Discussion of “Uncertainty of excess density and settling velocity of mud derived from in situ measurements” by M. Fettweis [Estuarine Coastal & Shelf Science 78(2), June 2008. doi: 10.1016/j.ecss.2008.01.007]

The author discussed an important issue in mud floc knowledge, which is the uncertainties in the measurements of excess density and settling velocity. He pointed out the lack of accuracy in measuring instruments, and the statistical nature of the variables. However, the author did not discuss the limitations of the theories and semi-empirical formula which he used. Some assumptions in the calculations also need to be discussed in more detail; and some calculations are not mathematically correct.