Groundwater Variations Research Articles

Groundwater Variations From Autocorrelation and Receiver Functions

AbstractUsing a 20‐year continuous broadband record and two independent single‐station techniques—ambient noise autocorrelation and receiver functions—we document a relationship between subsurface seismic response and groundwater levels (GWLs) in the Gulf Coast Aquifer System of southern Texas. We find that a surge of GWL following three consecutive hurricanes and documented at an adjacent monitoring well is accompanied with changes in receiver function power spectra and ambient noise autocorrelations. Using a simple physical model, we show that GWL changes should affect P‐ (VP) more strongly than S‐wave (VS) velocities, consistent with our observations and previous ones based on inter‐station correlations. Agreement between receiver function and ambient noise analyses shows that both can be used to reliably estimate temporal changes in subsurface properties on long timescales. Due to their sensitivity to VP, single‐station techniques respond more strongly to GWL changes, making them useful for characterizing and monitoring aquifer systems.

Does Crop Rotation Enhance Groundwater Health? A Review of the Winter Wheat Fallow Policy in the North China Plain

Agricultural water management is a vital component of realizing the United Nation’s Sustainable Development Goals because of water shortages worldwide leading to a severe threat to ecological environments and global food security. As an agro-intensified irrigation area, the North China Plain (NCP) is the most important grain basket in China, which produces 30%–40% of the maize and 60%–80% of the wheat for China. However, this area has already been one of the largest groundwater funnels in the world due to long-term over-exploitation of groundwater. Due to the low precipitation during the growing period, winter wheat requires a large amount of groundwater to be pumped for irrigation, which consumes 70% of the groundwater irrigation. To alleviate the overexploitation of groundwater, the Chinese government implemented the Winter Wheat Fallow Policy (WWFP) in 2014. The evaluation and summarization of the WWFP will be beneficial for improving the groundwater overexploitation areas under high-intensity irrigation over all the world. So far, there have been few attempts at estimating the effectiveness of this policy. To fill this gap, we assessed the planting area of field crops and calculated the evapotranspiration of crops based on remote-sensed and meteorological data in the key area—Hengshui. We compared the agricultural water consumption before and after the implementation of this policy, and we analyzed the relationship between changes in crop planting structure and groundwater variations based on geographically weighted regression. Our results showed the overall classification accuracies for 2013 and 2015 were 85.56% and 82.22%, respectively. The planting area of winter wheat, as the most reduced crop, decreased from 35.71% (314,053 ha) in 2013 to 32.98% (289,986 ha) in 2015. The actual reduction in area of winter wheat reached 84% of the target (26 thousand ha) of the WWFP. The water consumption of major crops decreased from 2.98 billion m3 of water in 2013 to 2.83 billion m3 in 2015, a total reduction of 146 million m3, and 88.43% of reduced target of the WWFP (166 million m3). The planting changes of winter wheat did not directly affect the change of shallow groundwater level, but ET was positively related to shallow groundwater level and precipitation was negatively related to shallow groundwater levels. This study can provide a basis for the WWFP’s improvement and the development of sustainable agriculture in high-intensity irrigation areas.

Global GRACE Data Assimilation for Groundwater and Drought Monitoring: Advances and Challenges

AbstractThe scarcity of groundwater storage change data at the global scale hinders our ability to monitor groundwater resources effectively. In this study, we assimilate a state‐of‐the‐art terrestrial water storage product derived from Gravity Recovery and Climate Experiment (GRACE) satellite observations into NASA's Catchment land surface model (CLSM) at the global scale, with the goal of generating groundwater storage time series that are useful for drought monitoring and other applications. Evaluation using in situ data from nearly 4,000 wells shows that GRACE data assimilation improves the simulation of groundwater, with estimation errors reduced by 36% and 10% and correlation improved by 16% and 22% at the regional and point scales, respectively. The biggest improvements are observed in regions with large interannual variability in precipitation, where simulated groundwater responds too strongly to changes in atmospheric forcing. The positive impacts of GRACE data assimilation are further demonstrated using observed low‐flow data. CLSM and GRACE data assimilation performance is also examined across different permeability categories. The evaluation reveals that GRACE data assimilation fails to compensate for the lack of a groundwater withdrawal scheme in CLSM when it comes to simulating realistic groundwater variations in regions with intensive groundwater abstraction. CLSM‐simulated groundwater correlates strongly with 12‐month precipitation anomalies in low‐latitude and midlatitude areas. A groundwater drought indicator based on GRACE data assimilation generally agrees with other regional‐scale drought indicators, with discrepancies mainly in their estimated drought severity.

