The Nutrient Simulation Module I (NSMI) is capable of simulating algae, nutrient, and oxygen cycling. NSMI can model up to 15 water quality constituents (state variables) in the water column, as listed in below table. This module allows users to selectively activate or deactivate any state variable, providing flexibility in its application. When a state variable is activated (on), NSMI computes associated pathway fluxes, when deactivated (off), no pathway fluxes are computed for that variable. If a state variable is bypassed, the user does not need to provide input parameters, boundary conditions, or initial conditions. However, the water quality model results may not be reasonable when some of these state variables are deactivated due to interactions among them. Therefore, care must be taken when turning off these state variables.
Concentrations of constituents are expressed in milligrams per liter (mg L-1). Symbols abbreviated as Chl, D, C, N, P and O2 refer to the weights of chlorophyll-a, dry biomass, carbon, nitrogen, phosphorus, and oxygen, respectively.
List of water quality state variables included in NSMI
Name | Definition | Units | Option |
Ap | Algae | µg-Chla L-1 | On/Off |
Ab | Benthic algae | g-D m-2 | On/Off |
OrgN | Organic nitrogen | mg-N L-1 | On/Off |
NH4 | Ammonium | mg-N L-1 | On/Off |
NO3 | Nitrate | mg-N L-1 | On/Off |
OrgP | Organic phosphorous | mg-P L-1 | On/Off |
TIP | Total inorganic phosphorous | mg-P L-1 | On/Off |
POC | Particulate organic carbon | mg-C L-1 | On/Off |
DOC | Dissolved organic carbon | mg-C L-1 | On/Off |
DIC | Dissolved inorganic carbon | mol L-1 | On/Off |
CBODi | Carbonaceous BOD group | mg-O2 L-1 | 0-10 |
DO | Dissolved oxygen | mg-O2 L-1 | On/Off |
N2 | Dissolved Nitrogen Gas | mg-N L-1 | On/Off |
PX | Pathogen | cfu (100 mL)-1 | On/Off |
Alk | Alkalinity | mg-CaCO3 L-1 | On/Off |
Schematic of the state variables and kinetic processes in NSMI provides an overview of the state variables and processes modeled by NSMI. Aquatic plants are divided into two broad categories: (1) those that move freely with water (floating algae) and (2) those that remain fixed or attached to the bottom (benthic algae). Both forms of algae are included in NSMI. Organic nitrogen, phosphorous and carbon are simulated as a single type of detrital organic matter, each with different parameters for decomposition and settling. In NSMI, Alkalinity (Alk) and Pathogen (PX) do not affect the other water quality state variables in the water column. Carbonaceous Biological Oxygen Demand (CBOD) impacts dissolved oxygen (DO), while the remaining water quality state variables interact with one another.
Schematic of the state variables and kinetic processes in NSMI