Environmental tracers and indicators bringing together groundwater,surface water and groundwater-dependent ecosystems: importance of scale in choosing relevant tools

Groundwater–surface water (GW–SW) interactions cover a broad range of hydrogeological and biological processes and are controlled by natural and anthropogenic factors at various spatio-temporal scales, from watershed to hyporheic/hypolentic zone. Understanding these processes is vital in the protection of groundwater-dependent ecosystems increasingly required in water resources legislation across the world. The use of environmental tracers and indicators that are relevant simultaneously for groundwater, surface water and biocenoses–biotope interactions constitutes a powerful tool to succeed in the management task. However, tracer type must be chosen according to the scale of interest and tracer use thus requires a good conceptual understanding of the processes to be evaluated. This paper reviews various GW–SW interaction processes and their drivers and, based on available knowledge, systemises application of conservative tracers and semi-conservative and reactive environmental indicators at different spatial scales. Biocenoses–biotopes relationships are viewed as a possible transition tool between scales. Relation between principal application of the environmental tracers and indicators, examples and guidelines are further proposed for examining GW–SW interactions from a hydrogeological and biological point of view by demonstrating the usability of the tracers/indicators and providing recommendations for the scientific community and decision makers.     

A large-scale study of hyporheic nitrate dynamics in a semi-arid catchment,the Tafna River,in Northwest Algeria

Very few studies have evaluated the role of the hyporheic zone (HZ) in aquatic ecosystem functioning or the factors driving hyporheic exchange flows on a large scale, especially in a semi-arid environment such as the Tafna watershed in Algeria. To understand this role through time and space, hydrogeochemical parameters, particularly nitrate concentrations (NO₃–N), were measured monthly between February 2013 and April 2014 in surface water (SW), interstitial water (IW) and groundwater (GW) along a 170-km stretch from the river’s source to the outlet into the main stream of the Tafna River and its Isser and Chouly tributaries. The significant longitudinal evolution of NO₃–N in the HZ was related to stream order and distance from the source. Moreover, the study indicated a significant difference between nitrate concentrations in the riffles (R) and pools (P) of the Tafna wadi. Principal component analysis (PCA) revealed the considerable impact of agriculture on nitrate concentrations. This study indicated on a large scale that nitrate-rich HZ contributed to increasing surface nitrate concentrations in upwelling sites and could be an important nitrate source for downstream SW, particularly during low-water (LW) periods when the Tafna can run dry on the surface. Thus, these results underline the importance of hyporheic zones functioning to the water quality of the watershed (process of enrichment and retention of nitrogen).     

Assessing hyporheic exchange and associated travel times by hydraulic, chemical, and isotopic monitoring at the Steinlach Test Site, Germany

First results of a multi-disciplinary hyporheic monitoring study are presented from the newly established Steinlach Test Site in Southern Germany. The site is located in a bend of the River Steinlach (mean discharge of 1.8 m³/s) underlain by an alluvial sandy gravel aquifer connected to the stream. The overall objective is a better understanding of hyporheic exchange processes at the site and their interrelations with microbial community dynamics and biochemical reactions at the stream–groundwater interface. The present paper focuses on the distribution of lateral hyporheic exchange fluxes and their associated travel times at the Steinlach Test Site. Water level dynamics in various piezometers correspond to the different domains of hydraulic conductivity in the shallow aquifer and confirms hyporheic exchange of infiltrated stream water across the test site. Hydrochemical compositions as well as increased damping of continuous time series of electrical conductivity (EC) and temperature at the respective piezometers confirmed the inferred distribution of hyporheic flowpaths. Mean travel times ranging from 0.5 days close to the stream to more than 8 days in the upstream part of the test site could be estimated from deconvolution of EC and δ¹⁸O–H₂O data. The travel times agree well with the presumed flowpaths. Mg/Ca ratios as well as model fits to the EC and δ¹⁸O data indicate the presence of an additional water component in the western part of the test site which most likely consists of hillslope water or groundwater. Based on the mean travel times, the total lateral hyporheic exchange flux at the site was estimated to be of the order of 1–2 L/s.     

