Abstract
Offshore windfarms (OWFs) offer part of the solution for the energy transition which is urgently needed to mitigate effects of climate change. Marine life has rapidly exploited the new habitat offered by windfarm structures, resulting in increased opportunities for filter- and suspension feeding organisms. In this study, we investigated the effects of organic matter (OM) deposition in the form of fecal pellets expelled by filtering epifauna in OWFs, on mineralization processes in the sediment. OM deposition fluxes produced in a 3D hydrodynamic model of the Southern Bight of the North Sea were used as input in a model of early diagenesis. Two scenarios of OWF development in the Belgian Part of the North Sea (BPNS) and its surrounding waters were calculated and compared to a no-OWF baseline simulation. The first including constructed OWFs as of 2021, the second containing additional planned OWFs by 2026. Our results show increased total mineralization rates within OWFs (27–30%) in correspondence with increased deposition of reactive organic carbon (OC) encapsulated in the OM. This leads to a buildup of OC in the upper sediment layers (increase by ∼10%) and an increase of anoxic mineralization processes. Similarly, denitrification rates within the OWFs increased, depending on the scenario, by 2–3%. Effects were not limited to the OWF itself: clear changes were noticed in sediments outside of the OWFs, which were mostly opposite to the “within-OWF” effects. This contrast generated relatively small changes when averaging values over the full modeling domain, however, certain changes, such as for example the increased storage of OC in sediments, may be of significant value for national / regional carbon management inventories. Our results add to expectations of ecosystem-wide effects of windfarms in the marine environments, which need to be researched further given the rapid rate of expansion of OWFs.
Highlights
Rising concern for global climate change has increased the urgency to lower carbon emissions from individual and industrial energy consumers (United Nations, 2015)
The diagenetic model was forced by the carbon deposition estimated by Ivanov et al (2021). This carbon deposition was estimated under different scenarios of Offshore windfarms (OWFs) development, by implementing a representation of the filtration and feces production processes associated to monopile fouling was solved with a horizontal resolution of 5 km, downscaled to 1 km over the Belgian Part of the North Sea (BPNS) using a two-way nesting procedure (Ivanov et al, 2020)
COAWST models the distribution of organic matter (OM) and sediment in the water column, which are subject to hydrodynamics, depositionerosion processes, and simple degradation processes
Summary
Rising concern for global climate change has increased the urgency to lower carbon emissions from individual and industrial energy consumers (United Nations, 2015). Offshore windfarms (OWFs), groupings of wind turbines on submerged sediments, offer part of the solution in the energy transition. The attraction of organisms extends beyond the surface of the turbine foundations. Fish species such as cod (Gadus morhua) and pouting (Trisopterus lusculus) are known to aggregate near turbine foundations (Reubens et al, 2011; Langhamer, 2012), and benthic communities of macrofauna have been observed to change, alongside a fining of the sediment and an enrichment with organic matter (OM) (Bergström et al, 2012; Coates et al, 2014; Leewis et al, 2018). Deposition of fecal pellets by the fouling fauna, as well as biomass falling from the structures is a likely source of this enrichment (Krone et al, 2013; Lefaible et al, 2019)
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