ/ρ0 ≈ O(10−5)—and their spatial distribution is largely determined by inertial forces, and in particular, by the discharge ratio. Downstream of the confluence, both rivers flow side by side and largely unmixed over long distances. In summer, with Δρ/ρ0 of O(10−3), the flow fields at the confluence are largely controlled by buoyancy forces. Atmospheric forcing during strong wind events and centrifugal forces caused by the meandering shape of the reservoir induce significant tilting of the isotherms, leading to localized high mixing rates. Mixing, in general, though is weak at this time of the year. In fall and early winter, density differences are largely controlled by conductivity differences between the incoming flows. The warmer Ebro water, with larger thermal inertia, flows beneath the colder Segre water. The spatial arrangement of the inflows is largely controlled by the discharge ratio and mixing between sources is strong, likely as a result of mixed water being denser than either of the incoming flows.

The effect of river water quality, its inflow rate, and temperature on planktonic food web composition and activities were studied in the eutrophic Sau Reservoir (Catalonia, NE Spain). We analyzed 8 longitudinal transects conducted between July 1996 and April 1999 covering a wide range of variability in both seasonal and spatial circulation patterns. To compare objectively the biological longitudinal gradients under seasonally fluctuating water levels and different types of water circulation patterns, we applied a model based on the relative distance of a sampling station from the river inflow. Even under different hydrological scenarios, the model was able to characterize epilimnetic food chain successions and locations of peaks of bacteria, heterotrophic nanoflagellates, ciliates, phytoplankton, and zooplankton along the longitudinal gradient. The amplitude of microbial peaks was directly related to the proportion of nutrient and organic carbon rich river water that mixed into the reservoir epilimnion. Enhanced abundances and activities of microbes were detected in spring and summer periods, mainly during events of river water overflow when a large proportion of the river was directly mixed into the epilimnion. Thus, the relative input of river water is suggested to be a useful predictor of the amplitude of the development of the epilimnetic microbial food webs in highly loaded canyon-shaped reservoirs. These results may have important implications in the context of global change in Mediterranean regions, where expected reductions in runoff may profoundly affect river water circulation patterns in reservoirs and hence organic carbon cycling in these ecosystems.

Low dissolved oxygen concentration in bottom layers of lakes and reservoirs usually indicates low water quality. In lakes, empirical models predicting anoxia are almost entirely based on the decay of plankton biomass, while in reservoirs recent findings suggest a prominent role of streamflow and load of organic carbon. This suggests a potential link between water quality in reservoirs and climate processes affecting streamflow. Here we support this hypothesis presenting evidence that both interannual climate variability and recent climate change, mainly consisting in a significant increase in potential evapotranspiration in the upstream basin, affected the oxygen content in a Mediterranean reservoir (Sau Reservoir, Spain). Using a 44-year monthly record, we found strong and consistent signatures of El Nino Southern Oscillation in the inflow and reservoir oxygen content. Spectral and wavelet techniques showed that the El Nino, streamflow, and reservoir oxygen content series oscillated in common periods, which coincided with the main El Nino variability modes. An empirical model explaining the annual oxygen content in the reservoir suggested that a decreasing streamflow trend reduced the oxygen content of the reservoir by about 20%, counteracting remediation measures implemented at the basin upstream the reservoir. Our results provide the first quantitative evidence of climate change effects on reservoir water quality using long-term instrumental data, and indicate that streamflow should be considered as a key variable in assessing climate change impact on reservoir water quality. These results are especially relevant in regions of the world where reservoirs are abundant and most climate models predict a decrease in runoff during the next decades. Both the expected trends and the sensitivity of reservoir water quality to global interannual climate variability should be considered for a correct management of water resources in the present and to design adaptation policies in the future.

Among the topics covered by Hutchinson’s Santa Rosalia article, the question of the shortening and lengthening of food webs occupies a central role. As Hutchinson realized, at the time scales of ecological studies, the impact of invader species on established food webs is the fastest shortcut to the shortening or lengthening of the food webs. The construction of thousands of dams in Spain during the last century has offered ecologists a good opportunity to test the effects of invader fish species on the plankton dynamics of these systems. In this article, a series of data related to the food web structure of Sau Reservoir is analyzed for the period 1997–2005. Parameters such as Secchi depth and chlorophyll concentration, as well as abundance and size structure of zooplankton, have been matched to the zooplankton dynamics in the reservoir. Most of the changes detected within this period are attributed to the introduction of zooplanktivorous fish in the reservoir. The Secchi depth measurements have showed a progressive diminution in the clear-water phase during recent years. These changes have been related to the decrease in the abundance of Daphnia and to the reduction of the size of zooplankton, which help to explain concomitant increases in the chlorophyll concentration in the same period. Other observed changes in the composition of the zooplankton community have been the substitution of Daphnia by Bosmina and the increase in the abundance of rotifers. Thus, the annual average abundance of Bosmina in 1997 was 70% of cladocerans, while in 2005 it reached 98%. In parallel, the percentage occurrence of individual rotifers was 40% of total zooplankton numbers but had risen to 85% at the end of the period. All these changes are attributed to the artificial expansion of the food web through stocking of the reservoir with zooplanktivorous fish (Rutilus rutilus and Alburnus alburnus). This study improves our understanding of the trophic relationships in the food web prior to the introduction of the fish.

