Valorisation des Référentiels Régionaux Pédologiques - Présentation d‘un script en langage Python® pour estimer le Réservoir Utilisable Maximal en eau des sols
(23/04/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Bordeaux Sciences Agro, Gip AtGeRi, Info&Sols, INRAE, SAS, INRAE, Institut Agro, CA
Artificial Recharge of the Shallow Alluvial Aquifer as an Adaptation Strategy in the Garonne Valley, France
The Garonne River is the primary river in the southwest part of France. The Quaternary alluvial aquifer along this River may represent a substantial water resource, especially for agricultural activities well-developed in the Garonne Valley. However, this shallow aquifer hosts numerous irrigation wells reducing the baseflow during the intensive pumping periods. It is recharged by rainfall, lateral inflow from the hillside (overlying terraces), and the river bed seepage during the flood periods. The aquifer sustains the River during the dry periods. Furthermore, the potential recharge of this aquifer is particularly sensitive to annual climate fluctuation and consequently affects the ecosystems and related socio-economy. Groundwater artificial recharge can be considered an innovative and sustainable nature-based solution. The runoff water from The Techno-Pole Agen – Garonne (TAG) zone is collected in retention basins and is a potential source to recharge the shallow alluvial aquifer. The study aims to model water infiltration and understand the aquifer response and, consequently, the effects on river low flow. Within the framework of this study, 132 wells/boreholes were used in to determine the groundwater level fluctuations and to create its maps. The measurements showed that the artificial recharge increased the groundwater level by more than 1 m close to the retention basin after the rainstorm event. Similarly, a three-dimensional (3D) groundwater model shows a similar magnitude aquifer response to the induced infiltration. Consequently, this model satisfactorily represents the interest of the artificial recharge of the alluvial aquifer and permits predictions about whether the aquifer can maintain the low flow of in the Garonne River. To this end, it was estimated that the infiltrated water would take about 4 months to reach the River, which is an appropriate time to sustain it during the dry periods.
(. vol. 385, pp. 53-58, 18/04/2024)
Bordeaux INP, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SMEAG
Changes in species richness with climate change in subalpine communities are dependent on regional environmental conditions and local functional composition
Abstract Questions Climate change may have different effects on species richness depending on regional climates, soil types and the functional composition of local communities. Location Subalpine belt of the Grandes Rousses (Alps) and Sancy mountain ranges (the Massif Central), France. Methods We compared changes in species richness in response to recent climate change in communities from two mountain ranges subjected to contrasting environmental conditions, with a more continental climate and drier soils in the Alps than in the Massif Central. Vegetation composition of 189 and 157 plots was assessed in 1997 and 2017–2018 in the Alps and 1988–1989 and 2022 in the Massif Central, respectively. Five species traits (height, lateral spread, leaf area, specific leaf area and leaf dry matter content) were measured on 108 and 144 species, respectively. Changes in vegetation composition and species richness along spatial environmental gradients were analysed with correspondence analysis at the Sancy site and canonical correspondence analysis at the Alpe d'Huez site. Changes in functional composition across sites were analysed with principal components analysis. Changes in species richness with climate change were analysed with repeated‐measure ANOVAs. Results In both mountain ranges summer temperatures increased and the hydric balance decreased over the past three decades, but snow cover duration decreased in the Alps only, whereas irradiance strongly increased in the Massif Central only. Functional composition was characterized by shorter and more conservative species in the Alps than in the Massif Central, which was dominated by tall exploitative species. Species richness overall decreased with climate change by ca 10% in the Alps but overall increased by ca 10% in the Massif Central. Species richness decreased in the Alps probably because of increasing competition induced by dwarf shrub encroachment due to decreasing snow cover duration, whereas species richness increased in the Massif Central probably due to increasing irradiance in a very nebulous climate. Conclusion The opposite changes in species richness observed in the two mountain ranges with recent climate change were likely to be explained by their contrasting climate and soil conditions driving different functional compositions and diversity–environment relationships.
