The effect of crab burrows on soil-water dynamics in mangroves

Many mangrove ecosystem services, such as carbon sequestration, are closely linked to mangrove soil water content, which in turn is thought to depend on animal burrow density and the properties of the sediment in which the burrows are constructed. We measured the water content in the sediment matrix between crab burrows across 26 plots in a typical, fine-grained (clay), mangrove soil in the Mekong Delta, Vietnam. We found that the water content of the sediment matrix remained more or less constant throughout the tidal cycle, and was independent of burrow density. Our results suggest that there is little exchange of water between the burrows and the associated sediment matrix and that burrows act as an independent pipe network transporting water through the mangrove soil. To check and extend our findings, we used a numerical groundwater model to simulate an idealized burrow in a range of sediment types. The model results confirmed that fine-grained mangrove sediments do not drain readily into adjacent animal burrows because of their very low permeability. Our results have important implications for understanding and forecasting mangrove carbon dynamics with sea level rise.