Rafael Marcé

Exploring the links between antibiotic occurrence, antibiotic resistance, and bacterial communities in water supply reservoirs

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.

Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir

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.

Assessment of the water supply:demand ratios in a Mediterranean basin under different global change scenarios and mitigation alternatives.

Spatial differences in the supply and demand of ecosystem services such as water provisioning often imply that the demand for ecosystem services cannot be fulfilled at the local scale, but it can be fulfilled at larger scales (regional, continental). Differences in the supply:demand (S:D) ratio for a given service result in different values, and these differences might be assessed with monetary or non-monetary metrics. Water scarcity occurs where and when water resources are not enough to meet all the demands, and this affects equally the service of water provisioning and the ecosystem needs. In this study we assess the value of water in a Mediterranean basin under different global change (i.e. both climate and anthropogenic changes) and mitigation scenarios, with a non-monetary metric: the S:D ratio. We computed water balances across the Ebro basin (North-East Spain) with the spatially explicit InVEST model. We highlight the spatial and temporal mismatches existing across a single hydrological basin regarding water provisioning and its consumption, considering or not, the environmental demand (environmental flow). The study shows that water scarcity is commonly a local issue (sub-basin to region), but that all demands are met at the largest considered spatial scale (basin). This was not the case in the worst-case scenario (increasing demands and decreasing supply), as the S:D ratio at the basin scale was near 1, indicating that serious problems of water scarcity might occur in the near future even at the basin scale. The analysis of possible mitigation scenarios reveals that the impact of global change may be counteracted by the decrease of irrigated areas. Furthermore, the comparison between a non-monetary (S:D ratio) and a monetary (water price) valuation metrics reveals that the S:D ratio provides similar values and might be therefore used as a spatially explicit metric to valuate the ecosystem service water provisioning.

Carbon dioxide emissions from dry watercourses

Abstract Temporary watercourses that naturally cease to flow and run dry comprise a notable fraction of the world’s river networks, yet estimates of global carbon dioxide (CO2) emissions from watercourses do not consider emissions from these systems when they are dry. Using data from a sampling campaign in a Mediterranean river during the summer drought period, we demonstrate that the CO2 efflux from dry watercourses can be substantial, comparable to that from adjacent terrestrial soils and higher than from running or stagnant waters. With an up-scaling approach, we show that including emissions from dry watercourses could increase the estimate of CO2 emissions from watercourses in our study region by 0.6–15%. Moreover, our results tentatively illustrate that emissions from dry watercourses could be especially important in arid regions, increasing the estimate of global CO2 emissions from watercourses by 0.4–9%. Albeit relatively small, the contribution of dry watercourses could help to constrain the highly uncertain magnitude of the land carbon sink. We foresee that in many areas of the world, the expected increase in the extent of temporary watercourses associated with future global change will increase the relevance of CO2 emissions from dry watercourses.

Tailoring dam structures to water quality predictions in new reservoir projects: assisting decision-making using numerical modeling.

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.

A calibration strategy for dynamic succession models including several phytoplankton groups

A fundamental problem in water quality modeling is adequately representing the changing state of aquatic ecosystems as accurately as possible, but with appropriate mathematical relationships without creating a highly complex and overly parameterized model. A model more complex than necessary will require more input and results in unaffordable calibration times. In this work we propose and test a calibration strategy for a one-dimensional dynamic physical-ecological model (DYRESM-CAEDYM) to reproduce the seasonal changes in the functional composition of the phytoplankton community existing in El Gergal reservoir (Seville, Spain). The community is described as a succession of functional groups with different response to environmental conditions. First, we performed a sensitivity analysis to identify the parameters to include in the calibration process, and then applied a global optimization algorithm to fit the model for each algal group in a sequential fashion. Finally we simulated all the functional groups adopting parameter values established during the group-by-group calibrations. Our results show that the performance of this approach is strictly related with: (1) the level of system description (i.e. the model structure and the number of functional groups simulated); (2) the level of information included in the calibration process (i.e. the observations); and (3) the non-linear interactions among functional groups. Functional segmentation of the model should be minimized even though groups with different environmental requirements must be discriminated. Although magnitudes of biomass peaks were not always estimated correctly, the calibrated model was able to predict peak sequence and timing of dominant phytoplankton groups. Thus our study showed that: (1) model structure and nature of observations adopted have to be in agreement with the level of organization in the system; (2) integration of automatic calibration strategies is a useful approach in complex deterministic ecological models.

The Effect of River Water Circulation on the Distribution and Functioning of Reservoir Microbial Communities as Determined by a Relative Distance Approach

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.

The Role of Allochthonous Inputs of Dissolved Organic Carbon on the Hypolimnetic Oxygen Content of Reservoirs

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 Nürnberg’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).

The Llobregat River Basin: A Paradigm of Impaired Rivers Under Climate Change Threats

The Llobregat River represents a paradigmatic example of an impaired river subject to emerging global change impacts. This chapter provides an introduction to the main geomorphological, geological, climatic, and biological features of the river basin, as well as an overview on the hydrological alterations and the intense management of water resources in the basin. The Llobregat hydrology has experienced a significant runoff reduction during the last decades. This decrease is related to climatic drift but also to the increasing forest land cover that has promoted a 25% reduction of the streamflow. The chapter also describes the human uses of the Llobregat River waters from a historical perspective, with particular emphasis on the difficulties that an intrinsically unpredictable river like Llobregat posed to the different human uses along history. The historical development makes emphasis on the industrial activities affecting water resources during the twentieth century. The chapter includes a detailed analysis of the present situation on water extractions, discharges, and diversions that define the Llobregat River Basin as a deeply impaired ecosystem, especially in the most downstream reaches.

Ecological classification of a set of Mediterranean reservoirs applying the EU Water Framework Directive: A reasonable compromise between science and management

Abstract 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.