Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

FP5

METROL Berichtzusammenfassung

Project ID: EVK3-CT-2002-00080
Gefördert unter: FP5-EESD
Land: Netherlands

A web based diagenetic reaction-transport Model to model anaerobic oxidation of methane

Anaerobic oxidation of methane (AOM) consumes around 80% of methane produced in marine sediments. Although the process was first documented three decades ago, significant progress in the mechanistic understanding of AOM has only occurred in the last few years. Given the vast methane reservoirs below the sea floor, the potential role of AOM in the regulation of atmospheric carbon stocks is widely recognized. Accordingly, one of the main aims of METROL is to characterize and model methane dynamics in ocean margin sediments.

The main goal of the modelling component was to integrate experimental and field data into tractable research and predictive modelling tools.

Reactive transport models (RTM) provide a mathematical means of coupling physical and biogeochemical processes within a single interpretative framework. RTMs are the most powerful tool presently available to advance our scientific understanding of the dynamic interplay between fluid flow, constituent transport and biogeochemical transformations. By integrating experimental, observational and theoretical knowledge about geochemical, biological and transport processes into mathematical formulations, RTMs provide the ground for prognosis.

Models of variable complexity are developed to:
- Quantitatively interpret observed methane and sulfate profiles in marine sediments;
- Determine the sensitivity of methane turnover in marine sediments on bioenergetic and kinetic limitations of the resident microbial communities;
- Predict the response of methane fluxes in ocean margin sediments to changes in environmental forcing.

Current status
A microbial growth model for AOM in coastal marine sediments has been developed. The model includes a comprehensive reaction network describing the production and consumption of methane, it explicitly represents the microbial biomasses and accounts for the thermodynamic limitations on the microbial reaction pathways.

Semi-theoretical methods are used to constrain the microbial growth parameters. The model and the results of a global parameter sensitivity analysis are available to the scientific community (Dale et al., in press).

One-dimensional reactive transport models have been developed within the BRNS (Biogeochemical Reaction Network Simulator) environment. The BRNS is a flexible, web-based modelling platform that consists of a MAPLE pre-processor, containing an automated procedure for generation of executable model (Automatic Code Generator, ACG) and a numerical engine of standard routines for solving non-linear partial differential equations. The ACG translates user-specified information (physical dimensions and parameters, state variables, reaction stoichiometries, rate equations, equilibrium constraints and boundary conditions), and can be linked to an AOM-specific, web-based Knowledge Base (KB). The BRNS-KB modelling tools can be accessed on-line via www.geo.uu.nl/~rtm.

A baseline BRNS model incorporating a simple reaction description of AOM is available via the METROL web page. This model allows for a rapid analysis of methane and sulfate pore water profiles in sediments, and an estimation of the rate of AOM. A series of increasingly more complex reaction network models have also been coupled to transport equations in the BRNS, and are the subject of forthcoming publications. Via the above web-link, potential users can built their own reaction network, or modify an existing one.

Key results
The most sensitive growth-related and kinetic parameters influencing the annual rate of AOM in nearshore marine sediments are those corresponding to hydrogenotrophic sulfate reduction and acetotrophic methanogenesis. Reactive transport calculations indicate that thermodynamic limitations play a major role in controlling the distributions of AOM rates in sediments.

Integrated AOM rates in the Kattegat, Skagarrrak and Aarhus Bay are independent of water depth. As shallow waters usually have higher rates of organic carbon deposition this is an unexpected finding. In all three areas, the free gas depth appears to be the main factor determining the depth of the sulfate-methane transition zone (SMTZ) and the integrated AOM rate. In a general sense, the BRNS models predict that the closer the SMTZ is located to the sediment-water interface, the higher the integrated rate of AOM.

Preliminary model exploration in the Bornholm Basin implies that he physical transport of methane and sulfate is the controlling factor in AOM. Ongoing model simulations will show whether this relationship is universally valid for gas-charged sediments.

Key innovations
Implementation of the BRNS to unravel the relative roles of environmental forcings (esp. organic matter input and temperature), microbial growth, thermodynamic driving forces and transport processes, in controlling AOM in ocean margins.

Application of a global sensitivity analysis to the complex geomicrobial AOM reaction system.

Verwandte Informationen

Reported by

Utrecht University
P.O. Box 80021
3508 TA Utrecht
Netherlands
Folgen Sie uns auf: RSS Facebook Twitter YouTube Verwaltet vom Amt für Veröffentlichungen der EU Nach oben