Preservation of exopolymeric substances in estuarine sediments
The surface of intertidal estuarine sediments is covered with diatom biofilms excreting exopolymeric substances (EPSs) through photosynthesis. These EPSs are highly reactive and increase sediment cohesiveness notably through organo-mineral interactions. In most sedimentary environments, EPSs are partly to fully degraded by heterotrophic bacteria in the uppermost millimeters of the sediment and so they are thought to be virtually absent deeper in the sedimentary column. Here, we present the first evidence of the preservation of EPSs and EPS-mineral aggregates in a 6-m-long sedimentary core obtained from an estuarine point bar in the Gironde Estuary. EPSs were extracted from 18 depth intervals along the core, and their physicochemical properties were characterized by (i) wet chemical assays to measure the concentrations of polysaccharides and proteins, and EPS deprotonation of functional groups, (ii) acid–base titrations, and (iii) Fourier transform infrared spectroscopy. EPS-sediment complexes were also imaged using cryo-scanning electron microscopy. EPS results were analyzed in the context of sediment properties including facies, grain size, and total organic carbon, and of metabolic and enzymatic activities. Our results showed a predictable decrease in EPS concentrations (proteins and polysaccharides) and reactivity from the surface biofilm to a depth of 0.5 m, possibly linked to heterotrophic degradation. Concentrations remained relatively low down to ca. 4.3 m deep. Surprisingly, at that depth EPSs abundance was comparable to the surface and showed a downward decrease to 6.08 m. cryo-scanning electron microscopy (Cryo-SEM) showed that the EPS complexes with sediment were abundant at all studied depth and potentially protected EPSs from degradation. EPS composition did not change substantially from the surface to the bottom of the core. EPS concentrations and acidity were anti-correlated with metabolic activity, but showed no statistical correlation with grain size, TOC, depth or enzymatic activity. Maximum EPS concentrations were found at the top of tide-dominated sedimentary sequences, and very low concentrations were found in river flood-dominated sedimentary sequences. Based on this observation, we propose a scenario where biofilm development and EPS production are maximal when (i) the point bar and the intertidal areas were the most extensive, i.e., tide-dominated sequences and (ii) the tide-dominated deposit were succeeded by rapid burial beneath sediments, potentially decreasing the probability of encounter between bacterial cells and EPSs.
(Frontiers in Microbiology. vol. 13, n° 1664-302X, 18/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Unibas, IC2MP [Poitiers], UP, INC-CNRS, CNRS, GEOPS, INSU - CNRS, CNRS, BIC, UB, INSERM, CNRS, AORI, UTokyo, BGS, UB, CNRS
Contrasting effects of siderophores pyoverdine and desferrioxamine B on the mobility of iron, aluminum, and copper in Cu-contaminated soils
Siderophores are biogenic metallophores that can play significant roles in the dynamics of a range of metals, including Cu, in the soil. Understanding the impact of siderophores on the mobility and the availability of metals in soil is required to optimize the efficiency of soil remediation processes such as phytoextraction. This study compared the ability of siderophores desferrioxamine B (DFOB) and pyoverdine (Pvd) to mobilize metals in a series of Cu-contaminated soils, and investigated the extent their metal mobilization efficiency changed over time and with the level of Cu contamination of the soil. Siderophores were supplied (or not) to Cu-contaminated soils and metal mobility was assessed through their total concentration in 0.005 M CaCl2 extract. DFOB selectively mobilized Fe and Al while Pvd also mobilized Cu and Ni, Co, V and As but to a lesser degree. The 1:1 relationship between DFOB in the CaCl2 extract and Fe + Al mobilized from the solid phase suggests that DFOB mobilized metals by ligand-controlled dissolution. The accumulation of Cu in soil enhanced the adsorption of DFOB and Pvd at the surface of soil constituents and the mobilization of Fe to the detriment of Al by the two siderophores. The metal mobilization efficiency of DFOB and to a lesser extent of Pvd decreased over 22 days. According to N-15-Pvd analyses, Pvd degradation at least partly contributed to the progressive reduction in the metal mobilization efficiency of Pvd. The processes behind these results and the relevance of these results for manipulating the availability of Cu (and Fe) in soil are discussed.
