Effect of macropores on pore-water flow and soil conditions in salt marshes subject to evaporation and tides

Macropores such as crab burrows are commonly distributed in salt marsh sediments. They are well recognized to act as preferential flow paths, affecting physical and biogeochemical processes in salt marshes. While previous studies have examined the effect of macropores on pore-water flow in salt marshes, how and to what extent do macropores behave and interact with tide-induced flow and saturation-dependent soil evaporation remain unclear. This study conducted process-based and three-dimensional numerical simulations and examined effects of macropores on pore-water flow and soil conditions in salt marshes subject to evaporation and tides. The results demonstrate that in the marshes subject to inundating tides (tides flood marsh platform at high tides), macropores alter the pore-water flow and enhance the tide-induced water exchange between marsh soils and tidal water. Additionally, macropores increase the tidally averaged soil saturation in the shallow soil layer. As a result of higher soil saturation, soil evaporation is increased. In contrast, marshes subject to non-inundating tides (marsh platform is lower than high tidal level) do not show remarkable relationships with evaporation or soil saturation. Increases in the mean sea level increase soil saturation and reduce soil evaporation in marshes subject to inundating tides. These findings help to understand the chemical transport and soil conditions in salt marshes, which hold the key to protecting and restoring salt marshes.