Aquatic Oxygen Calculations

1. Reaeration

Water surface reaeration can be a source or a sink for Dissolved Oxygen (DO) depending on the difference between the water surface and the air. It is computed using a first order function based on wind speed, water temperature, and elevation.

DOₛ = Kₐ₀(Cₛ - DOₛᵤᵣꜰ)/Z

2. Dissolved Oxygen Consumption

Dissolved Oxygen increases in the daylight due to photosynthesis and decreases at night due to respiration from fish, phytoplankton, and nitrification processes. The calculations for these consumptions are below:

Fish Respiration:

Fᴿ = 2014.45 + 2.75 Wₙ - 165.2 x Tₜ + 0.007 x Tₜ² - 0.21 x Wₙ x Tₜ

Phytoplankton Respiration:

DOₚᴿ = -1.133 + 0.0038 x SDD + 0.000014 x SDD² + 0.081 x Tₜ - 0.000749 x Tₜ² - 0.00035 x SDD x Tₜ

Nitrification:

Dₒₙᴿ = 4.57 x kₙᴿ x Nᴿ / V

3. Sediment and Organic Matter Oxidation

Sediment respiration rates and oxidation rates of organic matter are dependent on the water temperature relative to a reference temperature.

Sediment Respiration Rate:

DOₛₑₜ = Kₛₑₛ x θ x (Tₜ - Tᵣₑₜ) / Z

Oxidation of Organic Matter:

DOₘ = Kₒₘ x θ x (Tₘₐₘ - Tₘ) / Z