Noble Jacob

Estimation of snow and glacier melt contribution to Liddar stream in a mountainous catchment, western Himalaya: an isotopic approach

ABSTRACT Snow- and glacier-dominated catchments in the Himalayas are important sources of fresh water to more than one billion people. However, the contribution of snowmelt and glacier melt to stream flow remains largely unquantified in most parts of the Himalayas. We used environmental isotopes and geochemical tracers to determine the source water and flow paths of stream flow draining the snow- and glacier-dominated mountainous catchment of the western Himalaya. The study suggested that the stream flow in the spring season is dominated by the snowmelt released from low altitudes and becomes isotopically depleted as the melt season progressed. The tracer-based mixing models suggested that snowmelt contributed a significant proportion (5–66 %) to stream flow throughout the year with the maximum contribution in spring and summer seasons (from March to July). In 2013 a large and persistent snowpack contributed significantly (∼51 %) to stream flow in autumn (September and October) as well. The average annual contribution of glacier melt to stream flow is little (5 %). However, the monthly contribution of glacier melt to stream flow reaches up to 19 % in September during years of less persistent snow pack.

Taxonomy of groundwater quality using multivariate and spatial analyses in the Tuticorin District, Tamil Nadu, India

AbstractA holistic appraisal of the quality of groundwater from the Tuticorin District has been conducted using multivariate statistical and spatial analyses. The objectives of the study were to delineate the spatial and temporal variabilities in groundwater quality and to understand its suitability for human uses. A total of 100 groundwater samples were collected and analyzed for major cations and anions during pre-monsoon and post-monsoon. Water quality index rating was calculated to quantify overall water quality for human consumption. The PRM samples exhibit poor quality in greater percentage when compared with POM due to the dilution after rainfall. Correlation, factor analysis, and plot of the factor scores reflect the seawater intrusion and weathering process. The mineral stability diagrams indicated that the groundwater is in equilibrium with kaolinite and Ca-montmorillonite, whereas Gibbs plot showed that the chemical composition of groundwater in both districts is controlled by the natural weathering processes irrespective of seasons. The major water type identified in this study is the Ca2+–Mg2+–HCO3− type, which degrades into predominantly Na+–Cl−–SO42− more saline groundwater toward the coast.

Estimating mean residence time of karst groundwater in mountainous catchments of Western Himalaya, India

ABSTRACT The mean residence time (MRT) of karst groundwater in three mountainous catchments of the Western Himalaya was estimated using multiple approaches: the tritium method, the sine wave model and tracer tests. Water samples were collected from precipitation, glacier melt, streams and karst springs for δ2H and tritium analysis during 2012 and 2013. High tritium values were observed in winter precipitation and low values in summer precipitation. The variation of tritium in karst springs was similar to that of the streams, whereas glacier melt showed lower tritium values. The MRT of cold karst springs was shorter than that of warm karst springs. The tracer breakthrough curves (TBC) retrieved for different springs suggested a short travel time for groundwater and possibly conduit flow. Deterioration of water quality and variation in flux magnitude are the two main practical consequences of the short travel time of karst groundwater in the region. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR K. Heal

Letter to the Editor: Radon isotope assessment of Submarine Groundwater Discharge (SGD) in Coleroon River Estuary, Tamil Nadu, India

I have read with much interest the article ‘‘Radon isotope assessment of Submarine Groundwater Discharge (SGD) in Coleroon River Estuary, Tamil Nadu, India’’ authored by Prakash et al. 2018 (https://doi.org/10.1007/s10967-0185877-2) that describes the estimation of SGD in Coleroon River Estuary, Tamil Nadu, India from the continuous Rn measurement of groundwater and pore water samples at three different locations for a period of 10 days. In this context, I would like to state that, most of the SGD studies carried out worldwide using Rn isotopes are based on the continuous monitoring of Rn in coastal seawater and not by continuous monitoring of Rn in groundwater [1–7]. Also, the SGD fluxes are generally calculated using Rn mass balance in the coastal seawater. However, the authors measured the temporal variation of Rn in groundwater/pore water, and they calculate the SGD rates using the same Rn mass balance equation [1, 5] derived for coastal seawater, which, according to me, is not correct. The dynamics of coastal seawater and groundwater are completely different and are governed by various physical processes. Hence, the variation of Rn in groundwater with respect to tidal cycles is not the same as that of coastal seawater. Therefore, the calculation of SGD rates from the variation of Rn in groundwater is questionable. Also, I am quite skeptical about the accuracy of Rn measurement attaining a minimum detectable activity of 5 Bq/m for 20 min of counting when the sample is collected in 125 ml bottle. The reference for the measurement procedures of Rn in groundwater is also not cited in the paper.

Distribution of environmental tritium in rivers, groundwater, mine water and precipitation in Goa, India

Tritium concentration in rivers, groundwater, precipitation and mine pits water, all over Goa state was characterized to find out spatial and temporal variability of tritium. Twenty four water samples were collected during pre-monsoon and post-monsoon and analyzed for their tritium concentration. The mean tritium concentration in surface and sub-surface hydrosphere is 2.5 (±0.6) TU. The mean concentration of tritium in rivers, groundwater, mines pits water and rain water are 2.9 (±0.5) TU, 1.95 (±0.5) TU, 2.5(±0.3) TU and 3.1(±0.1) TU respectively. The tritium distribution in all the samples shows modern precipitation (post-1950) component in surface and sub-surface hydrosphere of Goa. The HYSPLIT4.0 air mass trajectory model and atmospheric circulation pattern suggest that the moisture origin was from the Arabian Sea and this low tritium moisture is diluting the tritium concentration of surface hydrosphere near the coastal area. The tritium concentration in surface hydrosphere shows more and more enrichment as one move inland (i.e. away from the coast). Significant seasonal change is observed in the surface hydrosphere. The pre-monsoon samples showed higher tritium concentration than post-monsoon samples. This may be due to high rate of re-evaporation of water and a reduction in the supply of oceanic moisture during the summer (pre-monsoon).

Environmental Isotope Investigation to Understand the Groundwater Recharge from Irrigation Tanks in Thirumal Area, Madurai

Madurai is a water scarce, semiarid region in southern part of Peninsular India. Currently, tank-fed agriculture development programme is being implemented in this region by utilizing the large number of traditionally existing minor irrigation tanks. Hence, an isotope hydrological investigation has been conducted in the Thirumal village, Madurai district to demarcate the zone of influence (i.e., the command area) of the cascade of tanks (4 tanks) and to quantify the groundwater recharge to the downstream wells. Pre (October 2011) and post (February 2012) monsoon samples were collected from the irrigation tanks, open wells upstream and downstream of the tanks etc. and analysed for δ2H, δ18O and hydrochemistry. The downstream well samples lie in a mixing line between the tank water and the rainwater in the δ18O - δ2H plot, indicating groundwater recharge from the irrigation tanks and the area of influence of these tanks were demarcated. The tanks contribution to the downstream wells varies from 97% at 20 m to 41% upto 880m for the first tank, 93% at 60m to 26% at 880m for the second tank, 95% at 30m to 18% at 940m for the fourth tank and varies from 25% at 20 m to 9% at 550m for the third tank.