Cave drip water solutes in south-eastern Australia: Constraining sources, sinks and processes

Carol V Tadros; Pauline C Treble; Andy Baker; Stuart Hankin; Regina Roach

doi:10.1016/j.scitotenv.2018.10.035

Cave drip water solutes in south-eastern Australia: Constraining sources, sinks and processes

Sci Total Environ. 2019 Feb 15;651(Pt 2):2175-2186. doi: 10.1016/j.scitotenv.2018.10.035. Epub 2018 Oct 4.

Authors

Carol V Tadros¹, Pauline C Treble², Andy Baker³, Stuart Hankin⁴, Regina Roach⁵

Affiliations

¹ ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia; Connected Waters Initiative Research Centre, UNSW Sydney, Kensington, NSW 2052, Australia. Electronic address: Carol.Tadros@ansto.gov.au.
² ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia; Connected Waters Initiative Research Centre, UNSW Sydney, Kensington, NSW 2052, Australia.
³ Connected Waters Initiative Research Centre, UNSW Sydney, Kensington, NSW 2052, Australia.
⁴ ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
⁵ NSW National Parks and Wildlife Service, Sydney, NSW, Australia.

PMID: 30326450
DOI: 10.1016/j.scitotenv.2018.10.035

Abstract

Constraining sources and site-specific processes of trace elements in speleothem geochemical records is key to an informed interpretation. This paper examines a 10-year data set of drip water solutes from Harrie Wood Cave, south-eastern Australia, and identifies the processes that control their response to El Niño-Southern Oscillation events which varies the site water balance. The contributions of aerosol and bedrock end-members are quantified via hydrochemical mass balance modelling. The parent bedrock is the main source for the drip water solutes: Mg, Sr, K and trace elements (Ba, Al, V, Cr, Mn, Ni, Co, Cu, Pb and U), while atmospheric aerosol inputs also contribute significantly to drip water trace elements and Na, K and Zn. A laboratory investigation evaluating water-soluble fractions of metals in soil samples and soil enrichment factors provided a basis for understanding metal retainment and release to solution and transport from the soil zone. These results identified the role of the soil as a sink for: trace metals, Na and K, and a secondary source for Zn. Further, soil processes including: cation exchange, K-fixation, metal adsorption to colloids and the release of Zn associated with organic matter degradation further modify the chemical composition of the resultant drip waters. This research is significant for the south-eastern Australian region, as well as other sites in a karst setting with clay-rich soil. In particular these results reveal that the response of drip water chemistry to hydroclimatic forcing is non-linear, with the greatest response observed when the long-term gradient in the cumulative water balance reverses. This longer-term drip water monitoring dataset is significant because it provides the pivotal framework required to reliably identify suitable trace element proxies for interpretation in geochemical speleothem records on multi-decadal timescales.

Keywords: Aerosols; Cation exchange; Colloidal mobilisation; K-fixation; Karst soils; Trace element.