bioirrigation

Bioirrigation is the process by which burrowing and other infaunal organisms actively exchange water between the overlying water column and sediment pore waters. Through pumping, ventilation of their burrows, and the movement of water within networks of tunnels and chambers, these organisms induce advective transport that enhances solute exchange across the sediment–water interface. Bioirrigation differs from passive diffusion by generating directed flows that can rapidly supply oxygen deeper into sediments and flush metabolic wastes toward the exterior.

As a component of biogeochemical cycling, bioirrigation alters redox conditions, nutrient fluxes, and organic matter degradation. By increasing oxygen penetration and mixing, it promotes nitrification and subsequent denitrification, as well as iron, manganese, and phosphate cycling. It also accelerates the breakdown of organic matter and can affect the emission or uptake of gases such as carbon dioxide and methane. The magnitude of bioirrigation depends on organism identity and density, burrow geometry, season, and sediment permeability; some taxa provide strong irrigation while others contribute mainly to bioturbation without extensive ventilation.

Bioirrigation is studied in marine, estuarine, and freshwater sediments and is relevant to nutrient management, contaminant fate, and sediment remediation strategies. Researchers measure it with tracer experiments (such as dyes or salt tracers), microsensor profiles of oxygen and nutrients, pore-water sampling, and mathematical models that incorporate irrigation terms alongside diffusion. Limitations include spatial and temporal variability, interactions with other biogeochemical processes, and potential resuspension or mobilization of sediments or pollutants under certain conditions.