Biogeochemical Cycles - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 130

settling, and algal/epiphyton mortality. Biogenic silica is lost from the system
through settling. Dissolution of biogenic silica and sediment release of dissolved
silica processes include a temperature rate multiplier for temperature correction.
In CE-QUAL-R1, 57 there is only one state variable for the silicon cycle, dissolved
silica, that is incorporated into the third algal group (diatoms) during photosynthesis.
No silica recycling takes place in this model; thus, silica is lost from the system
once used by diatoms.
CE-QUAL-ICM 56 incorporates two siliceous state variables, available silica and
particulate biogenic silica. For practical purposes, available silica is equivalent to
dissolved silica although sorption of available silica to inorganic solids occurs.
Diatoms utilize dissolved silica and recycle both dissolved and particulate biogenic
silica through metabolic activities and predation. Particulate silica dissolves in the
water column or settles to the sediment. A portion of the settled particulate biogenic
silica dissolves within the sediment and returns to the water column as dissolved
silica. To present the adsorption of dissolved silica to the newly formed metal
particles, dissolved silica is partitioned into dissolved and particulate fractions
according to a linear adsorption isotherm.
The HEM-3D 90 model applies kinetic process descriptions from CE-QUAL-ICM.
Both models use the same predictive sediment submodel, described in the nitrogen and
phosphorus cycle modeling sections, to simulate the sediment release of dissolved silicon.
Dissolution rates of particulate biogenic silicon to dissolved silicon are presented
in Table 4.24.

4.1.5.4 Modeling of Dissolved Oxygen

WASP5 simulates dissolved oxygen and associated variables using the EUTRO5
module. The user can operate EUTRO5 at various complexity levels for dissolved

TABLE 4.24
Particulate Biogenic Si to Dissolved Si Dissolution Rate (day − 1 )

Min. Max. Avg. Location Reference As Cited in Explanation

0.127 0.177 Sacca di

Scardovari, Italy

Viel et al., 1991 Viel et al. 97 Anoxic

conditions,
in the
sediment

0.06 Chesapeake Bay Wollast, 1974 Cerco and

Cole 91

0.04 Chesapeake Bay Vanderborght et

al., 1977

Cerco and
Cole 91

0.017 Chesapeake Bay Grill and

Richards, 1964

Cerco and
Cole 91

0.03 Chesapeake Bay Cerco and Cole,

1994

Cerco and
Cole 91

Model value,
20°C