|
Work Package 4:
Ecosystem Scale Modelling |
Objectives and technical aim
Objectives are to describe and predict carrying capacity, using ecological modelling. Ecosystem models with variable spatial resolution will be used, in order to combine hydrodynamics, biogeochemistry and shellfish population dynamics from multi-year simulations. The specific objectives, for each culture environment (Loch Creran, Waterford estuary, Eastern Scheldt), are
-(a) To integrate external forcing from watershed and coast in ecosystem scale models;
-(b) To simulate the major internal processes responsible for energy flow;
-(c) To describe and predict growth for relevant cultivated species, at resolutions that are adequate for fisheries and resource management.
The modelling framework will facilitate an assessment of carrying capacity based on a detailed understanding of the governing processes in different culture environments. Where applicable, a limited set of easily quantifiable ecosystem parameters will be developed as a simplified generic carrying capacity model.
|
Description
of the technical work
To model carrying capacities for the ecosystems listed above, the following tasks will be carried out:
(1) - Spatial framework for ecological modelling
The data (WP1, WP2) and tools (WP6) produced in KEYZONES will be used to define system boundaries (model domains) and areas which may be considered homogeneous, in order to set up a grid system for simulation.
(2) - Application and/or development of hydrodynamic models
Circulation and boundary conditions for our different culture environments will be simulated to allow the upscaling of the key processes to a larger scale ecosystem framework. The main objectives of the hydrodynamic modelling are to parameterize exchanges at the grid boundaries established for each system, and to force boundary exchange of water and water properties. Detailed hydrodynamic modelling will be based, where appropriate, on the well tested Delft3D package.
(3) - Description of ecosystem-scale processes
Modelling the interaction between the ecosystem and cultivated species requires the description of biogeochemical mechanisms which are important in energy supply to the target organisms. This requires a modelling approach which simulates the seasonality of key drivers of shellfish growth and mortality, such as chlorophyll, organic and inorganic particulate matter, dissolved oxygen and nutrients. The ecosystem scale simulations, which will be different for each culture environment, due to differences between systems, form a template for coupling the generic shellfish models and determining exploitation carrying capacity. The multi-year models will integrate processes (/including transport) using a time step of hours to days, and must therefore be coupled to models which simulate exchange (at the system boundaries) and circulation (within the bay) at a finer scale. The latter models typically run for short periods of time (months) with a few state variables. This will be done, as required, within one modelling platform (Delft3D), or between different modelling platforms (Delft3D for hydrodynamics and water quality, EcoWin2000 for ecological modelling).
(4) - Coupling of ecosystem-shellfish models
The shellfish models (WP3) will simulate physiology and growth in each main cultured species, and will be incorporated as objects in the ecosystem models - The EcoWin2000 model has been used for over 10 years in shellfish carrying capacity work in Ireland, China and Portugal. Only a part of the shellfish population is harvested, and therefore a carbon-based model simulating production per se is inadequate. The multi-year model will thus incorporate a standard population dynamics model, considering several cohorts, thereby linking with our socio-economic considerations (WP5 and WP6). The population model will be explicitly coupled to the biogeochemical model, and will impose allometric variations in growth and mortality for different cohorts. The multi-year simulations will account as fully as required for human interactions with the cultivated species. These models are powerful tools for holistic management of shellfish culture in the systems, but they are not designed to provide detailed information regarding management at the farm level. They will, however, provide results for food depletion in different areas of the ecosystems, categorized as model boxes, and so should be useful for site selection in broad terms. The philosophy for integration of the various modelling components will be as described in (3). The detailed multi-year ecosystem carrying capacity models will be validated by
- (i) A mass-balance approach;
- (ii) Against field data (using both spatial and temporal distributions and budgets). |
Installation instructions and a brief overview for B2K
are located here