(Journal of Vegetation Science. vol. 35, n° 1100-9233, 16/04/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UREP, VAS, INRAE, UB
Vegetation response in SE France to the millennial-scale climate variability of the last glacial period
Deep-sea pollen records from the Western European margin indicate that regional vegetation oscillated between open forest and steppe during the Last Glacial period (ca. 115-27 ka), in response to the millennial scale climate variability, specifically the Dansgaard-Oeschger, (D-O) cycles and Heinrich events (HE). The magnitude of the forest expansions during D-O warming events was modulated by orbital parameters. However, the vegetation response in the north-western Mediterranean region during this period remains poorly understood due to the fragmentary nature of the available sequences. In this study, we present a new well-chronologically constrained high-resolution marine pollen record from the Gulf of Lion (MD99-2343, 40°29'N, 4°01'E) documenting the vegetation response in southeastern France during Marine Isotope Stages (MIS) 4 to 2 (~73-27 ka). Initial findings highlight that the extent of the temperate forest expansions in SE France, i.e. the forest colonizing the Rhône valley, in response to D-Os warming events is modulated by precession, as previously indicated by Western European margin pollen records located in the Mediterranean region below 40°N. In Western Europe, the HEs are all characterized by steppe expansions, but the new pollen analysis documents another scenario with an increase in forest cover during HE 6. We hypothesize that the combination of minima in precession and local atmospheric and marine processes in the Gulf of Lion allowed the development of the temperate forest in SE France during HE 6, while the expansion of open environments occurred in Western Europe.
(14/04/2024)
UB, UBM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, LCE, CNRS, UFC, UBFC, UQAT, LMJL, CNRS, Nantes univ - UFR ST, Nantes Univ
Modelling the transport of microplastics in the Gironde estuary: Sensitivity to physical processes and their parameterizations
Studying microplastic transport in estuaries is challenging due to the dynamic interplay between river and ocean, compounded by the diverse properties exhibited by these particles. Lagrangian particle-tracking numerical modelling is a relevant tool for investigating microplastic transport dynamics, dispersion patterns, and vertical distribution. However, these models oversimplify the parametrizations of crucial estuarine processes by ignoring the effect of varying water density or vertical diffusion coefficients. In this study, we implement a hydrodynamic and improved particle tracking model in the macrotidal Gironde estuary (SW France) to explore the relative importance of different physical processes (time-space varying vertical diffusivity and water density, beaching-refloating, bottom resuspension) and provide a better understanding of microplastic dispersion and potential trapping. The simulated particle trajectories and density distributions from our findings indicate a limited influence of the spatio-temporal variability of vertical turbulence on floating particles, with a notable impact observed for settling particles, showing its significance in particle resuspension. Despite the time-space-varying water density, the effect on the transport patterns of both floating and settling microplastics is relatively lower, while the phenomenon of beaching-refloating increases the particle's residence time within the upper estuary. The higher river discharge during the spring season flushes floating particles downstream, with a portion reaching the open sea, while settling particles persist within the estuary during both seasons. Notably, denser microplastic particles tend to accumulate in the upper estuary region during summer, where the estuarine turbidity maxima have been identified.
