Effect of episodic rainfall on aqueous metal mobility from historical mine sites

Valencia-Avellan, M, Slack, R, Stockdale, A and Mortimer, RJG ORCID: https://orcid.org/0000-0003-1292-8861, 2018. Effect of episodic rainfall on aqueous metal mobility from historical mine sites. Environmental Chemistry, 14 (8), pp. 469-475. ISSN 1448-2517

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Abstract

The increasing frequency and magnitude of episodic rainfall events may affect historical metal mining areas by remobilisation and deposition of metal-rich sediments and enhancing metal-rich run off, impacting river water quality. This study assesses the effects of episodic rainfall in a Carboniferous headwater catchment contaminated by historical Pb and Zn mining. Comprehensive hourly water chemistry measurements combined with modelling using PHREEQC, WHAM/Model VII and WHAM-FTOX were used in this assessment. For the episodic event, we measured flow increases from a baseline of 0.05 to 2.12 m3 s−1 at peak flow. Changes in metal concentration were most marked for ephemeral tributary, with Pb increasing from a baseline concentration of 55 μg L−1 to a peak of 576 μg L−1. Behaviour for Pb showed great affinity to form organic complexes or bind to colloidal Al and Fe oxides, whereas for Zn and the tributary flowing subsurface a more complex behaviour was observed. For example, the dissolution of secondary metal carbonate minerals (e.g. smithsonite (ZnCO3)) is likely constrained by higher concentrations of carbonate and bicarbonate derived from increased bedrock weathering under flow conditions induced by episodic rainfall. The abundance of secondary mineral sources and circumneutral pH present during episodic rainfall are important factors controlling the mobilisation of Pb and Zn. Furthermore, episodic rainfall events could enhance metal toxicity but there are aggravating and mitigating factors that depend on site-specific chemical changes. Overall, this study highlighted the complexity of metal mobility and toxicity during these events.

Item Type:	Journal article
Publication Title:	Environmental Chemistry
Creators:	Valencia-Avellan, M., Slack, R., Stockdale, A. and Mortimer, R.J.G.
Publisher:	CSIRO
Date:	21 March 2018
Volume:	14
Number:	8
ISSN:	1448-2517
Identifiers:	Number Type 10.1071/EN17133 DOI
Divisions:	Schools > School of Animal, Rural and Environmental Sciences
Record created by:	Linda Sullivan
Date Added:	21 Mar 2018 11:17
Last Modified:	30 Apr 2018 15:14
URI:	https://irep.ntu.ac.uk/id/eprint/33069

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