Analysis and Prediction of Groundwater Level Trends Using Four Variations of Mann Kendall Tests and ARIMA Modelling

In this study monthly, annual and seasonal groundwater variation trends of Warangal district (2000–2015) were examined for forty observation wells using four variations of non-parametric Mann Kendal (MK) methods. Magnitudes of trends were computed using the Sen’s slope estimator. Results conclude that on a monthly time series, three observation wells (31, 32 and 37) experienced significant positive trends (positive Z-statistics), whereas other wells experienced significant negative trends among forty. Wells 2, 17, 22, 33, 38, 39, 40 noticed strong significant negative trends. Using MK-1/MK-2/MK-3/MK-4 for monthly series, around 23/33/23/23% of cases exhibited positive trends (both significant and insignificant) and 77/67/77/77 % of cases exhibited negative trends. Median of trend slopes for groundwater levels (GWLs) were negative in monthly, seasonal and annual timescale. Seasonally trend slope was observed as a decreasing trend in the pre-monsoon period. Annually trend slope was varying approximately from −0.4 mm/year to +0.4 mm/year. ARIMA models were fitted for each well to predict the parameters of the models and to forecast (2015) using monthly GWLs from 2000 to 2014. ARIMA(2,1,2), ARIMA(2,0,1), ARIMA(4,0,0), ARIMA(1,1,1), ARIMA(1,0,1), ARIMA(1,0,2) and ARIMA(2,0,0) fitted for most of the Wells. Using these models GWLs were predicted and the performance of the predicted levels was analyzed using the correlation coefficient (R2) and Akaike Information Criteria (AIC) values.

Seasonal variation in the groundwater dependency of two dominant woody species in a desert region of Central Asia

Groundwater is an important water source for plants in desert regions and greatly affects the performance and survival of desert plants. Moreover, the effects of groundwater variations on desert plants are not completely understood. This study aims to investigate the groundwater dependency of two dominant woody species (Haloxylon ammodendron and H. persicum) in the Gurbantunggut Desert of Central Asia, and evaluate their water use and physiological responses under a decline in groundwater depth. Oxygen stable isotopes of soil water, groundwater and xylem water as well as the IsoSource model were used to determine seasonal variations in the water sources of the two studied species along a groundwater depth gradient. In addition, the plant water potential and stomatal conductance were measured to determine the physiological performance. (1) Although both species extracted groundwater, H. ammodendron was much more groundwater dependent; (2) the two species exhibited significant seasonal variations in their degree of groundwater dependency, which was relatively lower in the wet season, and higher during the dry period; and (3) when the groundwater availability declined, both species reduced their groundwater use, although only H. ammodendron exhibited a significantly negative physiological response. This study demonstrated that plants with different water sources respond differently to the decline of groundwater depth and the effects of groundwater drawdowns are determined by the groundwater dependency of desert plants. A better understanding of desert plant responses to water availability variations is crucial for modeling, predicting and managing desert ecosystems in the context of global change.