(14/04/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The exceptional winter flood of Loire river 2021: an unexpected source of methane in the inner estuary
Particles generating Maximum Turbidity Zones (MTZ), in estuaries undergo several cycles of deposition/resuspension cycles before definitive burial or expelling towards the continental shelf. Positioning and spatial coverage depend on its morphology, riverine discharge and tidal dynamics. In the Loire estuary, the decadal flood of February 2021 displaced a lot of material from the upper to the lower estuary. Consequently, cores sampled at four sites upstream Paimboeuf (15 km from estuarine mouth) showed very dark cohesive sediments while those taken at two stations downstream, within the MTZ, showed a thick (10-50 cm), unconsolidated layer of a light-brown sediment over a darker-cohesive one. More striking, these four upstream stations, covering a river line of some 40 km, showed gas ebullition generating numerous cracks on the first decimetres of interface cores. A few months later (June 2021), interface and long cores were sampled and methane analysed at three stations along the salinity gradient (two upstream and one downstream of Paimboeuf). Upstream, the entire interface and long cores showed methane saturated samples (about 2 mmol L-1) and cracks remained ebullitive. Near Paimboeuf, the cores were no longer ebullitive and a clear sulphate-methane transition zone (SMTZ) was observed at 50 cm depth. Downstream, the SMTZ was located at 30 cm depth. These results suggest that the important currents induced by the 2021 winter flood eroded a significant layer of sediment to generate depressurization and allow methane to escape in the upper estuary while the lower estuary remained capped by enough sediment to maintain the SMTZ. They also showed that the decrease of riverine discharge allowed the MTZ to migrate upstream stopping methane to escape in the mid estuary while the upper estuary continued to release methane through ebullition four months after the erosion event. Crack formation and methane release also affected benthic fluxes, increasing total oxygen uptake by a factor of ten (94 mmol m-2 d-1) compared to diffusive flux, for example. The rare opportunity to document such processes because of extreme navigation conditions, particularly for the deployment of the corer, allows us to emphasize that winter flooding can be an important source of methane that is immediately transferred to the atmosphere due to shallow depth of estuaries and must be taken into consideration for budgets and fluxes between reservoirs. This process must also be taken into account for a better understanding of other estuarine biogeochemical cycles, such as oxygen and nutrient cycles, as crack formation and methane release significantly increase their benthic fluxes.
(14/04/2024)
LPG-ANGERS, LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CHROME, UNIMES, MIAME, UPPA, INRAE, OFB, Institut Agro, LPG, CEA
Impacts des néonicotinoïdes sur la biodiversité
(12/04/2024)
ECOSYS, INRAE, RiverLy, INRAE, IFREMER, UMR BAGAP, ESA, INRAE, Institut Agro, ICE, VAS, ULH, NU, UCBL, LBBE, UCBL, VAS, CNRS, LBBE, UCBL, VAS, CNRS, LCE, CNRS, UFC, UBFC, DECOD, IFREMER, INRAE, Institut Agro, Institut Agro, OFB Service Santé Agri, OFB - DRAS, OFB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR Eco&Sols, Cirad, IRD, INRAE, Institut Agro, UMR Marbec - Station Sète, UMR MARBEC, IRD, IFREMER, CNRS, UM, EMMAH, AU, INRAE, IMBE, AU, AMU, CNRS, CUFR, URAFPA, UL, INRAE, UR HYCAR, INRAE, DEPE, INRAE
Hypoxia also occurs in small highly turbid estuaries: the example of the Charente (Bay of Biscay)
Abstract. The French coast facing the Bay of Biscay (North-East Atlantic) is characterised by the presence of small macrotidal and turbid estuaries, including the Charente, which is geographically located between the two large estuaries of the Gironde and the Loire (south-west France). Multi-year, multi-site and high-frequency water quality surveys have shown that the Loire and, to a lesser extent, the Gironde suffer from summer hypoxia. These observations raised the question of the possible occurrence of hypoxia, particularly in one of these small estuaries, the Charente, which flows into the Bay of Marennes-Oléron, the first oyster-farming area in France. Unlike its two large neighbours, the Charente estuary is not continuously monitored, although it is subject to similar climatic changes and anthropogenic pressures, making it impossible to assess potential risks to the ecosystem. Here we present a first study of dissolved oxygen in the Charente estuary based on a combination of longitudinal studies along the estuary axis and instrumented sites to determine the intensity and spatial extent of deoxygenation. Temperature, dissolved oxygen and conductivity sensors were deployed at several sites during the summers of 2018, 2019 and 2020 to record temperature, salinity and dissolved oxygen every 15 min. The high-frequency dataset is compared with a long-term low-frequency dataset (1975–2022; 8–12 measurements per year) to determine whether or not there is a deterioration in the oxygenation of the Charente estuary. The high-frequency dataset shows a high variability in dissolved oxygen (DO) with a clear influence of the tidal cycle. During summer, DO concentrations are often below 5 mg L−1 and sometimes even below 2 mg L−1, indicating the presence of a summer estuarine oxygen minimum zone with an extension along the estuarine axis of about 20–25 km. Temperature is the main factor controlling DO in the Charente estuary, which limits preventive management strategies and, in the context of global warming, raises questions about the long-term suitability of estuarine conditions for the needs of the biological communities, particularly migratory fish.
