Primary production model

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Primary production in streams and rivers - Model
Macrophytes, phytoplankton and/or algae attached at the river bottom synthesize organic matter and release oxygen into the water in dependence on the available light. The oxygen concentration in the river water increase. The process is shown as gross primary production (BPP). During night, there is no photosynthesis.
The community respiration (Resp) is the respiration of the primary producers and all the other bacteria, fungi, and animals in the river (=total ecosystem respiration). Respiration reduce the oxygen concentration in the river water. Respiration is assumed to be constant over the entire 24 h day. Diurnal oxygen curves of some natural like streams and rivers show, that at least during the night there are often only low changes in the respiration rate.

The resultant oxygen concentration is shown by the blue graph.

Atmospheric oxygen exchange (K₂(Cs-C)) cause a decrease of the difference between oxygen saturation concentration and the real oxygen concentration dissolved in the river water. The atmospheric oxygen exchange coefficient is calculated according to WOLF (1974), where the value of K depends on the flowing velocity (V), the depth (H) of the channel, and the roughness of the river bed (M, for Manning-coefficient): K₂(20°C) = (3 + 40/M) * V/H² + H/2.
Temperature dependence of K could be calculated by K₂(t) = K(20°C) * C^(t-20) assuming C is 1.024 (TSIVOGLOU et al. 1976).

Michael Böhme, Boehme@gmx.de

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