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

Macropores created by crab burrowing are commonly found in vegetated coastal wetlands. However, their impact on surface water‐groundwater interactions and salt transport is insufficiently understood. In this study, we used numerical models to quantify the impact of crab burrows with random spatial distribution, morphology, and openings on groundwater flow and salt transport in creek‐marsh systems. Results showed that these burrows can lead to a more complex network of preferential flow paths and burrow flushing capabilities than those with a single pipeline. The velocity magnitude varied over seven orders in the burrowed mud layer. Local increases in the hydraulic gradient occurred in the burrows, leading to faster water circulation and salt transport as well as turnover of soil aeration. The salinity front in the burrowed marsh reached two‐m deeper than in the unburrowed marsh. Burrow flushing depth and intensity is significantly enhanced in burrows with multiple openings. This study emphasized the complexity of tortuous burrows regulating groundwater flow and solute transport through modeling realistic crab burrows. This work supports fiddler crabs as ubiquitous “ecoengineers” who can produce more significant impact on local hydrological cycle and ecosystem‐scale geochemical processes than previously indicated. Fiddler crabs are commonly regarded as “ecoengineers” for salt marshes, as their burrowing activity has great impact on ecological and environmental processes. This study provides innovative approaches for numerical simulations that can quantitatively evaluate the potential impact of crab burrows on groundwater flow and salt transport by considering burrow morphology. Our results showed that crab burrows can form complex preferential flow path networks, which in turn accelerates groundwater and salt circulation and enhances porewater exchange between burrows and the sediment matrix. Further, the burrow flushing depth and intensity were primarily controlled by the morphology (burrow shape, branch, and entrance) of crab burrow. For burrows with only one entrance, local circulation developed, limiting the burrow flushing to a relatively shallow depth and delaying the downward migration of salt. For burrows with multiple entrances, a more complex network of preferential flow paths will form, enhancing the bidirectional exchange between surface water and groundwater through the burrows. This study highlights the importance of biological disturbance on hydrology, which affects behavior and function of salt marshes. Local circulation within burrows enhances porewater exchange between crab burrows and the sediment matrixCrab burrows facilitate soil aeration and alter flow paths/rate depending on burrow morphologiesCrab burrows have the potential to enhance terrigenous groundwater discharge in the creek‐marsh system Local circulation within burrows enhances porewater exchange between crab burrows and the sediment matrix Crab burrows facilitate soil aeration and alter flow paths/rate depending on burrow morphologies Crab burrows have the potential to enhance terrigenous groundwater discharge in the creek‐marsh system