U. Saravana Kumar

Determination of recent sedimentation rates and pattern in Lake Naini, India by 210Pb and 137Cs dating techniques

Abstract Environmental 210 Pb (natural) and 137 Cs (anthropogenic) dating techniques were applied to determine recent sedimentation rates and pattern in Lake Naini, Uttar Pradesh, India. Core samples from different locations in the lake were collected and analysed for 210 Pb and 137 Cs. From the analysis it appears that the lake is not reducing in depth at a rate reported by earlier investigations. Recent sedimentation rate, estimated by the 210 Pb dating technique, has been found to be fairly constant at one location (the mean dry mass sedimentation rate being 0.112±0.010 g cm −2 a −1 ) but varying at other locations in the lake (the dry mass sedimentation rates ranging from 0.026±0.010 to 0.421±0.050 g cm −2 a −1 ). At all locations the short-term rates (for the last three decades) derived from 137 Cs, a fall-out nuclide, have been observed to be marginally higher compared to long-term (last 120–150 yr) rates deduced from 210 Pb. The spatial and depthwise distribution of 137 Cs and 210 Pb and spatial variation of surface 210 Pb/ 137 Cs in the obtained sediment cores of the lake, along with their textural properties (like porosity and water content), provide preliminary information on the existence of different depositional zones throughout the lake and on the physico-chemical nature of the sedimentation process in the lake (i.e., bioturbation, slumping, sediment focusing, land erosion/land slide etc).

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.

Isotope Hydrogeological Factors Control Transport of Radon-222 in Hard Rock Fractured Aquifer of Bangalore, Karnataka

Radon-222 is a daughter element of radium-226 and are member of the uranium decay series. Radon-222 concentrations in groundwater of Bangalore city in different geological units were measured in 42 tube wells. The study area is underlain by Granite, Migmatite, Granodiorite and Gneiss rock and many dolerite dykes. The radon-222 concentration in groundwater is widely varying and ranging from 14 to 1000 Bq/L with an average value of 172.4 Bq/L. Significant differences in the radon-222 concentrations in groundwater among geological units were observed. The radon-222 distribution in groundwater is related to the presence of uranium in aquifer materials of the various rock types. Uranium concentration in groundwater is ranging from 0.2 to 523 μg/L. Transport of radon-222 through bedrock by water depends mainly on the percolation of water through the pore and along fractured planes of the rocks. Rn-222 cannot travel farther than several hundred meters away from their origin because of its short half-life of 3.8 days. It may travel the farthest within fractured or fissured geological formation where groundwater movement is fastest. The study shows that radon concentration in groundwater is controlled by geohydrological and hydrochemical characteristics of the study area.