Una Nova associació de plantes aquàtiques als Pirineus: El Ranunculo eradicati-Potametum alpini

Hom descriu una nova associació de plantes aquàtiques pròpia dels estanys pirinencs de la zona subalpina. L'associació, Ranunculo eradicati-Potametum alpini, esta relacionada amb el Potametum filiformis dels Alps i és dominada per Potamogeton alpinus, P. Berchtoldii i Ranunculus trichophyllus ssp. eradicatus. Es desenvolupa en llacs d'aigues amb una càrrega iònica relativament elevada, en el context dels estanys pirinencs (conductivitat: 15.1-78.2 &mciro;S cm-1; alcalinitat: 100-650 μeq l-1; concentració de calci: 59-331 µg-at l-1), on substitueix els poblaments d'isoètids àmpliament estesos en molts llacs d'alta muntanya.The Ranunculo eradicati-Potametum alpini, a new association of aquatic plants, is described from the subalpine pyrenean lakes. It is related to the Potametum filiformis from the Alpine range and it is dominated mainly by Potamogeton alpinus, P. Berchtoldii and Ranunculus trichophyllus ssp. eradicatus. The association develops in soft-water lakes with a conductivity ranging from 15 to 78.2 µS cm-1, water alkalinity ranging from 100 to 650 μeq l-1 and calcium carbonate concentration ranging from 59 to 331 μg-at l-1. These values are relatively high when compared with other Pyrenean lakes where isoetid populations develop. Water alkalinity seems to be the main environmental factor determining the kind of aquatic macrophytic vegetation in Pyrenean lakes

Recovery of submersed vegetation in a high mountain oligotrophic soft-water lake over two decades after impoundment

Este artículo contiene 13 páginas, 5 figuras, 2 tablas.Recovery of the submersed vegetation is a target for the management of soft-water shallow lakes if they are to meet water quality and biodiversity standards. Knowledge of patterns of macrophyte space occupation and time to recovery is poor and mostly restricted to free floating species or riparian vegetation. Here we use pre- and post-impact monitoring data over 20 years showing the evolution of submersed aquatic vegetation of lake Baciver (Pyrenees), and develop models to infer space occupation and time to recovery. We use pre-impact macrophyte distribution in relation to bathymetry-derived data to fit logistic models to further simulate lake equilibrium scenarios. Depth and slope were found to be the best predictors, and models suggested that an assemblage dominated by Sparganium angustifolium was, at time of this study, over 95% of its potential distribution area. A dense, newly grown monospecific Isoetes lacustris population occupied\10% of its potential area and model projections suggest that it will take decades to recover. An I. lacustris residual population remains below the estimated depth threshold for survival and is bound to disappear. The lake appears to evolve towards a new steady-state where the current lake hypsography promotes the expansion of algae (Nitella sp.) over angiosperms.This study was funded by the Red de Parques Nacionales of the Spanish Ministry of the Environment (PN I?D?I ref. 118/2003 and AQUAREST ref. OAPN 212/2010) and Intramural CSIC (Consejo Superior de Investigaciones Cientı´ficas) ref. 0065.Peer reviewe

Functional diversity of macrophyte communities within and between Pyrenean lakes

Submersed vegetation is a common feature in about 70% Pyrene an high mountain (>1500 m a.s.l.) lakes. Isoetids and soft-water elodeids are common elements of this underw ater flora and can form distinct vegetation units (i.e. patches of vegetation dominated by different species) within complex mosaics of vegetation in shallow waters (<7 m). Since is oetids exert a strong influence on sediment biogeochemistry due to high radial oxygen loss, we examined the small scale characteristics of the lake environment (water and sediment) associated to vegetation patches in order to ascertain potential functional differences among them. To do so, we characterised the species composition and biomass of the main vegetation units from 11 lakes, defined plant communities based on biomass data, and then related each community with sediment properties (redox and dissolved nutrient concentration in the pore water) and water nutrient concentration within plant canopy. We also characterised lake water and sediment in areas without vegetation as a reference. A total of twenty-one vegetation units were identified, ranging from one to five per lake. A cluster analysis on biomass species composition suggested seven different macrophyte communities that were named after the most dominant species:Nitella sp.,Potamogeton praelongus, Myriophyllum alterniflorum, Sparganium angustifolium , Isoetes echinospora,Isoetes lacustris and Carex rostrata . Coupling between macrophyte communities and their immediate environment (overlying water and sediment) was manifested mainly as variation in sediment redox conditions and the dominant form of inorganic nitrogen in pore-water. These effects depended on the specific compositi on of the community, and on the allocation between above- and belowground biomass, and could be predicted with a model relating the average and standard deviation of sediment redox potential from 0 down to -20 cm, across macrophyte communities. Differences in pore-water total dissolved phosphorus were related to the trophic state of the lakes. There was no correlation between sediment and water column dissolved nutrients. However, nitrate concentrations tended to be lower in the water overlaying isoetid communities, in apparent contradiction to the patterns of dissolved nitrates in the pore-water. These tendencies were robust even when comparing the water over laying communities within the same lake, thus pointing towards a potential effect of isoetids in reducing dissolved nitrogen in the lakes

