Status quo seafloor integrity and hydrographic conditions

Vera Van LanckerM. Baeye, L. Kint, G. Montereale Gavazzi, N. Terseleer, D. Van den EyndeKoninklijk Belgisch Instituut voor Natuurwetenschappen – OD NatuurInstitut royal des Sciences naturelles de Belgique – DO Nature

Opportunities with new RV Belgica

Financing monitoringZAGRI monitoring programmeMOZ4 contract Flemish AuthoritiesMSFD Monitoring programme MONIT.be

https://www.belspo.be/belspo/NewRV/

Monitoring s.l. framework @RBINS

Overall goals

1) Quantification of natural and human-induced variability of sediment characteristics and processes

2) Process- and system understanding and modellingnear- and far-field

3) Building seabed knowledge supporting a more sustainable use of marine raw materials

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Seabed4Usee Interactive display

SOURCE TERMS (e.g., for modelling particle dispersion)Characteristics of the seabed? e.g., sediments, and geology

What is released from the vessel? e.g., particle sizeBehaviour of the particles? Flocculation?

Increases in suspended particulate matter concentration?

DEPOSITION in near field leading to increased sediment dispersal, by expanding sand ripple

fields, risking burial of gravel beds?

DEPOSITION in far field leading to smothering (i.e. mixing of fine-grained particles), impacting

on ecosystem functioning in gravel areas?

EU Marine Strategy Framework DirectiveAssessing changes in hydrographic conditions

and seafloor integrity with focus on quantifying physical disturbance and loss

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EU Marine Strategy Framework DirectiveBelgian physical indicators of Seafloor Integrity

Areal extent/distribution EUNIS level 2 Habitats + gravel beds, remain within the margin of uncertainty of the sediment distribution, with reference to the Initial Assess.

4

Ratio of the hard substrata surface area versus the soft sediment surface area does not show a negative trend.

Mixedsediments

Mud to sandy Mud

Coarse sediments

Sand/muddy Sand

GRAVEL

MUD SANDSand to mud ratio (n.t.s) 4:1 9:1

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80

GRAVEL BEDS

Significant monitoring effort requiredusing multibeam depth and backscatter

+sampling and visual observations

Water-column sediment properties in the near field of dredging vessels Measurements

RV Belgica ST1909

Multi-sensor bottom mount

Satellite overpass

Aggregate extraction:

Overflow samples

Overflow samplesParticle-size distribution

25 mu

300 mu

Satellite image of a dredging plume

SPMc peak around 10 mg/l

NEAR FIELD, Water-column sediment properties

Suspended Particulate Matter concentration – SPMc (mg/l)

Mean particle sizes in the water column (micron)

Neap Spring Neap Spring Neap

Results Noordhinder Sector 4aMulti-sensor bottom-mount time series (48 days, 2019) – here from an acoustic backscatter sensor

RV Belgica SPMcwater samples

@2-3 mab

300 micron flocsneap tide

180 micron mineral particlesspring tide

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10

15

20

Sector 4a – mg/l

Results @ 1.5 mabmab: meter above bottom

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B

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NEAR field, Main findings on water-column sediment properties:

From # 2436 water filtrations since 2011:• Indicative SPMc sandbanks 10- 20 mg/l vs gullies around 5 mg/l • Near-bed concentrations are highestNatural dynamics PLUS resuspension of overflow deposits and buffered finer grained material

BlighBank

Oost-hinder

Noordhinder

Oosthinder 4b – 4c cross-bank TRANSECTS Noordhinder 4a cross-bank TRANSECTS Noordhinder 4a, STATIONARY 13h cycle

A CB

Bottom @25m

Water level

RV Belgica ST1909. Suspended particulate matter concentration (mg/l). Extrapolated to 0.5 mab

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NEAR FIELD, Seabed sediment propertiesReineck boxcoring + core slicing (1 cm)

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hin

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Oo

sth

ind

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Case studies Oosthinder and Noordhindersandbank, Sectors 4c/4a:

timeseries of samples in combination with acoustic monitoring (COPCO)

Extraction leads to sediment segregation, with redistribution of sediments leading to:

1. Depletion in very fine sands and mud2. Decrease in calcium carbonate content3. Mixing of organic matter into the seabed matrix 4. Grain-size changes, both fining and coarsening

• Effect on biology and ecosystem functioning studied by ILVO (Talk Annelies De Backer)

See Poster Lars Kint

FAR FIELD, Multibeam + Sampling + Visual observations Testing of a Sandification hypothesis, based on MBES time series analysesIdentification of Geological and Anthropogenic Markers to depict small-scale changes

Dataset from 2000 (Van Lancker et al., 2007) Datasets 2018 (Flanders Hydrography)

Process, scale and systematics?Drivers?

