ABSTRACT Amos, C.L.; Kassem, H.; Bergamasco, A.; Sutherland, T.F., and Cloutier, D., . The mass settling flux of suspended particulate matter in Venice Lagoon, Italy. A multidisciplinary study of the stability of the tidal flats of Venice Lagoon has provided field and laboratory data on the factors influencing the mass settling rates of material in suspension. This work was performed using two in situ benthic flumes (Sea Carousel and Mini Flume) in association with a wide range of physical and biological measurements undertaken during the summer of 1998 and the subsequent winter. Also, controlled experiments on erosion/sedimentation of prepared beds were carried out using Lab Carousel, a laboratory equivalent of Sea Carousel. Particle size and mass settling rates were found to be largely independent of suspended sediment concentration but strongly controlled by the antecedent bed shear stresses that led to the suspension. Results between the three flume types differed because of differences in the induced stress history created in each case. Comparable results were obtained by normalizing mass settling rate to the mean friction velocity of the flow during settling, i.e . the Rouse parameter , and by use of the mean dimensionless particle diameter (D * ). Results fell in line with results on carbonate and silica sands of the inlets of the lagoon. The mean particle diameter (d f ) varied in proportion to the applied shear stress and shear rate (G) suggesting that the suspended particles were eroded aggregates not floccules. The effective density of these aggregates was least (∼16 kgm −3 ) at the largest sizes (d f > 1 × 10 −4 m) and greatest (∼160–1600 kgm −3 ) at the smallest sizes (d f < 1 × 10 −4 m). The lack of an increase in d f at low shear rates suggests that flocculation was not taking place. The mean deposition threshold (all experiments) was 0.68 Pa, which is less than the mean erosion threshold from these sites (0.78 Pa).

ABSTRACT Sutherland, T.F. and Amos, C.L., 2020. An in situ assessment of seabed stability in Baynes Sound, British Columbia, Canada. Journal of Coastal Research, 36(3), 472–486. Coconut Creek (Florida), ISSN 0749-0208. The Sea Carousel, an annular flume, was deployed to examine ( in situ ) fundamental parameters of seabed stability in Baynes Sound, British Columbia, Canada. Sediment grain size, water and organic contents, and chlorophyll and phaeopigment concentrations were collected to establish a hierarchy of factors associated with seabed stability. Sediment stability increased toward the Sound entrance in concert with decreases in water, organic, and silt–clay contents and a transition from cohesive to noncohesive properties. Bed-stress estimates, based on the quadratic stress law and turbulent kinetic energy (TKE) methods, showed a decrease in the drag coefficient from the inner (0.04) to the outer (0.0015) Sound. Surface erosion thresholds ranged between 0.04 to 0.28 Pa, whereas the friction coefficients ( e.g., the failure envelop) were on average 12°, representing normally consolidated sediments. Type I (floc) erosion occurred at low shear stresses, whereas type II (mass) erosion happened at higher values. Erosion rates ( E , for type I erosion) fitted a power function of excess shear stress ( E m = τ 0 – τ crit , z ) m with zero offset, where 0.81 < m < 2.32. The lowest and highest values for a given excess-shear stress occurred in the inner Sound and outer Sound, respectively. Settling of (resuspended) sediment after an exponential decay law [ d ( SSC )/ dt ] = SSC 0 (exp – kt ), where k fell within that of published values (3 < k < 539). Higher values of k (fastest settling) were observed in the inner Sound relative to the outer Sound. The sedimentation diameter ( d s ) fell in a coarse–silt to fine-sand range and was larger in the outer Sound, reflecting a coarsening of bed sediments.

ABSTRACT Amos, C.L.; Christian, H.; Buckley, D.E., and Daborn, G.R., 2019. The stability, settling character, and strength of seabed sediments in the Miramichi estuary, Canada. Journal of Coastal Research , 35(3), 509–523. Coconut Creek (Florida), ISSN 0749-0208. A survey of seabed stability was undertaken in the Miramichi estuary, New Brunswick, Canada: a region subject to intense industrial pollution, channel dredging and maintenance, and the passage of commercial ships. The estuary has a diverse fauna that has been described. The impact of natural and industrial activities on the indigenous fauna is largely unknown. Reworking of dredge spoil tailings has been considered the main cause of sediment dispersal in the system, yet there have been no direct measurements of this. As a result, a study was undertaken to determine the character and stability of dredge spoils and the natural estuarine sediments in which they sit, using the benthic flume Sea Carousel over the years 1991, 1993, and 1994. As well, a limited program of seabed and water column sampling and monitoring was undertaken using a variety of techniques in order to provide a setting for the measurements of stability. Results showed that tidal influence on resuspension was small compared with storm (and ship) waves and other “events” that appeared to be anthropogenic in origin. The erosional and depositional character of natural (control) sites were similar to those from other estuaries described in the literature despite the strong anthropogenic influences. Surprisingly, the strength of disposed dredge spoils (collected using a clam-shell bucket) was similar to the natural sediments at the control site, even after only a few hours of disposing. The stability of the disposed material did not change measurably after 1 year. The erosion flux ( E ) was found to be a power function of the excess bed shear stress: E = 1.9 × 10 -3 (τ 0 – τ c,z ) 0.71 kg/m 2/ s. The settling of eroded material took place as aggregates at a mean rate of 1.1 × 10 -3 m/s, which corresponds to a mean sedimentation diameter of 75 microns (very fine sand). The fluid mud potential of the system is low: laboratory settling experiments showed that suspended silts/clays underwent free settling at a rate proportional to initial concentration to a maximum concentration of 18 g/L; hindered settling (and fluid mud development) was evident above this value.

