Modelling of the offshore wind farm footprint on organic and mineral particle deposition flux

Abstract

<p>Being an important source of renewable energy, offshore wind farms (OWFs) are currently flourishing in European coastal seas, with a largely unknown long-term impact on the environment. By providing hard substrate habitat to fouling species (such as the blue mussel), who filter water and excrete rapidly sinking fecal pellets, OWFs change the sediment composition and its carbon balance through biodeposition. </p><p>Here we coupled a hydrodynamic model (including tides), a wave model and a sediment transport model with a description of organic carbon dynamics. The coupled model was run for the Southern Bight of the North Sea under different scenarios: i) no OWFs; ii)  current OWF placement; and iii) several scenarios for future OWF placement in a new concession area, that differ in the number of installed monopiles and their placements.</p><p>Simulations showed that the tidal remobilization of mineral particles by the dominant current is orders of magnitude higher than their biodeposition from the OWFs. The total organic carbon (TOC) flux, however, appeared to be highly altered (up to 50%) by OWF biodeposition, especially in 5 km vicinity of the monopiles. At a greater distance (5 - 30 km away from the monopiles), the TOC biodeposition flux decreases. The majors alteration in the TOC flux is aligned with the major axis of the regional tidal current and the main direction of the residual current, with local residual gyres acting as TOC traps.</p><p>A future OWF, whose current concession zone overlaps a protected Natura 2000 area with its gravel beds acting as biodiversity hotspots, is expected to affect them through TOC biodeposition flux alteration. However, the magnitude of the impact appeared to be strongly dependent on the monopile placement, and very little on the number of monopiles. The gravel beds will experience a 50% TOC influx increase, if the monopiles are placed over them or just next to them, but already at 3 km distance this increase would be less than 10 %.</p>

Impacts of human activities on the supply of marine ecosystem services: A conceptual model for offshore wind farms to aid quantitative assessments

“… General information 1: Impact assessment 2: Part of conceptual model 3: Complexity 4: Linking (Ecosystem) component ES Selected model Reference Model variables Description Indicators High/Medium/Low Linked to: Nutrient cycle in sediment Mediation of wastes Regression model Toussaint et al, 2021 [ 52 ] Denitrification, % organic matter, % fine sediment, irrigation potential, bio-irrigation rate Regressions between sediment parameters and nutrient processes Nitrogen removed (tonnes N/km 2 /year) Low Community composition Climate regulation Accumulation rate formula Middelburg, 2019 [ 53 ] C accumulation, sediment accumulation rate, porosity, dry density, C deposition Formula of carbon storage resulting from an increased flux Carbon stored (tonnes C/km 2 /year) Low C deposition by filter feeders, community composition Food web Wild aquatic animals EMBENS Ecopath model Pint et al, 2021 [ 54 ] Biomass, production, consumption, landings, discards, diet Full food web and fisheries model, with a.o. biomass and harvests Biomass (tonnes/km 2 ) Landings (tonnes/km 2 /year) Medium/high Community composition, possibly biochemical, socio-economic models, habitat preferences, … (Biofouling) Filter feeders Mediation of wastes, climate regulation COAWST model (output) Ivanov et al, 2021 [ 55 ] Mussel density, C deposition, filtration, chlorophyll-α co...…”