Groundwater Chloride Research Articles

Removal of 1,2-dichloroethane in groundwater using Fenton oxidation

Among the chlorinated aliphatic hydrocarbons, 1,2-dichloroethane (1,2-DCA) is widely used for the synthesis of vinyl chloride monomers. Despite the high demand for 1,2-DCA, it poses a risk to the environment because it is persistent and carcinogenic. Therefore, in this study, several reagents (dithionite, hydrosulfide, sulfite, persulfate, sulfate radicals, and hydroxyl radicals) were evaluated for the degradation of 1,2-DCA. Among these, the hydroxyl radicals generated by the Fenton reaction were the most suitable oxidant, decomposing 92% of 1,2-DCA. Chloride, one of the final oxidized products, was observed, which supported the oxidation reaction. Moreover, with an increasing concentration of hydroxyl radicals, the degradation of 1,2-DCA increased. Furthermore, sufficient amounts of hydrogen peroxide were more important than Fe(II) in the decomposition of 1,2-DCA. The radical reaction can generate larger molecules via the degradation of 1,2-DCA, which are degraded over time. The applicability of Fenton oxidation was evaluated using real 1,2-DCA-contaminated groundwater. Although the degradation of target contaminant was lowered due to the alkaline pH and the presence of chloride and bicarbonate ions in groundwater, the Fenton reaction was still efficient to oxidize 1,2-DCA. These results indicate that Fenton oxidation is an effective technique for the treatment of 1,2-DCA in contaminated groundwater.

CMBEAR: Python-Based Recharge Estimator Using the Chloride Mass Balance Method in Australia.

The chloride mass balance (CMB) method is widely used to estimate long-term rates of groundwater recharge. In regions where surface water runoff is negligible, recharge can be estimated using measurements of chloride concentrations of groundwater and precipitation, and an estimate of long-term average rainfall. This paper presents the Chloride Mass Balance Estimator of Australian Recharge (CMBEAR), a Jupyter (Python) Notebook that is set up to rapidly apply the CMB method using gridded maps of chloride deposition rates across the Australian continent. For an Australian context, the chloride deposition rate and rainfall maps have been provided. Thus, CMBEAR requires only a spreadsheet with the groundwater chloride concentration, the latitude and longitude of the sample location, and some simple user inputs. CMBEAR may be easily applied in other regions, providing that a gridded chloride deposition map is available. Recharge estimates from CMBEAR are compared against published applications of the CMB method. CMBEAR is also applied to a large dataset from the Northern Territory and is used to produce a gridded map of recharge for western Victoria. CMBEAR provides a reproducible and straightforward approach to apply the CMB method to estimate groundwater recharge.

Nitrate Removal in an Electrically Charged Granular-Activated Carbon Column.

Nitrate removal from groundwater remains a challenge. Here, we report on the development of a flow-through, electrically charged, granular-activated carbon (GAC)-filled column, which effectively removes nitrate. In this system, the GAC functioned as an anode, while a titanium sheet acted as a cathode. The high removal rate of nitrate was achieved through a combination of electrosorption and electrochemical transformation to N2. The column could be readily regenerated in situ by reversing the polarity of the applied potential. We demonstrate that in the presence of chloride, the mechanism responsible for the observed nitrate removal involves a combination of electroadsorption of nitrate to the anodically charged GAC, electroreduction of nitrate to ammonium, and the oxidation of ammonium to N2 gas by reactive chlorine and other oxidative radicals (with nearly 100% N2 selectivity). Given the ubiquitous presence of chloride in groundwater, this method represents a ready, green, and sustainable treatment process with significant potential for the remediation of contaminated groundwater.

Decision tree for estimating groundwater contaminant through proxies considering seasonality and soil saturation.

