Fingerprinting dissolved organic compounds : a potential tool for identifying the surface infiltration environments of meteoric groundwaters

Stillings, M. and Lunn, R.J. and Shipton, Z.K. and Lord, R.A. and Thompson, S. and Knapp, M. (2024) Fingerprinting dissolved organic compounds : a potential tool for identifying the surface infiltration environments of meteoric groundwaters. Geoenergy. ISSN 2755-1725 (In Press)

[thumbnail of Stillings-etal-Geoenergy-2024-Fingerprinting-dissolved-organic-compounds]
Preview
 Text. Filename: Stillings-etal-Geoenergy-2024-Fingerprinting-dissolved-organic-compounds.pdf
Accepted Author Manuscript
License: Creative Commons Attribution 4.0 logo
Download (2MB)| Preview

Abstract

Current methods for tracing decades-old groundwaters rely on isotope geochemistry, to determine groundwater age and altitude at the point of infiltration. Temporal and spatial variability in atmospheric conditions, and water-rock interactions, can make the interpretation of isotopes uncertain. Here, we propose a new method of groundwater tracing based on fingerprinting of natural dissolved organics. We present our initial findings from the Grimsel Test Site in Switzerland, located within a fractured granite. Using two-dimensional gas chromatography, we derive detailed organic fingerprints from surface soils at several locations and show that different soils produce distinctly different dissolved organic signatures. We then compare the soils with groundwater and lake water using a non-targeted approach using principal component analysis and hierarchical cluster analysis. Our analysis finds three statistically significant clusters. Most groundwaters are clustered with the lakewater samples, but two are clustered with soil from the highest altitude surface sampling location. We hypothesize that for samples to form a significant cluster, they must have derived from a common environment, with a unique combination of organic compounds. For groundwaters to cluster with soil samples or lakewater, we theorize there must be a hydraulic connection between the type of infiltration environment and the groundwater sampling locations within each cluster. Our research demonstrates that organic molecules derived from the surface environment can be used to discriminate near-surface environment(s) through which meteoric groundwater has infiltrated. Organic fingerprinting could prove a powerful tool for improved understanding of groundwater flow systems, particularly when combined with other complementary techniques.

CORE (COnnecting REpositories)