Spatio-temporal groundwater variations associated with climatic and anthropogenic impacts in South-West Western Australia

South-West Western Australia (SWWA) is a critical agricultural region that heavily relies on groundwater for domestic, agricultural and industrial use. However, the behaviours of groundwater associated with climate variability/change and anthropogenic impacts within this region are not well understood. This study investigates the spatio-temporal variability of groundwater in SWWA based on 2997 boreholes over the past 36 years (1980–2015). Results identify the decline in groundwater level (13 mm/month) located in the central coastal region of SWWA (i.e., north and south of Perth) to be caused by anthropogenic impacts (primary factor) and climate variability/change (secondary). In detail, anthropogenic impacts are mainly attributed to substantial groundwater abstraction, e.g., hotspots (identified by above 7 m/month groundwater level change) mostly occur in the central coastal region, as well as close to dams and mines. Impacts of climate variability/change indicate that coupled ENSO and positive IOD cause low-level rainfall in the coastal regions, subsequently, affecting groundwater recharge. In addition, correlation between groundwater and rainfall is significant at 0.748 over entire SWWA (at 95% confidence level). However, groundwater in northeastern mountainous regions hardly changes with rainfall because of very small amounts of rainfall (average 20–30 mm/month) in this region, potentially coupled with terrain and geological impacts. A marked division for groundwater bounded by the Darling and Gingin Scarps is found. This is likely due to the effects of the Darling fault, dams, central mountainous terrain and geology. For the region south of Perth and southern coastal regions, a hypothesis through multi-year analysis is postulated that rainfall of at least 60 and 65–70 mm/month, respectively, are required during the March–October rainfall period to recharge groundwater.

Review of time-lapse microgravity correction due to shallow groundwater variation

Microgravity surveys can be applied for reservoir monitoring, such as monitoring of hydrocarbon or geothermal reservoirs. One factor that needs to be corrected from gravity data in reservoir monitoring is the gravity signal due to shallow groundwater variation. The correction due to shallow groundwater effect shall be calculated from groundwater change, in this case can be measured from groundwater table change. So far, correction due to shallow groundwater variation in microgravity data is calculated against the influence of groundwater mass change in the saturated zone only, while the change of mass of groundwater in the unsaturated zone is ignored, thus giving an over-estimated correction result. The purpose of this paper is to review time-lapse microgravity correction due to shallow groundwater variation by including the influence of groundwater mass variation in the unsaturated zone. This review includes a case study using three-point piezometer groundwater data. The correction due to groundwater mass variation in the unsaturated zone is obtained by calculating the difference between the total water content at two measurements over a certain time interval. The calculation of total moisture content in the unsaturated zone is based on a soil-water retention curve that describes the relationship between moisture content and pore pressure. Considering the effect of water mass in the unsaturated zone, the total correction due to shallow groundwater variation has a smaller range, about 35% to 50% compared to the correction that only considers the effect of water mass in the saturated zone alone.

Garden irrigation as household end-use in the presence of supplementary groundwater supply

Garden irrigation is a significant and variable household water end‑use, while groundwater abstraction may be a notable supplementary water source available in some serviced residential areas. Residential groundwater is abstracted by means of garden boreholes or well points and – in the study area – abstracted groundwater is typically used for garden irrigation. The volume irrigated per event is a function of event duration, frequency of application and flow rate, which in turn are dependent on numerous factors that vary by source – including water availability, pressure and price. The temperature variation of groundwater abstraction pipes at residential properties was recorded and analysed as part of this study in order to estimate values for three model inputs, namely, pumping event duration, irrigation frequency, and flow rate. This research incorporates a basic end‑use model for garden irrigation, with inputs derived from the case study in Cape Town, South Africa. The model was subsequently used to stochastically evaluate garden irrigation. Over an 11-d period, 68 garden irrigation events were identified in the sample group of 10 residential properties. The average garden irrigation event duration was 2 h 16 min and the average daily garden irrigation event volume was 1.39 m3.