Characterizing the interaction of groundwater and surface water in the karst aquifer of Fangshan,Beijing (China)

Correct understanding of groundwater/surface-water (GW–SW) interaction in karst systems is of greatest importance for managing the water resources. A typical karst region, Fangshan in northern China, was selected as a case study. Groundwater levels and hydrochemistry analyses, together with isotope data based on hydrogeological field investigations, were used to assess the GW–SW interaction. Chemistry data reveal that water type and the concentration of cations in the groundwater are consistent with those of the surface water. Stable isotope ratios of all samples are close to the local meteoric water line, and the ³H concentrations of surface water and groundwater samples are close to that of rainfall, so isotopes also confirm that karst groundwater is recharged by rainfall. Cross-correlation analysis reveals that rainfall leads to a rise in groundwater level with a lag time of 2 months and groundwater exploitation leads to a fall within 1 month. Spectral analysis also reveals that groundwater level, groundwater exploitation and rainfall have significantly similar response periods, indicating their possible inter-relationship. Furthermore, a multiple nonlinear regression model indicates that groundwater level can be negatively correlated with groundwater exploitation, and positively correlated with rainfall. The overall results revealed that groundwater level has a close correlation with groundwater exploitation and rainfall, and they are indicative of a close hydraulic connection and interaction between surface water and groundwater in this karst system.     

Hydrological connectivity of alluvial Andean valleys: a groundwater/surface-water interaction case study in Ecuador

The Andean region is characterized by important intramontane alluvial and glacial valleys; a typical example is the Tarqui alluvial plain, Ecuador. Such valley plains are densely populated and/or very attractive for urban and infrastructural development. Their aquifers offer opportunities for the required water resources. Groundwater/surface-water (GW–SW) interaction generally entails recharge to or discharge from the aquifer, dependent on the hydraulic connection between surface water and groundwater. Since GW–SW interaction in Andean catchments has hardly been addressed, the objectives of this study are to investigate GW–SW interaction in the Tarqui alluvial plain and to understand the role of the morphology of the alluvial valley in the hydrological response and in the hydrological connection between hillslopes and the aquifers in the valley floor. This study is based on extensive field measurements, groundwater-flow modelling and the application of temperature as a groundwater tracer. Results show that the morphological conditions of a valley influence GW–SW interaction. Gaining and losing river sections are observed in narrow and wide alluvial valley sections, respectively. Modelling shows a strong hydrological connectivity between the hillslopes and the alluvial valley; up to 92 % of recharge of the alluvial deposits originates from lateral flow from the hillslopes. The alluvial plain forms a buffer or transition zone for the river as it sustains a gradual flow from the hills to the river. Future land-use planning and development should include concepts discussed in this study, such as hydrological connectivity, in order to better evaluate impact assessments on water resources and aquatic ecosystems.     

Thermal infrared remote sensing in assessing groundwater and surface-water resources related to Hannukainen mining development site,northern Finland

Mining development sites occasionally host complicated aquifer systems with notable connections to natural surface water (SW) bodies. A low-altitude thermal infrared (TIR) imaging survey was conducted to identify hydraulic connections between aquifers and rivers and to map spatial surface temperature patterns along the subarctic rivers in the proximity of the Hannukainen mining development area, northern Finland. In addition to TIR data, stable isotopic compositions (δ ¹⁸O, δD) and dissolved silica concentrations were used as tracers to verify the observed groundwater (GW) discharge into the river system. Based on the TIR survey, notable GW discharge into the main river channel and its tributaries (61 km altogether) was observed and over 500 GW discharge sites were located. On the basis of the survey, the longitudinal temperature patterns of the studied rivers were found to be highly variable. Hydrological and hydrogeological information is crucial in planning and siting essential mining operations, such as tailing areas, in order to prevent any undesirable environmental impacts. The observed notable GW discharge was taken into consideration in the planning of the Hannukainen mining development area. The results of this study support the use of TIR imagery in GW–SW interaction and environmental studies in extensive and remote areas with special concerns for water-related issues but lacking the baseline research.     

