366 Nadia Pinardi et al.
17.5.2 The ecosystem modeling
Large and coastal scale ecosystem models have been developed during the past
two decades. Experimental evidence in the last decade has shown how important is
the coupling between physical conditions and pelagic food web processes (McGillicuddy et al., 1998). Thus a major effort has been put in the three-dimensional coupling of hydrodynamics and biogeochemical cycles and its numeric al
representation. At the same time, laboratory and field observations have empirically determined trophic interaction rates within functional group parameterizations of the marine food web. For an overview of ecosystem modeling see Hoffman
et al.(1998). Here we will try to outline some basic formalism used in complex ecosystem models such as the European Regional Seas Ecosystem Model (ERSEM)
described in Baretta et al. (1995) and Vichi (1998).
The basic equations describe the rate of change of an ecosystem state variable
C(x,y,z,t) as composed oftwo parts:
ac aCI aCI
at=atp+at B
(29)
where the P subscript defines the time rate of change due to physical processes and
the B subscript indicates the rate of change due to biochemical processes. In the
model of Baretta et al. (1995) C represents concentrations of chemical elements
either dissolved in the water or in the functional organism groups. Chemical constituents and their rate of change describe the organisms and its evolution in each
functional group. The chemical currencies considered up to now are carbon, C,
nitrogen, N, phosphorus, P, and silica (Si). Naturally this list should be enlarged to
consider various calcium (Ca), iron (Fe) and other nutrients which are already
known to limit phytoplankton growth in certain open ocean areas.
The physical rate of change is written in general terms as:
~~Ip = -u· VC+ V· (KhVC) + ;z( Kv~~)
(30)
The particle sedimentation velocity could augment the vertical part of the advection term ifthis is relevantly different from fluid velocity. Advective effects in ecosystem equations have been studied theoretically by Robinson (1997) and
differentiated from biochemical rate terms.
The time rate of change due to biological processes is given by a complex food
web representation for both the pelagic and benthic compartments and it is here
reproduced in Fig. 17.9a. The model contains dissolved nutrients described above
and ammonium, a representation of the pelagic phytoplankton functional group
subdivided into different size classes, a pelagic bacteria group, dissolved and particulate organic matters, mesozooplankton and dissolved gases compartment. The
pelagic environment interacts with the physical environment not only through the
advection and diffusion processes but also responding to the temperature and salinity field values, as indicated in Fig. 17.9b. Another important coupling with the
17.5.2 The ecosystem modeling
Large and coastal scale ecosystem models have been developed during the past
two decades. Experimental evidence in the last decade has shown how important is
the coupling between physical conditions and pelagic food web processes (McGillicuddy et al., 1998). Thus a major effort has been put in the three-dimensional coupling of hydrodynamics and biogeochemical cycles and its numeric al
representation. At the same time, laboratory and field observations have empirically determined trophic interaction rates within functional group parameterizations of the marine food web. For an overview of ecosystem modeling see Hoffman
et al.(1998). Here we will try to outline some basic formalism used in complex ecosystem models such as the European Regional Seas Ecosystem Model (ERSEM)
described in Baretta et al. (1995) and Vichi (1998).
The basic equations describe the rate of change of an ecosystem state variable
C(x,y,z,t) as composed oftwo parts:
ac aCI aCI
at=atp+at B
(29)
where the P subscript defines the time rate of change due to physical processes and
the B subscript indicates the rate of change due to biochemical processes. In the
model of Baretta et al. (1995) C represents concentrations of chemical elements
either dissolved in the water or in the functional organism groups. Chemical constituents and their rate of change describe the organisms and its evolution in each
functional group. The chemical currencies considered up to now are carbon, C,
nitrogen, N, phosphorus, P, and silica (Si). Naturally this list should be enlarged to
consider various calcium (Ca), iron (Fe) and other nutrients which are already
known to limit phytoplankton growth in certain open ocean areas.
The physical rate of change is written in general terms as:
~~Ip = -u· VC+ V· (KhVC) + ;z( Kv~~)
(30)
The particle sedimentation velocity could augment the vertical part of the advection term ifthis is relevantly different from fluid velocity. Advective effects in ecosystem equations have been studied theoretically by Robinson (1997) and
differentiated from biochemical rate terms.
The time rate of change due to biological processes is given by a complex food
web representation for both the pelagic and benthic compartments and it is here
reproduced in Fig. 17.9a. The model contains dissolved nutrients described above
and ammonium, a representation of the pelagic phytoplankton functional group
subdivided into different size classes, a pelagic bacteria group, dissolved and particulate organic matters, mesozooplankton and dissolved gases compartment. The
pelagic environment interacts with the physical environment not only through the
advection and diffusion processes but also responding to the temperature and salinity field values, as indicated in Fig. 17.9b. Another important coupling with the