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Changes along the Belgian part of the North Sea

BelSPO-SSD Strategic Research Network 2007-2011. Changes along the Belgian part of the North Sea. vera.vanlancker@mumm.ac.be. N. Increasing human pressure. In Quest4D compilation of distribution and intensity of human activity, incl. the extent of fisheries’ impact on the seabed

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Changes along the Belgian part of the North Sea

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  1. BelSPO-SSD Strategic Research Network 2007-2011 Changes along the Belgian part of the North Sea vera.vanlancker@mumm.ac.be

  2. N Increasing human pressure In Quest4D compilation of distribution and intensity of human activity, incl. the extent of fisheries’ impact on the seabed Quantitative analysis of fishing marks, based on multibeam backscatter data Example Thornton Bank Disposal of dredged material 2006: 12 106 TDM Marine Aggregates Average 1.5 106 m³/yr Coastal protection may demand >10 106 m³ Surface area: 3600 km² R. Janssens, 2009 ?Cumulative impact? Maes et al., 2005

  3. Main problems in impact studies • No baseline information - No historic reference points • Significance of impacts? Time-scale of change? • Cumulative impacts? – Far field influence? • Links between cause and effect? • Threshold of habitat change? • What is natural and what is anthropogenically-steered???

  4. Changes in bathymetryChanges in sedimentsChanges in macrobenthos Partner: RBINS, Dep. Invertebrates / Ghent University, Marine Biology Section

  5. Long-term vs. short- to medium-term changes • Decifering natural vs anthropic change • Natural change: • Sediment volumes and bedform changes against hydro-meteorological conditions • Influence of storms on sediment transport • Anthropic change: • Analysis of short- to medium-term changes against intensity data of anthropic activities (e.g. data on disposal of dredged material and aggregate extraction)

  6. Varying sediment volumes over sandbank areas Surveys 9609 9611 9612 9702 9709 9711 9802 9803 maximum change 9609 0.05 0.03 0.09 0.01 0.05 0.05 0.04 0.09 9611 -0.02 0.03 -0.04 0.00 0.00 -0.01 -0.04 9612 0.05 -0.02 0.02 0.02 0.01 0.05 9702 -0.08 -0.03 -0.03 -0.04 -0.08 9709 0.04 0.04 0.03 0.04 9711 0.00 -0.01 -0.01 9802 -0.01 -0.01 9803 0.00 maximum change 0.00 0.05 0.03 0.09 -0.08 0.05 0.05 0.04 Baland Bank bathymetric surveys. Matrix of all the intersurvey volume differences per surface unit (m³/m²). The maximum differences are indicated in italic. Surveys are indicated as YYMM. Natural vs anthropic • Natural evolution • Sediment volumes vs hydro-meteo from measuring piles (Flemish Authorities) • Wind • High- and low frequency waves • Currents • Water levels Decifering threshods of ‘natural’ change Event–driven vs. yearly-averaged changes • Findings along ‘undisturbed’ near coastal small sandbank: • Enhanced SW conditions bring in sediment • Persistent NW and NE conditions evoque erosion • Overall shallowing of the area Scenario’s will be used to predict sediment transport changes, due to climate change Van Lancker, in prep.

  7. Anthropic change: case study on the disposal of dredged material Vibrocore Stiff clay from maintenance dredging works and increase of mud pebbles

  8. 1 Analysis of bathymetric data 2 Analysis of corresponding data on the disposal of dredged material Short-term impact Active cooperation end-users Decifering thresholds of ‘anthropic’ change Medium-term impact 3 • Analysis of vibrocores: • top 25-50 cm highly dynamic • natural vs anthropic sedimentation patterns 1976-1979 1981-1985 Regional sedimentation beyond the disposal grounds, in the direction of navigation channels

  9. Sediment change analysis

  10. Period around 1900 Sand fraction is generally well-sorted Poorer sorting associated with gravel or shell hash areas

  11. Present-day Wide-spread worsening in sorting: esp. around harbours, near disposal and aggregate extraction sites

  12. Changes in skewness Present-day Mostly enrichment of (very) fine sands in the areas with more poorly sorted sediments

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