ALBERT

Description: A mixing model derived from first principles describes the bulk density (BD) of intertidal wetland sediments as a function of loss on ignition (LOI). The model assumes the bulk volume of sediment equates to the sum of self-packing volumes of organic and mineral components or BD = 1/[LOI/ k 1 + (1-LOI)/ k 2 ], where k 1 and k 2 are the self-packing densities of the pure organic and inorganic components, respectively. The model explained 78% of the variability in total BD when fitted to 5075 measurements drawn from 33 wetlands distributed around the conterminous United States. The values of k 1 and k 2 were estimated to be 0.085 -±0.0007 g cm −3 and 1.99 ± 0.028 g cm −3 , respectively. Based on the fitted organic density ( k 1 ) and constrained by primary production, the model suggests that the maximum steady state accretion arising from the sequestration of refractory organic matter is ≤ 0.3 cm yr −1 . Thus, tidal peatlands are unlikely to survive indefinitely a higher rate of sea-level rise in the absence of a significant source of mineral sediment. Application of k 2 to a mineral sediment load typical of East and eastern Gulf Coast estuaries gives a vertical accretion rate from inorganic sediment of 0.2 cm yr −1 . Total steady state accretion is the sum of the parts and therefore should not be greater than 0.5 cm yr −1 under the assumptions of the model. Accretion rates could deviate from this value depending on variation in plant productivity, root:shoot ratio, suspended sediment concentration, sediment-capture efficiency, and episodic events.