408
13 Transport and Mixing in Coastal Ecosystems
In particular, the correlation coefficient between frequency, N, and chlorophyll
a at 2 m depth significantly increases with phytoplankton particle size. The
mean Brunt-Viiisiilii frequency was calculated as an index of buoyancy restoring
forces over the upper 50 m, i.e.:
dp
6.p
dz ~ 6.z'
(13.29)
in which 6.z = 50 m. A positive size-dependent relationship between phytoplankton biomass and the frequency, N, suggests that the observed variability
in the large size fraction can be explained by their residence time in the euphotic
zone.
For the case of more complicated ecosystems which comprise of sea, lagoon
and rivers, two or three-dimensional coupled hydrodynamic and biochemical
models are required. A classic example of such an ecosystem is the Venice
Lagoon, Adriatic Sea system (Bergamasco et al., 1998). Venice Lagoon, located
on the northern coast of the Adriatic Sea, has an area of about 450 km 2 , 75%
of which is very shallow (less than 2 m), and only three channels, deeper than
6 m, join the lagoon to the sea. Small rivers which flow into lagoon supply
nitrogen and phosphorus of agricultural, industrial and municipal origin.
Hydrodynamics of the lagoon-sea ecosystem were modelled using the Princeton Ocean Model (Mellor, 1991). The resulting circulation model allows the
simulation of the three-dimensional fields of velocity, temperature, salinity, and
density under the forcing induced by astronomical and meteorological tides,
winds, and thermal and evaporative fluxes. This model is coupled with the
biochemical model which describes an evolution of the concentration of various
substances (Bergamasco et al., 1995):
8Ci
at + U'VCi = 'V (Ki'VCi) + Si(C, t),
(13.30)
in which Ci is the concentration of a particular substance i, Ki is the corresponding diffusion coefficient, and Si are the parametric and functional expressions
for modelling of primary production. Simulation results include the spatial and
temporal variations of the concentration of nutrients (mg N/l), phytoplankton
(mg C/l) and oxygen (mg O2/1).
13.3 Dispersion of River Plumes
Rivers are the main conduits of water, particulate and dissolved organic and
inorganic matter from the continents to the oceans. When freshwater and nutrient materials pass through the estuary, they do not disperse instantaneously
into the adjoining ocean water, but rather form a buoyant plumes of river water
which, under the influence of the longshore current, flow along the coastline.
13 Transport and Mixing in Coastal Ecosystems
In particular, the correlation coefficient between frequency, N, and chlorophyll
a at 2 m depth significantly increases with phytoplankton particle size. The
mean Brunt-Viiisiilii frequency was calculated as an index of buoyancy restoring
forces over the upper 50 m, i.e.:
dp
6.p
dz ~ 6.z'
(13.29)
in which 6.z = 50 m. A positive size-dependent relationship between phytoplankton biomass and the frequency, N, suggests that the observed variability
in the large size fraction can be explained by their residence time in the euphotic
zone.
For the case of more complicated ecosystems which comprise of sea, lagoon
and rivers, two or three-dimensional coupled hydrodynamic and biochemical
models are required. A classic example of such an ecosystem is the Venice
Lagoon, Adriatic Sea system (Bergamasco et al., 1998). Venice Lagoon, located
on the northern coast of the Adriatic Sea, has an area of about 450 km 2 , 75%
of which is very shallow (less than 2 m), and only three channels, deeper than
6 m, join the lagoon to the sea. Small rivers which flow into lagoon supply
nitrogen and phosphorus of agricultural, industrial and municipal origin.
Hydrodynamics of the lagoon-sea ecosystem were modelled using the Princeton Ocean Model (Mellor, 1991). The resulting circulation model allows the
simulation of the three-dimensional fields of velocity, temperature, salinity, and
density under the forcing induced by astronomical and meteorological tides,
winds, and thermal and evaporative fluxes. This model is coupled with the
biochemical model which describes an evolution of the concentration of various
substances (Bergamasco et al., 1995):
8Ci
at + U'VCi = 'V (Ki'VCi) + Si(C, t),
(13.30)
in which Ci is the concentration of a particular substance i, Ki is the corresponding diffusion coefficient, and Si are the parametric and functional expressions
for modelling of primary production. Simulation results include the spatial and
temporal variations of the concentration of nutrients (mg N/l), phytoplankton
(mg C/l) and oxygen (mg O2/1).
13.3 Dispersion of River Plumes
Rivers are the main conduits of water, particulate and dissolved organic and
inorganic matter from the continents to the oceans. When freshwater and nutrient materials pass through the estuary, they do not disperse instantaneously
into the adjoining ocean water, but rather form a buoyant plumes of river water
which, under the influence of the longshore current, flow along the coastline.