Abstract
Our investigations in an estuarine tidal flat system of Nanakita River showed that the sediment organic content fluctuated continuously in stations where macrobenthos biota had been maintained stably for a few decades. This suggests dynamic equilibrium of sediment organic content in those stations. The cycle period and range of the variations in sediment organic content and its physical mechanisms differed distinctly between non-cohesive and cohesive sediments. At stations where sediment resuspension and wash-outs of sediment organic matter at spring tides did not occur regularly, the sediments were cohesive, hence stably maintaining higher sediment organic contents compared with stations with non-cohesive sediments. Based on these results, we proposed conceptual models for processes maintaining the dynamic equilibrium of sediment organic content and the relationship between frequency of sediment resuspension and long-term averages of sediment organic content. It is expected that the conceptual application of dynamic equilibrium of sediment properties enhances restorations of tidal flat ecosystems.
