Offshore Windfarm Footprint of Sediment Organic Matter Mineralization Processes

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.

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

<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>

Upper Oligocene lithostratigraphic units and the transition to the Miocene in North Belgium

The presence of Chattian deposits in Belgium was confirmed in the early 20th century by correlation of their mollusc faunas with the type Chattian in Germany. Consequently, the Voort Formation in the Campine Basin and the Boncelles Sand on the northeastern Ardennes were established and assigned a Chattian age. Contacts with underlying Rupelian and overlying Burdigalian formations are marked by hiatuses, linked mainly to end-Oligocene Savian tectonics and reactivation of the Roer Valley Graben (RVG). On the Campine Block, only the lower part of the Chattian, the Voort Sand is deposited, increasing in thickness in the direction of the RVG and including a geophysically traceable clayey marker horizon allowing the mapping of this unit in the Campine Basin, into the Netherlands and even possibly link it to the hydrostratigraphic subdivision of the Chattian in the Lower Rhine Graben. Lithologically, these uppermost Paleogene Chattian deposits form the base of the Neogene sequence along the Southern Bight of the North Sea, characterised by predominantly glauconite-bearing sand. The Chattian sediments rapidly become thicker in the strongly subsiding RVG, resulting in a more continuous sedimentation with the development above the Voort Sand of a clay unit and another sand unit, forming together the Veldhoven Formation. In Belgium such sequence is only found in the RVG without biostratigraphic data. However, it can be demonstrated that lithostratigraphically this sequence is comparable to the better-studied Veldhoven Formation in the Netherlands where biostratigraphy revealed that the Veldhoven Formation grades into the Aquitanian to Burdigalian, crossing the Paleogene–Neogene boundary and separated from middle Miocene deposits by the Early Miocene Unconformity (EMU). It is proposed to harmonise Belgian and Dutch stratigraphic nomenclatures, making the more complete Veldhoven Formation applicable both in the Campine Basin and the Roer Valley Graben, and further north in the Netherlands. Within this scheme, the Belgian Voort Formation becomes the Voort Member as the lower part of the Veldhoven Formation, of which the middle Wintelre clayey and upper Someren sandy members are only recognised in the graben.

Satellite and In Situ Monitoring of Chl-a, Turbidity, and Total Suspended Matter in Coastal Waters: Experience of the Year 2017 along the French Coasts

The consistency of satellite and in situ time series of Chlorophyll-a (Chl-a), Turbidity and Total Suspended Matters (TSM) was investigated at 17 coastal stations throughout the year 2017. These stations covered different water types, from relatively clear waters in the Mediterranean Sea to moderately turbid regions in the Bay of Biscay and the southern bight of the North-Sea. Satellite retrievals were derived from MODIS/AQUA, VIIRS/NPP and OLCI-A/Sentinel-3 spectral reflectance. In situ data were obtained from the coastal phytoplankton networks SOMLIT (CNRS), REPHY (Ifremer) and associated networks. Satellite and in situ retrievals of the year 2017 were compared to the historical seasonal cycles and percentiles, 10 and 90, observed in situ. Regarding the sampling frequency in the Mediterranean Sea, a weekly in situ sampling allowed all major peaks in Chl-a caught from space to be recorded at sea, and, conversely, all in situ peaks were observed from space in a frequently cloud-free atmosphere. In waters of the Eastern English Channel, lower levels of Chl-a were observed, both in situ and from space, compared to the historical averages. However, despite a good overall agreement for low to moderate biomass, the satellite method, based on blue and green wavelengths, tends to provide elevated and variable Chl-a in a high biomass environment. Satellite-derived TSM and Turbidity were quite consistent with in situ measurements. Moreover, satellite retrievals of the water clarity parameters often showed a lower range of variability than their in situ counterparts did, being less scattered above and under the seasonal curves of percentiles 10 and 90.