Effect of temperature variations on the travel time of infiltrating water in the Amsterdam Water Supply Dunes (the Netherlands)

Travel time is one of the important criteria in the design of managed aquifer recharge systems for securing good drinking water quality. Traditionally, groundwater travel time has been modelled without considering the effect of temperature. In this study, a cross-sectional heat transport model was constructed for the Amsterdam dune filtration system (in the Netherlands) to analyse the effect of temperature on groundwater travel times. A groundwater flow model, a chloride transport model, and a heat transport model were iteratively calibrated with measured groundwater levels, chloride concentrations, and temperature series in order to improve model calibration and reduce model uncertainty. The coupled flow and heat transport model with temperature-dependent density and viscosity provided more accurate estimation of travel times. The results show that seasonal temperature fluctuations in the source water in the infiltration pond cause temperature variations in the shallow groundwater. Viscosity is more sensitive to temperature changes and has a larger effect on groundwater travel times. Groundwater travel time in the shallow sand aquifer increases from 60 days when computed with the traditional groundwater flow model to 73 days in the winter season and 95 days in the summer season when computed with the coupled model. Longer travel time is beneficial for water quality improvement. Thus, it is important to consider the effect of temperature variations on groundwater travel times for the design and operation of managed aquifer recharge systems.

Vegetation Response to Groundwater Variation in Arid Environments: Visualization of Research Evolution, Synthesis of Response Types, and Estimation of Groundwater Threshold.

Groundwater depth is an important environmental factor affecting vegetation growth and landscape dynamics in arid environments. This study applied a science mapping approach to visualize the development of groundwater-vegetation-related research, synthesized the vegetation response to changes in groundwater depth, and analyzed the change rate of the response curve to identify the groundwater threshold that is essential to conserve the groundwater-dependent terrestrial ecosystems. These ecosystems emerged as a research hotspot due to climate change, groundwater overexploitation, and the recognition of these ecosystems’ importance for sustainable development. There are two main types of response functions of vegetation to changes in groundwater depth—monotone and bell-shaped functions—among which the monotone function includes linear, curvilinear, and stepwise response. The shape of a response curve is mainly determined by the combined effects of oxygen stress, salinization, and water stress; oxygen stress and salinization dominate in shallow groundwater depth, while water stress dominates in deep groundwater depth. On a non-linear vegetation metric—groundwater depth response curve, the change rate analysis method is effective to identify the breakpoint that can be taken as a candidate threshold of groundwater depth. The results will add insight into the intellectual structure of the groundwater-vegetation interactions and provide practical reference for groundwater resource management, ecological conservation, and sustainable development in arid environments.

Spatial and temporal variability of groundwater recharge in a sandstone aquifer in a semiarid region

Abstract. With the aim to understand the spatial and temporal variability of groundwater recharge, a high-resolution, spatially distributed numerical model (MIKE SHE) representing surface water and groundwater was used to simulate responses to precipitation in a 2.16 km2 upland catchment on fractured sandstone near Los Angeles, California. Exceptionally high temporal and spatial resolution was used for this catchment modeling: hourly climate data, a 20 m×20 m grid in the horizontal plane, and 240 numerical layers distributed vertically within the thick vadose zone and in the upper part of the groundwater zone. The finest practical spatial and temporal resolutions were selected to accommodate the large degree of surface and subsurface variability of catchment features. Physical property values for the different lithologies were assigned based on previous on-site investigations, whereas the parameters controlling streamflow and evapotranspiration were derived from calibration to continuous streamflow at the outfall and to average hydraulic heads from 17 wells. Confidence in the calibrated model was enhanced by validation through (i) comparison of simulated average recharge to estimates based on the applications of the chloride mass-balance method to data from the groundwater and vadose zones within and beyond the catchment, (ii) comparison of the water isotope signature (18O and 2H) in shallow groundwater to the variability of isotope signatures for precipitation events over an annual cycle, and (iii) comparison of simulated recharge time series and observed fluctuation of water levels. The average simulated recharge across the catchment for the period 1995–2014 is 16 mm yr−1 (4 % of the average annual precipitation), which is consistent with previous estimates obtained by using the chloride mass balance method (4.2 % of the average precipitation). However, one of the most unexpected results was that local recharge was simulated to vary from 0 to >1000 mm yr−1 due to episodic precipitation and overland runoff effects. This recharge occurs episodically with the major flux events at the bottom of the evapotranspiration zone, as simulated by MIKE SHE and confirmed by the isotope signatures, occurring only at the end of the rainy season. This is the first study that combines MIKE SHE simulations with the analysis of water isotopes in groundwater and rainfall to determine the timing of recharge in a sedimentary bedrock aquifer in a semiarid region. The study advances the understanding of recharge and unsaturated flow processes and enhances our ability to predict the effects of surface and subsurface features on recharge rates. This is crucial in highly heterogeneous contaminated sites because different contaminant source areas have widely varying recharge and, hence, groundwater fluxes impacting their mobility.