The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a one-year cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L(-1)) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group L(o)). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir.

Lopez, P., R. Marce, J. Ordonez, I. Irrutia and J. Armengol. 2009. Sedimentary phosphorus in a cascade of five reservoirs (Lozoya River, Central Spain). Lake Reserv. Manage. 25:39–48. The concentration of phosphorus (P), carbon (C), and nitrogen (N) in superficial sediments in a cascade of five reservoirs (Pinilla, Riosequillo, Puentes Viejas, El Villar, and El Atazar) located along the Lozoya river (Central Spain) was determined. The mean reservoir values of sedimentary phosphorus, nitrogen, and carbon increased from the first reservoir (Pinilla) to the central one (Puentes Viejas) where they reached 62 μ molP/g(dw), 5.36 mmolC/g(dw)and 0.56 mmolN/g(dw), respectively. They then followed a decreasing trend until the last reservoir (El Atazar), which presented concentrations close to those of Pinilla. Phosphorus and nitrogen usually tended to increase from the river end to the dam at each reservoir, while carbon did not show a regular trend associated to the river flow. The amount of phosphorus ac...

Hypolimnetic oxygen content in lentic ecosystems has traditionally been modeled as a function of variables measured at the epilimnion, or that are supposed to drive epilimnetic processes, like total phosphorus load. However, in man-made reservoirs the river inflow can plunge into deep layers, directly linking the hypolimnion with the surrounding watershed. In these circumstances, organic matter carried by the river can influence the hypolimnetic oxygen content without important intervention of epilimnetic processes. Taking long-term data from two reservoirs in Spain, we applied an empirical regression approach to show that the dissolved organic matter carried by the river is the main driver shaping the hypolimnetic oxygen content. By contrast, typical variables commonly included in the modeling of the oxygen content in the hypolimnion (nutrient concentrations, chlorophyll a, and dissolved organic carbon measured in the water column) did not show any significant correlation. Interpretations from this regression approach were supported by a comparison between the monthly oxygen consumption in the hypolimnion and the monthly dissolved organic carbon load from the river inflow. We also revisited the prediction of the year-to-year variability of the Nurnberg’s anoxic factor in four reservoirs from Spain and the USA, explicitly including the allochthonous sources in the equations. These sources were significant predictors of the anoxic factor, especially in those systems subject to relatively high human impact. Thus, effects of allochthonous dissolved organic carbon should always be considered in empirical modeling and management of reservoir hypolimnetic processes related to oxygen content (for example, anoxia, nutrient internal loading, or phosphorus cycle resilience).

River water temperature is a common target of water quality models at the watershed scale, owing to its principal role in shaping biogeochemical processes and in stream ecology. Usually, models include physically-based, deterministic formulations to calculate water temperatures from detailed meteorological information, which usually comes from meteorological stations located far from the river reaches. However, alternative empirical approaches have been proposed, that usually depend on air temperature as master variable. This study explored the performance of a semidistributed water quality application modelling river water temperature in a Mediterranean watershed, using three different approaches. First, a deterministic approach was used accounting for the different heat exchange components usually considered in water temperature models. Second, an empirical approximation was applied using the equilibrium temperature concept, assuming a linear relationship with air temperature. And third, a hybrid approach was constructed, in which the temperature equilibrium concept and the deterministic approach were combined. Results showed that the hybrid approach gave the best results, followed by the empirical approximation. The deterministic formulation gave the worst results. The hybrid approach not only fitted daily river water temperatures, but also adequately modelled the daily temperature range (maximum–minimum daily temperature). Other river water features directly dependent on water temperature, such as river intrusion depth in lentic systems (i.e. the depth at which the river inflow plunges to equilibrate density differences with lake water), were also correctly modelled even at hourly time steps. However, results for the different heat fluxes between river and atmosphere were very unrealistic. Although direct evidence of discrepancies between meteorological drivers measured at the meteorological stations and the actual river microclimate was not found, the use of models including empirical or hybrid formulations depending mainly on air temperature is recommended if only meteorological data from locations far from the river reaches are available. Copyright © 2008 John Wiley & Sons, Ltd.

By contrast to the more regular and predictable temperate lakes, heat budgets and temperature dynamics in Mediterranean reservoirs are characterized by a marked interannual variability. In the present paper, the heat content, annual Birgean heat budget (ABHB), and thermal structure of Sau Reservoir were examined during a period of hypolimnetic withdrawal between 1980 and 1985, and during a period of withdrawal at intermediate depths between 1996 and 2003. The two study periods were also characterized by a wide range of stored water volume fluctuations. Results were used to develop and validate an empirical model to predict annual and monthly heat dynamics statistics and mixed layer depth as a function of hydraulic management parameters such as water volume and selective withdrawal depth. During the hypolimnetic withdrawal period elevated ABHB and deep mixed layer depths were recorded in the reservoir, which behaved as a heat trap. By contrast, intermediate depth withdrawal promoted a shallower and more stable thermocline, thus increasing the cold hypolimnetic water volume and decreasing heat content and ABHB. The study reveals that hydraulic management constitutes the main driver of the heat and thermal dynamics in reservoirs with multiple withdrawal outlets. By contrast with the increasing temperature trends recorded in many natural lakes, the hydraulic management in Sau Reservoir induced a progressive reduction in water temperature and heat content in the system, thus partially counteracting the possible deleterious effects of global warming. Our intensive study in a single, highly-dynamic ecosystem constitutes a new approximation to the study of thermal structure and heat dynamics in water bodies.

