Stable isotope dynamics of groundwater interactions with Ganges river

Abstract

Groundwater depletion has been an emerging crisis in recent years, especially in highly urbanized areas as a result of unregulated exploitation, thus leaving behind an insufficient volume of usable freshwater. Presently Ganges river basin, the sixth largest prolific fluvial system and sustaining a huge population in South Asia, is witnessed to face (i) aquifer vulnerability through surface waterborne pollutant and (ii) groundwater stress due to summer drying of river as a result of indiscriminate groundwater abstraction. The present study focuses on a detailed sub-hourly to seasonally varying interaction study and flux quantification between river Ganges and groundwater in the Indian subcontinent which is one of the first documentations done on a drying perennial river system that feeds an enormous population. Contributing parameters to the total discharge of a river at its middle course on both temporal and spatial scale is estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ 18 O and δ 2 H) and electrical conductivity data. Results from this model report groundwater discharge in river to be the highest in pre-monsoon, that is, 30%, whereas, during postmonsoon the contribution lowers to 25%; on the contrary, during peak monsoon, the flow direction reverses thus recharging the groundwater which is also justified using annual piezometric hydrographs of both river water and groundwater. River watergroundwater interaction also shows quantitative variability depending on river morphometry. The current study also provides insight on aquifer vulnerability as a result of pollutant mixing through interaction and plausible attempts towards groundwater management. The present study is one of the first in South Asian countries that provides temporally and spatially variable detailed quantification of baseflow and estimates contributing parameters to the river for a drying mega fluvial system.

Innovative Assessment of Mun River Flow Components through ANN and Isotopic End-Member Mixing Analysis

“…The precision of IEMMA outcomes, influenced by factors like isotopic fractionation [12,65], irrigation return flows [66], and groundwater contributions [25], introduces uncertainties in interpreting isotopic data, crucial for advancing hydrological model accuracy. Isotopic fractionation, the separation of isotopes during physical or chemical processes, can significantly affect δ 18 O signatures, potentially masking true source contributions [25,47,54]. Irrigation return flows, with distinct isotopic signatures, can alter a river's isotopic composition, skewing the analysis of tributary contributions [66].…”

“…The technique of Isotopic End-Member Mixing Analysis (IEMMA) leverages these isotopic signatures to detail the contributions of various sources to river flow, offering a deeper look into the hydrological cycle and tributary-main river interactions [21][22][23][24]. IEMMA has been extensively applied to trace the sources of river water, including rainfall, groundwater, and glacial melt contributions [22,25]. This helps in understanding the seasonal variability of river dynamics and the impact of climatic factors [21].…”

Innovative Assessment of Mun River Flow Components through ANN and Isotopic End-Member Mixing Analysis

“…The precision of IEMMA outcomes, influenced by factors like isotopic fractionation [13,68], irrigation return flows [69], and groundwater contributions [27], introduces uncertainties in interpreting isotopic data, crucial for advancing hydrological model accuracy. Isotopic fractionation, the separation of isotopes during physical or chemical processes, can significantly affect δ 18 O signatures, potentially masking true source contributions [27,50,57]. Irrigation return flows, with distinct isotopic signatures, can alter a river's isotopic composition, skewing the analysis of tributary contributions [69].…”

“…The technique of isotopic end-member mixing analysis (IEMMA) advantages these isotopic signatures to detail the contributions of various sources to river flow, offering a deeper look into the hydrological cycle and tributary-main river interactions [23][24][25][26]. IEMMA has been extensively applied to trace the sources of river water, including rainfall, groundwater, and glacial melt contributions [24,27]. This helps in understanding the seasonal variability of river dynamics and the impact of climatic factors [23].…”

Surface Water Isoscape Modeling in the Himalayan Region: An Alternative for Moisture Source Investigation, Hydrograph Separation, and Paleolatitude Estimation

“…We observe a great difference between LMWL and RRL evaporation losses in the three basins. The evaporation losses from surface water in the GRB, as indicated by RRL, appear to be consistently significant in the GRB, possibly because of the large urbanization (Das et al., 2021; Joshi et al., 2018; Lapworth et al., 2021) and abundances of surface water, such as wetlands, rivers, tributaries, lakes, canals, and shallow groundwater that stores water with a longer residence time (Lapworth et al., 2021). However, the lower slope (7.8) of LMWL in the IRB suggests a significant sub‐cloud evaporative effect of failing raindrops due to the arid impact of the basin and the addition of water from local moisture sources.…”