A model of fluff layer erosion and subsequent bed erosion in the presence of the bioturbator, <I>Hydrobia ulvae</I>

Abstract

Previous studies have shown that the gastropod Hydrobia ulvae destabilizes the top layers of ne-grained sediments. This process is mediated by the formation of a "biogenic" uff layer that includes tracks, faecal pellets and mucus. This uff layer has been shown to be easily resuspended before general bed erosion. In order to examine how uff layer and bed erosion interact, ume experiments were performed with uid sediments of varying water contents. Ten thousand snails were placed and allowed to crawl for 5 h on the sediment surface, and then the resuspended sediment mass was measured in response to step-wise shear stress increases. Two distinct erosion phases were observed: (1) initial resuspension of the uff layer and (2) the subsequent bed erosion. Both the bioturbation by snails and sediment water content interacted positively to increase erosion rates during the phase of uff layer erosion. The presence of a uff layer due to the snail's activities did not affect rates of subsequent bed erosion. A vertical model (1DV) was developed to simulate the succession in time of the two distinct erosion phases. Within this deterministic model, erosion rates of the uff layer depend on the quantity of sediment that is present in the uff layer. Previous behavioral observations of track formation mechanisms were integrated into model equations to account for the snail density and the water content dependence. The observed bed erosion was fairly well reproduced by considering the variation with depth of the sediment density as measured in the experiments. This model suggests a new approach for assessing the erosion of natural sediments under the in uence of H. ulvae population density, water content and tidal currents.

Influence of benthic macroinvertebrates on the erodability of estuarine cohesive sediments: Density- and biomass-specific responses

“…3). The compensating stabilization of surface sediment resulting from the mucus trails deposited during snail locomotion (Orvain et al, 2003) is apparently not sufficient to counteract for the missing microphytobenthic EPS production. observed a doubling of erosion rate with an increase in H. ulvae density from 10,000 to 50,000 ind m À2 (w15e75 g AFDW m…”

A review of subtidal benthic habitats and invertebrate biota of the Strait of Georgia, British Columbia

“…The 811 fine, often flocculent bottom material may take some time to settle once it is suspended via 812 bioturbation (c.f. Orvain et al, 2003). This is likely the case at fish farms, for example, where 813 organic ooze under the nets is sometimes resuspended by falling debris (e.g.…”

Heavy metal concentrations inCipangopaludina chinensis(Reeve, 1863) and relationships with sediments in Saint-Augustin Lake, Québec City (Qc, Canada)

“…C. chinensis is a filter feeder, detritivore and necrophore that feed non-selectively on organic and inorganic matter on lake bottom substrate as well as benthic and epiphytic algae and bacteria (Dillon, 2000). C. chinensis bioturbation activities can re-suspend sediments that become a source for phosphorus in the water column (Orvain et al, 2003) which in turn can lead to algal blooms. Re-suspended sediments and algal blooms result in higher turbidity (Orvain et al, 2003) The bioturbation activity can further impact mineralization of organic matter and accelerate nutrient cycling in eutrophic systems (Risgaard-Petersen, 2003;Biswasa et al, 2009).…”