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

Abstract

The concentrations of trace elements (TEs) in large boreal rivers can fluctuate markedly due to changing water levels and flow rates associated with spring melt and variable contributions from tributaries and groundwaters, themselves having different compositions. These fluctuating and frequently high concentrations create regulatory challenges for protecting aquatic life. For example, water quality criteria do not account for changes in flow regimes that can result in TE levels that may exceed regulatory limits, and neither do they account for the markedly different lability and bioaccessibility of suspended solids. This review addresses the geochemical and biological processes that govern the lability and bioaccessibility of TEs in boreal rivers, with an emphasis on the challenges posed by the colloidal behaviour of many TEs, and their relationship to the dissolved fraction (i.e., <0.45 μm in size). After reviewing the processes and dynamics that give rise to the forms and behaviour of TEs in large boreal rivers, their relevance for aquatic organisms and the associated relationships between size and lability and bioaccessibility are discussed. The importance of biological variables and different forms of TEs for limiting lability and bioaccessibility are also addressed. Two case studies emphasize seasonal fluctuations and accompanying changes in the distribution of TE amongst different size fractions and associated colloidal species in large boreal rivers: the Northern Dvina and one of its tributaries, the Pinega River, both in Russia, and the Athabasca River in Alberta, Canada. Water quality in the Athabasca River is briefly discussed with respect to Canadian guidelines.

Mercury Export From Freshwater to Estuary: Carbocentric Science Elucidates the Fate of a Toxic Compound in Aquatic Boreal Environments

“…Following this finding, iron and carbon colloidal carrier phases were shown to transport rare earth and trace elements in boreal and subarctic rivers (Anderson et al, 2006;Dahlqvist et al, 2007;Pokrovski et al, 2010;Krickov et al, 2019;Cuss et al, 2020). Complexation of trace elements by OM in colloidal form would decrease their lability (Aiken et al, 2011;Stockdale et al, 2014;Cuss et al, 2020). Recently, technical advances have allowed the two iron-colloid phases to be distinguished (Herzog et al, 2020): Fe-OM complexes and Fe(oxy)hydroxides (as nanoparticles or associated with chromophoric molecular matter) and especially ferrihydrite, which is a common weathering product of Febearing minerals in boreal regions and an efficient trace metal sorbent in the aquatic environment (Wetzel, 2001;Jokinen et al, 2020).…”

“…In 2002, Pokrovsky and Schott revealed the presence, in boreal Russian rivers, of two pools of colloids composed of organicrich and Fe-rich particles, considered to be the most important potential carriers for other elements, which they divided into four groups with different distribution patterns: 1) dissolved simple anions; 2) elements mainly adsorbed on carbon-based colloids; 3) elements mainly adsorbed on iron-rich colloids; and 4) elements almost equally distributed between carbon colloids and iron colloids (the last being more common; Lyvén et al, 2003). Following this finding, iron and carbon colloidal carrier phases were shown to transport rare earth and trace elements in boreal and subarctic rivers (Anderson et al, 2006;Dahlqvist et al, 2007;Pokrovski et al, 2010;Krickov et al, 2019;Cuss et al, 2020). Complexation of trace elements by OM in colloidal form would decrease their lability (Aiken et al, 2011;Stockdale et al, 2014;Cuss et al, 2020).…”

“…An important characteristic of colloids is their ability to become involved in aggregation reactions, as well as in hydrophilic (e.g., metal ions) and hydrophobic (e.g., oil and other hydrophobic pollutants) binding interactions (Wetzel, 2001;Santschi, 2018). The size and structure of colloids are heavily influenced by changes in water chemistry such as pH, redox potential, ionic strength, and DOM concentration and type, causing aggregation or dispersal of the components and associated elements (Cuss et al, 2020). In 2002, Pokrovsky and Schott revealed the presence, in boreal Russian rivers, of two pools of colloids composed of organicrich and Fe-rich particles, considered to be the most important potential carriers for other elements, which they divided into four groups with different distribution patterns: 1) dissolved simple anions; 2) elements mainly adsorbed on carbon-based colloids; 3) elements mainly adsorbed on iron-rich colloids; and 4) elements almost equally distributed between carbon colloids and iron colloids (the last being more common; Lyvén et al, 2003).…”

Asymmetrical Flow Field-Flow Fractionation Methods for Quantitative Determination and Size Characterization of Thiols and for Mercury Size Speciation Analysis in Organic Matter-Rich Natural Waters

“…Additionally, Hg can bind to various inorganic particle surfaces ( Tiffreau et al, 1995 ; Bonnissel-Gissinger et al, 1999 ). Found as nano-colloidal species, particles are more likely to remain in surface waters and control the reactivity of trace metals bound to them despite their low concentrations ( Lead and Wilkinson, 2006 ; Waeber et al, 2012 ; Cuss et al, 2020 ). Therefore, determination of the physicochemical speciation of Hg and the amount of Hg bound to DOM is of high relevance to understand its fate and bioavailability in surface waters.…”

Sorption Behavior and Aerosol–Particulate Transitions of 7Be, 10Be, and 210Pb: A Basis for Fallout Radionuclide Chronometry

“…FRN speciation is determined by interacting cofactors including production source, depositional process, aerosol chemistry, and particle age, and through these factors, FRN atmospheric deposition represents multiple aerosol populations . Further, upon interaction with terrestrial particulate matter (PM), the speciation of FRNs is likely to evolve with different mixtures of primary minerals, surface coatings, and organic compounds. − Faced with this complexity, a central challenge to FRN applications remains: do the beryllium isotopes 7,10 Be and 210 Pb trace congruent pathways via bulk aerosol, soil, and sediment, or are they fractionated through associations with specific aerosol and particulate populations?…”