(Geoderma. vol. 420, n° 0016-7061, pp. 115897, 15/08/2022)
UMR ISPA, Bordeaux Sciences Agro, INRAE, LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Within-species variation of seed traits of dune engineering species across a European climatic gradient
Within-species variation is a key component of biodiversity and linking it to climatic gradients may significantly improve our understanding of ecological processes. High variability can be expected in plant traits, but it is unclear to which extent it varies across populations under different climatic conditions. Here, we investigated seed trait variability and its environmental dependency across a latitudinal gradient of two widely distributed dune-engineering species (Thinopyrum junceum and Calamagrostis arenaria). Seed germination responses against temperature and seed mass were compared within and among six populations exposed to a gradient of temperature and precipitation regimes (Spiekeroog, DE; Bordeaux, FR; Valencia, ES; Cagliari, IT, Rome, IT; Venice, IT). Seed germination showed opposite trends in response to temperature experienced during emergence in both species: with some expectation, in populations exposed to severe winters, seed germination was warm-cued, whereas in populations from warm sites with dry summer, seed germination was cold-cued. In C. arenaria, variability in seed germination responses disappeared once the seed coat was incised. Seed mass from sites with low precipitation was smaller than that from sites with higher precipitation and was better explained by rainfall continentality than by aridity in summer. Within-population variability in seed germination accounted for 5 to 54%, while for seed mass it was lower than 40%. Seed trait variability can be considerable both within- and among-populations even at broad spatial scale. The variability may be hardly predictable since it only partially correlated with the analyzed climatic variables, and with expectation based on the climatic features of the seed site of origin. Considering seed traits variability in the analysis of ecological processes at both within- and among-population levels may help elucidate unclear patterns of species dynamics, thereby contributing to plan adequate measures to counteract biodiversity loss.
(Frontiers in Plant Science. vol. 13, n° 1664-462X, pp. 1-11, 11/08/2022)
JNU, ROMA TRE, ROMA TRE, UniCa, CIDE, CSIC, DZMB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Compilation of Southern Ocean sea-ice records covering the last glacial-interglacial cycle (12–130 ka)
Antarctic sea ice forms a critical part of the Southern Ocean and global climate system. The behaviour of Antarctic sea ice throughout the last glacial-interglacial (G-IG) cycle (12 000-130 000 years) allows us to investigate the interactions between sea ice and climate under a large range of mean climate states. Understanding both temporal and spatial variations in Antarctic sea ice across a G-IG cycle is crucial to a better understanding of the G-IG regulation of atmospheric CO 2 , ocean circulation, nutrient cycling and productivity. This study presents 28 published qualitative and quantitative estimates of G-IG sea ice from 24 marine sediment cores and an Antarctic ice core. Sea ice is reconstructed from the sediment core records using diatom assemblages and from the ice core record using sea-salt sodium flux. Whilst all regions of the Southern Ocean display the same overall pattern in G-IG sea-ice variations, the magnitudes and timings vary between regions. Sea-ice cover is most sensitive to changing climate in the regions of high seaice outflow from the Weddell Sea and Ross Sea gyres, as indicated by the greatest magnitude changes in sea ice in these areas. In contrast the Scotia Sea sea-ice cover is much more resilient to moderate climatic warming, likely due to the meltwater stratification from high iceberg flux through "iceberg alley" helping to sustain high sea-ice cover outside of full glacial intervals. The differing sensitivities of sea ice to climatic shifts between different regions of the Southern Ocean has important implications for the spatial pattern of nutrient supply and primary productivity, which subsequently impact carbon uptake and atmospheric CO 2 concentrations changes across a G-IG cycle.
