The stability of sublittoral, fine‐grained sediments in a subarctic estuary

Abstract

The erodibility of natural estuarine sediments was measured in situ along a longitudinal transect of Manitounuk Sound, Hudson Bay, using the benthic flume Sea Carousel. Sedimentation processes along the transect varied from continuous, rapid, post-glacial sedimentation in the inner Sound, to glacial outcrops and seabed reworking of the outer Sound. The grain size and physical bulk properties reflect changes in depositional environment and correlate with sediment erosion threshold stress (TJ, erosion rate (E), erosion type and still-water mass settling rate. There was a steady increase in T~ (0.8-2.0 Pa) with distance down the Sound in parallel with the decreasing sedimentation rate (0.003-0.001 m yr -') and increasing sediment bulk density (1650-2010 kg m -'). The near-surface friction coefficient varied up to 68" in proportion to the clay content of post-glacial material. Glacial sediments were characterized by variable results and generally higher friction coefficients. Seabed erosion in Sea Carousel began with surface creep of loose aggregates, pellets and organic debris. This was followed by Type I bed erosion at rates that varied between 0-0002 and 0.0032 kg ms -(mean 0.0015). Type I peak erosion rate was inversely related to applied bed shear stress (z,). Type II erosion succeeded Type I, often after a broad transitional period. Simulations of suspended sediment concentration in Sea Carousel were made using four commonly used erosion ( E ) algorithms. The best results were obtained using Krone's dimensionless ratio relationship: E = M ( T~/ T~-~) .Simulations were highly sensitive to the definition of erosion threshold with sediment depth [z,(z)]. Small errors in definition of TJZ) caused large errors in the prediction of suspended sediment concentration which far exceeded differences between the methods tested.

Observed dissolved and particulate nitrogen concentrations in a mini flume

“…3), with maximum concentrations (c.a., 320-380 mg l -1 ) measured at T5 and T10 after the highest TSS had been applied. These SPM:shear stress relationships are similar in shape to those reported in the Tamar Estuary (Bale et al, 2006) and other muddy estuaries (Amos et al, 1996;Widdows et al, 2004).…”

Resuspension potential of surficial sediments in Saguenay Fjord (Québec, Canada)

“…The value of 10 min was used in order to homogenize the results (Hydraulics Research Station, 1980; Amos et al, 1996). Laws for individual deployments have determination coefficient (r 2 ) range between 0.67 and 0.94 but a composite law would have a r 2 of only 0.58 (Moreau et al, 2003):…”

Enhanced erodibility of fine-grained marine sediments by Hydrobia ulvae

“…Rhoads, 1974;Yingst and Rhoads, 1978;Nowell et al, 1981;Grant and Gust, 1987;Paterson, 1989). Several studies have demonstrated that bacteria, benthic diatoms and some macrozoobenthic organisms may modify the erosion threshold of soft-bottom substrata (Paterson, 1989;Underwood and Paterson, 1993;Yallop et al, 1994;Austen et al, 1999;Tolhurst et al, 1999) and some have also attempted to quantify erosion rates of cohesive sediments (Amos et al, 1992(Amos et al, , 1996(Amos et al, , 1997Sutherland et al, 1998;Willows et al, 1998;Andersen, 2001a).…”