The impact of sudden cold waves over Europe on future viticulture practices
(23/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR EGFV, UB, Bordeaux Sciences Agro, INRAE
Exploring the Susceptibility of Turbid Estuaries to Hypoxia as a Prerequisite to Designing a Pertinent Monitoring Strategy of Dissolved Oxygen
Globally, there has been a decrease in dissolved oxygen in the oceans, that is more pronounced in coastal waters, resulting in more frequent hypoxia exposure for many marine animals. Managing hypoxia requires an understanding of the dynamics of dissolved oxygen (DO) where it occurs. The French coast facing the Bay of Biscay (N-E Atlantic Ocean) hosts at least a dozen tidal and turbid estuaries, but only the large estuaries of the Gironde and the Loire, are subject to a continuous monitoring. Here, we compared the DO dynamics in these two systems, in order to evaluate to what extent it is possible to predict the sensitivity to hypoxia of a tidal and turbid estuary based on its most common and easily accessible characteristics (the estuary surface area and length, liquid and solid discharge, suspended particulate load, water renewal time, presence of cities). Whereas the hyperturbid Gironde estuary is the longest (170 km), implying longer water and particle residence times, and is bordered by a large metropole (>750,000 inhabitants), only episodic summer hypoxia events (DO < 2 mg L−1) were recorded in its urban Garonne subestuary. In contrast, the turbid Loire estuary, smaller in terms of surface area and length, experiences permanent summer hypoxia. This demonstrates the inability to evaluate the susceptibility of a tidal and turbid estuary to hypoxia only by considering its general characteristics. We urge that there is a need for a pertinent DO survey strategy based on an initial assessment of DO in a specific estuary based on longitudinal investigations, in particular during the warm season (as higher water temperatures decrease DO solubility), for detecting the potential zones of minimum DO.
(Frontiers in Marine Science. vol. 6, n° 2296-7745, pp. 8, 21/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EABX, IRSTEA
First insight into the phenolic content of Spartina maritima: isolation, characterization and quantification of four C-glycosidic flavonoids
Abstract The phenolic content of Spartina maritima was investigated using chromatographic and spectroscopic techniques. Aqueous methanolic extracts were prepared from plant collected in different seasons in the Bay of Arcachon (French Atlantic coast). High performance liquid chromatography (HPLC) with diode array detection (DAD) coupled with mass spectrometry allowed identification of four major phenolics in the aerial tissue, all belonging to the C-glycosidic-flavonoid class. They were isolated from the crude extracts, and their structures were assigned to isovitexin, isoscoparin and their respective 2″-O-glucosides on the basis of NMR, mass and UV spectroscopies. The seasonal variation of the flavonoid content was quantified over the period January 2013 to May 2015. The total concentration found ranged from 1.73 to 4.60 mg g−1 dry wt for isovitexin derivatives, and 0.88–2.66 mg g−1 dry wt for isoscoparin derivatives. The phenolic content of the rhizomes was very low and mainly dominated by coumaric acid (0.03–0.08 mg g−1), along with ferulic acid (≤0.06 mg g−1). The lack of significant concentrations of flavonoids in the rhizome contrasts with the aerial tissue. This work constitutes the first phenolic profiling of S. maritima and should provide a foundation for further studies, considering the reported biological activities of C-glycosidic flavonoids, and the lack of knowledge of the phenolic chemistry of the genus Spartina.
(Botanica Marina. vol. 62, n° 0006-8055, pp. 379-389, 13/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Photodegradation of Myrigalone A, an Allelochemical from Myrica gale : Photoproducts and Effect of Terpenes
This study investigated the environmental fate of myrigalone A, a light absorbing natural herbicide found on leaves and fruits of Myrica gale. Myrigalone A was irradiated in water and as a dry solid deposit to simulate reactions on leaves, alone and in the presence of the terpenes generated by Myrica gale. The phototransformation was fast (t1/2 = 35 min in water). Analyses by liquid chromatography coupled to high resolution orbitrap electrospray mass spectrometry (MS) and gas chromatography-MS revealed the formation of 11 photoproducts in water and solid and 9 in gaseous phase. Some were detected in the leaf glands and oil covering the fruits of Myrica gale, which suggested that photodegradation occurred in the field. Moreover, myrigalone A photoinduced the oxidation of terpenes that in turn protected it against photolysis. This highlights the need for additional research on the effect of terpenes on the photodegradation of pesticides on vegetation.
