Speciation and hydrological transport of metals in non-acidic river systems of the Lake Baikal basin: Field data and model predictions

Abstract

The speciation of metals in aqueous systems is central to understanding their mobility, bioavailability, toxicity and fate. Although several geochemical speciation models exist for metals, the equilibrium conditions assumed by many of them may not prevail in field-scale hydrological systems with flowing water. Furthermore, the dominant processes and/or process rates in non-acidic systems might differ from well-studied acidic systems. We here aim to increase knowledge on geochemical processes controlling speciation and transport of metals under nonacidic river conditions. Specifically, we evaluate the predictive capacity of a speciation model to novel measurements of multiple metals and their partitioning, under highpH conditions in mining zones within the Lake Baikal basin. The mining zones are potential hotspots for increasing metal loads to downstream river systems. Metals released from such upstream regions may be transported all the way to Lake Baikal, where increasing metal contamination of sediments and biota has been reported. Our results show clear agreement between speciation predictions and field measurements of Fe, V, Pb and Zn, suggesting that the partitioning of these metals mainly was governed by equilibrium geochemistry under the studied conditions. Systematic over-predictions of dissolved Cr, Cu and Mo by the model were observed, which might be corrected by improving the adsorption database for hydroxyapatite because that mineral likely controls the solubility of these metals. Additionally, metal complexation by dissolved organic matter is a key parameter that needs continued monitoring in the Lake Baikal basin because dependable predictions could not be made without considering its variability. Finally, our investigation indicates that further model development is needed for accurate As speciation predictions under non-acidic conditions, which is crucial for improved health risk assessments on this contaminant.

Water in Central Asia: an integrated assessment for science-based management

“…Moreover, there is observational evidence that large-scale permafrost thaw in mountain regions of Central Asia has decreased the annual maximum flows and increased the annual minimum flows (Törnqvist et al 2014), due to a dampening effect of increased groundwater storage in areas of reduced permafrost. In particular, decreased maximum flows may have large impacts beyond the mountain regions, due to the importance for basin-wide sediment and pollutant transport Pietroń et al 2015;Thorslund et al 2016).…”

“…On the shores of the Caspian Sea, rising sea levels since the late 1970s and a recent stabilization at 2 m above the historical level have affected and sometimes completely submerged oil and gas fields located on the seashore, polluting coastal zones and the marine ecosystems (Dahl and Kuralbayeva 2001). A region that well exemplifies the environmental risks of mining is the Selenga River-Lake Baikal Basin, where coal, gold, copper, wolfram and molybdenum are extracted from relatively shallow deposits Kasimov et al 2017;Sandmann 2012;Thorslund et al 2012Thorslund et al , 2016. Over the past 15 years, the Mongolian government has been particularly active in encouraging foreign mining companies to start business in Mongolia (Farrington 2005).…”

Patterns of soil contamination, erosion and river loading of metals in a gold mining region of northern Mongolia

“…As a consequence, the topographically lowest part of the catena consists of residual natural fluvisols and technosols of mining dumps (see the Electronic Supplementary Material (S1.1) for further details). Since the bedrock and soils of the region are carbonate rich, the river water contains large fractions of calcium and bicarbonates , contributing to its high pH (observed to reach values above 9; Thorslund et al 2016).…”

“…River discharge, mass flows and hydro-meteorological data River discharge was measured and water samples were collected for chemical analysis, during two field campaigns in the Tuul River, along the Zaamar Goldfield mining site, one in June 2012 and one in September 2013 (see Thorslund et al 2016 for more information on the site). Sample collection and discharge measurement were done simultaneously at two cross sections (T5b, longitude 104.331, lat.…”

Heavy Metals Transport Simulation by Physically Based Distributed Modeling Approach (Case Study: Harrach River, Algeria)

“…The increased water pollution caused by urban, industrial and agricultural activities are directly related to the constant growth in the number of people living in river basins 1) . Heavy metal can be exposed to the environment through anthropogenic processes, such as mining and other industrial activities 2) .…”