Recovery of submersed vegetation in a high mountain oligotrophic soft-water lake over two decades after impoundment

Recovery of the submersed vegetation is a target for the management of soft-water shallow lakes if they are to meet water quality and biodiversity standards. Knowledge of patterns of macrophyte space occupation and time to recovery is poor and mostly restricted to free floating species or riparian vegetation. Here we use pre- and post-impact monitoring data over 20 years showing the evolution of submersed aquatic vegetation of lake Baciver (Pyrenees), and develop models to infer space occupation and time to recovery. We use pre-impact macrophyte distribution in relation to bathymetry-derived data to fit logistic models to further simulate lake equilibrium scenarios. Depth and slope were found to be the best predictors, and models suggested that an assemblage dominated by Sparganium angustifolium was, at time of this study, over 95% of its potential distribution area. A dense, newly grown monospecific Isoetes lacustris population occupied <10% of its potential area and model projections suggest that it will take decades to recover. An I. lacustris residual population remains below the estimated depth threshold for survival and is bound to disappear. The lake appears to evolve towards a new steady-state where the current lake hypsography promotes the expansion of algae (Nitella sp.) over angiosperms

Estanys de l’Albera i basses dels secans de Lleida: quines característiques ambientals determinen les seves comunitats i la seva biodiversitat?

En aquest estudi, hem realitzat una comparació de les comunitats biològiques dels estanys i les basses temporànies de dues àrees de clima diferenciat, al massís de l’Albera (Alt Empordà) i als secans de Lleida (Segrià). L’objectiu del treball ha estat identificar les variables ambientals que determinen la composició d’aquestes comunitats, com la biodiversitat, la dinàmica temporal i la congruència taxonòmica en termes de riquesa d’espècies que es pugui donar entre els grups florístics i faunístics seleccionats. S’han observat diferències entre regions pel que fa a la dinàmica al llarg del cicle d’inundació, essent més marcada als estanys de l’Albera que no pas a les de Lleida, per a tots els grups d’organismes. Quant als patrons de congruència taxonòmica en termes de riquesa d’espècies, s’ha observat que la majoria de relacions no es mantenien entre regions. En conseqüència, suggerim que el clima pot trencar, a nivell regional, patrons de biodiversitat que es donen a nivell local.In this study we have compared the biological communities inhabiting seasonal pools in two different areas in Catalonia: the Albera mountain range and the Lleida steppes. We aimed at identifying the environmental variables that determine community composition in those habitats, as well as at describing the biodiversity attributes, the dynamics throughout the hydroperiod, and eventual relationships among taxonomic groups in terms of species richness. We observed interregional differences in community dynamics, with higher change between subsequent visits being observed in Albera rather than in Lleida seasonal pools, a pattern consistent across all the study groups. Regarding species richness patterns, we observed that most of the relationships across taxonomic groups did not hold when considering both regions. Therefore, we suggest climate may break, at a regional level, eventual biodiversity patterns existing at the local scale

Atmospheric Carbon Dioxide variability at Aigüestortes, Central Pyrenees, Spain

Unidad de excelencia María de Maeztu MdM-2015-0552In order to improve the understanding of the carbon cycle in the Pyrenean region, two atmospheric monitoring mountain stations were set up within the Long-Term Ecological Research node of Aigüestortes i Estany de Sant Maurici at Central Pyrenees, Spain. The atmospheric concentration of carbon dioxide (CO2) was measured over 2008-2014 and 2010-2014 at Estany Llong (ELL) site and Centre de Recerca d'Alta Muntanya (CRAM), respectively. Measurements were carried out fortnightly off-line with high precision instrumentation at ELL and every minute online with a lower precision sensor at CRAM in conjunction with meteorological variables. The two datasets were analyzed in this study, quantifying whenever possible annual growth rates (AGR), seasonal variability, and diurnal amplitudes. Results were also compared with the NOAA Marine Boundary Layer (MBL) reference product and CO2 data from other background monitoring stations. Four-harmonics adjusted CO2 data from ELL showed a high correlation with the NOAA MBL reference product for the same latitude (Spearman's rho ρ = 0.96). In addition, AGRs of CO2 at ELL correlated well with those observed at Mace Head (MHD) station (ρ = 0.94), suggesting that ELL can be considered a background station. Winter CRAM CO2 data was not statistically different from ELL data, while in summer, it was 5.5 ppm lower on average, suggesting a higher photosynthesis uptake. The amplitude of the CO2 diurnal cycle at CRAM was found to be exponentially related to the local mean daily temperature and dependent on forthcoming wind sector (N-NW or E-SE-S-SW). An increase in CRAM CO2 concentrations was observed under N-NW winds during daytime, which could be related to traffic emissions. This study demonstrates that the use of CO2 sensors with low precision but continuously corrected and periodically calibrated can be used for the study of local and regional CO2 sources and sinks

