Groundwater solute chemistry,hydrogeochemical processes and fluoride contamination in phreatic aquifer of Odisha,India

The work investigates the major solute chemistry of groundwater and fluoride enrichment(F^(-))in the shallow phreatic aquifer of Odisha.The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F^(-)contamination.A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F^(-) content.Groundwater is alkaline in nature(range of pH:6.6-8.7;ave.:7.9)predominated by moderately hard to very hard types.Average cation and anion chemistry stand in the orders of Ca^(2+)>Na^(+)>Mg^(2+)>K^(+) and HCO_(3)^(-)>Cl^(-)>SO_(4)^(2-)>CO_(3)^(2-) respectively.The average mineralization is low(319 mg/L).The primary water types are Ca-Mg-HCO_(3) and Ca-Mg-Cl^(-)HCO_(3),followed by Na-Cl,Ca-Mg-Cl,and Na-Ca-Mg-HCO_(3)^(-)Cl.Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination,etc.The ratio of Na^(+)/Ca^(2+)>1.0 comprises Na-HCO_(3)(Cl)water types with F^(-)>1.0 mg/L(range 1.0-3.5 mg/L)where the F^(-)bears geogenic source.Positive relations exist between F^(-)and pH,Na^(+),TDS,and HCO_(3)^(-).It also reflects a perfect Na-TDS correlation(0.85).The ratio of Na^(+)/Ca^(2+)<1.0 segregates the sample population(F^(-)range:1.0-4.0 mg/L)with the F derived from anthropogenic sources.Such water types include Ca-Mg-HCO_(3)(Cl)varieties which are recently recharged meteoritic water types.The F^(-) levels exhibit poor and negative correlations with the solutes in groundwater.The Na-TDS relation remains poor(0.12).In contrast,the TDS levels show strong correlations with Ca^(2+)(0.91),Mg^(2+)(0.80)and even Cl^(-)(0.91).The majority of the monitoring points with the anthropogenic sources of groundwater F^(-) are clustered in the Hirakud Canal Command area in the western parts of the state,indicating the role of irrigation return flow in the F^(-) contamination.

Recharge and vulnerability assessment of groundwater resources in North west India:Insights from isotope-geospatial modelling approach

Recent studies indicate dwindling groundwater quantity and quality of the largest regional aquifer system in North West India,raising concern over freshwater availability to about 182 million population residing in this region.Widespread agricultural activities have resulted severe groundwater pollution in this area,demanding a systematic vulnerability assessment for proactive measures.Conventional vulnerability assessment models encounter drawbacks due to subjectivity,complexity,data-prerequisites,and spatial-temporal constraints.This study incorporates isotopic information into a weighted-overlay framework to overcome the above-mentioned limitations and proposes a novel vulnerability assessment model.The isotope methodology provides crucial insights on groundwater recharge mechanisms(18O and 2H)and dynamics(3H)-often ignored in vulnerability assessment.Isotopic characterisation of precipitation helped in establishing Local Meteoric Water Line(LMWL)as well as inferring contrasting recharge mechanisms operating in different aquifers.Shallow aquifer(depth<60 m)showed significant evaporative signature with evaporation loss accounting up to 18.04%based on Rayleigh distillation equations.Inter-aquifer connections were apparent from Kernel Density Estimate(KDE)and isotope correlations.A weighted overlay isotope-geospatial model was developed combining 18O,3H,aquifer permeability,and water level data.The central and northern parts of study area fall under least(0.29%)and extremely(1.79%)vulnerable zones respectively,while majority of the study area fall under moderate(42.71%)and highly vulnerable zones(55.20%).Model validation was performed using groundwater NO3-concentration,which showed an overall accuracy up to 82%.Monte Carlo Simulation(MCS)was performed for sensitivity analysis and permeability was found to be the most sensitive input parameter,followed by 3H,18O,and water level.Comparing the vulnerability map with Land Use Land Cover(LULC)and population density maps helped in precisely identifying the high-risk sites,warranting a prompt attention.The model developed in this study integrates isotopic information with vulnerability assessment and resulted in model output with good accuracy,scientific basis,and widespread relevance,which highlights its crucial role in formulating proactive water resource management plans,especially in less explored data-scarce locations.

Assessment of surface and subsurface waterlogging, water level fluctuations, and lithological variations for evaluating groundwater resources in Ganga Plains

In the present study,the multi-temporal satellite images of IRS P6 LISS III were used to map waterlogging dynamics over different seasons.An area of 594.36 km2(6.75%)and 4.17 km^(2)(0.04%)was affected by surface waterlogging during pre and postmonsoon season,respectively.The average annual groundwater level fluctuations were calculated using 18 years(1990-2007)pre and postmonsoon groundwater level data to identify the areas which are under groundwater induced waterlogging conditions.The soil map clearly indicates that salinity and sodicity exhibit the highest severity and occur in areas with shallow groundwater levels.The hydrogeomorphical units mapped using IRS P6 LISS III satellite images are flood plain,alluvial plain,paleochannels,and oxbow lakes.The study revealed that 44.65%areas have very good to excellent groundwater resources.The litholog data clearly indicate an alternating sequence of clay and sand in which deep aquifers made up of coarse sand would be best suited for adequate water supply and good groundwater quality.The integrated study utilizing digital spatial data pertaining to waterlogging,soil salinity,water level fluctuation,and lithological variation proved that planning of any surface and subsurface water resources development activity should be taken up after assessments of said parameters.

A composite fall-slippage model for cliff recession in the sedimentary coastal cliffs

A composite fall-slippage model is proposed in this study for the Tertiary sedimentary coastal cliffs of Varkala in the western coastal tract of Peninsular India which are retreating landwards due to the combination of several factors.The fall model in the present study accounts both spring seepage and wave action,resulting in undercutting and this fall affects only the topmost laterite and the just below sandstone in the cliff.Slippage in this area affects all the litho-units and hence the geologic characteristics of all the litho-units are considered for developing the slippage model.This mathematically derived model can be used in other cliffs exhibiting the same morphology as well as the one controlled by the same influencing factors.This model differs from other models in incorporating multi-lithounits as well as multi-notches.Varkala cliffs form a part of the aspiring geopark in the Global Geopark Network and hence a study on the cliff recession is a pressing requirement.