Variability Of Groundwater Chemistry Research Articles

Spatiotemporal variability in groundwater chemistry of a mountainous catchment with complex geologic and climate gradients in south west India

Mountainous catchments are one of the world’s important water sources that sustains a major portion of global population and a rich biodiversity. The groundwater quantity and quality of mountainous watersheds depend generally on the geologic characteristics and climate gradients. Although many groundwater studies have been carried out in the midlands and lowlands of many river basins, not enough focus has been paid to the mountainous catchments of tropical watersheds. Here we report a case study on groundwater quality and controlling factors of a mountainous catchments of the Western Ghats mountain ranges of peninsular India—the Bhavani river basin, which is identified as a testbed for long-term monitoring of the Critical Zone process. A total of 88 water samples were collected seasonally for assessing various physico-chemical parameters, solute contents and scaling properties. Standard methods were followed for the estimation of various hydrochemical parameters in the open and borewell samples. The results of the study revealed that higher pH and Total Dissolved Solids (TDS) are noticed in the talc-tremolite dominated central zone whereas low values are recorded in the charnockite dominated areas. The major cations in the water samples are of the order Ca2+ > Mg2+ > Na+ > K+ and the anions are of the order HCO3− > Cl− > SO42−. The content of Cl− shows higher values in areas close to agricultural/settlement areas. An overall evaluation shows that the hydrochemistry of groundwater in the study area is influenced by both silicate and carbonate weathering. Mineral stability indices computed for the groundwater reveal that about 52% of the samples are supersaturated with carbonate minerals and often exhibit scaling due to solute overloading. Saturation Index and mineral stability diagram also support that the incongruent dissolution of aluminosilicate minerals (silicate weathering) is an important hydrochemical process controlling the chemistry of groundwater. Langelier saturation index (LSI) and Puckorius scaling index (PSI) show that a significant number of open well and borewell samples exhibit scaling tendency. Among the contributing factors that determine water quality of groundwaters, chemical weathering and anthropogenic activities play a significant role.

Nitrate dynamics in groundwater under sugarcane in a wet-tropics catchment

The transport of nitrogen (N) to groundwater and surface water in the form of nitrate (NO3-), as a by-product of the application of N-rich fertilisers, has been studied extensively. Yet, in the catchments adjacent to the Great Barrier Reef (GBR) in tropical north Queensland, Australia, NO3- transport in groundwater is not regularly monitored. An assessment of groundwater chemistry in the Liverpool Creek catchment of Queensland's wet-tropics region was conducted by regular sampling and analysis of groundwater over 12 months, through wet and dry seasons. A distinct spatial variability in groundwater chemistry was observed; groundwater aquifers with very low dissolved oxygen (DO) and NO3- consistently displayed relatively higher concentrations of sulphate (SO42-), sulphur (S2-) and ferrous iron (Fe2+) and low concentrations of dissolved organic carbon (DOC) (<2 ppm). Combined with averaged measured redox potential (Eh) of <250 mV, this indicates certain regions of the catchment have conditions favourable for removal of NO3- via autotrophic denitrification (DN), while other groundwater aquifers retained NO3– concentrations just above the acceptable trigger limits defined in regional water quality guidelines. Observations indicate that the naturally heterogeneous structure of the coastal alluvium contributes to the distinct variability in groundwater chemistry over small distances, with NO3- concentrations influenced by a combination of DN, lateral shallow drainage and potential adsorption to clay surfaces within the alluvial sediments.

Spatiotemporal variability in hydrochemistry of shallow groundwater in a small pre‐alpine catchment: The importance of landscape elements

AbstractTopography and landscape characteristics affect the storage and release of water and, thus, groundwater dynamics and chemistry. Quantification of catchment scale variability in groundwater chemistry and groundwater dynamics may therefore help to delineate different groundwater types and improve our understanding of which parts of the catchment contribute to streamflow. We sampled shallow groundwater from 34 to 47 wells and streamflow at seven locations in a 20‐ha steep mountainous catchment in the Swiss pre‐Alps, during nine baseflow snapshot campaigns. The spatial variability in electrical conductivity, stable water isotopic composition, and major and trace ion concentrations was large and for almost all parameters larger than the temporal variability. Concentrations of copper, zinc, and lead were highest at sites that were relatively dry, whereas concentrations of manganese and iron were highest at sites that had persistent shallow groundwater levels. The major cation and anion concentrations were only weakly correlated to individual topographic or hydrodynamic characteristics. However, we could distinguish four shallow groundwater types based on differences from the catchment average concentrations: riparian zone‐like groundwater, hillslopes and areas with small upslope contributing areas, deeper groundwater, and sites characterized by high magnesium and sulfate concentrations that likely reflect different bedrock material. Baseflow was not an equal mixture of the different groundwater types. For the majority of the campaigns, baseflow chemistry most strongly resembled riparian‐like groundwater for all but one subcatchment. However, the similarity to the hillslope‐type groundwater was larger shortly after snowmelt, reflecting differences in hydrologic connectivity. We expect that similar groundwater types can be found in other catchments with steep hillslopes and wet areas with shallow groundwater levels and recommend sampling of groundwater from all landscape elements to understand groundwater chemistry and groundwater contributions to streamflow.