Chloride ion is an important indicator of water quality. Field measurement of chloride is difficult whereas laboratory measurement is both time-consuming and chemical intensive. The conservative nature of chloride and good correlation with electrical conductivity (EC) justifies its use as proxy for chloride estimations. Comparison of the best regression models (RMs) and data-driven decision tree (DT) model enables appreciation of relative merits of the two approaches for this purpose. Quantitative improvements over the models from literature are, increase in correlation (RM: 0.70 to 0.77; DT: 0.70 to 0.78) and decrease in relative errors (RM: MARE: 0.88 to 0.65 and RMSRE: 1.91 to 0.92; DT: MARE: 0.88 to 0.40; RMSRE: 1.91 to 0.54); thereby, DT hasemerged as the better modeling approach for this case. Considering the influence of seasonality (pre-or post-monsoon) and degree of saturation of soil (water logged or water depleted) enabled the reduction of the correlation range (0.24-0.87) of the basic variables to a smaller range (0.44-0.89) for estimates of Cl-, along with relative error ranging from 0.35 to 0.57, the improvement being more pronounced for lower value of variable correlations. The overall comparison using the evaluation datasets between RM from literature and RM/DT models from this study exemplified that for the study area, the case-specific models developed using the data-driven tool: DT resulted in the most accurate estimation of chloride in groundwater from the chosen proxy: EC.

An integrated geospatial correlation analysis and human health risk assessment approach for investigating abandoned industrial sites

An integrated geospatial correlation analysis (GCA)-human health risk assessment (HHRA) approach was developed to investigate abandoned industrial sites featured by heterogeneous contamination data. Critical areas of high health risk concerns can be prioritized for remediation using the integrated approach. An abandoned chemical complex site in Hubei, China was investigated as a case study. GCA and HHRA were performed using soil and groundwater sampling data collected in 2016 and 2019. Benzene, chlorobenzene, dichlorobenzenes, 2-nitrochlorobenzene, and α-hexachlorocyclohexane were determined to be critical contaminants in soil. The 2019 sampling data revealed new contaminated locations that were not found in the 2016 sampling campaign. High concentrations (89.81–386.55 mg/L) of vinyl chloride were also found in groundwater samples. Several critical location clusters of high concentrations of dichlorobenzenes, chlorobenzene, and α-hexachlorocyclohexane were found within the site according to the GCA outcomes. These contaminants could pose significant cancer and non-cancer risks to onsite workers. The critical areas were ranked according to cancer and non-cancer risks estimated by HHRA, respectively, for informed remediation planning. Among the critical contaminants, α-hexachlorocyclohexane, 2-nitrochlorobenzene, and 1,4-dichlorobenzene in soil, as well as vinyl chloride in groundwater, contributed a predominant part to the total health risk. The integrated approach can be used to assess the contamination of other similar abandoned industrial complex sites.

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern- and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration.

Shale oil production and groundwater: What can we learn from produced water data?

As oil production in the Permian Basin surges, the impact of shale production on groundwater resources has become a growing concern. Most existing studies focus on the impact of shale production on shallow freshwater aquifers. There is little understanding of the shale development's impact on other groundwater resources (e.g., deep carbonate aquifers and deep basin meteoric aquifers). The possible natural hydraulic connections between shallow aquifers and formation water suggest such an impact can be consequential. This study explores the relationship between shale production and groundwater using produced water (PW) samples from active unconventional oil wells. Focusing on the most productive portion of the Permian Basin-the four-county region in Southeast New Mexico between 2007 and 2016, a large produced water dataset allows us to analyze the conditional correlations between shale oil production and PW constituents. The results suggest that (1) expanding from primarily conventional wells to unconventional wells during the recent shale boom has led to dramatic increases of the TDS, chloride, sodium, and calcium levels in groundwater (i.e., producing formation). (2) Nearby oil well density positively correlates with the TDS, chloride, and sodium levels in the PW samples.

High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting

In the High Plains (HP) region of northeastern New Mexico (NE NM), USA, underlying bedrock aquifers are utilized where the High Plains Aquifer is thin, absent, or unsaturated. These usage patterns, aquifer depletion, and increasing regional aridity imply that NE NM is a possible analogy for more easterly portions of the central HP. To examine the relationship between recharge, residence time, and hydrogeologic setting, 85 well and spring samples were analyzed for environmental tracers (δD, δ18O, δ13C, and limited tritium and carbon-14 activities). Approximately half of the wells were open to strata of the Dakota Group. δD was −105.0 to −41.7‰ (median −58.2‰) and δ18O was −13.7 to −4.4‰ (median −8.1‰). Overall, isotopic composition is correlated with elevation and influenced by hydrogeologic setting. Ten anomalously depleted waters, most near volcanic-capped mesas, may represent higher-elevation or winter-biased recharge, a different modern precipitation source, or recharge from a cooler climate. Recharge, estimated by chloride mass balance using groundwater chloride concentrations, averages 6 mm/year below 2,000-m elevation and 16 mm/year above 2,000 m. Tritium (nondetectable to 5.7 tritium units) and carbon-14 activities (modern carbon fraction 0.23–1.05) suggest that Holocene to modern waters occur, possibly as mixtures, and that alluvial channels and other surficial features promote recharge, likely at higher rates than regional averages. It is noteworthy that isotopically depleted waters in this study tended to be tritium-free. Additional residence time tracers and seasonal precipitation isotopic sampling could address recharge and the origin of depleted waters.