Statistical and Numerical Assessments of Groundwater Resource Subject to Excessive Pumping: Case Study in Southwest Taiwan

Groundwater, a salient water resource in Taiwan, has been subject to incessant and excessive pumping, inducing serious regional land subsidence and seawater intrusion. This study aims at assessing how excessive pumping impacts groundwater variations over the Pingtung Alluvial Plain (PAP) in Southwest Taiwan using both statistical and numerical techniques. We apply nonparametric methods to analyze the changing point and annual trend in various hydro-meteorological time series (e.g., rainfall, temperature, and groundwater levels (GLs)). Afterwards, we employ an integrated surface-subsurface model referred to as WASH123D to simulate GLs under the pumping-free scenario; any discrepancies identified between simulated and observed GLs could be an indicator of unregulated/illegal pumping. We find that annual GLs exhibit a significant increasing (decreasing) trend in the western (eastern) PAP. Our numerical experiment reveals diverging trends in simulated and observed GLs, mostly at the downstream of all the major tributaries, suggesting the consequence of unregulated/illegal pumping. Furthermore, upstream pumping may reduce lateral flow towards the downstream coastal area, triggering land subsidence in remote locations.

A preliminary geophysical analysis of gravity time-variation in Daejeon

A gravity time series slightly longer than a month acquired by using a Burris gravimeter at Daejeon, Korea has been analyzed. After removal of linear drift of the gravimeter, the observed data was found to closely match with the body tide prediction except; (i) small phase differences of each main tidal constituents and (ii) existence of long period component in the observed data. The r.m.s. observed gravity tide variation was 62.4 μGal. The overall g-factor was found as 1.165. The values of g-factor for the four main tidal constituents; M{nt2}, S2, O1, K1, were found as 1.166, 1.172, 1.168, and 1.142 respectively. The r.m.s. value of ocean tidal loading effect on gravity at Daejeon was 0.95 μGal during the time span. Both the rainfall and the atmospheric pressure change have induced gravity variations of amplitude of about 10 to 1 μGal. The long period component, which is clearly found in the observed spectrum, while not existent in the prediction, is possibly caused by the local ground water variation. It is desirable to have a few number of permanent gravity stations operating in Korean peninsula.

Modeling groundwater level fluctuations in Tehran aquifer: Results from a 3D unconfined aquifer model

Heavy groundwater withdrawal results in aquifer compaction and increases the risk of land subsidence hazard with significant economic, environmental, and social consequences. Having an accurate model for hydraulic pressure loss and groundwater level changes is one of the crucial factors in proper modeling and evaluation of land subsidence hazard. This paper investigates dynamics of groundwater variations in Tehran aquifer. By analyzing a comprehensive geological and hydrological data such as alluvium depths, hydraulic conductivity, piezometric measurements, and pumping well information, we model the hydraulic heads and evaluate the hydraulic conductivity. For validation of the model, groundwater level changes resulting from the model are compared with piezometric measurements for the period 2006–2011. The comparison shows a good consistency between the predicted and observed hydraulic head values with the maximum absolute error of less than 7 m and RMS error of about 5 m, that is about 2% error, considering that the hydraulic head values are between 850 and 1250 m. This shows the capability and accuracy of the proposed model to simulate and predict the aquifer hydraulic head distribution and its changes. The model also indicates high hydraulic conductivity in the northern and central parts of Tehran Plain, which is attributed to the river sedimentation there.

