DS0101 - Comprendre et prévoir les évolutions de l'environnement

Modelling the reMOBIlization of SEDiments and the release of associated contaminants – MOBISED

MOBISED : Modelling the reMOBIlization of SEDiments and the release of associated contaminants

In the past, hazardous contaminants from various effluents, were discharged into water bodies and accumulated within the bed stream sediments. Thus, stock of historical contaminants have been buried in sediments at various depths and could be re-suspended through the increase of water flow. In the context of climate change and increasing occurrence of heavy rainfalls, sediment stock from small streams will be more frequently re-suspended, with remobilization of contaminated layers.

What are the controlling paramaters of sediment resuspension

The MOBISED project aims at understanding the mechanisms involved in sediment mobilization and their consequences: <br />- From a precise characterization of sediment stock, combined with a fine knowledge of hydrodynamics, is it possible to prioritize chemical and physical parameters that trigger the sediment remobilization ? <br />- What is the influence of remobilization-deposition cycles, related to seasonal variations of hydrological conditions on contaminant partitioning ? <br />- In what extent sediments represent a reservoir for microorganisms? Do the sediments get enriched in particular species through surficial interactions? <br />- Do the hydrological conditions contribute to the selective release of contaminants in the river system? <br />According to these questions, we have identified several bottlenecks for the MOBISED project: <br />- Differentiation and quantification of in-stream erosion sediments and in-flow sediments: the multitracer approach proposed in MOBISED, which will combine markers of different natures which have been seldom reported in literature (i.e., organic molecules and macromolecules, major and trace elements, stable isotopes, mineral phases, microbes), is a promising approach. <br />- To integrate qualitative data in the modelling or compare and correlate experimental results with field data and the results of modelling, we should develop a specific statistical approach to be able to corroborate “discrete” variables resulting from molecular and microscopic descriptions of river samples, with quantitative or “continuous” variables resulting from hydrological measurements and hydro-morphodynamic modelling. <br />- 3D-hydrodynamic approach (TELEMAC-MASCARET 3D) is commonly used for marine environments or estuaries, but the application for small size rivers is challenging especially due to numerical stability issues. <br />-The flocculation-aggregation processes constitute a real bottleneck for the modelling of cohesive sediment transport. <br />

A first task is dedicated to the detailed study of contaminated sediments in order to evidence their chemical properties, their contaminant contents, and their physical and cohesive properties. A strong insight will be given to the mutual organization of constituents.
Hydrological monitoring will be carried out, thanks to preliminary instrumentation of short sections of the river. The first year will then be dedicated to site instrumentation, setting up and calibrating the hydrometric station, as well as the compilation of hydro-climatological data in order to establish a model for the relationship between rainfall and water flow. This model is crucial for the selection of sampling times, and the prediction of flood events. Indeed, high flow events are the most important contributions to sediment transport, and we will focus on several flood events and develop a well-fitted high resolution sampling campaign. Those high-resolution sampling campaigns will be combined with low resolution sampling campaigns at different periods of the year. Furthermore those in-situ observations of sediment resuspension will be combined with laboratory experiments to evidence the selectivity of contaminant release. The redistribution in the water column of sediment aggregates, as well as the associated contaminants, will be described in details, and compared to the reference hydrological regime of the stream. The compilation of hydrodynamics data with the detailed morphological description of the riverbed will provide a dataset for 2D and 3D modelling of sediment transport and redistribution.

Contaminated sediment tracing: the organic and mineral composition of contaminated sediments as well as the isotopic fingerprint of Zn and Pb allow to determine the historical contributions of contaminations in Zn, Pb, and polycyclic aromatic hydrocarbons (PAHs). Furthermore, the same data were used to precise the origin of settled material.
Recent surficial sediments are readily distinguished from the bottom contaminated sediments as they display a signature of geological background (watershed run-off) and the signs of a urban or domestic contamination.
The suspended solids (SPM) that were collected in different stations and upon various hydrological conditions present similar signatures than the recent surficial sediments, suggesting a similar origin.
The statisitical analysis of microbiological data suggests that (i) the partition of microbiological markers between water and suspended solids can vary from one marker to another and (ii) sediments are enriched in specific microbiological markers. The question about selectivity upon resuspension is reached.
- a first flood monitoring was performed in february 2016
- a specific shared space was built with access to all the data for all the partners, a data management plan was also created.

