THE EFFECT OF REAERATION AND BENTHIC ALGAE ON THE OXYGEN BALANCE OF AN ARTIFICIAL DITCH

In an artificial ditch, receiving a low nutrient input, processes affe cting DO (dissolved oxygen) were measured. Estimated process parameter s were implemented in a dynamic model to simulate continuously measure d DO. The processes modelled were primary production, respiration, sed iment oxygen demand and reaeration. Primary production by a benthic la yer of algae was found to dominate the oxygen balance. The contributio n of reaeration was also large, even at the observed oxygen concentrat ions which were close to equilibrium. Adaptation to ambient light cond itions was introduced in the description of benthic primary production . The reaeration coefficient was related to the continuously measured wind velocity. This resulted in a good agreement between simulated and measured DO concentrations, with a model efficiency of 89%.