How do macrofaunal activities impact biogeochemical cycling in anthropogenically disturbed sediment?

Marine coastal areas are important for ecosystem functioning because they provide a wealth of goods and services. Hence, it is a major challenge nowadays to understand and predict how human activities will affect marine sediment communities, benthic biogeochemical cycling and the link between them. In this study, we investigate biogeochemical fluxes and the contribution of macrofaunal activities (bioturbation and bio-irrigation) in sediment ranging from muddy to coarse, including two coarse sediment stations affected by human activity (installation of an offshore windfarm and aggregate extraction). For each station, we conducted triplicate closed-core incubations to measure oxygen, nutrients and DIC fluxes as well as bioirrigation rates by following the decreasing concentration of bromide in the water column over time. After the incubation, the macrofaunal community was identified and the bioturbation potential of the community calculated (BPc). Our results show the highest Sediment Community Oxygen Consumption (SCOC) in a fine sandy station inhabited by an abundant bioirrigating and bioturbating macrofaunal community and characterized by relatively high organic matter content. In the muddy station, the SCOC was 4 times lower and the DIC efflux much higher than the SCOC reflecting anaerobic mineralization processes happening in absence of bioirrigators. Within the coarse sediment stations characterized by poor organic matter content and inhabited by a limited macrofaunal community, the undisturbed station shows the highest irrigation rates associated with moderate SCOC and DIC efflux. In the disturbed stations, irrigation rate, SCOC and DIC efflux were low suggesting that physical disturbance decreases the efficiency of mineralization processes in coarse sediments. The overall results show that irrigation of the sediment affects biogeochemical cycling along a range of coastal sediments.

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