July 2019: 5-10 cm sand thicknessReduction in structural complexity

June 2007: 0 cm sand thickness Revisiting known hotspots of biodiversity

Barchan dune areas

Sandificationand

Smotheringinvestigated

following source-to-

sink concepts

FAR FIELD, Multibeam + Sampling + Visual observations FIELD

A. Norro

Micro-CT scans at 30 micron. UGCT GentMix of coarse and fine sand particles

Smothering of the seabed matrixScientific diving July 2019

Shallow cores in biodiversity hotspot – barchan dune area

FAR field, Seabed sediment properties

• Near-field changes • Segregation of sediment fractions, leading to increased sorting (poster Lars Kint) • Grain-size class transition dependent on extraction practice and geology (Talk Annelies De Backer)• Increased sediment resuspension, leading to higher sediment dispersal (HYPOTHESIS)• Extraction-induced increases in SPMc are spatially and temporarily highly variable

• Measurements in the far-field showing:• Loss of gravel occurrence. Burial by sand. Extension to be quantified.

• Revisiting historic multibeam data sets, as well as geological datasets, on-going• Identification of geological and anthropogenic markers for small-scale change detection

• Smothering, i.e. enrichment of fine-grained particles.

• Very poor baseline, comparative core samples are being collected • Complex source-to-sink dynamics, with different sources being considered

Synthesis w.r.t Marine Strategy Framework Directive

Timespan?(ir)Reversible?

Natural cyclicity?Drivers?

+VALIDATION

Naturally and anthropogenically-induced cumulative and in-combination effectsRecommendations on best practice reducing anthropogenic component

Forthcoming: MSFD 2nd cycle assessment, evaluating seabed change over larger areas using transect-

based and full-coverage approach. Integration of other seabed-related monitoring results

RBINS-ILVO-COPCO

To support findings, knowledge is increased on• Seabed nature

e.g. geology, sediments, geomorphology, biology

• Natural variability of water-column and seabed-related properties and processes

Harmonisation of methodological approaches at EU-scale, following recommendations of

EU Comm TG Seabed (MSFD-related)

What’s Next?Transcending the status quo

Including…

New paper on gravel bed characterization

Montereale Gavazzi et al.

On-going update potential gravel distribution, here only shown for Hinder Banks within Natura 2000 and northern exploration zone

Opportunities with RV BelgicaValidation via cross-team collaboration on RV Belgica

VIBROCORING

DeploymentFrames

and Other platforms

Multi-sensorWater-column and

Seafloor measurements@different frequencies

Joint campaigns

COPCO RBINS

ILVOOthers

Remote sensing

Multi-device Seafloor sampling

and visual observations

Laboratory space facilitating onboard analyses

Further reading

• Van Lancker, V., Baeye, M., Montereale Gavazzi, G., Kint, L., Terseleer, N., Van den Eynde, D. (2020). Monitoring of the impact of the extraction of marine aggregates, in casu sand, in the zone of the Hinder Banks. Period 1/1 – 31/12 2019 and Synthesis of results 2016-2019. Brussels, RBINS-OD Nature. Report <MOZ4-ZAGRI/I/VVL/2020/EN/SR01>.

• Wyns, L., Roche, M., Barette, F., Van Lancker, V., Degrendele, K., Hostens, K., & De Backer, A. (2021). Near-field changes in the seabed and associated macrobenthic communities due to marine aggregate extraction on tidal sandbanks: A spatially explicit bio-physical approach considering geological context and extraction regimes. Continental Shelf Research, 229, 104546.

Methodological development

• Fettweis, M., Toorman, E., Verney, R., Chapalain, M., Legrand, S., Lurton, X., Montereale Gavazzi, G., Roche, M., Shen, X., Van den Eynde, D., Van Lancker, V. (2020). INDI67: Developments of Indicators to improve monitoring of MSFD descriptors 6 and 7. Contract –BR/143/A2. Final Report. Belgian Science Policy 2020, Brain-be, Belgian Research Action through Interdisciplinary Networks, 53 pp.

• Montereale Gavazzi, G.O.A. (2019). Development of seafloor mapping strategies supporting integrated marine management: application of seafloor backscatter by multibeam echosounders. PhD Thesis, Ghent University, Ghent, Belgium, 392 pp.

• Montereale Gavazzi, Roche, M., Lurton, X., Degrendele, K., Terseleer, N., Van Lancker, V. (2018). Seafloor change detection usingmultibeam echosounder backscatter: case study on the Belgian part of the North Sea. Marine Geophysical Research, 39(1-2), 229-247.

• Montereale Gavazzi G., Kapasakali, D., Kerckhof, F., Deleu, S., Degraer, S. & Van Lancker, V. (2021). Subtidal natural hard substrate quantitative habitat mapping: interlinking underwater acoustics and optical imagery with machine learning. Remote Sens. 13, 4608. https://doi.org/10.3390/rs13224608