Exploring bacterial pathogen community dynamics in freshwater beach sediments: A tale of two lakes

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154434/1/emi14860.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154434/2/emi14860_am.pd

Erosion characteristics and floc strenght of Athabasca river cohesive sediments: towards managing sediment-related issues

Purpose: Most of Canada’s tar sands exploitations are located in the Athabasca river basin. Deposited cohesive sediments in Athabasca river and tributaries are a potential source of PAHs in the basin. Erosional behavior of cohesive sediments depends not only of fluid turbulence but on sediments structure and particularly the influence of organic content. This research tries to describe this behavior in Athabasca river sediments. Methods: An experimental study of cohesive sediments dynamics in one of the tributaries, the Muskeg river, was developed in a rotating annular flume. Variation of the shear stress allowed the determination of erosional strength for beds with different consolidation periods. Particle size measurements were made with a laser diffraction device operated in a continuous flow through mode. Optical analyses of flocs (ESEM and TEM) were performed with samples taken at the end of the experiments. Results: An inverse relationship between suspended sediment concentration (SS) and the consolidation period was found. The differences are related in this research to the increasing organic content of the sediments with consolidation period. The particle size measurements during the experiments showed differences on floc strength that are also related to changing organic content during different consolidation periods. ESEM and TEM observations confirm the structural differences for beds with different consolidation periods. The effects of SFGL on floc structure and in biostabilization of the bed are discussed. Conclusions: It is recommended in this paper that consolidation period should be taken into account for the modeling of erosion of cohesive sediments in the Athabasca river. Relating to transport models of pollutants (PAHs) it is highly recommended to consider flocs organic content, particularly algae, in the resuspension module.Environment Canada, CONACY

Development of novel 2D and 3D correlative microscopy to characterise the composition and multiscale structure of suspended sediment aggregates.

Suspended cohesive sediments form aggregates or 'flocs' and are often closely associated with carbo, nutrients, pathogens and pollutants, which makes understanding their composition, transport and fate highly desirable. Accurate prediction of floc behaviour requires the quantification of 3-dimensional (3D) properties (size, shoe and internal structure) that span several scales (i.e. nanometre [nm] to millimetre [mm]-scale). Traditional techniques (optical cameras and electron microscopy [EM]), however, can only provide 2-dimensional (2D) simplifications of 3D floc geometries. Additionally, the existence of a resolution gap between conventional optical microscopy (COM) and transmission EM (TEM) prevents an understanding of how floc nm-scale constituents and internal structure influence mm-scale floc properties. Here, we develop a novel correlative imaging workflow combining 3D X-ray micro-computed tomography (μCT), 3D focused ion beam nanotomography (FIB-nt) and 2D scanning EM (SEM) and TEM (STEM) which allows us to stabilise, visualise and quantify the composition and multi scale structure of sediment flocs for the first time. This new technique allowed the quantification of 3D floc geometries, the identification of individual floc components (e.g., clays, non-clay minerals and bacteria), and characterisation of particle-particle and structural associations across scales. This novel dataset demonstrates the truly complex structure of natural flocs at multiple scales. The integration of multiscale, state-of-the-art instrumentation/techniques offers the potential to generate fundamental new understanding of floc composition, structure and behaviour

Sediment-contaminant interactions and transport: a new perspective

Abstract This paper investigates the sediment structural controls over the transport and compartmentalization of Cd, Cu and Pb within flocculated sediments. The compartmentalization of contaminants within flocculated sediment particles demonstrates the complex underlying biogeochemical conttols of sediment contami nant interactions. The aims and objectives of the paper are to demonstrate (a) how the structure of suspended sediment particles will influence the transfer of metals within aquatic systems and (b) how the internal shoicture/composition of the particles promotes compartmentalization of metals in a selective manner

