Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province, India: Insinuation on CO2 Consumption

Abstract

Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline earth elements to total cations and HCO 3 [Cl + SO 4 reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO 4 , and NO 3 are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg-HCO 3 type progressively evolves to Ca + Na-HCO 3 and Na-Ca-HCO 3 class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO 3 and Ca + Mg vs HCO 3 supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation of CaCO 3 supported by improved correlation coefficients between Na + Ca vs HCO 3 and negative correlation of Ca vs HCO 3 , respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function of selective dissolution of olivine [ pyroxene followed by plagioclase feldspar.The data suggest siallitization (L \ R and R k ) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite) products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component range from 6.98 to 36.65 tons/km 2 /yr, respectively. The values of the CO 2 consumption rates range between 0.18 9 10 6 mol//km 2 /yr (groundwater) and 0.9 9 10 6 mol/km 2 /yr (surface water), which indicates that the groundwater forms a considerable fraction of CO 2 consumption, an inference, that is, not taken into contemplation in most of the studies.

Evaluating pollution potential of leachate from landfill site, from the Pune metropolitan city and its impact on shallow basaltic aquifers

“…Geochemistry of "typical" groundwater from basaltic aquifer There is fairly a good amount of information available on background chemistry of groundwater from uncontaminated basaltic aquifers (Pawar and Shaikh 1995;Pawar et al 2008). However, specifically, the studies on the chemistry of groundwater from Pune area are carried out by Pawar et al (1982).…”

“…Their findings indicate that while the wells piercing through basaltic, weathered basaltic, and doleritic dyke aquifers exhibit Ca+Mg-HCO 3 water type, the alluvial aquifers are dominantly characterized by Ca+Mg+Na-HCO 3 type. The ionic load of the groundwater is dominantly derived from weathering of ferromagnesian silicates (olivine and augite) and plagioclase feldspar, besides some contribution from zeolites (Pawar et al 2008). This information has been used in comparing the characteristics of groundwater modified by mixing of leachate derived from MSW in the study area.…”

“…Conversely, Fig. 1 (Pawar et al 2008). Furthermore, the cooling features such as columnar joints serve as hydrologic discontinuities, which in turn function as pathways for infiltration of rainwater.…”

“…The principal lithologic unit in the study area is basalt, which is distinguished by olivine (2-3%), pyroxene (augite; 24-47%), and plagioclase feldspar (labradorite; 40-65%) (Bean et al 1986;Subbarao et al 1994). Incongruent dissolution of these primary silicate minerals in the groundwater can be given as follows (Pawar et al 2008 Augite mHCO 3 /mSiO 2 = 6:1 and mCa/mMg = 1:1…”

Use of Landsat ETM+ data for delineation of water bodies in hilly zones

“…Some of them have used satellite data and GIS techniques for estimations of the total volume of water in man-made as well as natural water bodies (Bhagat 2008) and pollution in water bodies including oceans, rivers, lakes and groundwater (Kumar et al 2007;Pawar et al 2008). The estimations include the area covered and spread of water storage and river tracks in floods and ocean water in high tide conditions in coastal areas.…”