Characterisation of the physicochemical qualities of a typical rural-based river: ecological and public health implications

The physicochemical qualities of a typical rural-based river were assessed over a 12-month period from August 2010 to July 2011 spanning the spring, summer, autumn and winter seasons. Water samples were collected from six sampling sites along Tyume River and analysed for total nitrogen, orthophosphate, biochemical oxygen demand (BOD), temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), total dissolved solids (TDS) and turbidity. BOD regimes did not differ significantly between seasons and between sampling points and ranged from 0.78 to 2.76 mg/L across seasons and sampling points, while temperature ranged significantly (P < 0.05) between 6 and 28 °C. Turbidity varied significantly (P < 0.05) from 6 to 281 nephelometric turbidity units while TDS (range 24–209 ppm) and conductivity (range 47.6–408 mg/L) also varied significantly (P < 0.05) across sampling points with a remarkable similarity in their trends. Orthophosphate concentrations varied from 0.06 to 2.72 mg/L across seasons and sampling points. Negative correlations were noted between temperature and the nutrients, DO and temperature (r = ?0.56), and TDS and DO (r = ?0.33). Positive correlations were noted between TDS and temperature (r = 0.41), EC and temperature (r = 0.15), and DO and pH (r = 0.55). All nutrients were positively correlated to each other. Most measured parameters were within prescribed safety guidelines. However, the general trend was that water quality tended to deteriorate as the river flows through settlements, moreso in rainy seasons.     

Measurement of seasonal variability of hydro-environmental characteristics of Kuwait Bay

To fill in the large existing data gap, this study presents results of a comprehensive data set from Kuwait Bay (KB), showing the horizontal and vertical distribution of its prominent hydrodynamic variables (i.e., water temperature, seawater salinity, seawater density) and water quality variables (i.e., chlorophyll-a concentration, turbidity, dissolved oxygen (DO) concentration, DO saturation, apparent oxygen utilization, photosynthetic active radiation). Field measurements were carried out between 11 September 2014 and 17 August 2015 covering number of monitoring stations in the entire bay. The results revealed significant seasonal variations and apparent three-dimensional features of the measured variables exemplifying the necessity of not considering the bay as a well-mixed water body in the future oceanographic studies anytime of the year. However, well-mixed conditions (with the Brunt-Vaisala frequency of about 0.0002 s^?1) were existent only in the winter. Bay’s water column began stratifying in late spring, and these were significantly intensified (with the Brunt-Vaisala frequency of about 0.0008 s^?1) during the summer and early autumn. The stratification, together with the increase oxygen demand for decomposition processes and decrease in DO solubility in summer, led to the formation of a lower DO water mass (daytime DO concentration <4.2 mg l^?1) at the lower layers. Results also suggested that the water of the KB is more transparent (indicated by lower turbidity) compared to the adjacent sea water. Measurement of light intensity along the water column indicated that the light extincts rapidly (i.e., the light reduced to approximately 10 % of the surface values at water depth of 2–6 m) in KB and many times absent at the water near the seabed. This study also suggested that the KB can be classified at a year-round negative, hypersaline, inverse, and hyperpycnal estuary.     

