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

Abstract

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.

Randomly Distributed Crab Burrows Enhance Groundwater Flow and Salt Transport in Creek‐Marsh Systems

“…This result may provide explanation for the field observations conducted by Arnaud et al. (2022), that the impact of crab burrows on groundwater drainage in the salt marsh cannot be easily observed.…”

“…Note that even in the burrowed marsh, the lowest saturation in the sediment at the monitor location (x = 2.555 m. z = 0.9 m) was 0.97, indicating only 3% porewater has been drained. This result may provide explanation for the field observations conducted by Arnaud et al (2022), that the impact of crab burrows on groundwater drainage in the salt marsh cannot be easily observed.…”

“…However, a recent study by Arnaud et al. (2022) argued that crab burrows act as an independent pipe network that has little exchange of water with the surrounding sediment matrix in a typical, fine‐grained (clay), mangrove soil in the Mekong Delta, Vietnam. Further, they supported this argument by simulating groundwater flow through an idealized burrow, finding that the sediments did not drain readily into the crab burrows because of their very low permeability.…”

“…For example, most studies confirm that crab burrows provide preferential flow conduits that promote vertical hydraulic connectivity between the overlying water and sediment porewater, thus enhancing solute transport (e.g., Harvey & Nuttle, 1995;Xu et al, 2022). However, a recent study by Arnaud et al (2022) argued that crab burrows act as an independent pipe network that has little exchange of water with the surrounding sediment matrix in a typical, fine-grained (clay), mangrove soil in the Mekong Delta, Vietnam. Further, they supported this argument by simulating groundwater flow through an idealized burrow, finding that the sediments did not drain readily into the crab burrows because of their very low permeability.…”

Effects of Large Macropores on Saline Water Evaporation From Marsh Soil

“…In natural salt marshes, macropores are irregular in geometry and depth. As reported by Arnaud et al (2022), macropores may have more than one opening and connect the marsh platform to tidal creeks, resulting in complex water exchange between macropores and surrounding soil. In addition, it has been reported that the impact of salt precipitation on evaporation is related to the type of efflorescence (i.e., crusty and patchy) (Eloukabi et al, 2013).…”