Preprint volume - SIBM

Pre-print Volume - Oral presentations
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
This requires the best-possible understanding of the processes and dynamics of a
system.
Geo-morphologically, the Mar Piccolo has two interacting basins with a double-layer
stratification in which we simulated the main bio-geo-physical processes related to
freshwater balance, salt budget, circulation exchange, vertical diffusion, light
attenuation, oxygen budget, nitrogen, phosphate and silicate budget, total carbon
regeneration and primary production. In this paper, we show and discuss the details of
phytoplankton growth modelling inserted as a block into the more complex ecosystem
model (Caroppo et al., 2010). The ecological modelling of Mar Piccolo is based on the
simulation software EXTEND-Sim ”(http://www.extendsim.com/).
In order to reconstruct the whole dynamics of Mar Piccolo phytoplankton communities
we built a three-group phytoplankton box-model that fundamentally follows the
modified formulation of the Villefranche Bay model (Ross & Nival, 1976). The
purpose is to reproduce three major plankton groups dynamics (e.g. diatoms,
dinoflagellates, and phytoflagellates) in order to simulate the normal seasonal
succession observed into Mar Piccolo ecosystem. For this specific case, some
approximations have been introduced adding linearly growth and light (mean daily
values) coefficients and reproducing the succession as a reflection of the differences
between groups’ maximum nutrients assimilation rates. The fundamental equation for
phytoplankton growth (PP) is based on the main forcing variables (nutrients and light)
taking into account death (Km), respiration (Kr), and a constant grazing parameter
(Kg), as in the following form:
PP
2
( t)
= ( PP(
t−
1)
∗(
Mu+
Ligth(
t)
* KI)
−(
Km+
Kr)
* PP(
t−1)
− Kg*
PP(
t−1)
)) * dt + PP(
t−1)
Extend calculates the growth per time step (day) and integrates it over time. Nutrients
uptake is based both on new and regenerated nitrogen concentrations into the top layer
of the Mar Piccolo basin, such as:
Mu = Mu + Mu
Nnew
in which Mu parameters follow the Michaelis-Menten kinetics both for regenerated and
new nitrogen. The light-growth dependency is simulated introducing an attenuation
parameter (KI) that depends on the Total Suspended Matter concentration into the
upper layer of the basin. The mortality rate (Km) and respiration loss (Kr) are
considered both population dependent and group-specific. Also the grazing coefficient
(Kg) is here considered dependent on the population dynamic with a time delay that
allows simulating a simplified predator-prey population response. All calculations into
the model are expressed in grams of carbon per area. The results here reported are
based on preliminary simulations of the Mar Piccolo model components, calibrated by
using existing observational data directly collected by the IAMC-CNR of Taranto, or
obtained from literature, and local Authorities.
Results - The ecological model of Mar Piccolo is deterministic in the sense that it is
driven by its external inputs of meteorology, light, external salinity variations. The land
runoff, nutrient, and organic loading (BOD) are calculated using available observations
of these and of the river and aquifer flows (years 2002-2003). The phytoplankton
growth is driven by the light and nutrient conditions, modified by the circulation and
Nreg
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
109