Modelling of Aquatic Ecosystems

1
Modelling of Aquatic Ecosystems

• Exercise 4
• 01.04.2009

2
Model exercise 4.1
3
Model exercise 4.1

• State variables
• concentration of algae (C.ALG),
• zooplankton (C.ZOO)
• phosphate (C.HPO4), O2 (C.O2),
• suspended particulate organic matter (C.POM),
• sedimented particulate organic matter (D.POM)
• Considered processes
• growth of ALG on HPO4, growth of ZOO on ALG,
• respiration and death of ALG and ZOO,
• mineralization of POM and SPOM,
• sedimentation of POM
• Considered interface fluxes
• oxygen exchange with the atmosphere,
• turbulent mixing between epi- and hypolimnion,
• sedimentation from epi- to hypolimnion

4
How does Ecosim use Stoichcalc?

• See page 266, 14.2.1 for the explanation of the
  process function
• See page 140 table 8.8 for all relevant process
  equations.

Process name
gro.ALG lt- new(Class "process",
name "gro.ALG", rate
expression(k.gro.ALG
exp(beta.ALG(T-T0))
..), stoich as.list(nu"gro.ALG.NO
3",)) prevol T
Definition of the process rate depending on
several different parameters.
These are the stoichiometric coefficients!!! In
exercise two we entered the coefficients
ourselves. - Here it takes them from the
calculated nu matrix. Here Ecosim is using
Stoichcalc!
Is it volume per time? (F area per time!)
5
Why is it important that some stoichiometric
coefficients are defined as 0/?

• Due to biological reasons. For example
• If algae die they do not use any phosphorus.
  However, mathematically this can happen in the
  model due to the mass conservation principle if
  the concentration of P in POM is higher than in
  algae! Therefore, we need a restriction of the
  maximum turnover of algae into POM.
• Compare to last exercise (3.3)

6
How are the values YALG.death, YZOO.death
calculated?
Calculation paramY.ZOO.death lt- min(1,
paramalpha.N.ZOO/paramalpha.N
.POM,
paramalpha.P.ZOO/paramalpha.P.POM,
paramalpha.C.ZOO/paramalpha.C.POM)
With this function we check whether N,P or C are
limiting the turnover of dead algae or ZOO into
POM. If none of the POM concentrations is higher
than the algae/ZOO concentration, Y is set to
one. This means that all the algae/ZOO are turned
into POM.
7
What happens when the oxygen content of POM is
set to 0.5 gO/gPOM instead of 0.39 gO/gPOM?
One of the changes is that zooplankton needs O2
to die! This is biological nonsense.
-gt We need to extend the restriction for
Y.ZOO.death This is not as simple as for N,P and
C since there are more substances
involved. Another option is to introduce
different POMs for dead algae and dead
zooplankton.
8
How is the metalimnion represented by the model
(4.2)?
metalimnion lt- new(Class "link",
name "Metalimnion", from
"Epi", to "Hypo",
qadv.spec list(C.POM expression(v.sed.POMA))
, qdiff.gen expression(A/h.metaKz)) T
he metalimnion is represented by the link between
the Epi- and the Hypolimnion and not by a reactor
itself!