Biological and biogeochemical methods for estimating bio-irrigation: a case study in the Oosterschelde estuary

Bio-irrigation, the exchange of solutes between overlying water and sediment by benthic organisms, plays an important role in sediment biogeochemistry. Quantification of bio-irrigation is done either through measurements with tracers, or more recently, using biological traits to derive the community (bio-) irrigation potential (IPc). Both these techniques were applied in a seasonal study of bio-irrigation in species communities of subtidal and intertidal habitats in a temperate estuary. A tracer time series with high-temporal resolution allowed to simultaneously estimate the pumping rate, and the sediment attenuation, a parameter that determines irrigation depth. We show that although the total pumping rate is similar in both intertidal and subtidal areas, there is deeper bio-irrigation in intertidal areas. This is explained by higher densities of bio-irrigators such as Corophium sp., Heteromastus filiformis and Arenicola marina in the intertidal, as opposed to the subtidal. The IPc correlated more strongly with the attenuation coefficient than the pumping rate, which highlights that this index reflects more the bio-irrigation depth rather than the rate.