Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight
<p>Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore extraction site. We studied the long-term effects of sand...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-06-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/18/3565/2021/bg-18-3565-2021.pdf |
| Summary: | <p>Sea-level rise demands for protection measures of endangered
coastlines crucial for the local population. At the island of Sylt in the SE
North Sea, shoreline erosion is compensated by replenishment with sand
dredged from an offshore extraction site. We studied the long-term effects
of sand extraction on bathymetry, geomorphology, habitats and benthic
fauna. Sand extraction created dredging holes about 1 km in diameter and up
to 20 m below the ambient seafloor level. Directly after dredging the
superficial sediment layer, inside the pits was dominated by coarse sand and
stones. Hydroacoustic surveys revealed only minor changes of bathymetry
<span class="inline-formula">></span> 35 years after sand extraction. Obviously, backfill of the
dredging pits was very slow, at a rate of a few millimeters per year, presumably
resulting from low ambient sediment availability and relatively calm
hydrodynamic conditions despite high wave energy during storms. Thus, a
complete backfill of the deep extraction sites is likely to take centuries
in this area. Hydroacoustic surveys and ground truthing showed that the
backfilled material is mainly very fine sand and mud, turning the previously
coarse sand surface into a muddy habitat. Accordingly, grab samples revealed
significant differences in macrozoobenthos community composition, abundance
and species density between recently dredged areas (<span class="inline-formula"><</span> 10 years ago),
recovery sites (dredging activity <span class="inline-formula">></span> 10 years ago) and undisturbed
sites (control sites). Overall, dredging turned the original association of
sand-dwelling species into a muddy sediment association. Since
re-establishment of disturbed benthic communities depends on previous
re-establishment of habitat characteristics, the low sedimentation rates
indicate that a return to a pre-dredging habitat type with its former
benthic community and habitat characteristics is unlikely. Since coarse sand
is virtually immobile in this area, a regeneration towards pre-dredging
conditions is also unlikely without human interference (e.g., mitigation
measures like depositing coarse material on the seafloor to restore the
sessile epifauna).</p> |
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| ISSN: | 1726-4170 1726-4189 |