Séminaires SAS


 AHLeGall    25/06/2015 : 21:15

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Le jeudi 25 juin 2015, de 14:00 à 15:30, en salle de réunion de l'UMR SAS (Agrocampus, Rennes), une animation scientifique est proposée sur le thème des

Le jeudi 25 juin 2015, de 14:00 à 15:30, en salle de réunion de l'UMR SAS (Agrocampus, Rennes), une animation scientifique est proposée sur le thème des

Cycles de l'azote et du carbone dans les sols et les eaux

Présentation
Nous profitons de la visite du Professeur Inamdar , professeur à l'Université du Delaware, dans le domaine de la biogéochimie et de l'hydrologie, pour vous inviter à assister à une animation scientifique sur les cycles de l'azote et du carbone dans les sols et les eaux.

Trois interventions entre 14h et 15h30 en salle de réunion à l'UMR SAS le jeudi 25 juin : Ben Abbott et Anniet Laverman de l'UMR Ecobio, et Sheeram Inamdar, vous trouverez ci dessous quelques détails sur leurs thèmes de recherche

Ben Abbott a rejoint l’OSUR en tant que chercheur postdoc dans le cadre du projet européen Marie Curie « Ecohydrological interfaces as critical hotspots for transformations of ecosystem exchange fluxes » (Interfaces).
Ses activités de recherche se situent dans les champs disciplinaires de l'écologie et la biogéochimie aquatique et terrestre. Il cherche à comprendre comment la gestion des activités agricoles peut influencer les cycles de carbone et d’azote dans les eaux et sols. Spécifiquement il s’intéresse aux contrôles de la dénitrification - le processus microbien qui réduit les nitrates en azote moléculaire gazeux – qui sont peu connus à l’échelle du bassin versant.

Anniet Laverman joins the OSUR as ‘charge de recherche’ CNRS. Her activities are within the fields of microbial ecology, biogeochemistry, and modeling. More specifically, her work consists of investigating microbial driven redox processes in aquatic sediments, with special emphasis on nitrate reduction. The driving-force behind nitrate reduction as well as most of the other biogeochemical processes occurring in sediments is the degradation of organic matter. The fate and fluxes of nutrients, metals and carbon, during the degradation of organic matter, depend on a suite of processes occurring in the sediment, both biotic and abiotic, as well as their transport. In order to understand these fluxes at the sediment interface, she uses an integrated approach determining microbial reaction rates under controlled laboratory conditions, in situ field measurements and reactive transport and large scale modeling.

Shreeram Inamdar :
http://udel.edu/%7Einamdar/

Hot moments of runoff carbon and nitrogen in watersheds

Biogeochemical “hot moments” are defined as episodes that can produce sharp changes in concentrations, composition, fluxes, and/or reactions rates for solutes in watersheds. Here we highlight the role of storm events and seasonal episodes in producing such changes for particulate and dissolved forms of carbon (C) and nitrogen (N). Understanding these changes is critical for advancing ecosystem science as well as management of our water resources. The study site is an intensively-studied forested watershed (nested 12 and 79 ha) located in the Piedmont region of Maryland, USA. Carbon and nitrogen concentrations have been measured for stream water and 10 distinct watershed sources over a period of seven years (2008-2014). Stream water sampling has been performed for storms using automated ISCO samplers and manual grab sampling during baseflow. Data are also available from in-stream, high-frequency (15-30 minutes) UV-vis based sensors. The composition of dissolved organic matter (DOM) has been characterized using a variety of UV and fluorescence metrics. Hydrologic flow paths and sources of carbon and nitrogen for stream runoff have been identified using an end-member mixing model.

Storms events, especially large tropical storms (TS), produced sharp increases in C and N fluxes with disproportionate increase in particulate forms beyond a specific precipitation threshold. Runoff from TS Irene (> 150 mm rain) in just 59 hours yielded nearly half and one-third of the annual stream water export of C and N, respectively, dominantly in particulate forms. Such large particulate inputs have the potential to modify the metabolic regime of downstream aquatic ecosystems. Storms following drought conditions, with hydrologically-disconnected streams, produced a sharp increase in “labile” protein-like DOM. This increase was attributed to the “first-flush” of labile DOM that had mineralized and accumulated in streams over the preceding dry period. Similar pulse increases in protein-like DOM in stream water were also observed in early autumn which resulted in sharp drops of stream water nitrate-N concentrations. We attribute this response to increase in heterotrophic metabolism following labile C input from freshly-fallen leaves. These insights into biogeochemical hot moments are important given that climate-change is expected to alter the storm intensity and frequency, drought severity, and length and timing of pheno-seasons.


Contact OSUR :
Anne Jaffrézic (INRA SAS, Agrocampus Ouest)
Laurent Jeanneau, Ophélie Fovet