Seasonal Variations in Groundwater of the Phreatic Aquiferous Formations in Douala City-Cameroon: Hydrogeochemistry and Water Quality

This study was to determine the seasonal variations of groundwater, the influence of the rock formations on the groundwater solute chemistry and groundwater domestic-agro-industrial quality using hydrogeochemical tools and physicochemical parameters; Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters; in the rainy season, pH ranged from, 4.6-7.1; EC, 0.023-1.63 mS/cm; Temperature, 26.3-290C andTDS, 0.015-1.09 mg/L and in the dry season pH ranged from 5-7.2; EC, 0.01-1.61 mS/cm; Temperature, 24.4-29.50C andTDS, 0.01-1.08 mg/L. Forty groundwater samples; 20 per season, wet and dry were analysed. Themajor ions fell below WHO acceptable limits for both seasons. The sequences of abundance of major ions were, Ca2 >K >Mg2 >NH4 >Na , HCO3->Cl->SO42->NO3->HPO42- in wet season and Ca2 >Mg2 >K >Na >NH4 , HCO3->Cl->SO42->HPO42->NO3- in dry season. Ion-exchange, simple dissolution and uncommon dissolution processes determined groundwater character. Groundwater ionic content was as a result of ion exchange from rock-weathering. Water types are; MgCl and MgHCO3 in both seasons. Hydrogeochemical facies are; Ca-Mg-Cl-SO4, characteristic of groundwater some distance along its flow path and Ca-Mg-HCO3, characteristic of freshly recharged groundwater from precipitation. The groundwater indices of; Sodium Percent (% Na), Residual Sodium Carbonate (RSC) , Kelley’s ratio (KR), Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC), Total Dissolved Solid (TDS), USSL and Wilcox index were determined, evaluated and found to be suitable for agro-industrial uses in all seasons. Permeability Index (PI) , Water quality index (WQI) and Magnesium Adsorption Ratio (MAR) were not suitable in some areas and in some seasons.

Hydrochemical variation of the karst groundwater impacted by the contaminant discharge from a tourism hotel

Hydrochemical variation of the karst groundwater impacted by the contaminant discharge from a tourism hotel

Seasonal microbial variation accounts for arsenic dynamics in shallow alluvial aquifer systems.

Determining the temporal variation of microbial communities in groundwater systems is essential to improve our understanding of hydrochemical dynamics in aquifers, particularly as it relates to the fate of redox-sensitive contaminants like arsenic (As). Therefore, a high-resolution hydrobiogeochemical investigation was conducted in the As-affected alluvial aquifer systems of the Jianghan Plain. In two 25 m-deep monitoring wells, the seasonal variation in the composition of groundwater microbial communities was positively correlated with the change in groundwater level (R = 0.47 and 0.39 in NH03B and NH05B, respectively, P < 0.01), implying that the latter could be a primary driver of the seasonal microbial dynamics. In response to the fluctuating groundwater level, iron (Fe) reducers within the Desulfuromonadales were dominant (9.9 ± 4.7% among different sampling sites) in groundwater microbial communities during the monsoon season and associated with high concentrations of Fe(II) and As, while the predominance (16.7 ± 15.2% among different sampling sites) of iron-oxidizers the Gallionellaceae was accompanied by low Fe(II) and As in the non-monsoon season. These results suggest that microbially-mediated iron reduction/oxidation may have governed the seasonal mobilization/scavenging of As in groundwater. Our results provide new insights into mechanisms responsible for seasonal variations in groundwater As concentrations in similar aquifer systems.

