Resolving and modeling the effects of Fe and Mn redox cycling on trace metal behavior in a seasonally anoxic lake

Abstract

Vertical profiles of the dissolved and particulate (Ͼ0.45 m) concentrations of Fe, Mn, Co, Ni, Cu, Pb, Al and Ba were determined on two occasions (14 and 22 August 1996) during summer stratification in a seasonally anoxic lake (Esthwaite Water, UK). The results were combined with contemporaneous in situ measurements of water-column remobilization of the metals from settling particles at the base of the suboxic zone and other ancillary measurements. The combined data were interpreted with the aid of an equilibrium speciation model (WHAM6), incorporating metal-humic interactions and a surface-complexation description of binding to Fe and Mn oxides. The behavior of all the metals was related in different ways to the position of the O 2 -H 2 S interface and to Fe and Mn redox cycling. In the region of the O 2 -H 2 S interface the behavior of Co and to a lesser degree Ni was dominated by Mn redox cycling. Ba behavior was dominated by the biogenic precipitation and dissolution of barite and to a lesser degree by Mn redox cycling. The behavior of Al was linked to both Mn and Fe redox cycling, although the extent of binding to the oxides and to humic substances was poised with respect to pH. Unlike the other metals, the profiles of Pb and Cu showed little variation above the dissolved sulfide maximum, but modeling indicated that binding of Pb was significant to both Mn and Fe oxides. The featureless nature of the Cu profiles in the upper part of the water column was linked to its overriding association with dissolved humic substances. Below the dissolved sulfide maximum, Co, Ni, Ba, Cu, Pb and Mn were all affected by sulfide precipitation, probably through a common association with FeS. In the case of Co, Ni, Cu and Pb, inverse relationships between the measured dissolved and particulate concentrations were attributed to the coexistence of both filterable and nonfilterable FeS particles and associated mass balance effects. The observed behavior of the metals in relation to the role played by Fe and Mn oxides was generally consistent with WHAM6 predictions. The model predictions highlighted the fact that trace metal speciation in general, and binding to Mn and Fe oxides in particular, can be highly sensitive to the variations in solution conditions found in freshwater systems.

Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

“…7 and 8) points to iron sulfide as a sink for Co and Ni. The link between Ni and Co cycles with that of Fe and Mn established in thermokarst lake sediment is in accordance with previous studies on temperate freshwater environments (Huerta-Diaz et al, 1998;Hamilton-Taylor et al, 2005).…”

Small Boreal Lake Ecosystem Evolution under the Influence of Natural and Anthropogenic Factors: Results of Multidisciplinary Long-Term Study

“…An influx of Fe(II) from the sediments is supported by the concave shape of the Fe profiles, which points towards diffusive processes from the sediment rather than production processes within the water column. This result is in agreement with the large body of evidence from temperate lakes, showing that the seasonal increase in iron in the anoxic bottom waters is largely due to a release from the sediment [28]. In addition to low molecular weight (LMW, <1 kDa) phytoplankton exometabolites, important process responsible for the production of LMW organic ligands in the surface layers may be the photooxidation of DOM (e.g., refs.…”

“…In contrast, in summertime, the photoreaction of Fe(III) under the visible range of light and UV may produce labile (<100 Da) Fe, as shown in experiments on boreal stream waters [33]. The poorly understood process that is responsible for colloidal metal production in the hypolimnion involves iron sulfide formation in the anoxic zone of sediment porewater and the adjacent water column [28]. These FeS nanoparticles are capable of scavenging some trace metals [34,35].…”

Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances

“…Examples include 71 the acidification of soils [7][8][9][10][11][12][13][14] and surface waters [15] , trace metal behaviour in soils [16][17][18][19][20][21][22] , surface 72 waters [23][24][25][26][27][28][29][30][31] and groundwaters [32] , lake sediment diagenesis [33,34] , rare earth geochemistry [35-73 37] , iron and manganese geochemistry [38][39][40][41] , radionclide geochemistry [42][43][44][45] , organic matter 74 solubility in soils [46,47] , catchment modelling [48,49] , interactions of metals with biota [50,51] , 75 ecotoxicology [52][53][54][55][56][57][58][59] and Critical Loads …”