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Geo-Mar Lett (2012) 32:123137 DOI 10.1007/s00367-011-0266-7
ORIGINAL
Hydro-meteorological influences and multimodal suspended particle size distributions in the Belgian nearshore area (southern North Sea)
Michael Fettweis & Matthias Baeye & Byung Joon Lee &
Peihung Chen & Jason C. S. Yu
Received: 21 February 2011 /Accepted: 6 November 2011 /Published online: 29 November 2011 # Springer-Verlag 2011
Abstract Suspended particulate matter (SPM) concentration and particle size distribution (PSD) were assessed in a coastal turbidity maximum area (southern North Sea) during a composite period of 37 days in JanuaryApril 2008. PSDs were measured with a LISST 100X and classified using entropy analysis in terms of subtidal alongshore flow. The PSDs during tide-dominated conditions showed distinct multimodal behaviour due to flocculation, revealing that the building blocks of flocs consist of primary particles (<3 m) and flocculi (15 m). Flocculi comprise clusters of clay minerals, whereas primary particles have various compositions (calcite, clays). The PSDs during storms with a NE-directed alongshore subtidal current (NE storms) are typically unimodal and characterised by mainly granular material (silt, sand) resuspended from the
seabed. During storms with a SW-directed alongshore subtidal current (SW storms), by contrast, mainly flocculated material can be identified in the PSDs. The findings emphasise the importance of wind-induced advection, alongshore subtidal flow and highly concentrated mud suspensions (HCMSs) as regulating mechanisms of SPM concentration, as well as other SPM characteristics (cohesiveness or composition of mixed sediment particles) and size distribution in a high-turbidity area. The direction of subtidal alongshore flow during SW storm events results in an increase in cohesive SPM concentration, HCMS formation, and the armouring of sand; by contrast, there is a decrease in cohesive SPM concentration, no HCMS formation, and an increase in sand and silt in suspension during NE storms.
Introduction
Knowledge of the size distribution of suspended particulate matter (SPM) is needed to understand and predict sediment dynamics (Eisma 1986; van Leussen 1994; Curran et al. 2007; Mikkelsen et al. 2007; Winter et al. 2007; Bowers et al. 2009; Lee et al. 2011). Natural SPM comprises many different substances with time- and site-specific concentrations and can be subdivided into inorganic and organic fractions. The inorganic fraction consists mainly of clay minerals as well as carbonates and other non-cohesive minerals (Berlamont et al. 1993; Fettweis...