(Biogeosciences. vol. 21, n° 1726-4170, pp. 1785-1800, 10/04/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Species‐group responses improve our understanding of the effects of community dominants on subordinate species along a grazing gradient
AbstractQuestionsPlant communities have been shown to include several functional groups of species that may have contrasting responses to the effects of dominant neighbours, although potentially balancing at the community level. We aimed to assess the potential of species‐group vs community‐level responses of subordinate species to explain variation in the effects of the dominant shrub Artemisia sieberi on understorey species along a grazing intensity gradient in arid steppes of northeast Iran. We also aimed to assess whether species‐group responses help explain variation in community composition.LocationsAn Artemisia steppe community in Golestan National Park (northeast Iran).MethodsWe used the relative interaction index (RII) to quantify the effects of a shrub on the cover of the 12 most frequent subordinate species. We conducted a first principal component analysis (PCA) on species RII followed by cluster analysis to group species depending on their responses to the shrub, and a second PCA on subordinate species composition.ResultsAt the community level, subordinate species showed strong competition at the low grazing level, weak facilitation at the intermediate level and weak competition at the high grazing level; a unimodal pattern with a switch back to competition in extremely disturbed conditions that is inconsistent with ecological theories. However, species‐group analyses showed contrasting subordinate species responses, supporting either the decrease in competition with increasing disturbance scenario or the collapse of facilitation, but never a switch back to competition as predicted by recent facilitation theory along resource gradients. Moreover, these contrasting species‐group responses significantly explained community composition.ConclusionsOur study provides new evidence, along a grazing intensity gradient, that communities include different species groups with contrasting responses to dominant species.
(Applied Vegetation Science. vol. 27, n° 1402-2001, 01/04/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Density‐dependent effects of parasitism on the activity of a benthic engineer species: potential impact on ecosystem functioning
While parasitism is a common lifestyle on Earth, its importance for the functioning of marine ecosystems has been overlooked for a long time. In particular, parasites have significant potential to influence central ecological processes through their impacts on hosts that serve as ecosystem engineers. Using an ex situ experimental approach, we explored the effects of trematode parasites on the engineering bioturbation activity of a common and abundant bivalve along European Atlantic soft‐bottom coastlines, the peppery furrow shell Scrobicularia plana , as well as knock‐on effects for nutrient exchanges at the sediment–water interface (SWI). Trematodes negatively impacted the host's ability to transport sediment particles and solutes in a density‐dependent way, with parasite burden explaining 22–31% of the inter‐individual variability. This could be explained by parasitism impairing the bivalve physiological state and ability to burrow, as we observed a decrease in the condition index and the burrowing depth of the bivalves with an increase in the number of parasites they host. In contrast, the influence of S. plana on benthic biogeochemical fluxes did not vary significantly according to parasitic burden over a short time scale. Here, we focused on the effects of trematode parasites on the behaviour of S. plana alone, and thus excluded other macrofaunal organisms. We should next test whether trematodes modulate the structure and functioning of benthic communities dominated by S. plana to better understand and quantify the engineering role of parasites in soft‐bottom coastal environments.
(Oikos. vol. 2024, n° 0030-1299, pp. e10400, 01/04/2024)
AD2M, CNRS, SBR, SU, CNRS, STAMAR, INSU - CNRS, SU, CNRS, SBR, SU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS