Hydrochemical Variations Research Articles

Impact of formations geology factors on groundwater quality

Garmsar plain is one of the central desert sub-basins in Semnan province with a warm and dry desert climate. After the HablehRood River, which is the main source of surface water of the area, the groundwater resources of Garmsar plain have a vital role in supplying agricultural and industrial demands; hence, the quality assessment of the groundwater is very important since it has a very great impact on the environment. This study aims to analyze the water quality of the area and determine the effects of geological formations on the hydrochemical deterioration of the groundwater quality in the area. To this aim, the hydrochemical environment of the region was simulated using Qa.Aq, Rockwors16, and GIS10.1 using the upstream of the basin chemical water and groundwater hydrochemistry data, the Garmsar study area was simulated. Besides, mineral saturation indices, hydrochemical water facies, and the total amount of soluble materials were determined, and the diagram of one or more effective hydrochemical variables was drawn. The results show that the most important factor in groundwater quality is the interaction between water and geological facies.

Heavy metal transport driven by seawater-freshwater interface dynamics: The role of colloid mobilization and aquifer pore structure change

Co-transport of colloidal substances and pollutants is a pivotal link that significantly affects the environment of coastal groundwater. The effect of colloid mobilization and aquifer pore structure change on heavy metal transport driven by seawater-freshwater interface dynamics is not fully understood. In this study, packed column experiments were conducted to model the seawater intrusion (SWI) and freshwater replenishment (FWR) processes using a sampled medium from a coastal sandy aquifer. Hydrodynamic, hydrochemical variables, and heavy metal (Pb, Cu, Cd) transport during the propagation of the seawater-freshwater interface were tested and analyzed. During the SWI stage, cation exchange induced heavy metal liberations, and it developed peak concentrations synchronized with the seawater-freshwater interface at the pore volume of 1.00. The colloid-facilitated transport for heavy metals was the predominant mechanism in the FWR stage, characterized by a peak release lagging the interface propagation by approximately 0.5 pore volumes. Because the colloidal fraction was mobilized during aquifer desalination, it lagged behind the decline of the salinity gradient. Furthermore, Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations explained that the replenishment decreased the depth of the secondary energy minimum of the colloids; meanwhile, the thickness of the electrical double layer increased from 0.63 nm to 10.14 nm, resulting in a repulsive energy barrier up to 3,213 kT. The transport of colloids led to a reduction in porosity from 18.16% to 2.28% of the total immobile domain. At these times, the dimension of the transported colloids evolved, showing a size-selective transport and therefore regulating the total emission fluxes of the heavy metals. These mechanisms were proposed to be incorporated in colloid filtration theory for targeting the coastal scenario.

Influences of overlapped riparian groundwater mounds on interaction between surface water and groundwater

AbstractA losing river usually produces riparian groundwater mounds. Knowledge of influences of the mound on riparian hydrological processes is still limited. To fill the gap, we measured the annual regime of riparian groundwater at a cross‐section of a river channel in a semi‐arid valley where the water transfer is running. Results show that the hydrologic processes were totally controlled by the water transfer. The river runoff was dominated by the transferred water. Regulation of the water transfer caused river stage fluctuations that were companied by hydrochemical variations of the river water. The water transfer enhanced infiltration into the riparian zone. Consequently, the river water and the riparian groundwater kept connection during the one‐year observation. The annual recharge and the input of total dissolved solids (TDS) from the river to the riparian zone reached 195.8 m3 and 125.0 kg, respectively. Furthermore, the Pearson's r between the river stage and riparian groundwater level was 0.98 at 2 m, 0.94 at 20 m, and 0.93 at 40 m (α = 0.01) from the riverside, respectively. The curved river produces the convergence of hydraulic gradients, which drives the overlap of groundwater mounds. The overlap is evidenced by anomalies in water level, hydrochemistry, and temperature of the riparian groundwater at the cross‐section. When the river stage and adjacent groundwater level went down, the overlap locally reversed the hydraulic gradient to point to the river hindering the recharge from the river. Hence, the average daily recharge from the river decreased from 1.10 to 0.59 m3. The riparian groundwater discharged into the river after quick declines of the river stage. In total, 39.2 m3 of riparian groundwater discharged into the river accounting for 20% of the annual recharge from the river. The impact of the hydrochemical variation of the river water on the riparian groundwater was also blocked due to the overlap. Also 20% of the TDS input was returned to the river. The overlap reduced the impact of the water transfer on the local environment.

Neurocomputing Modelling of Hydrochemical and Physical Properties of Groundwater Coupled with Spatial Clustering, GIS, and Statistical Techniques

Groundwater (GW) is a critical freshwater resource for billions of individuals worldwide. Rapid anthropogenic exploitation has increasingly deteriorated GW quality and quantity. Reliable estimation of complex hydrochemical properties of GW is crucial for sustainable development. Real field and experimental studies in an agricultural area from the significant sandstone aquifers (Wajid Aquifer) were conducted. For the modelling purpose, three types of computational models, including the emerging Hammerstein–Wiener (HW), back propagation neural network (BPNN), and statistical multi-variate regression (MVR), were developed for the multi-station estimation of total dissolved solids (TDS) (mg/L) and total hardness (TH) (mg/L). A geographic information system (GIS) was used for the spatial variability assessment of 32 hydrochemical and physical properties of the GW aquifer. A comprehensive visualized literature review spanning several decades was conducted in order to gain an understanding of the existing research and debates relevant to a particular GW and artificial intelligence (AI) study. The experimental data, pre-processing, and feature selection were conducted to determine the most dominant variables for AI-based modelling. The estimation results were evaluated using determination coefficient (DC), mean bias error (MBE), mean square error (MSE), and root mean square error (RMSE). The outcomes proved that TDS (mg/L) and TH (mg/L) correlated more than 90% and 70–85% with Ca2+, Cl−, Br−, NO3−, and Fe, and Na+, SO42−, Mg2+, and F− combinations, respectively. HW-M1 justified promising among all the models with MBE = 1.41 × 10−11, 1.14 × 10−14, and MSE = 7.52 × 10−2, 3.88 × 10−11 for TDS (mg/L), TH (mg/L), respectively. The accuracy proved merit for the overall development of and practical estimation of hydrochemical variables (TDS, TH) (mg/L) and decision-making benchmarks.

Application of Multivariate Approaches to the Hydro-chemical Assessment of the Ghodaghodi Lake, Sudurpaschim Province, Nepal

Wetlands are considered the most diverse and productive ecosystems in the world, providing life-sustaining ecological services. Hydrochemical variables of the Ghodaghodi Lake situated in Far west Nepal were studied using multivariate statistical approaches to investigate the characteristics of water quality of the lake. A total of 10water samples were collected and analyzed for water temperature, pH, electrical conductivity, total dissolved solids, total hardness, salinity, dissolved oxygen, major ions, and dissolved Si in the pre-monsoon season during 2017.The water quality assessment was carried out by applying sodium percentage, sodium adsorption ratio, permeability index, Kelly’s ratio, magnesium adsorption ratio, action ratio of soil structural stability, and water quality index. Multivariate statistical techniques were used to evaluate the geochemical and anthropogenic processes and to identify factors influencing the ionic concentrations. The results revealed that the water was slightly alkaline with low ionic strength and remarkable spatial variations. The hydrochemistry of the lake was mainly controlled by rock weathering as the dominant Ca2+-HCO3- facies. The principal component analysis provided three major components exhibiting the diverse sources of natural and anthropogenic chemicals, including agricultural fertilizers, leakage of sewages near the human settlements, etc. The measured hydrochemical parameters indicate that lake water lies within the safe drinking water and irrigational standards. However, special consideration should be taken to control the concentrations of NO3- due to increasing anthropic activities.

Vertical environmental gradient drives prokaryotic microbial community assembly and species coexistence in a stratified acid mine drainage lake

Acid mine drainage (AMD) lakes are typical hydrologic features caused by open pit mining and represent extreme ecosystems and environmental challenges. Little is known about microbial distribution and community assembly in AMD lakes, especially in deep layers. Here, we investigated prokaryotic microbial diversity and community assembly along a depth profile in a stratified AMD lake using 16S rRNA gene sequencing combined with multivariate ecological and statistical methods. The water column in the AMD lake exhibited tight geochemical gradients, with more acidic surface water. Coupled with vertical hydrochemical variations, prokaryotic microbial community structure changed significantly, and was accompanied by increased diversity with depth. In the surface water, heterogeneous selection was the most important assembly process, whereas stochastic processes gained importance with depth. Meanwhile, microbial co-occurrences, especially positive interactions, were more frequent in the stressful surface water with reduced network modularity and keystone taxa. The pH was identified as the key driver of microbial diversity and community assembly along the vertical profile based on random forest analysis. Taken together, environmental effects dominated by acid stress drove the community assembly and species coexistence that underpinned the spatial scaling patterns of AMD microbiota in the lake. These findings demonstrate the distinct heterogeneity of local prokaryotic microbial community in AMD lake, and provide new insights into the mechanism to maintain microbial diversity in extreme acidic environments.

Assessment of the seasonal variations in hydrochemistry of Oued Fodda dam, Algeria

Abstract This study was carried out on the surface water of Oued Fodda dam in western Algeria, and aimed to evaluate the seasonal variations of chemical characteristics with the aim to define the processes controlling the mineralization of surface water in this dam. The results showed significant variations in the majority of parameters during the study period from 2009 to 2013, indicating slightly alkaline water, and a SO4-Cl-Ca-Mg water type. Principal component analysis (PCA) and cluster analysis (CA) were used to explain the correlations between the parameters analysed, and the probable sources of surface water contamination. The calculation of saturation indices (SI) of water indicated undersaturated water with respect to halite (NaCl), and equilibrium with respect to the other minerals. While, the temporal variation of physico-chemical parameters such as EC, TDS, SO4 2-, Cl-, Ca2+, Mg2+ indicated a reverse adjustment between physico-chemical parameters and water volumes (WV) in this dam, which can be explained by the weathering of silicate and carbonate minerals, these were justified by the use of ionic ratios, diagrams and scatter plots and multivariate statistical techniques. Conversely, evaluation of the organic water pollution level in this dam showed a water quality from moderately to severely polluted.

Two Mechanisms of Earthquake-Induced Hydrochemical Variations in an Observation Well

Due to frequent large earthquakes in the Lanping-Simao fault basin—located in China’s Yunnan Province—the Simao observation well has observed groundwater discharge, as well as Ca2+, Mg2+, and HCO3− concentrations every day between 2001–2018. Over 18 years of observations, M ≥ 5.6 earthquakes within a radius of 380 km from the well were seen to cause hydrochemical variations. In this study, we investigated CO2 release and groundwater mixing as possible causes of regional earthquake precursors, which were caused by the characteristics of the regional structure, lithology, water-rock reactions, and a GPS velocity field. Precursory signals due to CO2 injection are normally short-term changes that take two months. However, groundwater mixing linked to earthquakes was found to take, at the earliest, 15 months. The proportion of shallow water that contributes to mixing was found to significantly increase gradually with the stronger regional strain. These finding delineate the two mechanisms of earthquake-induced hydrochemical variations in an observation well, and would contribute to a better understanding of chemical changes before events in the Simao basin.

Using integrated models to analyze and predict the variance of diatom community composition in an agricultural area

With the growing demand of assessing the ecological status, there is the need to fully understand the relationship between the planktic diversity and the environmental factors. Species richness and Shannon index have been widely used to describe the biodiversity of a community. Besides, we introduced the first ordination value from non-metric multidimensional scaling (NMDS) as a new index to represent the community similarity variance. In this study, we hypothesized that the variation of diatom community in rivers in an agricultural area was influenced by hydro-chemical variables. We collected daily mixed water samples using ISCO auto water samplers for diatoms and for water-chemistry analysis at the outlet of a lowland river for a consecutive year. An integrated modeling was adopted including random forest (RF) to decide the importance of the environmental factors influencing diatoms, generalized linear models (GLMs) combined with 10-folder cross validation to analyze and predict the diatom variation. The hierarchical analysis highlighted antecedent precipitation index (API) as the controlling hydrological variable while water temperature, Si2+ and PO4-P as the main chemical controlling factors in our study area. The generalized linear models performed better prediction for Shannon index (R2 = 0.44) and NMDS (R2 = 0.51) than diatom abundance (R2 = 0.25) and species richness (R2 = 0.25). Our findings confirmed that Shannon index and the NMDS as an index showed good performance in explaining the relationship between stream biota and its environmental factors and in predicting the diatom community development based on the hydro-chemical predictors. Our study showed and highlighted the important hydro-chemical factors in the agricultural rivers, which could contribute to the further understanding of predicting diatom community development and could be implemented in the future water management protocol.

