TRAMAT

Name: TRAMAT
Start: 2016-03-30
End: 2016-04-11
Location: English Channel

Type	Oceanographic cruise
Ship	Côtes De La Manche
Ship owner	CNRS until 2019 - IFREMER since 2020
Dates	30/03/2016 - 11/04/2016
Chief scientist(s)	LAGUIONIE Philippe
	INSTITUT DE RADIOPROTECTION ET DE SURETÉ NUCLÉAIRE Laboratoire de Radioécologie de Cherbourg-Octeville (LRC) RUE MAX POL FOUCHET BP 10 50130 OCTEVILLE +33(0)2 33.01.41.00 https://www.irsn.fr/
DOI	10.17600/16009600
Objective	The aim of the TRAMAT cruise was to better understand the behavior of fine particles within an heterometric sediment mainly composed of coarse particles, and to contribute to develop and validate the MARS model heterometric sediment transport module.

Scientific context

The Fukushima accident remains, to date, the largest accidental release of radionuclides into the marine environment. It resulted in particularly high concentrations in water, living species, and sediments, which will be measurable in the medium and long term near the coast and across the entire North Pacific. This accident highlights the need for operational tools to quickly model and predict the fate of radionuclides released into the sea in order to assess the impact of radioactivity on marine ecosystems. Developing reliable methods to evaluate the impact of an accidental release on the marine environment requires improving our knowledge on: (1) processes at the land-ocean interface; (2) the dispersion of radionuclides in water masses; (3) the fixation and transport of radionuclides by particulate matter on various spatio-temporal scales; (4) the transfer of radionuclides within food chains; and (5) the sensitivity and vulnerability of affected ecosystems. These five research areas form the framework of the ANR AMORAD project (Improvement of prediction models for radionuclide dispersion and impact assessment in the environment; ANR-11-RSNR-0002), to which the TRAMAT campaign is attached.

The evolution of concentrations measured in the marine environment near the accident site confirms what has been observed in the English Channel and the Irish Sea: the medium- and long-term persistence of pollutant concentrations is largely controlled by the dynamics of sediment transport. Once pollutants are fixed by suspended matter, sedimenting particles can retain traces for years, with transport dynamics unique to them. Radionuclides released under controlled conditions by industry can serve as valuable markers to track these movements.

Understanding the transport of radionuclides via particulate matter involves: (1) hydro-sedimentary modeling in regions close to contamination sources (in the short term) or further away (in the long term); (2) improving models by incorporating processes observed in situ that are still poorly understood; (3) comparing model results with in situ measurements. In situ observation of particulate matter now benefits from many punctual or integrated measurement tools such as the DYSPI (Dynamic Sediment Profiler Imagery developed jointly by IFREMER and IRSN) (Blanpain et al., 2009), the AQUASCAT (suspended sediment profiler, AQUATEC GROUP®) (Moore et al., 2013), the LISST (in situ granulometer, SEQUOIA®) (Pedocchi and García, 2006), particle tracing via the measurement of radionuclides they carry (Boust, 1999), or stratified sampling in facies at hydro-sedimentary equilibrium (sampling by divers).

References :

Blanpain, O., du Bois, P.B., Cugier, P., Lafite, R., Lunven, M., Dupont, J., Le Gall, E., Legrand, J., Pichavant, P., 2009. Dynamic sediment profile imaging (DySPI): a new field method for the study of dynamic processes at the sediment-water interface. Limnology and Oceanography: Methods, 7, 8-20.

Boust, D., 1999. Distribution and inventories of some artificial and naturally occurring radionuclides in medium to coarse-grained sediments of the channel. Continental Shelf Research, 19, 1959-1975.

Moore, S.A., Dramais, G., Dussouillez, P., Le Coz, J., Rennie, C., Camenen, B., 2013. Acoustic measurements of the spatial distribution of suspended sediment at three sites on the Lower Mekong River. The Journal of the Acoustical Society of America, 133, 3227-3227.

Pedocchi, F., García, M.H., 2006. Evaluation of the LISST-ST instrument for suspended particle size distribution and settling velocity measurements. Continental Shelf Research, 26, 943-958.

Main results

Data acquired and analyses carried out at sea and on shore

The objective of the TRAMAT campaign was to better understand the fate of fine particles in a predominantly coarse heterometric sediment and to contribute to developing and then validating the sedimentary transport module of coarse heterometric mixtures of the MARS model. The ultimate aim is to have models with known uncertainties for simulating the dispersion, transport and transfer of pollutants (including radionuclides) within the marine ecosystem. Sediment transport mechanisms were highlighted by in situ monitoring of hydraulic and particulate characteristics at and near the water-sediment interface using DYSPI (https://doi.org/10.4319/lom.2009.7.8. The DYSPI was submerged during 6 periods of 6 to 24 hours on 3 different study sites during periods of high tides on different sedimentary facies. At the same time, sediment samples with the Shipeck grab were taken to complete the database created following the TRACES 2014 and TRACES 2015 campaigns.

At each study site: Mont Saint-Michel Bay (Site_BDM; March 31 and April 1, 2016), Saint-Brieuc Bay (Site_BSB; April 3 and 8, 2016) and off Vauville (Site_Vauville; the 5 and April 10, 2016) the bottom was first characterized using videos taken from a towed frame and a sample taken by Shipeck grab in order to choose the immersion site for the DYSPI structure. The structure was then submerged at the determined location for periods longer than 6 hours. The instruments deployed on the structure were: a mini-pépito, an ADCP, two ADVs, an Aquascat, a Wetlabs turbidity probe, two NKE turbidity probes, a LISST, a settling bench and two sediment traps.

Numerous technical issues were encountered with the DYSPI. The usable videos pertain to the Site_BSB locations (April 3-4 and April 8-9) and Site_Vauville (April 5).

The processing of the collected data began but had to be interrupted following an internal reorganization of the Cherbourg-Octeville Radioecology Laboratory (IRSN) in 2015. In particular, the in situ measurements conducted with the Aquascat, the Wetlabs turbidity probe, the NKE turbidity probe, and the LISST could not be calibrated using the suspended particulate matter (SPM) samples collected in situ at the time of measurement.

The usable data were uploaded into the SeaNoe database (Laguionie Philippe, 2024, In-Situ Visualization of Bedload in the English Channel, SEANOE, https://doi.org/10.17882/101597).

Figure: TRAMAT - Location of study sites (Site_x) and sampling locations with the Shipeck grab (SH_x).

Published data

Laguionie Philippe (2024). In-Situ Visualization of Bedload in the English Channel. https://doi.org/10.17882/101597

Bibliography

References of Technical Reports

Laguionie, P.; Périer, V.; Bailly du Bois, P.; Beryouni, K.; Boust, D.; Cazimajou, O.; Connan, O.; Fievet, B.; Godinot, C.; Lamotte, M.; et al. (2018) INvestigations Sur La DIspersion et Les Transferts de Radionucléides Dans Le GOlfe Normand-Breton - Volet SEDIments; Institut de Radioprotection et de Sûreté Nucléaire (IRSN), RT/PSE-ENV/2018-00049; p. 80.