Joan Armengol

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.

The thermal structure of Sau Reservoir (NE: Spain): a simulation approach

Abstract 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.

Changes in the epilimnetic bacterial community composition, production, and protist-induced mortality along the longitudinal axis of a highly eutrophic reservoir

We studied changes in the epilimnetic bacterial community composition (BCC), bacterial biomass and production, and protistan succession and bacterivory along the longitudinal axis of the canyon-shaped, highly eutrophic Sau Reservoir (NE Spain) during two sampling campaigns, in April and July 1997. Longitudinal changes in BCC from the river inflow to the dam area of the reservoir were detected by using oligonucleotide probes targeted to the kingdom Bacteria, to the alpha, beta, and gamma subclasses (ALFA, BETA, and GAMA) of the class Proteobacteria, and to the Cytophaga/Flavobacterium (CF) cluster. In general, the inflow of the organically loaded Ter river, with highly abundant allochthonous bacterial populations, induced a clearly distinguishable longitudinal succession of the structure of the microbial food web. The most dynamic changes in microbial parameters occurred at the plunge point, the mixing area of river water and the reservoir epilimnion. Changes within members of BETA and CF were the most important in determining changes in BCC, bacterial abundance and biomass. Much less relevant changes occurred within the less abundant ALFA and GAMA bacteria. From the plunge point downstream, we described a significant shift in BCC in the form of decreased proportions of BETA and CF. This shift spatially coincided with the highest values of heterotrophic nanoflagellate bacterivory (roughly doubled the bacterial production). CF numerically dominated throughout the reservoir without any marked longitudinal changes in their mean cell volume. In contrast, very large cells affiliated to BETA clearly dominated in the allochthonous bacterial biomass brought by the river. BETA showed a marked downstream trend of decreasing mean cell volume. We conclude that the observed BCC shift and the longitudinal shift in food web structure (bacteria-heterotrophic nanoflagellates-ciliates) resulted from highly complex interactions brought about by several major factors: varying hydrology, the high localized allochthonous input of organic matter brought by the river, downstream changing substrate availability, and selective protistan bacterivory.

Algal biomass in a disturbed Atlantic river: water quality relationships and environmental implications

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.

Chemical and Biological Changes in the Ter River Induced by a Series of Reservoirs

The climatological and topographical characteristics of the Iberian peninsula have made the construction of reservoirs a necessity. Thus, more than 700 reservoirs have been constructed since the beginning of the century, one hundred of which have been the object of intensive study (Margalef et al. 1976). Nevertheless, the effect of these reservoirs on rivers is practically unknown. Garcia de Jalon (1984) reached a similar conclusion in a survey of existing literature on this topic. In this study we attempt to quantify the biological and chemical effects of three reservoirs located in the middle section of the River Ter. An earlier study suggested that these reservoirs had affected the macroinvertebrate communities residing below the reservoirs (Prat 1981). Because a flood occurred during our study we were also able to monitor the regulatory efficiency of these reservoirs.

Phosphorus budgets and forms of phosphorus in the Sau reservoir sediment: An interpretation of the limnological record

The phosphorus compounds in the sediment of Sau reservoir have been analysed and related to the annual phosphorus budgets from 1965 to 1969. With the increase of eutrophy, the phosphorus inputs leave the water in two ways: to the sediment and to the water outflow. The second way becomes more important throughout the eutrophication process.

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.

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.

Planktonic food web structure along the Sau Reservoir (Spain) in summer 1997

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.