Heat tracing to determine spatial patterns of hyporheic exchange across a river transect

Significant spatial variability of water fluxes may exist at the water-sediment interface in river channels and has great influence on a variety of water issues. Understanding the complicated flow systems controlling the flux exchanges along an entire river is often limited due to averaging of parameters or the small number of discrete point measurements usually used. This study investigated the spatial pattern of the hyporheic flux exchange across a river transect in China, using the heat tracing approach. This was done with measurements of temperature at high spatial resolution during a 64-h monitoring period and using the data to identify the spatial pattern of the hyporheic exchange flux with the aid of a one-dimensional conduction-advection-dispersion model (VFLUX). The threshold of neutral exchange was considered as 126 L m^?2 d^?1 in this study and the heat tracing results showed that the change patterns of vertical hyporheic flux varied with buried depth along the river transect; however, the hyporheic flux was not simply controlled by the streambed hydraulic conductivity and water depth in the river transect. Also, lateral flow dominated the hyporheic process within the shallow high-permeability streambed, while the vertical flow was dominant in the deep low-permeability streambed. The spatial pattern of hyporheic exchange across the river transect was naturally controlled by the heterogeneity of the streambed and the bedform of the stream cross-section. Consequently, a two-dimensional conceptual illustration of the hyporheic process across the river transect is proposed, which could be applicable to river transects of similar conditions.     

Continuous Monitoring Reveals Drivers of Dissolved Oxygen Variability in a Small California Estuary

Estuarine ecosystem diversity and function can be degraded by low oxygen concentrations. Understanding the spatial and temporal patterns of dissolved oxygen (DO) variation and the factors that predict decreases in DO is thus essential to inform estuarine management. We investigated DO variability and its drivers in Elkhorn Slough, a shallow, well-mixed estuary affected by high nutrient loading and with serious eutrophication problems. Long-term (2001–2012), high-resolution (15 min) time series of DO, water level, winds, and solar radiation from two fully tidal sites in the estuary showed that hypoxia events close to the bottom are common in the summer at the more upstream estuarine station. These events can occur in any lunar phase (spring to neap), at any time of the day, and both on sunny or cloudy days. They are, however, short-lived (lasting in average 40 min) and mainly driven by momentary low turbulent diffusion around slack tides (both at high and low water). Tidal advective transport explains up to 52.1% of the daily DO variability, and the water volume (or DO reservoir) contained in the estuary was not sufficient to avoid hypoxia in the estuary. Solar radiation was responsible for a positively correlated DO daily cycle but caused a decreased in the averaged DO in the summer at the inner station. Wind-driven upwelling reduced the average DO at the more oceanic station during spring. The approach we employed, using robust techniques to remove suspect data due to sensor drift combined with an array of statistical techniques, including spectral, harmonic, and coherence spectrum analysis, can serve as a model for analyses of long-term water quality datasets in other systems. Investigations such as ours can inform coastal management by identifying key drivers of hypoxia in estuaries.     

Spatial characteristics of surface water quality in the Haicheng River (Liao River basin) in Northeast China

Spatial variations of the water quality in the Haicheng River during April and October 2009 were evaluated for the national monitoring program on water pollution control and treatment in China. The spatial autocorrelation analysis with lower Moran’s I values displayed the spatial heterogeneity of the 12 physicochemical parameters among all the sampling sites of the river. The one-way ANOVA showed that all variables at different sampling sites had significant spatial differences (p < 0.01). Based on the similarity of water quality characteristics, cluster analysis grouped the 20 sampling sites into three clusters, related with less polluted, moderately polluted and highly polluted sites. The factor analysis extracted three major factors explaining 76.4 % of the total variance in the water quality data set, i.e., integrated pollution factor, nitrogen pollution factor and physical factor. The results revealed that the river has been severely polluted by organic matter and nitrogen. The major sources leading to water quality deterioration are complex and ascribed to anthropogenic activities, e.g., domestic and industrial wastewater discharges, agricultural runoff, and animal rearing practices.     

