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Distinct seasonal differences in diurnal oxygen oscillations

Oxygen time series of an IGB-station monitoring River Spree upstream Berlin, germany, from April until December 1992.
The blue line shows measured oxygen data, the red line is the calculated saturation oxygen concentration ('Sättigungskonzentration'). The difference between the two lines indicate sub- or supersaturation.
Because there are shown hourly values, you see the whole range oxygen oscillated each day.
Diurnal changes are highest in spring during phytoplankton spring bloom ('Frühjahrsblüte'). When there is a net accumulation of the photosynthetically synthesized organic matter in the river, oxygen supersaturation occurs and oxygen is released from water into the atmosphere.
During clear water phase ('Klarwasserstadium') phytoplankton biomass in the river water decrease. Primary production also decrease, but respiration is high. So oxygen concentration falls deep below saturation, diurnal changes are low.
The summer phytoplankton bloom ('Sommerblüte') is charakterized by high diurnal oscillations. But only afternoon peaks sometime reach saturation, i.e. community respiration exceeds primary production all the summer. To some extend the organic substrates come from allochthonous sources: from upstream the section under investigation with better conditions for primary production or from terrestrial ecosystems.
In late autumn and winter diurnal changes are low, and the absolute oxygen values remain 2 - 3 mg/l below saturation.
For more information look at Böhme (1994a).

 Michael Böhme, Boehme@gmx.de

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