suggests that inorganic C was higher in excavated soil than that in deposited soil. This difference also implies that excavating activities accelerated the mineralization of the organic matter from organic C to inorganic C, as observed in previous studies (for example, Otani and others 2010). Alternatively, excavated sediments might be richer in carbon carbonate relative to the deposited ones because of the differences in the selectivity between trapping (selective) and excavating (non-selective) processes (see below for more). In addition, deposition into burrows was repeatedly flooded by tidal water, which resulted in a great loss of carbonate. Thus, the total C concentration of the excavated soil significantly exceeded that of the deposited soil and background soil