Benthic sediment as stores and sources of bacteria and viruses in streams:A comparison of baseflow vs. stormflow longitudinal transport and residence times

International audienceThe presence of bacteria and viruses in freshwater represents a global health risk. The substantial spatial and temporal variability of microbes leads to difficulties in quantifying the risks associated with their presence in freshwater. Fine particles, including bacteria and viruses are transported and accumulated into shallow streambed (i.e., benthic) sediment, delaying the downstream transmission during baseflow conditions but contributing to their resuspension and transport downstream during stormflow events. Direct measurements of pathogen accumulation in benthic sediments are rare. Until now, the dynamic role of benthic sediment as both a store and source of microbes, has not been quantified. In this study, we analyze microbial abundance in benthic sediment along a 1 km reach of an intermittent Mediterranean stream receiving inputs from the effluent of a wastewater treatment plant, a known point source of microbes in streams. We sampled benthic sediment during a summer drought when the wastewater effluent constituted 100% of the stream flow, and thus, large accumulation and persistence of pathogens along the streambed was expected. We measured the abundance of total bacteria, Escherichia coli (as a fecal indicator), and presence of enteric rotavirus (RoV) and norovirus (NoV). The abundance of E. coli, based on qPCR detection, was high (4.99∙102 g/cm2 or ∼ 1 ng/μL) along the first 100 m downstream of the wastewater effluent input and in general decreased with distance from the source, with presence of RoV and NoV along the study reach. A particle tracking model was applied, that uses stream water velocity as an input, and accounts for microbial exchange into, immobilization, degradation, and resuspension out of benthic sediment during baseflow and stormflow. Rates of exchange into benthic sediment were 3 orders of magnitude higher during stormflow, but residence times were proportionately lower, resulting in increased longitudinal connectivity from up to downstream during stormflow. Model simulations demonstrated mechanistically how the rates of exchange into and out of the benthic sediment resulted in benthic sediment to act as a store during baseflow and a source during stormflow

Wastewater treatment plant effluent inputs influence the temporal variability of nutrient uptake in an intermittent stream

Wastewater treatment plant (WWTP) effluents alter water chemistry and in-stream nutrient uptake rates of receiving freshwaters, thus changing the magnitude and fate of the nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams can vary strongly over time due to the seasonal occurrence of floods and droughts, causing temporal variability of nutrient uptake. We assessed the temporal patterns and the controlling factors of net nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled the longitudinal concentration profiles of ambient dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) along a 800 m reach on 47 sampling dates between 2001 and 2017, encompassing a wide range of hydrological conditions. We estimated net nutrient uptake in the receiving stream. In 72% of the dates, high rates of net ammonium uptake co-occurred with net releases of either nitrate or nitrite. This pattern suggests that the receiving stream has a high nitrification capacity. Conversely, 75% of the dates did not show any longitudinal pattern in SRP concentration, suggesting that uptake and release processes for this element were either counterbalanced or both occurred at very low rates. Finally, net ammonium uptake was low when the stream had a low dilution capacity (< 40%) and ammonium concentration was high. Overall, we demonstrate that consideration of the receiving stream’s dilution capacity is imperative to the management of freshwaters to guarantee an adequate dilution of WWTP effluent inputs and avoid saturation of in-stream nutrient uptake capacity under low flow conditions in urban landscapes

Los lixiviados de las helófitas promueven la desnitrificación en ríos receptores de efluentes de plantas de tratamiento

nicas de bioingeniería empleando plantas acuáticas son utilizadas en la restauración de cursos fluviales, ya que reducen el exceso de nitrógeno (N) de la columna de agua y retienen metales pesados. A su vez, los lixiviados de su hojarasca pueden servir como una fuente adicional de materia orgánica disuelta lábil (DOM), que puede promover la respiración aeróbica y la eliminación de N a través de la desnitrificación. Probamos los efectos de los lixiviados de hojarasca de Iris pseudacorus y Phragmites australis en la estructura y actividad de biofilms de agua dulce cultivadas en canales alimentados por efluentes de una planta de tratamiento de aguas residuales (PTAR). Todas las fuentes de DOM aumentaron significativamente la respiración aeróbica y la desnitrificación del biofilm en comparación con los controles. Los resultados sugieren que la limitación en la biodisponibilidad de DOM puede ser aliviada mediante la utilización de lixiviados de helófitas.Instituto de Limnología "Dr. Raúl A. Ringuelet