Application of Cl/Br ratio to demarcate the fresh-saline water interface in coastal aquifers of northern Tamilnadu, Southern India

Geochemical parameters, chloride and bromide were used as tracers to demarcate the extent of saline water intrusion in the northern part of Tamilnadu coastal aquifer which served as a hub for major pumping well fields for supply of drinking water to Chennai city. 158 groundwater samples were collected during pre & post monsoon period to analyse the hydrochemical variations across this temporal stretch and two major water types were interpreted from the analytical data. During pre-monsoon period, Na–Cl is dominant followed by Na–HCO3 type and during post monsoon, the groundwater in the central and eastern part shift towards Na–HCO3 type from Na–Cl type. Bromide is absent in the freshwater samples, while the mixed water samples have varying bromide concentrations. In the study area, Br concentration in groundwater ranged from 0 to 22.1 mg/l while the seawater sample had Br concentration of 63 mg/l. The Cl/Br ratios of groundwater of the study area ranged from 0.01 to 188 while that of the seawater figured at 288. The groundwater of the eastern and north-eastern portion of the study area has Cl/Br ratio between 75 and 188 and this value has a similar signature to that of seawater. The continental part of the study area has Cl/Br ratio less than 50 which corresponds to that of the intermittent zone between the seawater and rainwater. Spatial distribution of Cl/Br ratio and their variation across distance from the coast indicate the remnants of seawater in the aquifer material upto 19–20 km inland and the ratio tends to decrease beyond 20 km distance. The study explores the applicability of the Cl/Br ratios for defining the extent and movement of he freshwater-saline water interface in a coastal region, which can be used by the water managers, administrators and planners for effective management and protection of available groundwater resources.

Water table fluctuations affect dichloromethane biodegradation in lab-scale aquifers contaminated with organohalides

Dichloromethane (DCM) is a toxic industrial solvent frequently detected in multi-contaminated aquifers. It can be degraded biotically or abiotically, and under oxic or anoxic conditions. The extent and pathways of DCM degradation in aquifers may thus depend on water table fluctuations and microbial responses to hydrochemical variations. Here, we examined the effect of water table fluctuations on DCM biodegradation in two laboratory aquifers fed with O2-depleted DCM-spiked groundwater from a well-characterized former industrial site. Hydrochemistry, stable isotopes of DCM (δ13C and δ37Cl), and bacterial community composition were examined to determine DCM mass removal and degradation pathways under steady-state (static water table) and transient (fluctuating water table) conditions. DCM mass removal was more pronounced under transient (95%) than under steady-state conditions (42%). C and Cl isotopic fractionation values were larger under steady-state (εbulkC = −23.6 ± 3.2‰, and εbulkCl= −8.7 ± 1.6‰) than under transient conditions (εbulkC = −11.8 ± 2.0‰, and εbulkCl = −3.1 ± 0.6‰). Dual C-Cl isotope analysis suggested the prevalence of distinct anaerobic DCM degradation pathways, with ΛC/Cl values of 1.92 ± 0.30 and 3.58 ± 0.42 under steady-state and transient conditions, respectively. Water table fluctuations caused changes in redox conditions and oxygen levels, resulting in a higher relative abundance of Desulfosporosinus (Peptococcaceae family). Taken together, our results show that water table fluctuations enhanced DCM biodegradation, and correlated with bacterial taxa associated with anaerobic DCM degradation. Our integrative approach allows to evaluate anaerobic DCM degradation under dynamic hydrogeological conditions, and may help improving bioremediation strategies at DCM contaminated sites.

Space-time hydrochemical variations and water quality of Euphrates river

Space-time hydrochemical variations and water quality of Euphrates river

Temporal responses of hydrochemical variables and dissolved Fe(II) to flooding at a lake riparian wetland under different vegetation revealing by high resolution DGT

