Geochemical and biological controls on the ecological relevance of total, dissolved and colloidal forms of trace elements in large boreal rivers: review and case studies

Complete List of Authors: Cuss, Chad W; University of Alberta, SWAMP lab, Department of Renewable Resources Glover, Chris; Athabasca University, Faculty of Science and Technology and Athabasca River Basin Research Institute Javed, Muhammad; University of Alberta, SWAMP lab, Department of Renewable Resources Nagel, Andrew; University of Alberta, Department of Biological Sciences Shotyk, William; University of Alberta, SWAMP lab, Department of Renewable Resources

The input of relatively large particles occurs primarily through mechanical processes: 1) Surface 121 runoff and associated weathering following rain events or during spring freshet deposits clay (< 2 122 m particle size), silt (2-63 m), and sand (63 m -2 mm) particles into rivers and lakes; 2) 123 Wind erodes exposed rocks and soils, transporting particles to surface waters either in dry form  Stanton et al. 2007). Trace elements with variable oxidation 138 states include many of the transition metals (including Co, Cr, Cu, Fe, Hg, Mn, Mo, V, and Tl), 139 as well as some metalloids (As, Sb), non-metals (such as Se) and actinides (e.g. U). 140 In general, the majority of particulate-phase TE are introduced via physical weathering 141 processes and transport on the surface or in air, whereas TE introduced by in-situ chemical 142 weathering and subsurface transport processes are predominantly dissolved. Since the majority  Figure 5C shows that Al 3+ is the dominant 171 aluminum ion in solution at pH < 4.5, and, more importantly, that the solubility of gibbsite is at 172 its minimum in the pH range between 6 and 8 (Faure 1998). 173 Sample filtration and associated artefacts 174 The partitioning between 'dissolved' (i.e. < 0.45 m by filtration) and 'particulate' (i.e. >    is known to participate in complexation reactions with both As(III) and As(V), where functional 279 groups such as amino acid groups (R-NH 2 ) and thiols (R-SH) complex with the reduced state

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This mechanism may be very important for certain metals, since uptake rates for lipophilic metal 563 complexes are often more than ten times higher than those for similar hydrophilic complexes    allow TE access to the gut epithelium, and thus gain access to an additional surface for uptake.

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The biogeochemistry of the digestive surface can be complex, with rapid and substantial changes concentration of free TE close to transport sites, therefore increasing uptake.

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As noted above, at the microscale, water flowing over an uptake surface will affect TE  (Tables 2 and 3).

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The distribution of TE amongst the dissolved size fractions in PR and SD reflects their 815 size-based distribution amongst major forms, corresponding with their assignation to Groups 1-5 816 ( Table 2)

Concentration and size-based distribution of trace elements 862
Although comprehensive hydrometric and water quality data were available for the AR, reliable 863 size-resolved TE data were only available for the autumn baseflow period (Table 4) Mn, 51% of total Pb, and 43% of total Ni,). This is expected behaviour for non-mobile indicators 917 of physical weathering and sparingly soluble TE; however, As (Group 5, soluble TE with 918 variable behaviour) was also predominantly found in recalcitrant residual form (96% of total As).

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This contrasts with the other oxyanion-forming Group 1 elements, which were present in  exceeded CCME guidelines during spring freshet (Table 2). Consequently, the concentrations of 986 Al, As, Cu, Fe, and Zn will be further elevated in the AR during and immediately following 987 snowmelt, to the extent that CCME guidelines are likely to be exceeded (Table 4; Figure 13).

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These water quality guidelines (WQG) set by CCME are designed to protect aquatic

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Page 90 of 103 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews D r a f t Figure 3: Major geochemical transport pathways for trace elements entering surface freshwaters (Note regarding : It is widely agreed that the net fluxes of TE pass from the water into the sediments across the sediment-water interface; however, this will not be true whenever the concentration of TE in the water is undersaturated with respect to the various complexes and mineral forms of TE that could form, e.g. in headwaters or meltwaters). D r a f t  D r a f t     D r a f t