Multiple New Paralytic Shellfish Toxin Vectors in Offshore North Sea Benthos, a Deep Secret Exposed

In early 2018, a large easterly storm hit the East Anglian coast of the UK, colloquially known as the ‘Beast from the East’, which also resulted in mass strandings of benthic organisms. There were subsequent instances of dogs consuming such organisms, leading to illness and, in some cases, fatalities. Epidemiological investigations identified paralytic shellfish toxins (PSTs) as the cause, with toxins present in a range of species and concentrations exceeding 14,000 µg STX eq./kg in the sunstar Crossaster papposus. This study sought to better elucidate the geographic spread of any toxicity and identify any key organisms of concern. During the summers of 2018 and 2019, various species of benthic invertebrates were collected from demersal trawl surveys conducted across a variety of locations in the North Sea. An analysis of the benthic epifauna using two independent PST testing methods identified a ‘hot spot’ of toxic organisms in the Southern Bight, with a mean toxicity of 449 µg STX eq./kg. PSTs were quantified in sea chervil (Alcyonidium diaphanum), the first known detection in the phylum bryozoan, as well as eleven other new vectors (>50 µg STX eq./kg), namely the opisthobranch Scaphander lignarius, the starfish Anseropoda placenta, Asterias rubens, Luidia ciliaris, Astropecten irregularis and Stichastrella rosea, the brittlestar Ophiura ophiura, the crustaceans Atelecyclus rotundatus and Munida rugosa, the sea mouse Aphrodita aculeata, and the sea urchin Psammechinus miliaris. The two species that showed consistently high PST concentrations were C. papposus and A. diaphanum. Two toxic profiles were identified, with one dominated by dcSTX (decarbamoylsaxitoxin) associated with the majority of samples across the whole sampling region. The second profile occurred only in North-Eastern England and consisted of mostly STX (Saxitoxin) and GTX2 (gonyautoxin 2). Consequently, this study highlights widespread and variable levels of PSTs in the marine benthos, together with the first evidence for toxicity in a large number of new species. These findings highlight impacts to ‘One Health’, with the unexpected sources of toxins potentially creating risks to animal, human and environmental health, with further work required to assess the severity and geographical/temporal extent of these impacts.

First Comprehensive Quantitative Multi-Parameter Assessment of the Eutrophication Status from Coastal to Marine French Waters in the English Channel, the Celtic Sea, the Bay of Biscay, and the Mediterranean Sea

The first quantitative and comprehensive assessment of the eutrophication status from coastal to offshore French waters was performed within the Marine Strategy Framework Directive (MSFD descriptor 5) for the English Channel, the southern bight of the North Sea, the Celtic Seas, the Bay of Biscay and the Western Mediterranean Sea. Based on a combination of different data sources (in situ, satellite, and modeling products), a fully-integrated dataset was generated over the period 2010–2016. Using the best available knowledge on the eutrophication process and definition, the assessment procedure was implemented considering nutrient pressures, and direct and indirect effects of excessive inputs. The different steps of the assessment were: (i) Establishment of assessment levels and thresholds, (ii) development of methodology for aggregation and integration of data, and (iii) qualification of the Environmental Status. We investigated how reliable this assessment procedure was when considering other complementary information. Results highlighted that, despite efforts in recent decades to reduced nutrient inputs, the pressure on coastal marine ecosystems was still high. We discuss options for improving the coherence between MSFD and other similar approaches and associated monitoring programs. This study identifies areas where an increased monitoring effort is needed to improve the assessment and where environmental management actions are of priority.

