Silicate

The unit models silicate as a nutrient for algal growth.

Description

All algae and plants need small amounts of silicate in order to grow. Certain types of phytoplankton (particularly diatoms) use silicon to strengthen their cell walls. The availability of silicates is therefore crucial to their growth. When such species are dominant, silicate becomes a limiting nutrient.

Silicon is most readily available for biological uptake as soluble orthosilic acid. This is derived from the breakdown of silicate polymers originating from soil runoff. Silicon is also recycled from the decay of dead diatoms. Conventionally, this available form of silicon is measured in terms of its equivalent silica concentration.

In the 1D Water Quality Solver, silicate is modelled as a dissolved substance. It limits algal growth by a Michaelis-Menten relationship in the same way that phosphates and nitrates do. When the MACROPHYTES and/or BENTHIC ALGAE units are being simulated with the PHYTOPLANKTON module then the SILICATE module tracks the detrital silicon in the water column and on the bed.

General

The SILICATE module must be run in conjunction with the PHYTOPLANKTON module. The SILICATE module simulates the transported variable names:

• Silicate (mg/l)
• Detrital silicon (mg/l)

The SILICATE module simulates the following variable names on the bed:

• Pore water silicate (mg/l)
• Fluffy detrital silicon (g/m²)
• Bed detrital silicon (g/m²)