|The physical and biological impact of sand extraction: a case study of the western Baltic Sea|
|Krause, J.C.; Diesing, M.; Arlt, G. (2010). The physical and biological impact of sand extraction: a case study of the western Baltic Sea. J. Coast. Res. SI 51: 215-226|
|In: Journal of Coastal Research. Coastal Education and Research Foundation: Fort Lauderdale. ISSN 0749-0208, more|
aggregates; mining; side-scan sonar; sediment micro- profiles; macrozoobenthos; SAB approach; sensitive benthic species; dredging furrows; recolonisation; recovery
In autumn 1997, approximately 320,000 m³ of sand were extracted from a site located ca. 2.5 km off Wustrow, Germany, Western Baltic Sea. The physical impacts of dredging on the sea floor are assessed on the basis of side-scan sonar, sediment texture, and oxygen profile approaches. Benthic macrofaunal effects are analysed, in terms of species, abundance, and biomass (SAB), addressing the responses of sensitive and non-sensitive species. Seabed modification was patchy within the dredging site. Morphology, texture, and oxygen characteristics returned to pre-dredging conditions over most of the site, during the first year of post-dredging. A smaller part of the area deepened by ca. 5 m and caused by multiple dredge furrows, was altered more drastically. During the year following the extraction, a shift to finer sediments with a higher organic carbon content and reduced oxygen levels was observed, at this location. Sensitive benthic species abundance did not recover to pre-impact levels, within a year after dredging. Slow recovery of the sensitive species can be overlooked easily by common environmental assessment measures, such as the SAB approach. Related to benthic habitats, environmentally-sound dredging practices should consider the various impacts that the creation of deep pits can have on the seabed, and compared those of shallow and isolated furrows.