Modeling the effect of chloride contaminant migration on groundwater

Municipal solid waste (MSW) is considered to be one of the biggest challenges facing most of the developing countries including Egypt. Notwithstanding the fact that there are various methods used in the disposal of MSW, landfilling remains an attractive disposal method out of purely economical aspects. This study presents the effect of improper landfilling of waste on groundwater quality. Moreover, a commercial software package has been used in this study to simulate the effect of liner deterioration over time and contaminant migration on groundwater underneath the sanitary landfill site. This model has been validated using three groundwater samples collected from the landfill site over different periods. Two samples were collected from the downstream point, while the third samples were collected from upstream point. The model output and analyzed samples indicated that the concentration of chloride in groundwater downstream El-Sadat landfill is almost double the concentration of the chloride the upstream samples. The downstream shows chloride concentrations of 250: 287 mg/lit and model results after 4000 days show a concentration of 245: 250 mg/lit, compared to 125 mg/lit in the upstream. The model results and the measured concentrations are in satisfactory agreement.

Analysis of mining effects on the geochemical evolution of groundwater, Huaibei coalfield, China

Investigations were undertaken at the Xutuan and Renlou coal mines in Huaibei coalfield, Anhui Province, China to determine the effects of mining on the geochemical evolution of groundwater in the area. A total of 77 samples were collected between 1999 and 2017 from Neogene, Permian, and Carboniferous aquifers in two coal mines for hydrogeochemical analysis. The variation of hydrochemical types and the difference of Cl− and TDS suggest that the groundwater in the Neogene aquifer flow from the Xutuan coal mine to the Renlou coal mine. The high concentrations of chloride in groundwater in the Permian aquifer may be associated with recharge from the Neogene aquifer under the effects of mining. Principal component analysis and the results of chemical analysis of water samples were used to explore the water–rock processes in the three aquifers. The results suggest that the main controlling process of the Xutuan coal mine is ion exchange between Na+ and Ca2+, while the principal chemical processes in the Renlou coal mine are likely to be ion exchange and reverse ion exchange between Na+ and Ca2+. Mining will lead to the decline of the Neogene aquifer potentiometric heads and the compaction of aquifer sediments. This, in turn, could lead to the development of fissures caused by mining which could increase the hydraulic connection between the Neogene and the Permian aquifer, and increase the ion-exchange intensity of the Permian aquifer. The inverse geochemical modeling results of groundwater flow-paths in the Neogene and Carboniferous aquifers suggest that reverse ion-exchange process is taking place in these aquifers, which provides additional evidence for geochemical evolution. This combined method of using various lines of evidences from hydrogeology, multivariate statistical analysis, hydrogeochemical research, and geochemical models can explain the hydrogeochemical evolution processes of groundwater at a deeper level.

Evaluation of Water Resources Vulnerability in the Coastal Areas of the Yellow Sea and Bohai Sea under Seawater Intrusion——A case study of Longkou City, Shandong Province

In view of the increased vulnerability of water resources system caused by seawater intrusion in the coastal areas of the Yellow Sea and Bohai Sea, this paper based on the VSD(Vulnerability Scoping Diagram) model to construct the water resource vulnerability evaluation index system of “exposure-sensitivity-adaptive capacity” under seawater intrusion. Then use entropy-TOPSIS method to evaluate water resource vulnerability and divide the levels. In addition, take Longkou City of Shandong Province as an example to conduct empirical research. The results show that the water resource vulnerability of Longkou City is at a strong vulnerability level. The water resources system is under obvious pressure. Population density, per capita GDP, temperature and precipitation change are the main factors of the system pressure. Seawater intrusion has a high degree of impact on water resources vulnerability and water resource system is more sensitive to groundwater level, chloride concentration and other stimuli. The improvement of water use efficiency and scientific and technological investment contribute to the significant enhancement of the adaptability of the water resources system of Longkou City.

Electrocoagulation-electrooxidation for mitigating trace organic compounds in model drinking water sources

In-situ water treatment can be accomplished using electrochemical treatments such as electrocoagulation (EC), which generates coagulants, and electrooxidation (EO), which generates oxidants (e.g., free chlorine and reactive oxygen species) via electrolysis using boron-doped diamond electrodes. In sequential EC-EO, EC can remove oxidant scavengers present in dissolved organic carbon (DOC), thereby improving the efficacy of downstream oxidation via EO. This study evaluated sequential EC-EO (and each process independently for comparison) for mitigating the trace organic compounds (TOrCs) acyclovir (ACY), trimethoprim (TMP), and benzyldimethyldecylammonium chloride (BAC-C10) in model groundwaters and surface waters. EO-only removed greater than 70% of ACY and TMP but negligible BAC-C10 in model groundwaters. In model surface waters, EO-only removed ∼55–75% BAC-C10, but had less removal for ACY and TMP (∼20–55%), primarily due to DOC interference. Sequential-EC-EO was investigated to better gauge the potential process improvement due to the addition of EC ahead of EO. EC removed 74 ± 7% DOC from model surface water and improved downstream EO treatment relative to EO-only by a factor of 3.4 for ACY, 1.7 for TMP, and 1.4 for BAC-C10. When treating model groundwater, EC-EO resulted in no improvement compared to EO-only for ACY and TMP. BAC-C10 removal was attributed to the particle separation step between EC and EO rather than electrochemical inputs. EO-only treatment was more energy efficient for model groundwater compared to model surface waters based on electrical energy per order (EEO) values. Sequential EC-EO further improved the energy efficiency for treating model river water.

Quality aspects of the Doñana groundwater resources (SW-Spain) before the intensification of agriculture

This article presents the initial hydrochemical status of the Almonte-Marismas aquifer system in 1966 – before agricultural intensification. The investigated aquifer is of critical importance for the groundwater dependent Doñana wetland areas of the National and Natural park of Doñana (SW – Spain). The analytical database involves 158 samples collected in 1966 by the Food and Agriculture Organization (FAO) and the Geological Survey of Spain (IGME), including electrical conductivity, hardness, chloride, bicarbonate, sulphate, calcium, magnesium, sodium, and potassium in groundwater that generate information about the initial hydrochemical state before the intensification of agricultural activity. These historical data existed as hardcopy lab reports and were introduced into a MS Access database. The parameters EC, Cl, SO4 and K of the year 1966 show a variety of spatial patterns before intensification and suggest five different types of influence: (i) natural lagoon systems, (ii) creeks or rivers, (iii) irrigated areas, (iv) urban areas, and (v) marshes. The results suggest that anthropogenic activities such as fertilizer use, domestic activities and wastewater in surface streams downstream of urban areas are responsible for elevated parameter values in most of the observation points, although their specific contributions cannot be determined based on the available data of 1966. In the marshes (north) area, apart from fertilizer use elevated geogenic salinity may also contribute to high parameter concentrations for intensive irrigated crop cultivation and proximity to the Guadalquivir River.

Implications of carbonates and chlorides contamination in groundwater: Examples from textile tie and dye markets in some parts of Southwestern Nigeria

