Architects of the underworld: bioturbation by groundwater invertebrates influences aquifer hydraulic properties

The hydraulic properties of aquifers are critical to the storage and transmission of water to meet the needs of an increasingly groundwater-dependent global community. The hydraulic properties of aquifers can also influence the biota present, but inversely, invertebrate burrowing (bioturbation) may also influence the hydraulic properties and the flow of water through sediments. The aim of this study was to test whether groundwater invertebrates were capable of influencing the hydraulic properties of aquifer sediments in an experimental setting. Groundwater amphipods were added to sediment-filled laboratory columns, and the effective porosity (n_eff ) and longitudinal dispersivity (α_L) of the sediments were compared before and after 2 months of amphipod activity. The n_eff of columns without amphipods decreased significantly over time whereas in columns containing eight amphipods it remained relatively constant, and in columns with four amphipods it was highly variable. There was no difference in α_L between columns with amphipod density or over time. These findings suggest that the amphipods were maintaining the amount of pore space that was actively contributing to transport but their activity was not influencing the distribution of flow paths, and amphipod density is critical to causing or maintaining changes in hydraulic properties.