ABSTRACT Sutherland, T.F.; Garcia-Hoyos, L.M.; Poon, P.; Krassovski, M.V.; Foreman, M.G.G.; Martin, A.J., and Amos, C.L., 2018. Seabed attributes and meiofaunal abundance associated with a hydrodynamic gradient in Baynes Sound, British Columbia, Canada. The distribution of seabed geotechnical, biochemical, and meiofauna attributes was examined in Baynes Sound, British Columbia, between 2009 and 2014. Among attributes measured were sediment porosity, organic carbon and nitrogen, and trace element concentrations ( e.g ., zinc, copper), which increased with increasing sediment fines content toward the head of the Sound. A ternary plot (sand-silt-clay percentages) revealed a constant clay/silt ratio across a range of sand proportions with textures ranging from well-sorted sand at the high-energy SE entrance to silt-dominated mud in the depositional basin. These sediment textures were related to modeled maximum velocity values within 5 m of the seabed ( U max,5 ), with highest values (restricted entrance) and lowest values (deep basin) representing sand depositional and mud depositional facies. Sediment porewater sulfide fell into an oxic category (0–700 μM), exhibiting a lack of variation and organic enrichment within the Sound. The first principal component analysis (PCA) factor described the alignment between fine sediments, organics, Cu and Zn, and meiofauna attributes and accounted for 49% of the total variance. The second PCA factor (19% of total variance) described the relationship between U max,5 and sediment grain size fractions >0.5 mm and an indirect association with water depth and fine sand (0.105–0.250 mm). Meiofauna were associated with a medium sand fraction (0.25 mm) characterized by low-porosity and low-organic sand loam textures. Although the range in abundance was relatively greater for nematodes, harpacticoid copepods revealed a stronger response to changes in sediment geotechnical and organic attributes, suggesting these taxa may be used to describe seabed variations or potential perturbations.

ABSTRACT Amos, C.L.; Brylinsky, M.; Forbes, D.L.; Robertson, A.; Thompson, C.E.L., and Kassem, H., 2018. Stability of seabed sediments in the embayments of North Rustico, Prince Edward Island, Canada. This paper describes a series of 15 deployments of the annular benthic flume Sea Carousel made along the two estuaries of North Rustico, Prince Edward Island (PEI), Canada: The Hunter River estuary and the Wheatley River estuary. The study was part of a wider study on the environmental impact of coastal changes and aquaculture ( Mytilus edulis ) development in the region. The study site was situated on the dynamic north shore of PEI that is characterised by sandy barrier islands, inlets and beaches, and muddy lagoons. The lagoons are dominated by the seagrass Zostera marina in the muddy outer parts and by Ulva lactuca in the eutrophic inner parts. The thresholds for surface erosion of cohesive sediments (0.10 < τ crit,o < 0.75) derived from trends of suspended sediment concentration ( C ) increased with distance ( d ) into the estuary: τ crit,o = 0.50 e −0.26 d (±0.05) Pa. Location in the estuary is the best predictor of bed stability. The next best predictor is surface sediment wet bulk density ( ρ b ), which takes the form: τ crit,o = 6.67 × 10 −4 ( ρ b ) − 0.55 Pa. Erosion rates ( E ) can only be correlated (significantly) with excess bed shear stress ( τ ex ) by incorporation of a time (depth)-varying erosion threshold. A power function emerged of the form: E = E o τ ex m kg/m 2 /s (0.28 < m < 1.06). The exponent is within the range of laboratory experiments reported in the literature. The still-water settling rates of eroded material are diagnostic of a wide range of sedimentation diameters varying from fine sand to medium silt. The deposition threshold ( τ d ) was evaluated in a laboratory equivalent of Sea Carousel (Lab Carousel) for sites RUS11 and RUS12 and yielded a mean value of 0.51 Pa. The exponential decay constant ( k ) for still-water settling is strongly dependent on initial concentration and suggests a constant settling rate that fits with data from a wide variety of settings throughout Canada.