The stability of a remediated bed in Hamilton Harbour, Lake Ontario, Canada

In situ measurements of lakebed sediment erodibility were made on three sites in Hamilton Harbour, Lake Ontario, using the benthic flume Sea Carousel. Three methods of estimating the surface erosion threshold (τ c(0)) from a Carousel time series were evaluated: the first method fits measures of bed strength to eroded depth (the failure envelope) and evaluates threshold as the surface intercept; the second method regresses mean erosion rate (E m) with bed shear stress and solves for the floc erosion rate (E f) to derive the threshold for E m = E f = 1 × 10 -5 kg m -2 s -1; the third method extrapolates a regression of suspended sediment concentration (S) and fluid transmitted bed shear stress (τ o) to ambient concentrations. The first field site was undisturbed (C) and acted as a control; the second (W) was disturbed through ploughing and water injection as part of lakebed treatment, whereas the third site (OIP) was disturbed and injected with an oxidant used for remediation of contaminated sediment. The main objectives of this study were: (1) to evaluate the three different methods of deriving erosion threshold; (2) to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts; and (3) to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability. Five deployments of Sea Carousel were carried out at the control site. Mean erosion thresholds for the three methods were: τ c(0) = 0·5 (±0·06), 0·27 (±0·01) and 0·34 (±0·03) Pa respectively. Method 1 overpredicted bed strength as it was insensitive to effects in the surface 1-2 mm, and the fit of the failure envelope was also highly subjective. Method 2 exhibited a wide scatter in the data (low correlation coefficients), and definition of the baseline erosion rate (E f) is largely arbitrary in the literature. Method 3 yielded stable (high correlation coefficients), reproducible and objective results and is thus recommended for evaluation of the erosion threshold. The results of this method correlated well with sediment bulk density and followed the same trend as marine counterparts from widely varying sites. Mass settling rates, expressed as a decay constant, k, of S(t), were strongly related to the maximum turbidity at the onset of settling (S max) and were also in continuity with marine counterparts. Thus, it appears that differences in salinity had little effect on mass settling rates in the examples presented, and that biological activity dominated any effects normally attributable to changes in salinity. Bedload transport of eroded aggregates (2-4 mm in diameter) took place by rolling below a mean tangential flow velocity (U y) of 0·32 ms -1 and by saltation at higher velocities. Mass transport as bedload was a maximum at U y = 0·4 ms -1, although bedload never exceeded 1% of the suspended load. The proportion of material moving as bedload was greatest at the onset of erosion but decreased as flow competence increased. Given the low bulk density and strength of the lakebed sediment, the presence of a bedload component is notable. Bedload transport over eroding cohesive substrates should be greater in estuaries, where both sediment density and strength are usually higher. Significant differences between the ploughed and control sites were apparent in both the erosion rate and the friction coefficient (∅), and suggest that bed recovery after disruption is rapid (< 24 h). τ c(0) increased linearly with time after ploughing and recovered to the control mean value within 3 days. The friction coefficient was reduced to zero by ploughing (diagnostic of fluidization), but increased linearly with time, regaining control values within 6 days. No long-term reduction in bed strength due to remediation was apparent.Fil: Amos, Carl L.. Southampton Oceanography Centre; Reino UnidoFil: Droppo, Ian G. National Water Research Institute; CanadáFil: Gomez, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Murphy, Tom P.. National Water Research Institute; Canad

Impacts of wildfire on effective sediment particle size: implications for post-fire sediment budgets

Recent work in an Australian catchment has shown that severe wildfires followed by rainstorm events lead to redistribution of topsoil and export of sediment to the local river network. Considering the affinity of nutrients and other contaminants for fine sediment, and the potential for considerable downstream impacts, a sound understanding of the fine-sediment delivery from burnt systems is required. However, past work has shown that fire can modify the particle size distribution of the soil through formation of robust sand-sized aggregates comprising fine clays and silts. Image analysis confirmed the presence of fire-modified soil aggregates in our study area. Analysis of aggregate form and fluvial behaviour showed that fire-modified aggregates are fused, dense and inorganic in nature with settling velocities of an order of magnitude faster than unburat soil aggregates or classic riverine flocs. This implies an increased potential for storage of nutrient-rich fine sediment within slope units, flood plains and river channels. The unusual behaviour of these composite particles should be considered in the construction of post-fire fine-sediment budgets.8 page(s

Structural characteristics and behavior of fire-modified soil aggregates

8 page(s