Geoscience Reference
In-Depth Information
Mineralization from organic to inorganic phosphorus is affected by temper-
ature and phytoplankton population, and thus the following relation for
K
OP
is used:
C
Phy
k
mPc
T
−
20
K
OP
=
K
OP
(
20
)θ
(12.87)
OP
+
C
Phy
where
θ
OP
is the temperature coefficient for organic phosphorus mineralization,
about 1.08.
Again, the settling term in Eq. (12.85) is valid only in the 1-D and depth-averaged
2-D models, and it has a different form in the 3-D and width-averaged 2-D models,
as shown in Eq. (12.63).
Flux exchanges between water column and benthic sediment
Settled waste materials (sludge), phytoplankton, dead aquatic plant roots and leaves,
etc., that accumulate in the bed usually undergo decomposition, releasing nutrients to
the sediment interstitial water and removing oxygen from the overlying water. As a
result, the benthic sediment can be a substantial nutrient source and/or oxygen sink
to the overlying water column.
SOD and nutrient fluxes from the bed depend on the extent of organic materials
and the nature of the benthic community. Table 12.1 summarizes the range of SOD
values at 20
◦
C. Temperature effect in the 10-30
◦
C range can be accounted for by
T
−
20
S
SOD
(
T
)
=
S
SOD
(
20
)θ
(12.88)
sod
where
has a reported range of 1.040 to 1.130 (Zison
et al
., 1978) and a typical
value of 1.065. However, Eq. (12.88) probably overestimates below 10
◦
C, and SOD
approaches zero in 0-5
◦
C.
Many early models give lumped values for the oxygen and nutrient fluxes, without
resolving the details of the benthic processes. More recently, the following diffusion
θ
Table 12.1
Sediment oxygen demand ranges (Huber, 1993)
Location
SOD range
Source
gO
2
·
m
−
2
day
−
1
Municipal sewage sludge, outfall vicinity
2-10
Thomann and M. (1987)
Municipal sewage sludge, aged, d/s of outfall
1-2
Thomann and M. (1987)
Estuarine mud
1-2
Thomann and M. (1987)
Sandy bottom
0.2-1
Thomann and M. (1987)
Mineral soils
0.05-0.1
Thomann and M. (1987)
Measured in rivers and streams
0.02-44
Bowie (1985)
Measured in estuaries and ocean
0.1-11
Bowie (1985)
Measured in lakes and reservoirs
0.004-9
Bowie (1985)
