Oxygen with Sediment

The unit models the effect of particulate BOD on the river's oxygen balance. The transfer of organic material and dissolved substances between the water column, the bed and the pore water is also simulated.

Description

The DISSOLVED OXYGEN module simulates the oxygen balance in the water column due to the decay of organic material, the nitrification of ammonia and reaeration from the atmosphere. BOD can also be present in the system in the form of particulate material which can settle on to the river bed and interact with the pore water. Particulate BOD, like dissolved BOD, is simulated using a fast and slow decay rate.

Particulate BOD settles in proportion to the amount of suspended solids that settles (see SEDIMENT). Initially the particulate BOD settles into the fluffy layer. As it decays it continues to exert an oxygen demand on the overlying water. However, once the fluffy layer is filled to its maximum capacity, excess material is passed into the consolidated bed layer where it continues to decay and exerts an oxygen demand on the entrained pore water. The module creates variable names which track the particulate BOD in the water column, fluffy layer and consolidated bed.

Dissolved substances (BOD, ammonia, nitrates, nitrites) are passed to the pore water from the water column in proportion to the amount of pore water which is entrained (see SEDIMENT). Dissolved BOD which is entrapped in the pore water will exert its oxygen demand within the pore water. The hydrolysis of organic nitrogen, the oxidation of ammoniacal nitrogen and nitrites, denitrification and the reduction of sulphates (see DISSOLVED OXYGEN ) are all simulated within the pore water. The module creates extra variable names to represent the substances in the pore water.

The module requires no additional data because all the necessary reaction rate data is declared in the DISSOLVED OXYGEN module.

General

The OXYGEN WITH SEDIMENT module must be run in conjunction with the DISSOLVED OXYGEN and SEDIMENT modules. If oxygen balance is being simulated in an estuary or coastal situation then the SALT module must be run as well because of the impact of salinity on saturated dissolved oxygen concentrations. Otherwise 1D Water Quality Solver will assume the model is simulating a river and the salinity is zero. If the simulation of the PHYTOPLANKTON module is required then the OXYGEN WITH SEDIMENT module must be included in the simulation.

The OXYGEN WITH SEDIMENT module simulates the following transported variable names:

• Suspended particulate fast BOD
• Suspended particulate slow BOD

The OXYGEN WITH SEDIMENT module also simulates the following variables:

• Pore water dissolved oxygen
• Pore water fast BOD
• Pore water slow BOD
• Fluffy particulate fast BOD
• Fluffy particulate slow BODBed particulate fast BOD
• Bed particulate slow BOD
• Pore water fast nitrogen
• Pore water slow nitrogen
• Pore water ammoniacal nitrogen
• Pore water nitrite-n
• Pore water nitrate-n
• Pore water hydrogen sulphide