TEMPORAL DYNAMICS OF GROUNDWATER DISSOLVED ORGANIC MATTER COMPOSITION IN NORTHEAST INDIA

Temporal variation in groundwater dissolved organic matter (DOM) affects numerous aqueous biogeochemical reactions (Rowland et al., 2007; Hofmann et al., 2020). Prominent seasonal variations in DOM composition in aquifers of Northeast India are not fully understood (Wilson et al., in review). In this study, we used fluorescence spectroscopy and bulk DOM measurements to quantify seasonal change in DOM composition in a transect of groundwater and surface water sites in West Bengal. The sampling period ranged from the onset of the monsoon season to late-July (2022), covering a critical point in seasonal hydrological conditions. Our findings revealed that bulk DOM remained relatively consistent in groundwater (n = 10) and ponds (n = 3), though there were distinct changes in fluorescent DOM (fDOM). A decrease in tryptophan-like fluorescence, relative to recalcitrant carbon, suggests that microbial activity may be inhibited by the onset of monsoon. The consistency in Cl^- and electrical conductively (EC) may confirm that the changes on this timescale are related to microbe metabolic processes, rather than infiltration of surface-derived material. On the other hand, a localized spike in redox potential (E_h) combined with increased fDOM and Fluorescence Index (FI) may suggest autochthonous production of organic matter, following the introduction of oxygenated water. Rivers (n = 2) exhibited an increased presence of terrestrially-derived DOM during the sampling period – this observation suggests that rivers may act as conduits for the transport of terrestrial DOM, particularly during the monsoon season. The observed changes in fDOM, physical parameters and geochemistry suggest complex interactions between hydrological processes and biogeochemical reactions within aquifers and surface waters. These findings contribute to a better understanding of the characteristics and dynamics of organic matter in the environment.

Acknowledgements

A DKO Fellowship is acknowledged for LAR and for GJLW’s PhD studentship. We acknowledge a Turing Scheme grant and IITKGP for facilitating the fieldwork.

References

Hofmann et al. (2020), FMICB, doi: 10.3389/fmicb.2020.543567

Rowland et al. (2007), Geobiology, doi: 10.1111/j.1472-4669.2007.00100.x

Wilson et al. (in review), Spatial and Seasonal Controls on Dissolved...