The interplay between hydrological and biogeochemical processes in riparian wetland was recognized to lead directly to the temporal variations of surface water quality. However, the effects of flooding and vegetation on the release and entrapment of heavy metals and nutrients in riparian wetland remain poorly understood. The study aimed at investigating the influences of flooding and vegetation on the hydrochemical and Fe-redox change in the soil porewater and shallow groundwater, in Poyang lake riparian wetland through hydrochemical monitoring and diffusive gradient technology (DGT). The hydrochemical profiles and results of PCA analysis on the temporal datasets both demonstrated that vegetation had significant influences on the hydrochemistry of rhizosphere depth zone (RDZ) and shallow groundwater depth zone (SGZ). The Ca, K, Na, Mg, Mn and DOC at RDZ of both plants showed significant increasing trends from pre-to post-flooding while were observed minor change at the SGZ. The extracted PC1-PC3 from PCA analysis suggested that mineral dissolution and fermentation were dominating processes that explained 64.1% of the hydrochemical variability under the wetting-drying cycle. The synchronous changes of Fe(II), SO42−, DOC and ORP were found to occur at the SGZ of Carex, implying the likely occurrence of Fe- and S- redox reactions. The Fe(II) DGT profiles evidenced the temporal iron reduction and oxidation occurring at the rhizosphere following the wetting-drying cycle, as also reflected by the high opposite Fe2+ and DO association through PCA analysis. The high resolution temporal-spatial Fe(II) distribution suggested also the interface between lake water and groundwater was relatively stable under flooding.These results highlight that the release of dissolved Fe(II) from the wetland rhizosphere driven by flood may result in the release of Fe-associated heavy metals from riparian wetland to surface water, and hence pose potential threats to the surface water quality. Thereby, the flow and flood should be properly controlled and vegetation effects need to be carefully considered in the water resources management of lake-floodplain system.

Brine chemistry matters: Isolation by environment and by distance explain population genetic structure ofArtemia franciscanain saline lakes

AbstractThe American brine shrimpArtemia franciscanais important in aquaculture and has become invasive in other continents, aided by dispersal via waterbirds. However, little is known about processes underlying its genetic diversity and population structure in its natural habitat in North America. These processes, including dispersal and local adaptation, are pivotal drivers of species distribution and community structure, and therefore central to aquatic biodiversity.We studied 15 populations in natural saline lakes of Saskatchewan, Canada to determine the influence of variation in geological history, water chemistry, lake size, and location. We aimed to determine the relative importance of isolation by distance and isolation by environment using the cytochromecoxidase subunit 1 gene (CO1) as a mitochondrial marker and five nuclear microsatellite markers.Geographic patterns for CO1 and microsatellites differed, with lakes clustering in different groups based on genetic distances according to the marker used. CO1 better indicated historical colonisation processes, suggesting potential routes of initial colonisation when lakes were formed after deglaciation 11,000–15,000 years ago.Differentiation between lakes based on nuclear markers was strongly related to variation in hydrochemistry, suggested by distance‐based redundancy analysis, but there was no indication of isolation by distance. The ratio between alkalinity and the sum of Ca and Mg concentrations was particularly important, although a lake with a high Cl concentration caused by potash mining also had a uniqueArtemiapopulation.Geochemistry is important in the adaptive radiation of anostracan crustaceans. Our study suggests that it also underlies intraspecific genetic variation between populations, promoting isolation by environment, and making dispersal ineffective when cysts are moved by birds between lakes with different hydrochemistry.​

A support vector regression model to predict nitrate-nitrogen isotopic composition using hydro-chemical variables

Nitrate is a prominent pollutant in surface and groundwater bodies worldwide. Isotopes in nitrate provide a powerful approach for tracing nitrate sources and transformations in waters. Given that analytical techniques for determining isotopic compositions are generally time-consuming, laborious and expensive, alternative methods are warranted to supplement and enhance existing approaches. Hence, we developed a support vector regression (SVR) model and explored its feasibility to predict nitrogen isotopic composition of nitrate (δ15N–NO3−) in a rural-urban river system in Southeastern China. A total of 16 easily obtained hydro-chemical variables were measured in the wet season (September 2019) and dry season (January 2020) and used to develop the SVR prediction model. The grading method utilized ~75% (35) of the samples for model building while the remaining 11 samples assessed model performance. Principal component analysis (PCA) extracted 7 principal components for SVR model inputs as PCA reduces superfluous variables. We optimized tuning parameters in the SVR model using a grid search technique coupled with V-fold cross-validation. The optimized SVR model provided accurate δ15N–NO3− predictions with a determination coefficient (R2) of 0.88, Nash-Sutcliffe (NS) of 0.87, and mean square error (MSE) of 0.53‰ in the testing step, and performed much better than the corresponding multivariate linear regression model (R2 = 0.60, NS = 0.58 and MSE = 1.76‰) and general regression neural network model (R2 = 0.66, NS = 0.65 and MSE = 1.45‰). Overall, the SVR model provides a potential indirect method to predict environmental isotope values for water quality management that will complement and enhance the interpretation of direct measurements of δ15N–NO3−.