(Climate of the Past. vol. 18, n° 1814-9324, pp. 1815 - 1829, 10/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Wave-induced mean currents and setup over barred and steep sandy beaches
Wind-generated surface waves breaking in the nearshore cause an increase in mean water levels, the wave setup, which can represent a significant fraction of storm surges developing both along open coasts and over sheltered areas such as coastal lagoons and estuaries. A common way to simulate the wave setup is to assume a balance between the barotropic gradient and the divergence of the depth-integrated wave-averaged momentum flux (radiation stress) associated with breaking waves in the surf zone. Field observations collected at several sandy beaches revealed that this depth-integrated approach could largely underestimate the wave setup close to the shoreline (by up to a factor of 2). The present study builds on Guérin et al. (2018) and further investigates how representing the depth-varying wave-induced forcing in modelling systems can improve the prediction of wave setup across the surf zone. We use data collected during two major field campaigns at Duck, N.C., combined with simulations with SCHISM, a threedimensional (3D) phase-averaged modelling system employing the vortex-force formalism to represent the effects of waves on currents. The ability of SCHISM to reproduce the surf zone circulation is first assessed with data collected during October 1994 (Duck94), which serve as a classical benchmark for 3D hydrostatic oceanic circulation models. The wave setup dynamics are then analysed during a storm event that occurred during SandyDuck. Consistent with the results of Guérin et al. (2018), we find that resolving the depth-varying nearshore circulation results in increased and improved wave setup predictions across the surf zone. At the shoreline, depth-integrated approaches based on the vortex-force formalism or the radiation stress concept underestimate the maximal wave setup by 10-15% and 30% on the 1:14 foreshore slope, respectively. An analysis of the 3D cross-shore momentum balance reveals that the vertical mixing is the second most important contributor (10-15% across the surf zone) to the simulated wave setup after the wave forces (80-90%), followed by the vertical advection whose contribution increases with the beach slope (up to 10% at the shoreline). Simulations performed with a phase-resolving numerical model suggest that the largest discrepancies observed at the shoreline in past studies likely originate from swash-related processes, highlighting the difficulties to disentangle wave and swash processes on steep foreshores in the field.
(Ocean Modelling. vol. 179, n° 1463-5003, pp. 102110, 04/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, VIMS
Antarctic sea ice over the past 130 000 years – Part 1: a review of what proxy records tell us
(Climate of the Past. vol. 18, n° 1814-9324, pp. 1729 - 1756, 02/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Geomorphological control of sandy beaches by a mixed-energy tidal inlet
Coastal areas adjacent to tidal inlets are highly valuable areas for marine ecosystems where a wide range of social and economic activities can be found. These areas can be differentiated from open coast due to their specific morphological behaviour caused by a complex nearshore bathymetry and interactions between wave and tidal forcing. The understanding of these interactions is usually limited by the lack of a systemic approach and the scarce availability of comprehensive datasets covering subtidal, intertidal and supratidal areas at large spatial and temporal scales. Here, the complementary use of different bathymetric and topographic datasets and the development of innovative methods using satellite imagery, offers the opportunity to develop a comprehensive understanding of the timescales and the key processes involved in the dynamics of tidal inlets and its control on the downdrift coast. The use of satellite-derived bathymetric maps, computed over the last two decades, showed two sequences of 8 and 9 years where large sandy shoals migrated along the tidal inlet and welded onto the downdrift coast. Although the study period covers one of the most energetic winter over the last decades, the most significant sediment volume changes (±300 m3/m) observed along the three kilometres of beach located south to the inlet were mostly attributed to the migration and welding of these sandy shoals, whereas the offshore wave forcing was of secondary importance. It was also demonstrated that these migrating and welding events had an impact on the pattern of the nearshore bathymetry and sandbars down to 10 km south to the inlet. Primary welding events near to the inlet are associated to the formation of kilometre-long and alongshore uniform nearshore sandbars that subsequently migrate further down the coast causing secondary welding events. The ability to understand and define the spatial and temporal boundaries at which beach behaviour is controlled by a local tidal inlet gives the opportunity to develop sediment compartment approach in order to make accurate predictions of future beach behaviour.