非稳态潜流交换过程研究进展

潜流交换研究涉及地表水-地下水系统交互作用的物理机制、影响因素和生化作用等方面,是近年来水文学、生态学、环境学等学科的研究热点。潜流交换过程包含水流运动、溶质运移以及能量传输过程。以稳态流动条件作为控制因素的潜流交换研究成果已经不能满足相关学科发展的要求。因此,近年来非稳态潜流交换过程的研究及其成果渐受关注。当前相关研...     

Small Spatial Scale Variation in Fish Assemblage Structure in the Vicinity of the Northwestern Gulf of Mexico Hypoxic Zone

Seasonal hypoxia [dissolved oxygen (DO)?≤?2 mg?l^?1] occurs over large regions of the northwestern Gulf of Mexico continental shelf during the summer months (June–August) as a result of nutrient enrichment from the Mississippi–Atchafalaya River system. We characterized the community structure of mobile fishes and invertebrates (i.e., nekton) in and around the hypoxic zone using 3 years of bottom trawl and hydrographic data. Species richness and total abundance were lowest in anoxic waters (DO?≤?1 mg?l^?1) and increased at intermediate DO levels (2–4 mg?l^?1). Species were primarily structured as a benthic assemblage dominated by Atlantic croaker (Micropogonias undulatus) and sand and silver seatrout (Cynoscion spp.), and a pelagic assemblage dominated by Atlantic bumper (Chloroscombrus chrysurus). Of the environmental variables examined, bottom DO and distance to the edge of the hypoxic zone were most strongly correlated with assemblage structure, while temperature and depth were important in some years. Hypoxia altered the spatial distribution of both assemblages, but these effects were more severe for the benthic assemblage than for the pelagic assemblage. Brown shrimp, the primary target of the commercial shrimp trawl fishery during the summer, occurred in both assemblages, but was more abundant within the benthic assemblage. Given the similarity of the demersal nekton community described here to that taken as bycatch in the shrimp fishery, our results suggest that hypoxia-induced changes in spatial dynamics have the potential to influence harvest and bycatch interactions in and around the Gulf hypoxic zone.     

Distribution of biochemical constituents in the surface sediments of western coastal Bay of Bengal: influence of river discharge and water column properties

Biochemical composition of surface sediment samples from off major and minor rivers along the east coast of India revealed that spatial distribution of sediment organic carbon (SOC) composition was mainly governed by differential characteristics of discharged water and associated biogeochemical processes in the water column. The northwest (NW) region of coastal Bay of Bengal was influenced by discharges from Ganges river while peninsular (monsoonal) rivers influenced the southwest (SW) region. The NW region characterized by low nutrients suspended particulate matter (SPM), high phytoplankton biomass in the water column and high SOC while contrasting to that observed in the SW region. The isotopic ratios of SOC (?22 ‰) in the NW region were close to that of organic matter derived from phytoplankton (?23 ‰) suggesting in situ production is the major source whereas terrigeneous source contributed significantly in the SW region (?19.6 ‰). Though low in situ biological production in the SW region, relatively higher total carbohydrates (TCHO) were found than in the NW and insignificant difference of total and free amino acid concentrations between NW and SW were resulted from faster removal of organic matter to the sediment in association with SPM in the SW region. Higher proteins concentrations than total amino acids indicate that nitrogenous organic matter is preserved in the former form. The protein to TCHO ratio was lower in the SW suggesting significant contribution of aged and non-living organic matter in this region.     

Sources of dissolved oxygen in monitoring and pumping wells

Groundwater monitoring and pumping wells set in anoxic aquifers require attention to keep the groundwater free of dissolved oxygen (DO). In properly constructed monitoring or pumping wells, two processes can however still introduce oxygen to anoxic groundwater: (1) permeation of oxygen through polymer materials such as silicone, PVC, HDPE or Teflon, and (2) thermally driven convection, which can occur in all types of piezometers or wells, regardless of construction material, when the water table or pressure head is close (<10 m) to the land surface. Here, field measurements (temperature and DO well loggings) from a monitoring well in Bilthoven, the Netherlands, are combined with analytical and numerical modelling to investigate the role of both processes on oxygenation of anoxic groundwater in wells. The results of numerical and analytical modeling show that both permeation and convection can introduce oxygen into anoxic wells to near saturation concentrations. In the field data gathered, convection is primarily responsible for oxygen intrusion up to a depth of around 12 m. Oxygen intrusion through convection and permeation in monitoring and pumping wells may influence groundwater sampling and analyses, and may contribute to well clogging, depending on site conditions. The combination of field and modelling provides new insights into these processes, which can be used for both groundwater sampling and pumping well design.     

