Bimodal diel dissolved oxygen curves and thermal stratification in polder ditches

In a polder ditch with a water depth of 50 cm, oxygen and temperature were measured continuously during 24 hours at 10 cm above the bottom and 10 cm below the surface. Two examples are given in which the diel oxygen curve of the lower electrode was bimodal. The curve of the upper electrode was unimodal in both cases. The occurrence of the bimodal curve could be explained by the turnover of the stratified water column after the surface started to cool in the late afternoon.