Biota (EEMS12)

EEMS allows users to simulate an unlimited number of algal and macrophyte groups, with each group assigned different parameters, such as half-saturation constants and uptake rates for nutrients according to the aquatic ecosystem model. To open the Macrophyte and Algae Options frame, RMC on the Biota option under Water Quality Model Control (Figure 1).  In the  Macrophyte and Algae Options frame, the algae and macrophyte parameters are classified following their kinetics processes. Depending on what is being simulated, the following tabs are displayed: General, Growth, Basal Metabolism, Predation, Diagenesis Linkage, and Vertical Migration, each of which is summarized below. 

Figure 1.  Water Quality Model Control.

1. General 

In the General tab (Figure 2), users can define the number of algae and macrophyte groups simulated in the model.  Users can also input the name and different general parameters for each group.

If an algal group is defined as a macrophyte, the Is Mobile box needs to be unchecked. The Fixed Biota subtab will be displayed and allow users to modify additional parameters and options for modeling the macrophyte.

Figure 2. Macrophyte and Algae Options: General.

2. Growth

The process of algae growth is described in the Growth tab (as shown in Algae and Macrophyte Options#Figure 3) with growth parameters and optimal temperature options. 

Figure 3. Macrophyte and Algae Options: Growth.

3. Basal Metabolism

Algae and Macrophyte Options#Figure 4 shows the Basal Metabolism tab, which includes General Options, Basal Metabolism Nutrient Fractions, Algae DOC Excretion, and Optimal Temperature Options. 

Figure 4. Macrophyte and Algae Options: Basal Metabolism.

4. Predation

Algae and Macrophyte Options#Figure 5 shows the Predation tab. If the checkbox for Winter Bloom in General Options is checked, the Optimal Temperature Options will be enabled. 

Figure 5. Macrophyte and Algae Options: Predation.

5. Vertical Migration

The EEMS 12 offers a modeling feature to simulate the vertical migration of algae, which is beneficial for algae bloom management and mitigation. Four options are available to determine the settling velocity of cyanobacteria and any other algal species.

Figure 6a shows the Vertical Migration subtab with the Constant Velocity approach, which is set as the default option in EE.

Figure 6a. Macrophyte and Algae Options: Vertical Migration - Constant Velocity (default option).

Figure 6b shows the setup for the Daily Cycle Velocity model option.  In this model, only the amplitude and phase shift of the cosine function are needed as input parameters.

Figure 6b. Macrophyte and Algae Options: Vertical Migration - Daily Cycle Velocity.

Users also can select the Daily Cycle Velocity with Depth-varying Light Effects option by checking the box Include Dept-varying Light Effects as shown in Figure 6c.

Figure 6c. Macrophyte and Algae Options: Vertical Migration - Daily Cycle Velocity with Depth-varying Light Effects.

Figure 6d shows the setup for the Dynamic Velocity model, based on Visser et al., 1997, which is the most advanced option in EE for the modeling of algae vertical migration.

Figure 6d. Macrophyte and Algae Options: Vertical Migration - Daily Cycle Velocity with Depth-varying Light Effects.

6. Fixed Biota

From EFDC+ 11, the kinetic of immobile or attached algae (macrophyte) is handled to grow upward from the bed layer through model layers. This feature provides an extension from the modeling of submerged macrophytes, which is originally attached and exists only at the bottom layer, to a suspended canopy such as suspended aquaculture farms. The attached algae parameter is presented in the Fixed Biota tab ( as shown in Algae and Macrophyte Options#Figure 7). A layered threshold value of biomass concentration is specified. The macrophyte growth upward is accomplished by moving the biomass of a layer to the layer above if the concentration in the layer is greater than a threshold concentration and the concentration in the upper layer is less than the same threshold concentration. Note that the Maximum Length/Height is only considered when the Threshold to Allow Growth Between Layers is set to zero.

The feedback of macrophyte growth and its density on the hydrodynamics is also optionally considered by checking the box Use Feedback to the Hydrodynamics in Hydrodynamic Feedback frame.

Figure 7. Macrophyte and Algae Options: Fixed Biota