The effect of DOC and nitrate river inputs on summer hypolimnetic oxygen and nutrient dynamics in the advective-dominated, canyon-shaped Sau Reservoir (Spain) was investigated using 11 years of monitoring data. River water entering the reservoir during summer was the main driver defining hypolimnetic oxygen and nutrient concentration. Thus, volume-normalized hypolimnetic oxygen concentration was highly correlated with the river DOC, but not significantly correlated with surrogates of the epilimnetic primary production or with in-lake features. Also, the areal extent of anoxia and nitrate concentration controlled total phosphorus content in the hypolimnion, suggesting that the river DOC and nitrate inputs control internal load of phosphorus. Because improvement of the river water quality was the consequence of implementation of advanced wastewater treatment plants in the reservoir watershed, we advocate these solutions to manage reservoir eutrophication problems. Our results should prompt reservoi...

Prescribed or natural drawdowns occur frequently in reservoirs but their effects on fish populations have been barely studied. As a consequence of a severe drought and the need to optimize water quality, a partial drawdown was prescribed in autumn 2005 to a eutrophic reservoir that provides water supply to a large metropolitan area (Barcelona, Spain). In order to avoid a potential massive fish kill given the reduced oxygen availability and high fish abundance, preventive purse seine fisheries were performed to reduce the fish stock. The fisheries had little effect on the fish assemblage because final population size structure and species composition did not change significantly. The species composition of the purse seine catches varied significantly during the drawdown with higher proportion of bleak (Alburnus alburnus) in pelagic water during the days of worst water quality, confirming that bleak is more tolerant than roach (Rutilus rutilus) to poor water quality and a potential good indicator of water pollution. The weight–length relationship (i.e. condition) of roach and bleak also varied significantly during the drawdown following the same tendency in both species, losing and recovering their weight (4.99% in roach and 5.96% in bleak) in only 16 days. The close relationship found between water quality and fish condition demonstrates that fish condition can be a good metric of the well being of fish, even for extreme short-term changes.

SUMMARY 1. Wind is considered the dominant factor controlling phytoplankton distribution in lentic environments. In canyon-shaped reservoirs, wind tends to blow along the main axis generating internal seiches and advective water movements that jointly with biological features of algae can produce a heterogeneous phytoplankton distribution. Turbulence generated by wind stress and convection will also affect the vertical distribution of algae, depending on their sinking properties. 2. We investigated the vertical and horizontal distribution of phytoplankton during the stratification period in Sau Reservoir (NE Spain). Sites along the main reservoir axis were sampled every 4 h for 3 days, and profiles of chlorophyll-a and temperature were made using a fluorescent FluoroProbe, which can discriminate among the main algal groups. Convective and wind shear velocity scales, and energy dissipation were calculated from meteorological data, and simulation experiments were performed to describe nonmeasured processes, like vertical advection and sinking velocity of phytoplankton. 3. Wind direction changed from day to night, producing a diel thermocline oscillation and an internal seiche. Energy dissipation was moderate during the night, and mainly attributed to convective cooling. During the day the energy dissipation was entirely attributed to wind shear, but values indicated low turbulence intensity. 4. The epilimnetic algal community was mainly composed of diatoms and chlorophytes. Chlorophytes showed a homogeneous distribution on the horizontal and vertical planes. Diatom horizontal pattern was also homogeneous, because the horizontal advective velocities generated by wind forcing were not high enough to develop phytoplankton gradients along the reservoir. 5. Diatom vertical distribution was heterogeneous in space and time. Different processes dominated in different regions of the reservoir, due to the interaction between seiching and the daily cycle of convective-mediated turbulence. As the meteorological forcing followed a clear daily pattern, we found very different diatom sedimentation dynamics between day and night. Remarkably, these dynamics were asynchronous in the extremes of the seiche, implying that under the same meteorological forcing a diatom population can show contrasting sedimentation dynamics at small spatial scales (approximately 10 3 m). This finding should be taken into account when interpreting paleolimnological records from different locations in a lake.

During summer 2001, zebra mussels (Dreissena polymorpha Pallas) were found (500 adults m−2) in the coupled reservoir system composed by Mequinenza, Riba-Roja and Flix (Ebro River, Northeast Spain). Two years later, mussels achieved densities of 4000 adults m−2, representing the first record of successful colonization by zebra mussels in the Iberian Peninsula. An August 2003 study investigated the environmental conditions that support the successful settlement of the zebra mussel populations during the stratification period. Flow patterns in the whole system and mussel populations near the dam were characterized. Chemical characteristics of water inputs, not the usual thermal stratification, determine the deep circulation of the Ebro River along the Riba-Roja reservoir, whereas water input from one tributary into Riba-Roja flows along the top of the water. Physico-chemical stratification of the water column seems to control the observed vertical distribution of zebra mussel biomass. Larger biomass...

