LAUSR

Purpose Two models serve to explain organic matter (OM) bioavailability in soil through the nature of the OM and/or its degree of attachment to the organo-mineral matrix. This work directly measures the extracted aerobic biomineralization of OM pools in order to determine the model more heavily affecting bioavailability in dam sediment. Materials and methods The OM from four dam sediments was extracted according to a physicochemical sequential protocol. For each step, an extracted phase and a residual phase were recovered. These extraction steps were then coupled with biochemical oxygen demand (BOD) measurements over a 20-day period. The BOD is measured as follows: (i) on the total sediment; (ii) on the residual phase, thus allowing for a BOD determination of the OM linked to the matrix (OM L ); and (iii) on the extracted free OM (OM F ). Results and discussion The total sediment BOD cannot be correlated with either the total extracted carbon or global C/N ratio. The BOD of each OM L has been assessed, revealing that the labile phase achieves the highest rate of aerobic biodegradability (2.3 mgO 2 /mgC), while contributing a small portion to total sediment biodegradability (6 to 22%). The other phases contributing to sediment biodegradability are particulate phase (labile) > weakly linked phase > strongly linked phases, with a corresponding contribution to BOD of 15–46% > 22–41% > 0–30%. An analysis conducted on the OM F shows that the BOD rates of the strongly linked phases are equivalent to those of the labile phases. Conclusion Organic matter bioavailability and, hence, its biodegradability are mainly affected by the strength of interaction with the organo-mineral matrix. The C/N ratio subsequently alters the biodegradability of bioaccessible OM from dam sediment.