Role of stratigraphy in governing pore water seepage from salt marsh sediments

Numerical modeling experiments have been used to study the effects of marsh stratigraphy on the seepage of pore water into tidal channels. If the mud‐sand contact lies at the elevation of the channel bottom and the hydraulic conductivity of the basal sand is at least an order of magnitude greater than the overlying mud, the locus of maximum seepage shifts from the tide line, as in a purely mud marsh, to the toe of the creek bank. The ratio of creek bank seepage to bottom seepage also shifts from greater than to less than one. Furthermore, as the ratio of the hydraulic conductivities of sand to mud increases, the ratio of the total seepage from the sand‐mud marsh to that from a pure mud marsh increases in a nonlinear fashion, reaching an asymptotic limit of about 20 at a conductivity ratio of about 1000. If the mud‐sand boundary is progressively lowered so that mud also lies beneath the channel, the seepage dynamics gradually revert toward those of a purely mud marsh. The ecological implications of these results for regularly flooded, low marshes are discussed.