Summary 1. Epilimnetic alkaline phosphatase activity (APA) was measured in longitudinal profiles of the canyon-shaped, eutrophic Sau Reservoir (Catalonia, Spain) during the autumn, winter and spring periods of 1997–2000. 2. The spatial pattern of APA depended on lake circulation. During periods of stable stratification, when the ratio of mixed to euphotic depth (zmix/zeu 2-μm size-fraction. APA increased towards the dam at the same time as the concentration of soluble reactive phosphorus (SRP) decreased. In periods of unstable stratification, deep mixing (zmix/zeu > 2.4) and low Chl a concentration, APA was low (2-μm (algal) size-fraction while, in the

The relationship of water quality and fish assemblages has been poorly documented in European reservoirs, despite being important for water management and ecological monitoring. We sampled the fish assemblages of 14 Spanish reservoirs by boat electrofishing in the littoral and multi-mesh gillnets in the limnetic zone. Simultaneously, we assembled eight physical descriptors and we measured 20 water quality features of the reservoirs. Multivariate analysis (ordination methods and generalised additive models) showed that altitude and trophic state (indicated by chlorophyll or nutrient concentrations) independently explained most of the variation of fish assemblages in these reservoirs. The most eutrophic reservoirs were dominated by common carp (Cyprinus carpio) whereas oligotrophic reservoirs presented other fish species intolerant to pollution rather native (such as brown trout, Salmo trutta). The absolute and relative abundance of common carp was strongly related to the trophic state of the reservoir and 40% of its variation was explained by total phosphorous concentration. Despite clear changes in species composition, there was no significant effect of water quality on overall fish richness or Shannon's diversity, suggesting that for such low richness assemblages species composition is a better indicator of cultural eutrophication of reservoirs than fish diversity This study was financed by the Catalan Water Agency (ACA), Government of Catalonia (CT02003134). Additional financial support was provided by the Spanish Ministry of Science and Technology (REN2003-00477) and the Ministry of Universities, Research and Information Society (DURSI), Government of Catalonia (Catalan Government Distinction Award for University Research 2004 to E.G.B.).

The average length of time water remains within the boundaries of an aquatic system is one of the key parameters controlling the system’s biogeochemical behavior. This time scale, which is generally referred to as the hydraulic residence time, provides a first order description of multiple and complex processes that create transport. This manuscript reviews the procedures to estimate transport time scales in reservoirs and explores, through the analysis of numerical simulations, the links between these time scales and the underlying hydrodynamic processes in a reservoir in North-Eastern Spain. The mean residence time scales undergo dramatic variations in time and in general, are comparable to the time scales of the systems’ variability itself, such as those associated with seasonal changes in stratification, allowing complex patterns of intermittent mixing events to determine residence time scales. We demonstrate that the temporal variations of mean residence times occur not only at seasonal time scales, but also at shorter scales. The time scales are closely related to mixing and transport processes occurring within the reservoir, at the inflow sections and at the watershed. © 2005 Elsevier B.V. All rights reserved.

Fluvial nutrient loads are usually calculated through a bilogarithmic regression relating flow and river nutrient concentration. This relationship, however, can be highly nonlinear, due to changes in watershed land uses over time. Also, retransformation of data can result in important biases, and available databases usually do not provide the statistical properties needed to apply parametric statistics or time-series analysis methods. The validity and advantages over customary methods of an Adaptive Neuro-Fuzzy Inference System (ANFIS) for estimating fluvial nutrient loads in watersheds under time-varying human impact was tested. Fluvial nutrient loads time-series were modeled in two watersheds of different size and human impact history. ANFIS and methods based on rating curves and ratio estimators were applied to compare results. The ANFIS approximation gave unbiased estimates of loads and showed advantages over the other methods: It allowed the implementation of a homogeneous, model-free methodology throughout the data series, avoiding the presence of artifacts in the final load histories; it fitted the observed concentration time-series better than the other procedures; it worked in real space without the need to logarithmically transform and retransform data; and it gave annual dispersion values, which could be interpreted as annual uncertainties. In addition, the parameters fitted during the ANFIS modeling could be ecologically interpreted, and were a valuable tool to describe features of modeled data and to understand historical changes in human impact on watersheds. MATLAB codes and instructions to implement the new method are provided.

Changes in the pelagic community structure and activity along the longitudinal axis of the eutrophic Sau Reservoir (Catalonia, NE Spain) were studied between 1996 and 1999. Samples were taken from several transects from river to dam, measuring dissolved organic carbon (DOC), bacterial abundance and production, chlorophyll a concentration, heterotrophic nanoflagelate (HNF) and ciliate abundances and their grazing rates, and zooplankton density. The role of microbial and classical food chains (i.e., based directly on phytoplankon) were compared in the Sau Reservoir by analysing river-to-dam gradients in biomass and carbon and their temporal changes. The detritic metabolic pathway was more important near to the inflow, due to high allochthonous organic matter loads allowing the rapid development of the microbial food web. Protozoans (HNF and ciliates) consumed most of the bacterial production (i.e., >50%) in the reservoir. As opposed to the systems of lower trophic status ciliate carbon biomass and bacterivory contributions were larger than those of the HNF. We estimated species-specific ciliate growing rates on bacteria and distinguished several periods with high importance of distinct ciliate communities.

