Characterization of Mechanisms and Processes Controlling Groundwater Recharge and its Quality in Drought-Prone Region of Central India (Buldhana,Maharashtra) Using Isotope Hydrochemical and End-Member Mixing Modeling

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO₃ facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ²H, δ¹⁸O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

     

Study on the saturation index of the carbonates in the groundwater using WATEQ4F, in layered coastal aquifers of Pondicherry

A study was conducted to bring out the relationship and behavior of different Saturation Index (SI) of carbonate minerals in layered coastal aquifers. Carbonates present in groundwater aids in different nature of the water like hardness, partial pressure of carbon-di-oxide (pCO₂), pH and saturation index of different carbonate minerals at various temperatures. The SI of the carbonates helps us to define the thermodynamic stability of water and to find out the geochemical behavior of water. 98 groundwater samples were collected from specific aquifers (alluvium, upper Cuddalore, lower Cuddalore and Cretaceous) during Pre-Monsoon (May 2007) and Post-Monsoon (January 2008) seasons. The physicochemical parameters such as pH, EC, Ca, Mg, Na, K, Cl, HCO₃, SO₄ and PO₄ were analyzed. Geochemical model, WATEQ4F was used to calculate the SI of different minerals. The SI was studied in relation to mHCO₃ concentration, pCO₂ and correlation between SI of different minerals.     

Tracer-based estimation of temporal variation of water sources: an insight from supra- and subglacial environments

ABSTRACT

The temporal variations in electrical conductivity and the stable isotopes of water, δD and δ¹⁸O, were examined at Chhota Shigri Glacier, India, to understand water sources and flow paths to discharge. Discharge is highly influenced by supraglacially derived meltwater during peak ablation, and subglacial meltwaters are more prominent at the end of the melt season. The slope of the best fit linear regression line for δD versus δ¹⁸O, for both supraglacial and runoff water, is lower than that for precipitation (snow and rain) and surface ice, indicating strong isotopic fractionation associated with the melting processes. The slope of the local meteoric water line (LMWL) is close to that of the global meteoric water line (GMWL), reflecting that the moisture source is predominantly oceanic. The d-excess variation in rainwater confirms that the southwest monsoon is the main contributor during summer while the remainder including winter is mostly influenced by westerlies.     

A study on the factors affecting the stable isotopic composition in precipitation of Tamil Nadu,India

Stable isotope measurements in precipitation help us to form the basic inference about the origin and the state of water in different environments. The precipitation samples collected during the South West Monsoon (SWM) during August 2007 from 37 different locations in the state help in deriving the first preliminary local meteoric water line (LMWL) for the Tamil Nadu State. The study reveals that there are three main sources of water vapours, namely South East Arabian Sea (SEAS), Indian Ocean (IO) and evaporation from local water bodies. There are wide variations in the altitude and amount of rainfall received in the state. It is also noted that there is a significant variation in the latitude and the distance from the coast. Hence, an attempt is made in this paper to study the factors controlling the composition of stable isotopes in precipitation with reference to amount of rainfall, latitude, altitude and the continental effect. The altitude and continental effect shows good correlation to the variations in stable isotope composition. Copyright © 2009 John Wiley & Sons, Ltd.     

Dissolved Organic Carbon in Multilayered Aquifers of Pondicherry Region (India): Spatial and Temporal Variability and Relationships to Major Ion Chemistry

Carbon, which is an essential element found in rocks and minerals, is used by biologically diverse life forms as a source of energy. Natural organic carbon is mainly derived from decomposing vegetation and other organic matter in the soil zone. Dissolved organic carbon (DOC) is an important component in biogeochemical cycling of elements characterized by high susceptibility to leaching. The significance of DOC was studied in layered coastal aquifers of the Pondicherry region during four different seasons. Pondicherry region has varied geological setup ranging from Cretaceous to Recent formations. A total of 324 groundwater samples were collected from various aquifers, namely Alluvium, Tertiary, Cretaceous, and Mixed formations, during different seasons of pre-monsoon, southwest monsoon, northeast monsoon, and post-monsoon. The samples were analyzed for major ions and DOC. The range of DOC in the study area is 0–10 mg/l. Very high DOC concentrations were measured in most of the samples from Alluvium and Upper Cuddalore Formation and in few samples from the Lower Cuddalore Formation. The relationships of DOC with other ions in this study indicate that the hydrochemistry of groundwater was controlled by both aerobic and anaerobic environments in the different formations of the study area.     

Isotope hydrochemical approach to understand fluoride release into groundwaters of Ilkal area,Bagalkot District,Karnataka, India

Isotope and hydrochemical investigations have been carried out in the Ilkal area of Karnataka, India, in order to determine the source and mechanism of fluoride release into groundwaters and to understand groundwater hydrochemistry. Agriculture, granite quarrying and rock-polishing industries are the main occupations in this area. Closepet granite, Peninsular gneiss and Dharwar schists are the major geological formations. Results show that the fluoride concentration in groundwater is 0.3–6.5 mg/L and it is found to increase from recharge area to discharge area. Fluoride variability is found to be influenced by the geology of the area and depth wise correlation was not observed. Water samples are unsaturated with respect to fluorite, indicating the possibility of further increase in fluoride in groundwater. Positive correlations between fluoride with sodium and bicarbonate in groundwater show that high fluoride content and alkaline sodic characteristics are the result of dissolution of fluoride bearing minerals, possibly derived from weathered granite and gneiss. A positive correlation between fluoride and δ¹⁸O, and the presence of high tritium in fluoride-contaminated groundwater, point to contribution from surface waters, contaminated by anthropogenic activities. Dumping of rock wastes that are rich in fluoride into the streams by the rock-polishing industries plays a significant role in contaminating groundwater.     

Geochemical characterization of groundwater from an arid region in India

A study on the geochemical processes in arid region of western India (Kachchh district) was carried out using major, minor, trace metal data and isotopic composition (δ²H, δ¹⁸O) of groundwaters. Results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments, dissolution of salts in root zone and incongruent dissolution of carbonate minerals. Common inorganic contaminants such as fluoride, nitrate and phosphate are within drinking water permissible limits. However, most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose. Trace metal data indicates no contamination from toxic elements such as arsenic and lead. An increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources. The chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition. Environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge. The processes responsible for observed brackishness are identified using chemical and isotope indicators, which are in agreement with subsurface lithology and hydrochemistry. These data though represent hydrochemical scenario of 2001 can still be used for understanding the long-term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models.