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Abstract

Deep-sea mining for polymetallic nodules is expected to have severe
environmental impacts because not only nodules but also benthic fauna
and the upper reactive sediment layer are removed through the mining
operation and blanketed by resettling material from the suspended
sediment plume. This study aims to provide a holistic assessment of the
biogeochemical recovery after a disturbance event by applying prognostic
simulations based on an updated diagenetic background model and
validated against novel data on microbiological processes. It was found
that the recovery strongly depends on the impact type; complete removal
of the reactive surface sediment reduces benthic release of nutrients
over centuries, while geochemical processes after resuspension and
mixing of the surface sediment are near the pre-impact state 1 year
after the disturbance. Furthermore, the geochemical impact in the
DISturbance and reCOLonization (DISCOL) experiment area would be
mitigated to some degree by a clay-bound Fe(II)-reaction layer, impeding
the downward diffusion of oxygen, thus stabilizing the redox zonation of
the sediment during transient post-impact recovery. The
interdisciplinary (geochemical, numerical and biological) approach
highlights the closely linked nature of benthic ecosystem functions,
e.g. through bioturbation, microbial biomass and nutrient fluxes, which
is also of great importance for the system recovery. It is, however,
important to note that the nodule ecosystem may never recover to the
pre-impact state without the essential hard substrate and will instead
be dominated by different faunal communities, functions and services.