Biological and biogeochemical methods for estimating bioirrigation: a case study in the Oosterschelde estuary

Emil De Borger,Ulrike Braeckman,Karline Soetaert,Tom Ysebaert,Justin Tiano

doi:10.5194/bg-17-1701-2020

Abstract

Abstract. Bioirrigation, the exchange of solutes between overlying water and sediment by benthic organisms, plays an important role in sediment biogeochemistry. Bioirrigation either is quantified based on tracer data or a community (bio)irrigation potential (IPc) can be derived based on biological traits. Both these techniques were applied in a seasonal study of bioirrigation in subtidal and intertidal habitats in a temperate estuary. The combination of a tracer time series with a high temporal resolution and a mechanistic model allowed for us 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 bioirrigation in intertidal areas. This is explained by higher densities of bioirrigators such as Corophium sp., Heteromastus filiformis and Arenicola marina in the intertidal, as opposed to the subtidal, areas. The IPc correlated more strongly with the attenuation coefficient than the pumping rate, which highlights that the IPc index reflects more the bioirrigation depth than the rate.

Highlights

Bioirrigation is the process in which benthic organisms actively or passively exchange sediment porewater solutes with the overlying water column as a result of burrowing, pumping and feeding activities (Kristensen et al, 2012)
Chlorophyll a concentrations in the upper 2 cm of the sediment varied from 3.76 ± 2.43 μg g−1 in Hammen to 20.60 ± 4.19 μg g−1 in Zandkreek and were higher in the intertidal (13.34±6.53 μg g−1) than in the subtidal (5.88±4.20 μg g−1) areas
The median grain size (d50) and silt content ranged from 59 μm with 52 % silt to 140 μm with 0 % silt

Summary

Introduction

Bioirrigation is the process in which benthic organisms actively or passively exchange sediment porewater solutes with the overlying water column as a result of burrowing, pumping (ventilation) and feeding activities (Kristensen et al, 2012). This exchange plays an important role in marine- and lacustrine-sediment biogeochemistry, as oxygen-rich water is brought into an otherwise subsediment or anoxic-sediment matrix.

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