Biogeochemical Cycles - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 131

oxygen simulation. Five state variables (dissolved oxygen, ultimate carbonaceous
biochemical oxygen demand, ammonia, nitrate, and phytoplankton carbon) are used
directly for dissolved oxygen balance calculations. Six processes related to dissolved
oxygen are considered. These processes are atmospheric reaeration, oxidation of
carbonaceous BOD, nitrification, sediment oxygen demand, phytoplankton growth,
and phytoplankton respiration.
In EUTRO5, the user can specify a single reaeration rate for the entire model
network, specify spatially variable reaeration rates, or let the model calculate the
reaeration rates. The model calculates both a flow- and a wind-induced reaeration
rate, and uses the larger value of the two. In the new version of WASP (WASP 6.x
developed by Wool et al. 101 ), another option for the reaeration calculation is provided
that sums up the flow- and wind-induced reaeration rates.
The kinetic expression for carbonaceous BOD oxidation in EUTRO5 contains
a first-order rate constant, an Arrhenius-type temperature correction factor, and a
Monod-type low dissolved oxygen correction function. The low dissolved oxygen
correction simulates the decline of aerobic oxidation rate as the dissolved oxygen
concentration approaches zero. The user specifies the half-saturation concentration
for dissolved oxygen, K BOD . Otherwise, the default value for this concentration is
zero in the model, allowing the reaction to proceed fully even under anaerobic
conditions.
AQUATOX 73 can simulate the effects of algae (either phytoplankton or periph-
yton), macrophytes, and animals on dissolved oxygen concentration. Algae and
macrophytes produce oxygen during photosynthesis and consume oxygen via res-
piration. Oxygen utilization during respiration of animals (zooplankton, benthic
invertebrates, benthic insects, and fish) is expressed as the sum of endogenous
respiration and dynamic action terms. Detritus is divided into eight compartments,
each of them contributing to dissolved oxygen consumption. The sum of organism
respiration plus detritus decomposition is defined as BOD in this model.
The processes included in the model developed by Park and Kuo 69 are the same
as those in EUTRO5. Although there is no low dissolved oxygen correction function
for carbonaceous BOD oxidation, such a correction function is included in the SOD
calculations in this model.
In CE-QUAL-W2, 58 epiphyte oxygen production via photosynthesis is also con-
sidered in addition to algal dissolved oxygen production. Five state variables used to
simulate organic matter include labile dissolved organic matter, refractory dissolved
organic matter, labile particulate organic matter, refractory particulate organic matter,
and carbonaceous BOD. Each of these five has different decay rates. Decay of organic
matter is allowed only when the dissolved oxygen concentration is greater than zero.
In CE-QUAL-R1, 57 oxidation of reduced anaerobic by-products (Fe 2+ , S 2− , Mn 2+ ),
macrophyte photosynthesis and respiration, and zooplankton and fish respiration are
modeled along with atmospheric reaeration, decomposition of labile and refractory
dissolved organic matter, algal photosynthesis and respiration, nitrification, sediment
decomposition, and detrital decomposition. Simultaneous oxidation and reduction
processes are initiated or suspended by the model when a given dissolved oxygen
concentration is reached. If the dissolved oxygen concentration falls below this given
concentration, reduction processes and sediment release of ammonium, phosphate,