We studied the planktonic food web in eutrophic Sau Reservoir (Catalonia, NE Spain). Along the longitudinal axis from the Ter River downstream to the dam, we characterized a microbial succession of food web dominance of bacteria-HNF-ciliates. The Ter River transports a large load of organic material into the reservoir, with a bacterial density of ∼9 · 106 large cells per ml. While at the first lacustrine station of the Reservoir HNF were the dominant bacterial consumers, at the others, an oligotrich ciliate, Halteria grandinella, was the main protozoan bacterivore. Most of the bacterial production in the reservoir epilimnion was consumed by grazing. The spatial succession of the reservoir microbial food webs was followed downstream by maximum densities of their potential predators among zoo-plankters – rotifers, and early developmental stages of copepods.

Benthic algal biomass was determined at 38 sites along the Oria, a river with intense human activity on its watershed. Water temperature, total suspended solids and nutrient concentration affected algal biomass in different ways. Lower values of algal biomass [(chlorophyll-a concentration and ash-free dry weight (AFDW)] were found in the headwaters and forested tributaries, but also at sites receiving high deposition of solids (due to the outflow from paper mills and quarries). Higher values of algal biomass (both chlorophyll-a and AFDW) were common both in the main stretch of the river and in some tributaries receiving urban sewage outflows. Averages and ranges of temperature and dissolved oxygen concentration were compared for two continuously monitored stations. One of them (forested, nutrient-poor) had low algal biomass, while the second (open, nutrient-rich) showed high chlorophyll-a concentration. Accumulation of algal biomass had environmental implications both in water quality and in the fish diversity of the Oria. Diel variations of dissolved oxygen were much higher (and reached hypoxia) at the site with higher biomass accumulation. The abundance of a fish community (dominated by cyprinids) more tolerant to hypoxia at that site can partly be attributed to the influence of algal biomass accumulation.

We conducted extensive studies on bacterivory and bacterial production over several seasons in 2 reservoirs: the meso-eutrophic R ˇ imov Reservoir in the Czech Republic and the highly eu- trophic Sau Reservoir in Spain. Based on abundance, seasonal dynamics, and cell-specific uptake rates of different ciliate taxa, as well as heterotrophic nanoflagellate bacterivory, we were able to quantify bacterivory by individual ciliate species, total ciliates, and aggregated protists in these sys- tems. With increasing trophic status, a higher portion of bacterial production was consumed by pro- tists, and there was a greater importance of ciliate grazing, accounting for 40 and 50% of the total protistan bacterivory in the epilimnion of the R ˇ imov and Sau reservoirs, respectively. Increases were attributable to the oligotrichs of the genus Halteria that often numerically dominate freshwater pelagic ciliate communities. In both reservoirs, the most important ciliate bacterivores in order of im- portance were: oligotrichs, primarily the bacterivorous Halteria spp., peritrichs, and scuticociliates. We also examined food vacuole content in natural populations of Halteria spp. to estimate the propor- tion of cells that had ingested algae. Our results and a review of previous reports on the abundance of Halteria spp. suggest that small halteriids are ecologically important bacterial consumers in meso- to eutrophic freshwater systems due to: (1) efficient uptake of prey over a large size spectrum (approxi- mately 0.4 to 5 µm), (2) high clearance rates on picoplankton-sized particles along with (3) high potential growth rate, and (4) lower vulnerability to metazooplankton predation compared to other common pelagic ciliates. Correspondingly, we suggest a revised concept of planktonic ciliate bacteri- vory, where the principal role is attributed to small omnivorous filter-feeding oligotrichous ciliates.

In this study, a 1D model of reservoir hydrodynamics DYRESM has been applied to Sau Reservoir, a river valley reservoir in the North-Eastern Spain. Simulation is undertaken for 3 years (1995–1997). Meteorological input data measured at the dam are only available from May of 1997. In this case the simulation results fit measured temperatures very well. In the remaining periods, some meteorological data (radiation, wind and rainfall) were obtained from two nearby stations. Simulated temperature distribution in 1996 is close to the observed one. In 1995, however, the simulated result is far from the observed data. Inflows , outflow and local meteorological events such as storms and gusts of wind seem to be responsible for the differences. By changing some parameters, the effects of flow, light extinction coefficient and outlet elevation on thermal stratification are investigated. Simulations demonstrate that the inflow with high temperature is the main factor controlling the thermal structure in Sau Reservoir and demonstrate that the effect of residence time on thermal stratification is manifested mainly by the changes in the depth of thermocline.

Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) method with the trilinearity constraint is proposed for the analysis of excitation–emission fluorescence data from Dissolved Organic Matter (DOM) in fresh water natural systems, and the results obtained are compared with those obtained with PARAFAC. The effects of different number of components and constraints on the stability of the proposed models are compared. MCR-ALS is shown to be an effective way to characterize and resolve DOM sources in natural fresh water systems from EEM data, with good correlation with experimentally measured DOM concentration values. MATLAB georeferenced mapping is used to illustrate the geographical distribution of resolved DOM contributions. MCR-ALS resolved EEM spectra are used to recognize the corresponding chemical groups assigned to possible DOM sources. Relationships between human activities and the environmental situation of the river system are discussed from these possible DOM sources.

Antibiotic resistance represents a growing global health concern due to the overuse and misuse of antibiotics. There is, however, little information about how the selective pressure of clinical antibiotic usage can affect environmental communities in aquatic ecosystems and which bacterial groups might be responsible for dissemination of antibiotic resistance genes (ARGs) into the environment. In this study, chemical and biological characterization of water and sediments from three water supply reservoirs subjected to a wide pollution gradient allowed to draw an accurate picture of the concentration of antibiotics and prevalence of ARGs, in order to evaluate the potential role of ARGs in shaping bacterial communities, and to identify the bacterial groups most probably carrying and disseminating ARGs. Results showed significant correlation between the presence of ARG conferring resistance to macrolides and the composition of bacterial communities, suggesting that antibiotic pollution and the spreading of ARG might play a role in the conformation of bacterial communities in reservoirs. Results also pointed out the bacterial groups Actinobacteria and Firmicutes as the ones probably carrying and disseminating ARGs. The potential effect of antibiotic pollution and the presence of ARGs on the composition of bacterial communities in lacustrine ecosystems prompt the fundamental question about potential effects on bacterial-related ecosystem services supplied by lakes and reservoirs. © 2013 Elsevier B.V., We thank Carles Borrego, Enrique Navarro, and Veronica Ribé for helpful discussions and comments to the article, and Jaime Ordóñez for help during field work. We also thank George A. Jacoby, Carmen Torres and Joan Jofre for providing us with bacterial strains. This research work was funded by the 1st Interdisciplinary Water Research Projects-ICRA Grants Program 2010 (Project RES2), the Spanish Ministry of Economy and Competitiveness for its financial support through the project SCARCE (Consolider-Ingenio 2010 CSD2009-00065), and by the European Union through the European Regional Development Fund (FEDER). This work was also partly supported by the Generalitat de Catalunya (Consolidated Research Group: Water and Soil Quality Unit 2009-SGR-965). Prof. Barceló acknowledges King Saud University for his visiting professorship.

In the context of an extensive study of 101 Spanish reservoirs, we have explored the relationship between transparency (0.11 ≤ SD ≤ 8.6 m) and a number of general limnological parameters. Principal components analysis has been used as a means to summarize these relationships in two distinct periods, winter and summer, revealing the grouping of variables associated to abioseston or with biomass. Multiple regression analysis has been used to quantify these relationships. Total labile iron, calcium and chlorophyll appeared to be the best regressors of turbidity among our variables. The association between total labile iron and turbidity can be explained by the widespread adsorption of metals onto particles. Total labile manganese and phosphorus showed a similar behaviour, especially in winter. The presence of a relatively large proportion of detrital matter in low-biomass eutrophic reservoirs in winter has been revealed by the analysis of Chla:C and Chla:N ratios. The fact that low ratios were associated with high iron concentrations gives support to this view. Also the C:P and N:P particulate atomic ratios differed from winter to summer. All these ratios appear to be very sensitive to the presence of a variable detrital component and, therefore, their use as indicators of the physiological state of phytoplanktonic populations is highly discouraged for these reservoirs.

[1] The lower Ebro River (Spain) is subject to the thermal and hydrological alterations caused by the system of reservoirs of Mequinenza, Riba-roja, and Flix and to the thermal effluent of the nuclear power plant of Asco, located 5 km downstream from the three reservoirs. In this paper, a modeling approach is used to determine the equilibrium temperature and recuperation distance at the study reach for different seasons and hydrological years. The intensity of the alteration caused by the reservoirs and nuclear power plant effluent is studied in reference to the equilibrium temperature and discharge rate. Mean daily water temperature downstream from the reservoirs is higher than mean daily equilibrium temperature in the fall and is lower during the rest of the year. Changes in the heat fluxes induced by thermal alteration are also addressed, showing important variations in evaporation and conduction to the atmosphere.

[1] The role of lacustrine systems in the global carbon cycle is a major topic in freshwater research. Most lakes release inorganic carbon to the atmosphere owing to the imbalance of net metabolism toward respiration. Most research on this topic relies on data collected in natural low-alkalinity lakes, and it therefore remains unclear what role human-made calcareous lakes play in the current paradigm. In this study, we reported inorganic carbon fluxes and net ecosystem production in a calcareous human-made reservoir in Spain using mass balances of inorganic carbon and dissolved oxygen. The inorganic carbon loadings reported are among the largest found in the literature, and the inorganic carbon pool in the reservoir depends on the net hydrological balance. The reservoir was identified as a net emitter of carbon dioxide (CO2) and showed persistent net heterotrophy, although we could not find any clear dependence of CO2 emissions on the metabolic balance. The variability of inorganic carbon and the net ecosystem production were poorly correlated, suggesting that additional internal processes govern the transformation of the dissolved inorganic carbon in the water column. Considering the significant decrease in surface alkalinity occurring during the summer, carbonate precipitation may be the dominant process confounding the relationship between metabolism and inorganic carbon variability. These results indicate that the CO2 dynamics may be weakly coupled to net metabolism in calcareous systems and that net heterotrophy may occur simultaneously with eutrophic conditions and low dissolved organic carbon concentration in flushed systems such as reservoirs.