Hydrochemical Characteristics and Controlling Factors of Typical Dolomite Karst Basin in Humid Subtropical Zone

The hydrochemical characteristics and variation rules of water in karst areas are important for the basic research of karst field. Because only a few researches focused on the hydrochemical characteristics of humid subtropical dolomite karst basins in the past, the Shanmuhe Basin and its subbasin Huangzhouhe Basin in Shibing Dolomite Karst World Natural Heritage Site in China were selected as the study area. A total of 215 water samples were collected and analyzed. It was found that the hydrochemical type of subtropical dolomite karst basin is HCO3-Ca·Mg type, which is different from that in limestone areas and shale districts, which is HCO3-Ca type for both; EC, Ca2+, Mg2+, HCO3-, Mg2+/Ca2+, and Mg2+/HCO3- have similar spatial variations, which are lower in allogenic water in the upstream in the northwest of the basin and become higher when the water enters the dolomite karst area in the mid and downstream of the basin, and SIC and SID of the allogenic water in the upstream are below zero, while those become saturated after entering the dolomite area in the mid and downstream; the monthly variation of hydrochemistry shows that the seasonal variation of ion concentration is not obvious, and there is a dilution effect in rainy seasons, but the variation of ion concentration is small and relatively stable; higher HCO3- concentration and Mg2+/Ca2+ in the pure dolomite basin are higher than those in the impure dolomite basin; the main influencing factors of the hydrochemical features are geological background especially the lithology, and the water chemistry is mainly controlled by rock weathering and water-rock interaction; rainfall import is low and the low concentrations of K+, Na+, NO3-, Cl-, and SO42- in water indicate that human activities have little effect on the hydrochemistry in the study area.

Groundwater Recharge Area Based on Hydrochemical and Environmental Isotopes Analysis in the South Bandung Volcanic Area

The determination of recharge areas needs to support the groundwater conservation in the southern volcanic Bandung area. This study aims to determine the recharge area based on environmental isotopes and hydrochemical. A sampling of 26 groundwater was carried out at springs, dug wells, and drilling wells. The variation in groundwater chemistry principally is controlled by a combination of ion exchange, silicate weathering, calcite, and dolomite dissolution of minerals. The hydrochemical facies were CaCl, CaMgCl, CaMgHCO3, CaHCO3, and NaKHCO3. The CaHCO3 facies describe moderate groundwater flows. The NaKHCO3 facies shows the mixing of shallow and deep groundwater. The recharge area in the central, proximal, and medial facies zone consists of 3 groups. Group I is considered water originating from local rainwater infiltration; Group II is considered the infiltration elevation which ranges from 980–1230 m asl; Group III estimated to be derived from the recharge elevation between 750–970 m asl, Group IV are more likely to show symptoms of evaporation or interaction with surface water. The discharge area is characterized by less active groundwater circulation, with dominant HCO3– and TDS value in the distal facies zone. Hydrochemical variation helped the identification of recharge areas in the volcanic facies.

Different responses of ecohydrological processes in the re-vegetation area between the dip and anti-dip slope in a karst rocky desertification area in southwestern China

Rocky desertification is an economic, social, and environmental problem, which refers to the processes and human activities that transform a karst area covered by vegetation and soil into a rocky landscape. The effects of different types of soil cover on ecohydrological processes during the revegetation of areas undergoing karst rocky desertification remain unclear. Taking different measures for different ecohydrological situations will benefit re-vegetation in karst rocky desertification areas. Monthly/heavy rainfall hydrochemical data and the δ13C of dissolved inorganic carbon (DIC) in karst water samples from January 2017 to December 2019 were obtained. This revealed the controlling mechanisms on hydrochemical processes by δ13CDIC under different soil cover conditions in the dip/anti-dip slopes of a karst trough valley in Ganxi Town, Chongqing City, southwestern China. Hydrochemical variations are controlled by climate, soil, and vegetation and show clear seasonality. The δ13CDIC values (−16.88‰ to −3.49‰) in the study area were higher than the theoretical value (−14.00‰). In addition, it was observed that rain accelerated soil erosion (R2=0.7) in the karst trough valley and human activities (exogenous acid) resulted in DIC loss. The slopes, soil, and bare rock cover on the dip slope were different from that on the anti-dip slope, leading to the difference in their re-vegetation statuses. In this study, we found that different vegetation restoration schemes and treatment measures should be implemented between the dip and anti-dip slope. The protection of soil and water resources, especially soil, is the key to ecological restoration in rocky desertification areas.