ABSTRACT Amos, C.L.; Umgiesser, G.; Ghezzo, M.; Kassem, H., and Ferrarin, C., 2017. Sea surface temperature trends in Venice lagoon and the adjacent waters. Two coastal lagoons and coastal waters in the northern Adriatic region, Italy, were examined to assess the anthropogenic impact on coastal sea surface temperature (SST). The first lagoon was the highly altered Venice lagoon, and the second was the largely natural Marano-Grado lagoon. There are converging lines of evidence for air warming in the Venice region since 1910 at a long-term rate of 0.095°C/decade. Since 1980, the warming has accelerated to 0.65°C/decade in the centre of Venice. The acceleration in air warming is also evident in the MOHAT4 data set from the northern Adriatic Sea, although the rate of warming is less (0.36°C/decade). This warming trend is mimicked in the HadISST1.1 data set of SST for the northern Adriatic Sea (0.33°C/decade), whereas no trend was detected before 1980. SST and air temperature in both Venice and Marano-Grado lagoons are highly correlated (r 2 = 0.8): SST is on average 2°C cooler than the northern Adriatic Sea is, although differences appear to be diminishing because of rapid warming in Venice lagoon since 2008 (up to 1.75°C/decade). The warming in the lagoons appears to be greatest during winter months. By contrast, the greatest (post-1980) warming in the northern Adriatic Sea occurs during summer months. Moderate Resolution Imaging Spectroradiometer (nighttime; MODIS) SST data shows that, on average, the Venice lagoon is 5% warmer than Marano-Grado lagoon is. This equates to a summertime mean temperature difference of 1.2°C. This difference is within the scatter of the data and suggests that there is no appreciable heat retention in the waters of the Venice lagoon because of local anthropogenic activity.

ABSTRACT Amos, C.L.; Martino, S.; Sutherland, T.F., and Al Rashidi, T., 2015. Sea surface temperature trends in the coastal zone of British Columbia, Canada. Coastal sea surface temperature (SST), measured daily at the British Columbia (BC) Lighthouse network of stations, has been analyzed in this paper. A network of 14 of the 27 stations had (near) continuous data sets. These stations were clustered previously into exposed (northern/outer) and sheltered (southern/inner) sites. SST trends, evaluated between 1973 and 2010, show that the temperature contrast between these clusters is becoming greater: The northern/exposed stations are strongly influenced by interdecadal (Pacific Decadal oscillation [PDO]) and multidecadal oscillations in the north Pacific that are coherent with HadISST1.1 data for the region. There is no statistically significant warming trend for this region. The stations in the Strait of Georgia are much less influenced by the PDO and show a statistically significant mean increase in SST of up to 0.56°C/decade (Anomaly 1). This is higher than the global average and contrasts markedly with the trends from the northern stations. The warming trends of the southern stations are significant at all months of the year but are most evident during summer (July–September). The summertime anomalies in temperature at Active Pass are significantly correlated ( p < 0.001) with the temperature of the Fraser River water. Temperature differences between the Strait of Georgia and the outer shelf (Anomaly 2) are increasing in time; this is particularly evident since 2000. Monthly averaged MODIS satellite data (4×4-km resolution) show that trends in SST at two selected sites in the Strait of Georgia are very similar to the BC Lighthouse measurements and support the spatial extrapolation of the Lighthouse measurements. At present rates of SST rise, the southern coastal waters of BC will be about 3°C warmer by the end of the 21st century.

An annular flume (Lab Carousel) was used to investigate the influence of shells on the erosion rates of an artificial laboratory cohesive bed (potters clay) under unidirectional flow. Specimens of articulated and disarticulated cockle shells ( Cerastoderma edule ), separated into six size classes (of maximum diameter from 13 to 26 mm), were used. The fluid-transmitted shear stresses and shell-induced bed erosion for the six classes were measured in triplicate, as well as shell settling velocity, sedimentation diameter, and shell drag coefficient. Bed erosion began after the shells started to move: erosion rates were influenced by shell size and the mode of transport. Two different modes of shell transport were observed: (i) rolling and saltation of articulated shells, and (ii) sliding and saltation of disarticulated shells. Peak bed erosion rates were associated with rolling and sliding modes of transport. Higher values of the solid-transmitted shear stress were calculated for saltating shells (in some cases two times higher), but contact with the bed was less frequent than rolling or sliding. The presence of cockle shells in an environment with hydrodynamic conditions strong enough to induce shell transport could significantly increase the loss of mass (erosion) of the surface bed or cliff. At Hythe intertidal area, where the shell specimens were collected, the presence of miniature furrows containing shells deposits in the troughs is widespread, and the troughs and walls show tool marks indicating shell abrasion.

The sensitivity of estimated suspended sediment transport rates was studied by applying existing current-wave fields within a coupled numerical model using the Bagnold and the Soulsby-van Rijn formulae. The study area was the Sylt-Rømø bight, an enclosed back barrier tidal basin located in the North Sea. The bight has an area of some 400 km 2 in which sand flats prevail. This work provides numerical estimates of sediment transport rates and shear velocities throughout the Sylt-Rømø tidal basin. Water levels, vertically-averaged two-dimensional current velocities and wave spectra were used as input from validated numerical model calculations. Four days covering a full storm period in April 1997 were selected for the calculations of total bed shear velocities and sediment transport rates. The simulation shows that during moderate wave conditions sediment transport mainly takes place in the tidal channels. However, with high wave energy present, sediment transport becomes more important in shallow areas. The general distribution of shear velocities and suspended sediment concentrations over the basin suggests a large erosion and resuspension of sediment in shallow areas by wave action which may not be so evident in the sediment transport rates because of the low current velocities. This suggests that storms will continue to erode shallow areas, thus increasing the tidal prism and probably the tidal currents which will result in the continuing export of sediment.