The next 12 months will be dedicated to :
-the building of a SWAT model relating rain falls and water flow.
-the monitoring of fall and winter floods
-the analysis of sediments and suspended matter at the molecular scale to evidence the contaminants status
-statistical analysis in order to evidence the contribution of sediments to the transported solids
-experiments of sediment resuspension in controlled conditions.

COMMUNICATIONS involving several partners
1. Kanbar H., Montarges-Pelletier E., Mansuy-Huault L., Losson B., Manceau L., Bauer A., Bihannic I., Gley R., Kazpard V., Villieras F. Industrial deposits in river sediments: temporal storage and imminent

Although European Water Policy and related legislation attempted to reduce the incoming wastewaters in natural aquatic media, water resource management remains a major concern. The objective to reach and maintain clean status of water bodies remains challenging due to the presence of contaminated sediments in numerous areas. In the past, hazardous contaminants from municipal and industrial wastewater effluents, and from agriculture, were discharged into water bodies and accumulated within the bed stream sediments. Thus, stock of historical contaminants have been buried in sediments at various depths and could be re-suspended through the increase of water flow. The thickness of sediments to be remobilized is highly dependent on sediment features, and will be strongly favoured by intense and sudden water discharges. In the context of climate change and increasing occurrence of heavy rainfalls, sediment stock from small streams will be more frequently re-suspended, with likely remobilization of deep and contaminated layers.
MOBISED project, taking advantage of the recent birth of a research cooperation network between Lorraine region and Luxembourg, aims to study the remobilization of sediments in a small river historically affected by mining and industrial activity (iron field of the North-east of France). Urbanization was subsequently associated with the development of highly industrialized areas, provoking contamination of surface waters with domestic wastewaters and urban run off.
The final objective of the project is to evidence the mechanisms involved in sediment remobilization and the consequences towards water quality. To achieve this goal, a multidisciplinary approach is proposed, involving (i) a precise and detailed characterization of sediments, including their chemical and physical properties, providing their contamination status as well as the nature and status of different kinds of contaminants (chemical and microbiological) (ii) a detailed description of hydroclimatology and river hydrodynamics (iii) experimental resuspension tests and high resolution sampling during several high flow events in order to obtain the distribution and composition of aggregates and contaminants in the water column and (iv) the monitoring of the riverbed morphology and the modelling of the sediment transportation.
The originality of MOBISED project lies in the combination of quantitative and qualitative approaches. Furthermore, different kinds of contaminants will be deeply investigated, in order to compare the behaviour of organic, metallic and bacterial species upon sediment remobilization. The chemical and microbial composition of bed sediments and suspended solids will be characterized at global, microscopic and molecular levels to provide insights in the sediment-contaminant interactions and the cohesive strength of sediments. Mineral, microbial and organic markers of streambed sediments as well as inflowing sediments will be researched in order to estimate the different sediment flows and implement the models.
The strengths of the MOBISED project are
- The development of a multi-technique approach at different scales.
- The differentiation and quantification of in-stream erosion sediments and in-flow sediments.
- The combination of laboratory and in-situ observations to evidence the selectivity of resuspension.
- The integration of qualitative data in the modelling of sediment transport.
- The application of a 3D-hydrodynamic approach to small size rivers.
- The modelling of cohesive sediment transport.

Project coordinator

Madame Emmanuelle Montargès-Pelletier (Laboratoire Interdisciplinaire des Environnements Continentaux)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CRPG/UMR 7358 Centre de Recherches Pétrographiques et Géochimiques
ANSES-LHN AG NAT SECUR SANIT ALIM ENV TRAVAIL
GEORESSOURCES/UMR 7359 Georessources
LCPME/UMR 7564 Laboratoire de Chimie Physique et Microbiologie de l'Environnement
CERGAPE/UL Centre d'Etude et de Recherche en Géographie de l'Aménagement des Paysages et de l'Environnement (CERGAPE/LOTERR)
CRP-GL Centre de Recherche Public - Gabriel Lippmann
LIEC/UMR7360 Laboratoire Interdisciplinaire des Environnements Continentaux

Help of the ANR 497,141 euros
Beginning and duration of the scientific project: October 2014 - 48 Months

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