(Marine Geology. vol. 450, n° 0025-3227, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
Distribution of modern dinocysts and pollen in the western Mediterranean Sea (Algerian margin and Gulf of Lion)
The Mediterranean Sea is generally described as an oligotrophic area where primary productivity is limited to a few coastal environments with nutrient-enriched fluvial input. However, several studies have revealed that the hydrology of the western Mediterranean has major seasonal productive patterns linked either to significant riverine input or to seasonal upwelling cells. This study aims to: i) discuss organic microfossils (i.e. pollen and dinoflagellate cyst assemblages, as well as other non-pollen palynomorphs) from two different productive areas of the western Mediterranean Sea, and ii) examine the importance of the interconnections between marine and continental influences responsible for modern palynomorph distributions. Based on 25 samples from the Gulf of Lion (GoL) and Algerian Margin, this study key findings are: i) that GoL marine productivity is driven by the combination of discharge from the Rhône River and seasonal upwelling mechanisms, ii) that the strong productive pattern of the northern African coast is driven by water density front mixings and related upwelling. These two patterns are discussed in the light of major links that provide a better understanding of the signatures of marine and continental bio-indicators. Typical differences in vegetation across the north-south climate gradient in the western Mediterranean Basin are highlighted by the larger ratio of Euro-Siberian to Mediterranean pollen taxa in the northern sector. Synoptic maps also illustrate the complex interactions of environmental drivers determining the distributions of continental and marine palynomorphs in the western Mediterranean Sea.
(Marine Micropaleontology. vol. 175, n° 0377-8398, 01/08/2022)
LGO, UBS, IFREMER, UBO EPE, CNRS, HNHP, MNHN, UPVD, CNRS, UMR ISEM, Cirad, IRD, EPHE, PSL, CNRS, UM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOTOP, EPM, UdeM, UQAT, UQAR, UQAM, [Total Energies. Anciennement : Total, TotalFina, TotalFinaElf]
Effect and response traits in severe environments in the context of positive plant–plant interactions. A commentary on: ‘Interspecific interactions alter plant functional strategies in a revegetated shrub-dominated community in the Mu Us Desert’
Studies of plant functional traits have considerably increased our understanding of the mechanisms driving plant–plant interactions and community assembly. In benign environments with dominant negative interactions, competitive outcomes are driven mainly by the advantage associated with particular trait values, and trait dissimilarity between interacting species appears necessary for stabilizing niche differences and species coexistence (Kraft et al., 2015). In severe environments, with positive plant–plant interactions (i.e. facilitation) being the main force driving species coexistence, species are more prone to benefit from facilitation by nurse plants when they are functionally dissimilar from their nurses (Navarro-Cano et al., 2019). In the most severe environments, with intense abiotic filters, only highly stress-tolerant species with strong functional similarity remain in the communities, which often leads to a collapse of positive interactions (Liancourt et al., 2017). Thus, the degree of functional similarity is a critical driver of plant–plant interactions in severe environments.
(Annals of Botany. vol. 130, n° 0305-7364, pp. 149–159, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Marine trematode parasites as indicators of environmental changes
Coastal ecosystems are threatened by growing pressures related to global change. The evaluation of an ecosystem’s biodiversity and status is by consequence of increasing importance to assess potentially undergone changes and predict their future trajectory for management and conservancy purposes. Biotic indicators sensitive to ecosystem changes are thus continuously sought for. Trematode parasite communities were examined as potential indicators of environmental changes, considering that the achievement of their complex life cycle is modulated by several factors. Indeed, the rule for trematode is that each species complete their cycle by a succession of three different host species and two free-living stages, thus depending on several biotic and abiotic factors. To this end, we examined the trematode community infecting the common cockle in Banc d’Arguin, Arcachon Bay, France. Monthly data extending over 16 years and sampled at a single station were compared to field book notes describing the changes of the closely surrounding landscape. In 2021, we also sampled cockles at 15 stations presenting different substrate features along the bank. Over time, seven out of nine changes of the trematode community structure presented concordances with changes in landscape. We hypothesize this was related to the environment heterogeneous substrate (i.e., temporal succession of oyster parks, bare sands and seagrass) with cascading effects on host populations. However, some changes could not solely be explained by changes in landscape. Our spatial study showed that the trematode communities exhibited intricate infection patterns with a complex interaction between substrate heterogeneity and larval dispersal ability of parasites. Thus, trematode communities might be potential indicators of subtle changes in the environment. However, it remains unclear which scale of environmental changes trematodes are actually sensitive to.
(Ecological Indicators. vol. 141, n° 1470-160X, pp. 109089, 01/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMS, UB, CNRS