An extensive survey of 100 reservoirs on the Iberian peninsula was carried out in 1987/88. Based on physical, chemical and biological data, several groups of reservoirs were differentiated. To contribute to the zooplankton component of this typology, we studied the species composition of rotifer communities from each reservoir. Data from all reservoirs were integrated separately (stratification and mixing periods) in a principal components analysis. No distinct communities were evident for the different reservoir types, suggesting that each type contains a series of rotifer assemblages, with gradual changes in species composition occurring in response to changes in environmental conditions.

Elastofibroma dorsi is a relatively rare soft-tissue tumor located at the infra-scapular level and/or subscapular regions. It usually occurs between the fourth and seventh decade of life, and is more common in females. We reviewed sixteen elastofibromas diagnosed in 12 patients (7 females, 58.3%). Four patients had bilateral elastofibromas. The most common symptom was pain. Presumptive diagnosis was made by physical examination. Chest ultrasound, computed tomography and/or magnetic resonance imaging were performed to confirm the diagnosis. Surgery was performed under general anesthesia. No major complications were observed. Elastofibromas are tumors of the chest wall with an uncertain impact. Surgical resection is indicated only in symptomatic patients.

The Ebro River is one of the longest rivers in Spain and it also has the greatest discharge. Its lower part is highly regulated and includes a system of three reservoirs (Mequinensa, Riba-roja and Flix). The water temperature is altered because of the release of hypolimnetic water and the use of water for cooling at the Ascó nuclear power plant. The thermal regime of the lower Ebro River on different time scales and the changes caused by anthropogenic factors, especially the system of reservoirs and the thermal effluent of the nuclear power plant, have been studied by installing a net of water temperature measuring stations and by using historical water temperature data provided by the thermal power plant at Escatrón. An increase of 2.3ºC in the mean annual water temperature could be demonstrated in the period 1955–2000 at this site. The effects of the system of reservoirs and of the nuclear power plant were the usual for this kind of structures and could be detected many kilometres downstream. In the summer, the cooling effect of the reservoirs and the warming effect of the nuclear power plant compensated each other. In winter, the warming effect of both summed up

Selection of reservoir location, the floodable basin forest handling, and the design of dam structures devoted to water supply (e.g. water outlets) constitute relevant features which strongly determine water quality and frequently demand management strategies to be adopted. Although these crucial aspects should be carefully examined during dam design before construction, currently the development of ad hoc limnological studies tailoring dam location and dam structures to the water quality characteristics expected in the future reservoir is not typical practice. In this study, we use numerical simulation to assist on the design of a new dam project in Spain with the aim of maximizing the quality of the water supplied by the future reservoir. First, we ran a well-known coupled hydrodynamic and biogeochemical dynamic numerical model (DYRESM-CAEDYM) to simulate the potential development of anoxic layers in the future reservoir. Then, we generated several scenarios corresponding to different potential hydraulic conditions and outlet configurations. Second, we built a simplified numerical model to simulate the development of the hypolimnetic oxygen content during the maturation stage after the first reservoir filling, taking into consideration the degradation of the terrestrial organic matter flooded and the adoption of different forest handling scenarios. Results are discussed in terms of reservoir design and water quality management. The combination of hypolimnetic withdrawal from two deep outlets and the removal of all the valuable terrestrial vegetal biomass before flooding resulted in the best water quality scenario.

[ES] La presencia de los embalses de Mequinenza, Riba-Roja y Flix en el tramo inferior del río Ebro ha dado lugar a una serie de alteraciones (reducción de la entidad y frecuencia de las avenidas, estabilización de caudales, etc.) que han favorecido el desarrollo de macrófitos sumergidos. La viabilidad diaria y anual del régimen de caudales del tramo inferior del río Ebro como consecuencia de la regulación ejercida por los embalses se analiza en este trabajo. Los principales efectos son: importantes variaciones diarias de caudal, un menor caudal los fines de semana y la estabilización de los caudales mínimos. Asimismo, se analiza la influencia de la proliferación de macrófitos en el comportamiento hidráulico del río. En el período estudiado (200-2006) el río presentó dos tipos de comportamiento hidráulico: un comportamiento que puede considerarse como ordinario, con el cauce limpio, y otro más lento, caracterizado por menores velocidades y mayores calados para un mismo caudal. Este segundo comportamiento coincidió con épocas de sequía, con caudales bajos durante gran parte del año y proliferación de macrófitos. El paso del comportamiento lento al comportamiento ordinario se produce con avenidas importantes, que tienen el poder suficiente para arrastrar a los macrófitos., Este trabajo ha sido financiado por el Programa de Recursos Hídricos del Plan Nacional de Investigación y Desarrollo y el Fondo Social Europeo, proyectos número CGL2004-05503-C02-01/HID, CGL2004-05503-C02-02/HID y CGL2008-06377-C02-02/BTE, y por el convenio con la Asociación Nuclear Ascó-Vandellós II. Hay que agradecer a la CHE y a la Asociación Nuclear Ascó-Vandellós II los datos proporcionados para la realización de este estudio.