(Journal of Agricultural and Food Chemistry. vol. 67, n° 0021-8561, pp. 7258-7265, 11/06/2019)
ICCF, SIGMA Clermont, INC-CNRS, UCA [2017-2020], CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CRIOBE, UPVD, EPHE, PSL, CNRS, PIAF, INRA, UCA [2017-2020]
Invasion mechanisms of Spartina anglica in salt marshes of the Bay of Arcachon and consequences for native vegetation species
Spartina anglica is a hybrid exotic cordgrass that inhabits coastal salt marshes. This species arrived in the Bay of Arcachon in the 1980s and since has importantly colonized the salt marshes and tidal flats formerly only occupied by the native Spartina maritima and Zostera noltei, respectively. This work aims at understanding, with an interdisciplinary perspective, the invasion mechanisms of this exotic cordgrass and the outcoming changes of its introduction in the Bay, both to the physical environment and to the native vegetation. Different approaches were considered in order to assess the niche occupancy by the exotic Spartina and its interactions with the native intertidal species, Spartina maritima and Zostera noltei.The analysis of aerial and satellite images has shown that, in about 30 years after the invasion, within a zone densely populated by the native Spartina, the global high marsh zone did not suffer significant changes with the arrival of the invasive species. Spartina anglica did not replace the existent marsh vegetation, it occupied empty niches along the intertidal area instead. Additionally, experimental works of cross transplantation and biomass measurements have corroborated that the native Spartina maritima offers resistance to the colonization by the exotic Spartina. It was also shown that the invasive occupies the same intertidal niche along the elevation and anoxic gradient than the native. The successful extension of Spartina anglica into the mudflat towards the inner Bay was related to its likely ability to tolerate physical disturbances, its strong growth plasticity in nutrient- and oxygen- rich patches and its self-facilitator behaviour. This latter trait is related to its strong ecosystem-engineering ability due to its prominent root system and consequent ability to ameliorate the oxygenation of highly anoxic soils.The main effect of the exotic Spartina species on the seagrass is related to its stronger ecosystem-engineering ability, favouring bed accretion up to levels that are not favourable to Z. noltei through enhancement of desiccation stress. However, hydrodynamic and altimetry measurements have shown that the process of bed accretion is slow and, due to the cordgrass’ specific preferential biomass allocation to roots, its efficiency is more linked to its resistance to erosion rather than sediment trapping.The results of this study provide relevant information for the definition of appropriate action and conservation strategies of marsh zones in the Bay of Arcachon, and in particular the importance of limiting physical disturbance and nutrient pollution that could disrupt the biotic resistance of the native cord grass. They also suggest a potentially important role of the exotic species in facing increasing Sea Level Rise.
(05/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal Variability, Impact of Urban Discharges and Influence on Micro-pollutant Speciation
This research has been conducted over the last 10 years to characterise the spatio-temporal variability of aquatic organic matter (OM) composition in the Seine River watershed upstream and downstream of Paris Megacity and its effect on micro-pollutants. For this purpose, a large number of samples were collected under different hydrological conditions, and, over 1 year, three representative sites were monitored monthly. Furthermore, the evolution of the OM composition along an urbanisation gradient, from upstream to downstream of the Paris agglomeration, was characterised, highlighting the very strong impact of urban discharges, especially during low-water periods. Substantial differences in the chemical composition are emphasised relative to the urban or natural origin of the organic matter. Dissolved organic matter (DOM) interactions with metallic and organic micro-pollutants were studied, allowing us to (1) identify the key role of DOM on their speciation and bioavailability in aquatic systems and (2) demonstrate that these interactions depend on DOM composition and origin. The essential role of urban DOM on the speciation of trace metals in the Seine River downstream of the Paris agglomeration is also shown.