Modelling fine-scale distribution and relative abundance of harbour porpoises in the Southern Bight of the North Sea using platform-of-opportunity data

Over the last 25 years, the harbour porpoise (Phocoena phocoena) has made a significant return to the Southern Bight of the North Sea and the English Channel due to a shift in distribution from northerly regions. Although the ecological drivers of this return are unclear, this species faces multiple threats in the region, including by-catch and habitat degradation. Ferry-based surveys were conducted year-round between November 2011 and June 2014 to assess the influence of environmental parameters upon the spatiotemporal distribution and relative abundance of harbour porpoises in the Southern Bight of the North Sea. A total of 1450 sightings of harbour porpoises were recorded during the 100 round-trip surveys carried out between Dunkirk (France) and Dover (England). Inter-annual and monthly variations in group size were observed, with largest groups recorded in 2014 (mean = 2.02) and in January (mean = 2.32). The relative abundance showed significant seasonal variation, with peaks recorded during winter months. An inter-annual increasing relative abundance was recorded during the study period. There was a seasonally dependent association with environmental variables, particularly depth, seabed roughness and current speed. Finally, predictions suggest large increases of the relative abundance in offshore habitats during winter months and over the study period.

Productivity and temperature as drivers of seasonal and spatial variations of dissolved methane in the Southern Bight of the North Sea, leading to a response from eutrophication and heatwaves

<p>Dissolved CH<sub>4</sub> concentrations in the Belgian coastal zone (BCZ) (North Sea) ranged between 1607 nmol L<sup>-1</sup> near-shore and 4 nmol L<sup>-1</sup> off-shore during field cruises in 2016, 2017, 2018 and 2019. Spatial variations of CH<sub>4</sub> were related to sediment organic matter (OM) content and gassy sediments. In near-shore stations with fine sand or muddy sediments, the CH<sub>4 </sub>seasonal cycle followed water temperature, suggesting methanogenesis control by temperature in these OM rich sediments. In off-shore stations with permeable sediments, the CH<sub>4</sub> seasonal cycle showed a yearly peak following the Chlorophyll-a spring peak, suggesting that in these OM poor sediments, methanogenesis depended on freshly produced OM delivery. The annual average CH<sub>4</sub> emission was 126 mmol m<sup>-2</sup> yr<sup>-1</sup> in the most near-shore stations (~4 km from the coast) and 28 mmol m<sup>-2</sup> yr<sup>-1</sup> in the most off-shore stations (~23 km from the coast), 1,260 to 280 times higher than the open ocean average value (0.1 mmol m<sup>-2</sup> yr<sup>-1</sup>). The strong control of CH<sub>4</sub> by sediment OM content and by temperature suggests that marine coastal CH<sub>4</sub> emissions, in particular in shallow areas, should respond to future eutrophication and warming of climate. This is supported by the comparison of CH<sub>4</sub> concentrations at five stations obtained in March 1990 and 2016, showing a decreasing trend consistent with alleviation of eutrophication in the area. This is also supported by the response to the European heatwave of 2018 that led to record-breaking temperatures in many countries across northern and central Europe. Average seawater temperature in July was 2.5°C higher than the mean from 2004 to 2017 for same month in the BCZ. The mean dissolved CH<sub>4</sub> concentration in surface waters in July 2018 (338 nmol L<sup>-1</sup>) was three times higher than in July 2016 (110 nmol L<sup>-1</sup>), and an extremely high dissolved CH<sub>4</sub> concentration in surface waters (1,607 nmol L<sup>-1</sup>) was observed at one near-shore station. The high dissolved CH<sub>4</sub> concentrations in surface waters in the BCZ in July 2018 seemed to be due to a combination of enhancement of methanogenesis and of release of CH<sub>4</sub> from gassy sediments, both most likely related to warmer conditions. The emission of CH<sub>4</sub> from the BCZ to the atmosphere was higher in 2018 compared to 2016 by 57% in July (599 versus 382 µmol m<sup>-2</sup> d<sup>-1</sup>) and by 37% at annual scale (221 versus 161 µmol m<sup>-2</sup> d<sup>-1</sup>). The European heatwave of 2018 seems to have led to a major increase of CH<sub>4</sub> concentrations in surface waters and CH<sub>4</sub> emissions to the atmosphere in the BCZ.</p>