Biotic and abiotic degradation of terrestrial organic matter discharged by Rivers (Rhône, Pô and Ebre) in the Mediterranean Sea (BALTOMS)

Project ID Card
Biotic and abiotic degradation of terrestrial organic matter discharged by Rivers (Rhône, Pô and Ebre) in the Mediterranean Sea (BALTOMS)
Acronym 
BALTOMS
Project Call 
2013
Project Dates 
2013 - 2018
Relevant OT-MED work packages  
WP2
Project leader 
Jean-François Rontani
Participants or laboratories 

Marie-Aimée Galeron (OT-Med PhD student)
Aurélie Portas (OT-Med Engineer)
Rontani J-F., Vaultier F., Bonin P., Guasco S. (MIO)
Radakovitch O. (CEREGE)

Context & Objectives  

Because riverine particulate organic matter (POM) consists of already highly degraded residues of terrestrial organisms (with a high content of lignin), it is generally considered as being refractory to decomposition in the ocean. It is surprising then that only a small fraction of the organic matter preserved in marine sediments appears to be land-derived. This suggests either that global budgets and distribution estimates are greatly in error, or that POM of terrestrial origin undergoes rapid and remarkably extensive remineralization at sea.

This project aims to understand the degradation of TOM (total organic matter) discharged by the Rhône River. into the Mediterranean. Thanks to seasonal sampling of POM and different laboratory experiments, we will try to explain why biotic and abiotic degradation of TOM is so intensive in seawater.

This original project is based on a ‘cross-biome’ study, i.e. taking into account both the terrestrial and aquatic environments and exchanges of matter and organisms between these two environments.

Main Results 

Using new lipid tracers specific to the degradation of terrestrial higher plants at the mouth of the Rhône River, we confirmed during the M-A. Galeron PhD thesis (funded by OT-Med) the role played by autoxidation in the degradation of terrestrial POM (TPOM) in estuaries. We could propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. We showed the role played by salinity in the induction of this LOX activity and provided an explanation for the differences observed in estuarine autoxidation levels (Figure 1). During the BALTOMS project (following this PhD work), we could then demonstrate that the increase of salinity in the Rhône estuary strongly impacts the composition of the bacterial community associated to TPOM, which gets closer gradually of that observed in the sea. Priming effects (enhanced mineralization of TPOM in the presence of fresh substrates from algal sources) appeared to play an important role in the biotic degradation of TPOM in the Rhône Estuary. The potamoplankton (freshwater plankton) formed within the Rhône River (dominated by diatoms) appeared to be a co-substrate well suited for the degradation of TPOM.

Abiotic degradation of terrestrial higher plant material discharged by rivers in Arctic, temperate and tropical zones

Publications
Galeron M-A., Amiraux R., Charriere B., Radakovitch O., Raimbault P., Garcia N., Lagadec V., Vaultier F. et Rontani J-F. (2015) Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers. Biogeosciences 12: 1431-1446.
Galeron M-A., Volkman J.K. et Rontani J-F. (2016) Oxidation products of betulin: new tracers for abiotic degradation of higher plant material in the environment. Org. Geochem. 91: 31-42.
Galeron M-A., Vaultier F. et Rontani J-F. (2016) Oxidation products of - and -amyrins: potential tracers of abiotic degradation of vascular plant organic matter in aquatic environments. Environ. Chem. doi.org/10.1071/EN15237.
Rontani J-F. et Galeron M-A. (2016) Autoxidation of chlorophyll phytyl side-chain in senescent phototrophic organisms: a potential source of isophytol in the environment. Org. Geochem. 97: 37-40.
Rontani J-F., Galeron M-A. et Aubert C. (2016) Electron ionization mass spectrometric fragmentation and multiple reaction monitoring quantification of trimethylsilyl derivatives of cucurbic acid and its 6,7-stereoisomers. Rapid Commun. Mass Spectrom. 30: 2253-2264.
Galeron M-A., Radakovitch O., Charriere B. et Rontani J-F. (2016) Metal ions and hydroperoxide content: main drivers of lipid autoxidation in river suspended particulate matter and higher plant debris? Journal Mar. Sci. Eng. doi. 10.3390/jmse4030050.
Rontani J-F., Galeron M-A., Amiraux R., Artigue L. et Belt S.T. (2017) identification of di- and triterpenoid lipid tracers to confirm the significant role played by autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic. Org. Geochem. 108: 43-50.
Galeron M-A., Radakovitch O., Charriere B., Vaultier F. et Rontani J-F. (2017) Impacts of coastal degradative processes: autoxidation a major player in the fate of terrestrial particulate organic matter in seawater. JGR-Biogeosciences 122: 1203-1215.
Galeron M-A., Radakovitch O., Charriere B., Vaultier F., Volkman J.K., Bianchi T.S., Ward N.T., Medeiros P., Sawakuchi H., Tank S., Kerhervé P. et Rontani J-F. (2018) Lipoxygenase-induced autoxidative degradation of terrestrial particulate organic matter in estuaries: a widespread process enhanced at high and low latitudes. Org. Geochem. 115: 78-92.
Bonin P., Prime A-H., Galeron M-A., Guasco S. et Rontani J-F. (2019) Enhancement of biotic degradation of terrestrial particulate organic matter in an estuarine salinity gradient: Interactive effects of organic matter pools and changes of bacterial communities. Aquatic Microbial Ecology 83: 147-159.
Additionnal Ressources 

Results for everyone to understand (in French) / Lire la fiche pédagogique pour tous les non-spécialistes

Video for everyone to understand on biodiversity (in French) / Video pédagogique pour tous sur la biodiversité

 

General information on the BALTOMS project / Information générale sur le projet BALTOMS : https://www.mio.osupytheas.fr/fr/cem/baltoms

Video summarising the BALTOMS PhD project : Video résumant le projet de thèse BALTOMS

This study is be integrated to the MERMEX (https://mermex.com.univ-mrs.fr/) program and more particularly to the WP3-Rivers work package