(. vol. 90, pp. 217-242, 03/06/2019)
LEESU, ENPC, UPEC UP12, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
ATMOSPHERIC CLIMATE CONTROL OF DIRECTIONAL WAVES IN THE UNITED KINGDOM AND IRELAND
Understanding multi-annual to decadal atmospheric climate controls on winter-wave climate is critical for coastal vulnerability assessment and future development of 'season ahead' forecasting of coastal risk. We examine the relationships between winter-average climate indices (NAO and WEPA) and directional wave power at 63 inshore locations throughout the United Kingdom and Ireland (UK&I). Analysis of hindcast wave data between 1980-2017 illustrate the extent of directional bi-modality, with 67% of inshore sites displaying directionally multimodal wave climates. Analysis of directional modes as a function of climatic indices illustrated the control exerted by NAO/WEPA on directional balance of inshore winter wave climate. Along Channel and southern North Sea coasts +WEPA significantly explains winter-averaged wave power for southwesterly wave directional modes (r = 0.58-0.77) and-NAO significantly explains variability in all easterly wave modes (r = 0.6-0.76), providing a mechanism for which 'season ahead' inshore wave climate forecasting and rotational beach response can be based.
(01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LETG - Brest, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN
CLIMATE CONTROL ON WINTER WAVE ACTIVITY IN THE NORTHEAST ATLANTIC AND IMPACTS ON BEACH EROSION AND RECOVERY ALONG THE WEST COAST OF EUROPE
The west coast of Europe is exposed to high-energy winter waves generated in the North Atlantic Ocean by low pressure systems traveling eastward. The present study builds on recent research on atmospheric and ocean wave climate in the North East Atlantic over the last 70 years using numerical weather and wave hindcast, in-situ sea-level pressure measurements, and beach response from a unique dataset of decadal beach morphological changes along the west coast of Europe. Interannual to decadal variability of winter wave activity in the North East Atlantic is strongly affected by the North Atlantic Oscillation (NAO) and the West Europe Pressure Anomaly (WEPA). It is found that extreme winter-mean wave heights become more frequent and variability increases, resulting in extreme winters such as that of 2013/14. We show that the recovery signature is site-specific and multi-annual, and that interannual variability of both erosion and recovery is well correlated with WEPA and NAO.
(01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LETG - Brest, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN
SHORECASTS: A BLIND-TEST OF SHORELINE MODELS
Predictions of shoreline change are of great societal importance, but models tend to be tested and tuned for the specific site of interest. To overcome this issue and test the ability of numerical models to simulate shoreline change over the medium scale (order of years) we have organized a non-competitive competition where participants were given data to train their model (1999-2014) and data to predict seasonal to inter-annual future changes (2014-2017). Participants were shown the observed shoreline changes only after submission of their modelling results. Overall, 19 numerical models were tested, the vast majority falling in the broad categories of "hybrid models" or "machine learning". Models were able to reproduce the mean characteristics of shoreline change but often failed to reproduce the observed rapid changes induced by storms.
(01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
CROSS-SHORE SANDBARS RESPONSE TO AN ARTIFICIAL REEF: AN INTERSITE COMPARISON
While a clear improvement concerning aesthetic considerations using soft submerged breakwater is undeniable, their design has often focused on wave energy decrease in their lee, overlooking their impact on the dynamics of the nearby nearshore sandbar(s). At the beach of Sète (southeast France), the submerged structure clearly affects the natural net offshore migration cycle (NOM) of the former double barred beach. On the contrary, at Narrowneck (Queensland, Australia), the deployment of a multi-functional submerged structure does not affect the cross-shore sandbar processes. These contrasting behaviors are addressed using high frequency video monitoring. After discussing observations at both field sites, a process-based morphodynamic model provides insight into the morphological sandbars response to artificial reefs.
(01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS