Spatial and seasonal controls on dissolved organic matter composition in shallow aquifers under the rapidly developing city of Patna, India

George J L Wilson; Chuanhe Lu; Dan J Lapworth; Arun Kumar; Ashok Ghosh; Vahid J Niasar; Stefan Krause; David A Polya; Daren C Gooddy; Laura A Richards

doi:10.1016/j.scitotenv.2023.166208

Spatial and seasonal controls on dissolved organic matter composition in shallow aquifers under the rapidly developing city of Patna, India

Sci Total Environ. 2023 Dec 10:903:166208. doi: 10.1016/j.scitotenv.2023.166208. Epub 2023 Aug 10.

Authors

Affiliations

¹ Department of Earth and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, The University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, United Kingdom.
² British Geological Survey, Maclean Building, Wallingford, Oxfordshire OX10 8BB, United Kingdom.
³ Mahavir Cancer Sansthan and Research Center, Phulwarisharif, Patna 801505, Bihar, India.
⁴ Department of Chemical Engineering, The University of Manchester, M13 9PL Manchester, United Kingdom.
⁵ School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT Birmingham, United Kingdom; LEHNA- Laboratoire d'ecologie des hydrosystemes naturels et anthropises, University of Lyon, France.
⁶ Department of Earth and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, The University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, United Kingdom. Electronic address: laura.richards@manchester.ac.uk.

PMID: 37567307
DOI: 10.1016/j.scitotenv.2023.166208

Abstract

The distribution and composition of dissolved organic matter (DOM) affects numerous (bio)geochemical processes in environmental matrices including groundwater. This study reports the spatial and seasonal controls on the distribution of groundwater DOM under the rapidly developing city of Patna, Bihar (India). Major DOM constituents were determined from river and groundwater samples taken in both pre- and post-monsoon seasons in 2019, using excitation-emission matrix (EEM) fluorescence spectroscopy. We compared aqueous fluorescent DOM (fDOM) composition to satellite-derived land use data across the field area, testing the hypothesis that the composition of groundwater DOM, and particularly the components associated with surface-derived ingress, may be controlled, in part, by land use. In the pre-monsoon season, the prominence of tryptophan-like components likely generated from recent biological activity overwhelmed the humic-like and tyrosine-like fluorescence signals. Evidence from fluorescence data suggest groundwater in the post-monsoon season is composed of predominantly i) plant-derived matter and ii) anthropogenically influenced DOM (e.g. tryptophan-like components). Organic tracers, as well as Eh and Cl^-, suggest monsoonal events mobilise surface-derived material from the unsaturated zone, causing dissolved organic carbon (DOC) of more microbial nature to infiltrate to >100 m depth. A correlation between higher protein:humic-like fluorescence and lower vegetation index (NDVI), determined from satellite-based land use data, in the post-monsoon season, indicates the ingression of wastewater-derived OM in groundwater under the urban area. Attenuated protein:humic-like fluorescence in groundwater close to the river points towards the mixing of groundwater and river water. This ingress of surface-derived OM is plausibly exacerbated by intensive groundwater pumping under these areas. Our approach to link the composition of aqueous organics with land use could easily be adapted for similar hydrogeochemical settings to determine the factors controlling groundwater DOM composition in various contexts.

Keywords: Dissolved organic matter characterisation; Fluorescence spectroscopy; Groundwater contamination; Parallel factor analysis (PARAFAC); Surface-groundwater interactions.