Geoscience Reference
In-Depth Information
4.1.5.2.5
Inorganic Phosphorus (Benthic)
∂
()
C
t
3
(
T
−
20)
(
T
−
20)
=
k
θ
a
(1
−
f
)
C
+
k
θ
f
C
(4.33)
1
PZD
4444
PZD
2
PC
4444
OP
3
4
1
OPD
44
OPD
2
44
D
8
3
8
∂
Algal decomposition
Mineralization
where
C
3
=
inorganic phosphorus concentration [mg P l
−1
]
k
PZD
=
anaerobic algal decomposition rate constant at 20
°
C [day
−1
]
θ
PZD
=
anaerobic algal decomposition rate temperature coefficient [none]
T
=
temperature [
°
C]
a
PC
=
phosphorus to carbon ratio [mg P mg
−1
C]
1
−
f
OP
=
fraction of dead and respired phytoplankton recycled to the phosphate
phosphorus pool [none]
C
4
=
phytoplankton carbon concentration [mg C l
−1
]
k
OPD
=
organic phosphorus decomposition rate constant at 20
°
C [day
−1
]
θ
OPD
=
organic phosphorus decomposition temperature coefficient [none]
f
D
8
=
fraction dissolved organic phosphorus [none]
C
8
=
organic phosphorus concentration [mg P l
−1
]
Sediment PO
4
3−
release rates for coastal marine environments are given in
4.1.5.3
Modeling of Silicon Cycle
Because silicon is the limiting nutrient for diatoms, its concentration is included in
eutrophication models as a state variable only if diatoms are simulated. The
EUTRO5, Eutrophication Module of WASP5, simulates total phytoplankton. There-
fore, silicon is not a state variable in EUTRO5. However, in the new version of the
WASP eutrophication module, the advanced eutrophication kinetics section will
allow modeling of three different algal species, one of which is diatoms. Therefore,
silicon will be a new state variable in the newer versions of WASP.
In some other eutrophication models, such as CE-QUAL-ICM,
56
CE-QUAL-
W2,
58
and CE-QUAL-R1,
57
silicon is a state variable.
CE-QUAL-W2
58
has two silicon state variables, namely, dissolved silicate and
particulate biogenic silica. Dissolved silicon is taken up by algae (diatoms and
epiphytes) for growth. In this model, no specific state variables are defined for
diatoms, blue-green algae, green algae, or any other group. However, the user can
assign algae groups by entering appropriate stoichiometric coefficients. For exam-
ple, if a nonzero value is assigned as the stoichiometric ratio for silica for an algal
group, that algal group will act as diatoms. In CE-QUAL-W2, the processes
considered for dissolved silica are adsorption of dissolved silica onto suspended
solids, particulate biogenic silica dissolution, respiration of algae/epiphyton, and
release of dissolved silica from sediment. Adsorption of dissolved silica onto
suspended solids is based on a partitioning coefficient. Dissolved silica is lost from
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