Identification of Recharge Processes in Groundwater in Hard Rock Aquifers of Madurai District Using Stable Isotopes

Stable isotopes of H and O are the integral parts of water molecule and serve as ideal tracers to understand the recharge processes in groundwater. Hence, a study has been conducted in hard rock aquifers of Madurai District of Tamilnadu to identify the recharge processes using stable isotopes. A total of 54 groundwater samples were collected representing the entire district from various lithounits during post monsoon. Samples were analysed for pH, EC, Ca2+, Mg2+, Na+, K+, Cl− HCO3−, SO42−, PO43−, H4SiO4, F−, δ18O and δD. Cl− and HCO3− were the dominant ions in groundwater samples. Average values of Cl− and HCO3− ranged from 247 and 244 mg/L in fissile hornblende biotite gneiss, 262 and 268 mg/L in Charnockite, 75 and 185 mg/L in quartzite, 323 and 305 mg/L in granite, 524 and 253 mg/L in floodplain alluvium rock types. Geochemical signatures of groundwater were used to identify the chemical processes that control hydrogeochemistry. Interpretation of δ18O and δD indicates recharge from the meteoric water in charnockite, quartzite, granite and some samples of fissile hornblende biotite gneiss. It is also inferred that recharge take place from evaporated water in floodplain alluvium and fissile hornblende biotite gneiss

Isomerization of Vaccenic Acid to cis and trans C18:1 Isomers During Biohydrogenation by Rumen Microbes

International audienceIn ruminants, cis and trans C18:1 isomers are intermediates of fatty acid transformations in the rumen and their relative amounts shape the nutritional quality of ruminant products. However, their exact synthetic pathways are unclear and their proportions change with the forage:concentrate ratio in ruminant diets. This study traced the metabolism of vaccenic acid, the main trans C18:1 isomer found in the rumen, through the incubation of labeled vaccenic acid with mixed ruminal microbes adapted to different diets. [1-13C]trans-11 C18:1 was added to in vitro cultures with ruminal fluids of sheep fed either a forage or a concentrate diet. 13C enrichment in fatty acids was analyzed by gas-chromatography-mass spectrometry after 0, 5 and 24 h of incubation. 13C enrichment was found in stearic acid and in all cis and trans C18:1 isomers. Amounts of 13C found in fatty acids showed that 95% of vaccenic acid was saturated to stearic acid after 5 h of incubation with the concentrate diet, against 78% with the forage diet. We conclude that most vaccenic acid is saturated to stearic acid, but some is isomerized to all cis and trans C18:1 isomers, with probably more isomerization in sheep fed a forage diet