The importance of water resources stored in reservoirs on a global scale is not matched with a sound knowledge of the possible impacts of climate change on reservoir water quality. This is especially relevant in the Mediterranean regions, where most countries rely on reservoirs to fulfill their water supply needs, and virtually all climate models predict increasing water shortage in the next 20 years. In this chapter, we summarize recent findings that will help to fill this gap in knowledge. Recently, a close coupling between streamflow entering reservoirs and its hypolimnetic oxygen content has been empirically established for a wide range of systems. In brief, high streamflow maintains anoxia at comparatively low levels. Therefore, we can expect a reduction in water quality following future reductions in runoff. To illustrate these effects, we analyzed a 44 year data set of oxygen measurements from Sau Reservoir in Spain to detect possible effects of climate variability on the extent of deep-water anoxia. In addition, we show that a trend of decreasing streamflow, related to climate change, has increased the risk of anoxia in the reservoir during the last decade. From these results, we propose a framework for climate change impact studies on reservoir water quality using streamflow and labile organic matter as master drivers. Finally, we identify the research required to improve our understanding of how reservoirs will behave in a changing climate, and give some guidelines on how to manage Mediterranean reservoirs under future “scarcity” conditions.

We examine environmental survey data to reveal partial aspects of the longitudinal structure and function of a Mediterranean river. The study area is the Ter River which experiences various disturbances (spates, pollution, reservoirs) that result in discrete patches along the river. In this paper, we use physico-chemical data to measure and interpret the dynamics of these patches through time and space. Principal Components Analysis (PCA) of the physico-chemical variables revealed longitudinal chemical structure (FI) and temporal variation in chemical composition due to discharge fluctuations (FII). We found that the chemistry of headwater regions is more constant than lower reaches since this river is heavily perturbed by human activities downstream. The chemistry of lower reaches is more time dependent. Temporal and spatial variation are not independent because both processes transform external energy into changes in ecosystem structure.

[ES] Uno de los procesos fluviales más directamente afectados por los embalses es el transporte de sedimentos. Para obtener estimas fiables de caudal sólido es necesario disponer de series continuas de datos, especialmente en ríos con régimen irregular como los de la Península Ibérica. En las últimas décadas, la mejora de los sistemas de recogida automática de muestras está contribuyendo notablemente al avance en el estudio del transporte sólido en suspensión. El presente trabajo se ha llevado a cabo en el tramo medio del río Ebro, entre Escatrón y Ribarroja. Se recogieron automáticamente muestras de agua para la determinación de la concentración de sólidos en suspensión y su composición (contenido orgánico e inorgánico) en el período comprendido entre noviembre de 1997 y septiembre de 1999. La retención del embalse de Mequinenza fue del 95%, muy superior a la del embalse d Ribarroja, 41%. La calidad del material sólido en suspensión también se ve modificada por la presencia de los embalses: a la salida la fracción orgánica se incrementa considerablemente debido a la sedimentación diferencial de la fracción inorgánica y a la producción de fitoplancton en los embalses., Parte del presente trabajo se ha llevado a cabo en el marco del convenio de colaboración con la CHE “Estudio de la dinámica sedimentaria y batimetría de precisión del embalse de Ribarroja” y de los proyectos CGL-2008-06377-C02-02/BTE y CGL-2008-06377-C01-02/BTE financiados por el Ministerio de Ciencia e Innovación. Se agradece la importante información de campo facilitada por la Confederación Hidrográfica del Ebro y por ENDESA.

[1] Application of semi-distributed hydrological models to large, heterogeneous watersheds deals with several problems. On one hand, the spatial and temporal variability in catchment features should be adequately represented in the model parameterization, while maintaining the model complexity in an acceptable level to take advantage of state-of-the-art calibration techniques. On the other hand, model complexity enhances uncertainty in adjusted model parameter values, therefore increasing uncertainty in the water routing across the watershed. This is critical for water quality applications, where not only streamflow, but also a reliable estimation of the surface versus subsurface contributions to the runoff is needed. In this study, we show how a regularized inversion procedure combined with a multiobjective function calibration strategy successfully solves the parameterization of a complex application of a water quality-oriented hydrological model. The final value of several optimized parameters showed significant and consistent differences across geological and landscape features. Although the number of optimized parameters was significantly increased by the spatial and temporal discretization of adjustable parameters, the uncertainty in water routing results remained at reasonable values. In addition, a stepwise numerical analysis showed that the effects on calibration performance due to inclusion of different data types in the objective function could be inextricably linked. Thus caution should be taken when adding or removing data from an aggregated objective function.