Abstract
Micro-structure in sediments of a tidal river, which is composed of microsites of various ranges of Eh level, is experimentally investigated. At first, the cytochrome oxidase activity in the sediments is measured to study the distribution of aerobic microorganisms. Sediments with a high ignition loss are high in the activity and dense in aerobic microsites down to 5mm from the water-sediment interface. On the other hand, those with a low ignition loss are low in the activity and rather disperse in aerobic microsites down to 4cm from the interface. Secondly, the reduction of tetrazolium salts in the sediments is examined to obtain distributions of reduced microsites. The results indicate that they exist patchy in the oxic and anoxic parts of the sediments and their spacial ratio increases with depth. Finally, Eh in the sediments is measured with handmade micro-electrodes with 17μm in tip diameter and 500μm in length, whose dimension is the same size or smaller than the average size of the microsites. The values of Eh measured in vertical and horizontal planes of the sediments range from positive to negative values.