Application of multivariate statistics in the analysis of groundwater geochemistry in and around the open cast coal mines of Barjora block, Bankura district, West Bengal, India

Inappropriate environmental management systems of open cast coal mines (OCCMs) often become a potential threat to aquifers, specifically unconfined alluvium aquifers. The present study area, a part of lower Gondwana coalfield, is an example of upper alluvium unconfined aquifer with shallow water table and lower multi-layered confined aquifers. Multivariate statistics has been effectively used as an aid to interpret different hydrogeochemical parameters to identify the prospective risk from OCCM and probable reasons responsible for variability in groundwater chemistry. Factor analysis has been used to identify the possible factors that control the variability of various chemical parameters in both pre-monsoon and post-monsoon times. Natural hydrogeologic environment (factor 1) is the major factor causing 53.34% and 51.01% of total groundwater-quality variation in post- and pre-monsoon times, respectively. In post-monsoon season, 13.33% variability is caused by anthropogenic activity (factor 2). Cluster analysis classifies 46 post-monsoon groundwater samples in three groups (clusters). Cluster 3, representing worst water qualities among the three clusters, has been significantly found in close proximity to the mines. ANOVA one-way analysis of cluster 3 groundwater samples shows higher concentration of TDS, Ca, Na, Cl, HCO3, and lower pH value in post-monsoon season than pre-monsoon season. Weathering and leaching of silicate minerals present in mine tailings and/or spoils by rain water may be the possible reason for degrading quality of groundwater. If this trend continues, then groundwater may become alkaline in nature with high (Na + K) concentrations in the long run, as indicated by Piper plot of all clustered samples.

Statistical analysis to characterize transport of nutrients in groundwater near an abandoned feedlot

Abstract. Surface water from a lagoon and groundwater samples from 17 wells within and near an abandoned feedlot in northwestern Minnesota, USA, were analyzed for carbon, nutrients, and field parameters. The feedlot is surrounded by wetlands that act as receptors of nutrients from the feedlot. Q- and R-mode multivariate analyses performed on total carbon (TC), inorganic carbon (IC), total organic carbon (TOC), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), soluble or dissolved reactive phosphorus (DRP), and total phosphorus (TP) indicated three groups of the chemical species, which reflected variability in groundwater chemistry. Factor analysis indicated approximately 82% of the variability in factor 1 was caused by TC, IC, TOC, and DRP, while in factor 2 approximately 79% of the variability was caused by NO2-N, NO3-N, and TP. In factor 3, only NH4-N contributed 31% of the variability. Groundwater isotope and spatial distribution analysis indicated reduced nitrate concentration from the source to the wetlands, with variation in NO2-N, NO3-N, and NH4-N concentrations attributed to the plant nutrient uptake, high rate of denitrification and/or the dissimilatory nitrate reduction to ammonium. This study indicated the value of multivariate analyses in characterizing variability in groundwater quality.

Temporal variability in groundwater chemistry in the Great Hungarian Plain during the period 1975–1989

Abstract In the southern part of the Great Hungarian Plain, chemical analyses of groundwater were performed during the period 1975–1989 in two water flow systems. Three types of temporal variations can be distinguished: a long term trend; a variation depending on sudden pressure decrease (both these types of variation can be seen in water hardness and iron concentration); and a regular fluctuation in COD and NH4 +. The first and second types occurred in both flow systems and are correlated with pressure depletion which in turn is reflected by water level decrease in wells. It was supposed that water with higher hardness and higher iron content moves from clayey layers to sand formations because of pressure depletion caused by withdrawal. Regular fluctuations of COD and NH4 + occurring only in the River Danube deposits were similar to the phenomenon of chemical oscillation but with different time and space scales between chemical and geochemical processes, the former having periods which are very long: 1.5...

The organic geochemistry of a sanitary landfill leachate plume

Leachate from the North Bay municipal landfill has contaminated an unconfined, sandy aquifer throughout the 700 m flow system from the site to a discharge zone at a creek. The major organic contaminants identified are aromatic hydrocarbons, especially substituted benzenes. The high groundwater velocity of about 75 m yr −1 and the low organic sorption properties of the sand have permitted non-transformed contaminants to spread throughout the total flow system. There is considerable temporal and spatial variability in groundwater chemistry. Most of the aqueous organic carbon has a nominal molecular weight of <2000 and the general decrease in the mass of this fraction relative to Cl indicates it is being mineralized significantly during transport. IR spectra indicate a general trend of increased aromaticity and decreased OH content of organic matter along the flow system. The aqueous organic matter has a significant apparent complexing capacity and so it is somewhat surprising that toxic metal concentrations in leachate-impacted groundwaters are low. In the leachate plume, this complexing capacity is taken up by major cations and H + and to a far lesser extent by toxic metals such as Pb, Cd or Zn. Dispersion is clearly responsible for considerable decrease in contaminant concentration along the flow system. Biotransformation under strictly anaerobic conditions has probably caused 1,1,1-trichloroethane and trichloroethylene to be restricted to the immediate vicinity of the landfill. A simple method of comparing the concentrations of pairs of organics at points along the flow system provides relative transformation rates for pairs of organics even with variable inputs from the landfill and dispersive dilution. Relative to ethylbenzene, o-xylene is rapidly lost from this system. O-xylene may be less persistent than m- or p-xylene; a result unexpected from previous studies of these dimethylbenzenes. In the initial, strictly anarobic segment of the flow system 1,2,4-trimethylbenzene and 1,4-dichlorobenzene are equally persistent, but in the final, less anaerobic segment, the former appears to be degraded more rapidly than the latter. Contaminant distributions in aquifers reflect the results of a number of processes integrated in a complex manner and so are difficult to interpret in terms of specific processes. However, they do provide evidence for what processes are most significant in real groundwater systems and they will also provide critical tests of how well laboratory-derived information relates to real groundwater contamination situations.