The scale effect on the soil spatial heterogeneity of Haloxylon ammodendron (C. A. Mey.) in a sandy desert

Haloxylon ammodendron Bge (C.A. Mey.) is a dominant shrub species in the Gurbantonggut Desert and plays an important role in preventing wind erosion and combating desertification, typically by developing fertile islands in desert ecosystems; however, such islands often depend on the scales. An experiment was conducted to determine the scale dependence for the soil spatial heterogeneity of H. ammodendron in the Gurbantonggut Desert using the soil pH, electrical conductivity (EC), soil organic carbon (SOC), and total nitrogen (TN). The results showed that the soil EC, SOC and TN were significantly higher at the individual scale than the population scale. Moreover, the coefficients of variation (CV %) of the soil parameters at the individual scale were greater than they were at the population scale, with all except for pH (CV = 4.35 % for individual scale and CV = 2.87 % for population scale) presenting a moderate degree of variability (10 % < CV < 100 %). A geostatistical analysis revealed a strong spatial dependence [C ₀ /(C ₀ + C) < 25 %] within the distance of ranges for the tested parameters at both scales. The kriging interpolation results presented significant accumulation of soil SOC and TN around the shrub center and formed a significant “fertile island” at the individual scale, whereas the soil EC was much lower at the shrub center. At the population scale, patch fragments of the soil chemical properties were observed; however, not all individuals presented significant fertile islands or salt islands, and the soil EC presented a similar distribution as SOC and TN. These differences suggested that different mechanisms controlled the spatial distribution of soil minerals at the two scales and that the spatial heterogeneities are scale-dependent in a desert ecosystem.     

A review on using heat as a tool for studying groundwater–surface water interactions

In terms of the research on groundwater–surface water heat-tracing methods, investigation of the interactions within the compound system of the groundwater–surface water–hyporheic zone can effectively reveal the relevant physicochemical processes and microbial properties. The evaluation of these properties represents a key component in qualitative and quantitative research on groundwater–surface water interactions. Therefore, this paper reviews the research results on groundwater–surface water interactions achieved by related researchers using heat as a natural tracer over the last decade. In connection with the application of heat-tracing theory to the basic principles of hyporheic exchange between groundwater and surface water, research on groundwater–surface water interaction through one-dimensional steady-state and transient-state heat transport analytical models, techniques to collect and analyze temperature time series data, and numerical simulation technology is reviewed. In addition, directions for future research using groundwater–surface water heat-tracing methods are suggested. First, hypothetical, difficult temperature boundary and hydrogeological conditions require further research. Second, hydrodynamic exchange capacity and the processes of heat exchange and solute concentration exchange in the hyporheic zone alongside riverbeds should be appropriately and accurately measured under multi-scale influences. Third, the overall study of the heat transport process inside the hyporheic zone induced by complex riverbed forms should be performed, and the response mechanism of riverbed hyporheic exchanges driven by riverbed form, the hydrodynamic force of surface water, and sediment permeability should be revealed. The objectives and goals of this paper are to encourage scholars interested in analyzing groundwater–surface water interactions using heat as a tracer to creatively solve practical problems and to improve the ecological functions of river aquatic habitats through new research results.     