The 234U/238U variations in groundwater from the Mondy area in response to earthquakes at the termination of the Tunka Valley in the Baikal Rift System

High 234U/238U activity ratio (AR4/8), identified in groundwater from the Elovka-Kultuk and Nilovka-Mondy inversion sections of the Tunka Valley, coincide with areas of earthquake concentrations. In order to substantiate an approach to earthquake prediction, spatial variations of this parameter were determined in natural water at the western termination of the valley and its temporal variations were monitored in water from the Mon-D well in the Mondy basin in 2013–2017. A recorded gradual decrease of AR4/8 values in water of this well, coeval with preparation and implementation of an earthquake with the energy class K=13.9 in the north of lake Khövsgöl, reflected crack closure that prevented deep water penetration in the Tumelik-Mondy aseismic zone. At the eastern termination of the valley, near the Kultuk village, decreasing AR4/8 values in groundwater were followed with their sharp increasing and transition to low-amplitude variations. Accordingly, crack closing was followed with their opening that facilitated the circulation of deep water and provided seismic events. Leveling of the Mondy anomaly in the Tumelik-Mondy aseismic zone, accompanied by a continuous activity of the Turan and Nilovka anomalies within the Nilovka-Mondy section, emphasized a specific role of the latter as an intermediate chain between the Khövsgöl segment of radial rifts, originated in front of the Hangay orogen, and the largest central basin of the Tunka Valley. The Kultuk, Zaktuy, and North-Tory AR4/8 and earthquake anomalies denoted boundaries of the Elovka-Kultuk section in the Khamardaban lithospheric block flattened at the edge of the Siberian platform basement.

Study of aluminium in groundwater using chemometric methods

ABSTRACTThe field dataset including physico-chemical characteristics of Khibiny alkaline massif groundwater aquifer was analysed for the first time by applying chemometric methods to explore the relationships between investigated parameters in both time and frequency domains. Elevated Al concentration in water of this aquifer is described as a serious health concern when used for the household water supply. The time series of 12 physico-chemical parameters were examined by using Pearson correlation, multiple linear regression and spectral analysis based on fast Fourier transform (FFT) algorithm. Computed pairwise correlation coefficients matrix revealed that pH values, NO3−, SO42−, Cl− and TDS correlate with Al concentrations at a statistically significant level (α-level = 0.05). The multiple regression model including Cl−, NO3− and pH explains up to 54% of Al concentrations temporal variation in groundwater. Fourier coefficients, power spectral density (PSD) and cumulative spectral power (CSP) were calculated for Al, pH, NO3− and Cl− time series to identify and analyse the strength of their variations as a function of frequency. Calculations revealed the spectrums of these variables include three main frequency bands corresponding approximately to 5–7, 13–17 and 20–34 month periods. The fluctuations within these bands contribute mostly to the total temporal variation of Al, Cl−, NO3− concentrations and pH values.

Physicochemical Quality Evolution of Groundwater from the Area of an Chemical Platform

The most important natural resource which cannot be optimally used and sustained unless its quality is properly assessed, is groundwater. In the present study, the physicochemical variations of groundwater from the area of an chemical platform were determinate. The physicochemical parameters determined for the groundwater were evaluated by comparing the results obtained with the the limits allowed under current legislation. For this study were examining 16 drillings for a period of five years. Water samples were collected quarterly from each sampling point in the study. The physico-chemical quality indicators analyzed for each source were: pH, chlorides, sulfates, bicarbonates, carbonates, sodium, calcium, magnesium, ammonium, filterable residue, suspended matter, mercury and CCO-Mn.Interpretation of physicochemical data revealed that groundwaters studied was neutral to slightly alkaline. The cations such as sodium (Na+) for all groundwaters studied it was in general found above the limit imposed under the laws in vigor in almost all studied drillings except drillings generally located upstream of the industrial platform. The anions such as chlorides (Cl-) exceeded, in general, the limit allowed under current legislation. The filterable residue concentration was observed in all the studied drillings and the parameter such as sulfate (SO42-), were within the limit allowed under current legislation for the most all studied drillings, for the whole period investigated. In general, the sulfate quality indicator exceeds the required limit, for drilling located downstream and in vicinity of the chemical platform.