Objectives: To evaluate the impact of common mineral dyes in effluents from dyeing processes on the quality of groundwater at Itoku and Asero, Abeokuta in Nigeria. Methods: Thirty-two (32) samples were examined by determining the In-situ parameters: Total Dissolved Solids (TDS), Electrical Conductivity (Ec) and pH with the aid of a multi-parameter portable meter(model Testr-35); Chemical parameters were determined with Atomic Absorption Spectrometry (AAS)and Titration methods for both cations and anions. Collected samples were analyzed for heterotrophic bacteria load using standard method. Findings: Elevated Ec-1830 µS/cm and TDS-1020mg/l values at Odutola-8 exceeded the WHO permissible limit with bicarbonate, carbonate and chlorides presence, in the water sample. DO at Ifote-6.0, Asero-6.8, Ifote-7.1, Asero carwash-7.9 was greater than WHO standard, specifying water that can support aquatic life and micro-organisms. However, other areas had low dissolved oxygen below the specified permissible limit. The results of the physicochemical parameters including; Chloride and Carbonate levels in effluent and groundwater in most of the studied sites were higher than the World Health Organization (WHO) permissible limits. Dye effluents and well water samples displayed high microbial loads. Predominant bacteria isolated from the effluent and groundwater included Aspergillus spp. Pseudomonas aeruginosa and Bacillus subtilis. Polycyclic aromatic hydrocarbon (PAHs) observed indicated probable human carcinogens found where dye fabrication processes were high and effective. Novelty: Dye effluents have high bacterial and fungal loads. Similarity in the predominant bacteria isolated from effluent and groundwater from the hand-dug wells indicated that the effluent from the dyeing processes is negatively impacting the groundwater and this may pose a risk to public health. High levels of Carbonates, bicarbonates and chlorides in groundwater indicate contamination; making the water unfit for human and animal consumption. Keywords: Minerals; dyes; contamination; groundwater; carbonates; chlorides

Aeration - Advanced Filtration (AAF) Treatment for Reducing Iron and Chloride in Natural Groundwater

The production of drinking water for the needs of rural communities generally stilldepend on natural water sources. Communities in rural areas usually use groundwaterfor their daily needs. The water supply in Sampang Regency, East Java Provincehas groundwater problem, i.e. the amount of iron and chloride in the water supplyexceed the maximum amount allowed by PERMENKES No. 492/2010. Therefore,this study proposes a method for drinking water treatment using diffused aeration,as pretreatment, and followed by filtration processing. This pretreatment is meantfor reducing iron. The filtration process is carried out in stages with an advancedfilter of low continuous discharge. The filter media uses resin activated carbon andmicrofiltration to remove suspended and dissolved ions. The results of aeration andfiltration processing (AAF) shows that the preprocessed water have Cl-removal of98.39%, TDS-removal of 97.394%, and iron-removal of 97.41%

Assessing groundwater pollution and potential remediation processes in a multi-layer aquifer system

Pumping-induced leakage across aquitards may induce a deterioration of water quality in multi-layer aquifer systems. It is critical to understand long-term trends of water quality parameters when assessing the sustainability of groundwater abstraction. Daily drinking water needs of 2.2 million people in Yinchuan region of northwest China are solely met by groundwater resources, but long-term groundwater withdrawal has created an extensive cone of depression (294 km2 in area) in confined aquifer causing increased vertical recharge. In this study, a model was established and calibrated with head data, then was incorporated with field tracer tests to provide key information on the hydro-dispersive characteristics of the contaminant for assessing both the current and future state of the aquifer system. The results confirmed a close association between water quality deterioration and high downward fluxes of high chloride groundwater, most notably near the center of the cone of depression. On a temporal scale, water quality degradation remains slow, largely due to the high, pre-existing storage of good quality water. Modeling suggests that the water quality in the upper confined aquifer will lose its potability over a 25 km2 and 50 km2 area within 200 years under the current and intensified pumping conditions, respectively. Elevated chloride values were also detected toward the east of the cone, highlighting the impact of hydrological settings on the vertical groundwater flow. Modeling of potential aquifer remediation shows an even slower response with a further 250 years or more required for potability to be restored in affected areas. The findings can provide valuable guidance to for decision makers and support the sustainable management of aquifer exploitation.

Comparative study of nanofiltration and ion exchange for nitrate reduction in the presence of chloride and iron in groundwater