Assessment of biannual seasonal variations in hydrochemistry of Kerwa reservoir located in hard rock formations of Central India

An investigation on the Kerwa reservoir water located in central parts of India (Bhopal, Madhya Pradesh) has been carried out to assess the hydrochemical variations in different seasons and possible influencing factors. Temporal chemical variations in reservoir water were evaluated for all the three seasons by analyzing two hundred forty surface water samples from ten different sites along the reservoir periphery covering inlet and outlet points. The analytical results indicate that Kerwa reservoir water is mildly alkaline, and the order of dominance for ions was found to be Ca2+ > Mg2+ > Na+ > K+ and HCO3− > Cl− > SO42−. The major chemical facies present are Ca-Mg-HCO3, Ca-Mg-Na-HCO3-Cl, Ca-Mg-HCO3-Cl, and Ca-Mg-Cl-HCO3. Piper and Chadha plots infer that seasonality exert a strong control on the water chemistry. Rainwater dominate the reservoir water chemistry during monsoon, evaporation dominates during summer, while multiple geochemical reactions control the reservoir water chemistry during winter. The extent of ion exchange was evaluated by chloro-alkaline indices as well as (Ca2+ + Mg2+)/(Na+ + K+) versus Na+-Cl− plot. Contribution of carbonate and silicate minerals was evaluated using characteristic ionic ratios and scatter plots. It is found that weathering of silicate rocks lead to higher Ca2+ and Mg2+ in the reservoir water, while evaporite dissolution and to a some extent ion exchange and base flows are found to control the Na+ and K+ concentrations. With the growing scenario of contamination in adjoining water bodies, the study on water quality and associated geochemical processes becomes necessary for Kerwa reservoir, which can form a potential freshwater reserve in this region for future generations.

Seasonal Variation on the Hydrochemistry and Height of Brackish-Water from Commodore Channel, Lagos, Nigeria

The current study deals with the evaluation of physicochemical characteristics, nutrient status, and variation in the height of surface water from the commodore channel, and its comparison with the hydrochemical characteristics of the monitoring borehole from the NIOMR Jetty, Lagos, Nigeria. We aim to further improve our understanding of the interrelationship of climate change and hydrological cycle, and its impacts in the Lagos coastal environments. The observed ranges of physicochemical characteristics of the surface water are dissolved oxygen (DO) 3.07-6.05mg/L; pH: 7.99-8.48; temperature 26.97-30.34°C, electrical conductivity (EC) 9680-47800mS/cm; salinity (Sal) 6.51-28.05‰ and water level 1.24-1.79m. The concentration of nutrient range from nitrite 10-36mg/l, nitrate 28-44mg/l, sulphate 38-90mg/l and phosphate 2-78mg/l. The analyzed hydrochemical characteristics from all the stations are within the desired values for healthy marine ecosystems when compared with Federal Ministry of Environment (FMENV) Nigeria permissible limits which are: DO >5 mg/l, pH 6.5-9, temperature <40°C, nitrite 1mg/l, nitrate 20mg/l, phosphate 5mg/l and sulphate 500mg/l; except low DO (<4.5mg/l) in January, November and December, and elevated nitrite, nitrate and phosphate values across the season. The low DO values may be attributed to enhanced transportation of non-biodegradable organic loads that utilize the available DO for chemical oxidation and microbial decomposition. While the enriched nitrite, nitrate and phosphate concentrations suggest enhanced productivity and influx of nutrients rich flood water from the anthropogenic source. Our study showed a coincidence in the highest brackish water height of the surface water (1.24m) from the commodore channel with the highest groundwater level (1.58m) in October. The lowest height of water levels was recorded in February and March at 2.23m and 1.79m for groundwater and surface water respectively. The similarities in the height of water levels were recorded with contrasting hydrochemical variables (e.g., high Ec vs. low Ec; and high Sal vs. low Sal), which confirmed the effect of rainfall/freshwater incursion on the surface water and simultaneous occurrence of subsurface pollution arising from seawater intrusion on the groundwater samples in October. This study had shown that a long term monitoring of rise in water levels and hydrochemical variables of surface and groundwater can be used to understand climate change and early warning predictions of flooding in coastal environments.