Interactions between groundwater and surface water: the state of the science

The interactions between groundwater and surface water are complex. To understand these interactions in relation to climate, landform, geology, and biotic factors, a sound hydrogeoecological framework is needed. All these aspects are synthesized and exemplified in this overview. In addition, the mechanisms of interactions between groundwater and surface water (GW–SW) as they affect recharge–discharge processes are comprehensively outlined, and the ecological significance and the human impacts of such interactions are emphasized. Surface-water and groundwater ecosystems are viewed as linked components of a hydrologic continuum leading to related sustainability issues. This overview concludes with a discussion of research needs and challenges facing this evolving field. The biogeochemical processes within the upper few centimeters of sediments beneath nearly all surface-water bodies (hyporheic zone) have a profound effect on the chemistry of the water interchange, and here is where most of the recent research has been focusing. However, to advance conceptual and other modeling of GW–SW systems, a broader perspective of such interactions across and between surface-water bodies is needed, including multidimensional analyses, interface hydraulic characterization and spatial variability, site-to-region regionalization approaches, as well as cross-disciplinary collaborations. Electronic Publication     

A Regional Survey of the Extent and Magnitude of Eutrophication in Mediterranean Estuaries of Southern California,USA

The magnitude and extent of eutrophication was assessed at 27 segments in 23 estuaries in the Southern California Bight (SCB) between October 2008 and 2009. We applied thresholds from the existing assessment frameworks from both the European Union and the U.S. National Eutrophication Assessment to measurements of three indicators [macroalgae biomass and cover, phytoplankton biomass, and dissolved oxygen (DO) concentration] to categorize eutrophic condition in each estuary. Based on these frameworks, a large fraction of segments had moderate or worse eutrophic condition—78 % based on macroalgae, 39 % for phytoplankton, and 63 % for DO. Macroalgal biomass exceeding 70 g dw m^?2 and 25 % cover was found at 52 % of sites during any sampling event and in 33 % of segments for 8 weeks or longer, a duration found to negatively impact benthic infauna. Duration of hypoxic events (DO?<?4 mg L^?1) was typically short, with most events less than one day; although 53 % of segments had at least one event longer than 24 h. Assessment frameworks of eutrophic condition are likely to evolve over time as the body of literature on eutrophication grows, including aspects such as the applicability of indicators in specific habitat types, indicator thresholds, and how event frequency and duration are incorporated. This paper informs this debate by discussing how eutrophic conditions in SCB estuaries are categorized using different indicators and thresholds. To this end, categorization of estuarine eutrophic condition was found to be very sensitive to the type of threshold, how data are integrated to represent duration or spatial extent, and how indicators are used as multiple lines of evidence.     

Implementation and evaluation of multivariate analysis for groundwater hydrochemistry assessment in arid environments: a case study of Hajeb Elyoun–Jelma, Central Tunisia

In most arid zones, groundwater (GW) is the major source of domestic, agriculture, drinking, and industrial water. Accordingly, the monitoring of its quality by different techniques and tools is a vital issue. The purpose of this paper is the evaluation of the combination of principal components analysis (PCA) and geostatistics as a technique for (1) identifying the processes affecting the groundwater chemistry of the detrital unconfined Middle Miocene Aquifer (MMA) of the Hajeb elyoun Jelma (HJ) aquifer (Tunisia) and (2) mapping the controlling variables for groundwater quality. This work is based on a limited database recorded in 22 wells tapping the aquifer and unequally distributed in the field. The proposed approach is carried out in two steps. In the first step, the application of PCA revealed that rock–water interaction, agriculture irrigation and domestic effluents could explain 85 % of the observed variability of the chemical GW quality of the MMA. As a result, two new variables are defined: V1 (rock–water interaction influence) and V2 (irrigation and domestic effluent influence). In the second step, the spatial variability of these variables over the extent of the MMA is mapped by applying a kriging interpolation technique. The results of this study suggest that, while both natural and anthropogenic processes contribute to the GW quality of the MMA, natural impacts can be considered as the most important.