Public concern on the groundwater contamination by nitrate has grown significantly in recent years.The objective of this study was to determine the appropriate treatment to reduce the nitrate content in the presence of other ions from groundwater, for which nanofiltration and ion exchange were evaluated. In nanofiltration, the effects of pressure, feed flow, initial composition, and performance were studied, in ion exchange the flow rate, initial composition, and resin regeneration process.Nanofiltration tests were carried out on four different commercial membranes: NF97, NF99, NF99H, and NF90. Among these, all membranes removed chloride but only NF97 and NF90 were able to remove nitrate in compliance with Chilean drinking water standard, showing rejections of 97% and 87%, respectively, in an optimum pressure range of 12–20 bar in which the NF90 produced 3.5 times more permeated water than NF97.For ion exchange tests, Purolite A520E resin was used, which decreased nitrate content to <1 mg/L. Results leading to the optimal flow within the exchange column indicated that residence time must be at least 2.1 min. The higher nitrate concentration in water did not lead to changes in the maximum resin capacity, 47.1 mg NO3−/g resin, but it did decrease the resin breakthrough capacity when initial concentration increased. Optimal regeneration was assigned to a 3% w/V NaCl solution and up-flow mode.Due to the ability to remove both nitrate and chloride, and being able to remove iron if necessary, nanofiltration was chosen as the appropriate treatment.

Potash fertilizer promotes incipient salinization in groundwater irrigated semi-arid agriculture

Incipient groundwater salinization has been identified in many arid and semi-arid regions where groundwater is increasingly used for irrigation, but the dominant processes at stake in such context are yet uncertain. Groundwater solutes originates from various sources such as atmospheric inputs, rock dissolution and fertilizer residues, and their concentration is controlled by hydrological processes, in particular evapotranspiration. Here, we propose a deconvolution method to identify the sources and processes governing the groundwater Chloride concentration in agricultural catchments, using the relative variations of Sodium and Chloride and using a neighbouring pristine catchment as a reference for the release rate of Na by weathering. We applied the deconvolution method to the case of the Kabini Critical Zone Observatory, South India, where groundwater was sampled in 188 farm tubewells in the semi-arid catchment of Berambadi and in 5 piezometers in the pristine catchment of Mule Hole. In Berambadi, groundwater composition displayed a large spatial variability with Cl contents spanning 3 orders of magnitude. The results showed that the concentration factor due to evapotranspiration was on average about 3 times more than in the natural system, with higher values in the valley bottoms with deep Vertisols. Linked with this process, large concentration of Chloride originating from rain was found only in these areas. At the catchment scale, about 60 percent of the Chloride found in groundwater originates from fertilizer inputs. These results show that Potassium fertilization as KCl is an important source of groundwater salinization in semi-arid context, and stress that identifying dominant drivers is crucial for designing efficient mitigation policies.

A ten year record of nitrate retention and solute trends in a Wisconsin sand plains stream: temporal variation at multiple scales

Nitrate retention is an important ecosystem service provided by streams which reduces nitrogen loads to downstream ecosystems. However, most inferences about nitrate retention and uptake in streams are based on measurements at sub-annual scales. Our objective was to evaluate variation in nitration retention and solute concentrations at weekly to decadal time scales. We measured nitrate and chloride concentration, nitrate flux and nitrate retention in Emmons Creek, a groundwater-dominated, nitrate-rich stream in central Wisconsin during a 10-year period. We used a two-station mass balance approach to measure nitrate retention while accounting for groundwater inputs. Surface water nitrate concentration, nitrate yield and nitrate retention exhibited strong seasonal variation. Seasonal Kendall tests revealed positive trends for surface water discharge, nitrate and chloride concentrations and groundwater chloride concentration, but not nitrate retention. Generalized additive mixed models (GAMM), accounting for serial autocorrelations, also indicated positive trends in surface water nitrate and chloride concentrations but no trend for nitrate retention. Nitrate retention averaged 370 mg NO3-N m−2 d−1 (± 316 SD) and was highest during the spring (512 mg NO3-N m−2 d−1 ± 319), followed by summer (460 ± 322), fall (340 ± 281) and winter (165 ± 212). Nitrate retention rates in Emmons Creek were relatively high compared to most published estimates. However, our results suggest that Emmons Cr. may have saturated its capacity to retain nitrate during a period when nitrate yield from its watershed increased, which is an important finding given the increases in N availability in many regions of earth.

Groundwater recharge estimation using chloride mass balance: a case study of Nsukka local government area of Enugu State, Southeastern, Nigeria

Due to the unplanned growth of urbanization, industrialization and ever-growing population in Nsukka local government of Enugu State, the groundwater exploitations have increased dramatically. For proper planning and management of groundwater resources, there is need for a reliable estimate of groundwater recharge of the area. In the present study, for the first time, the chloride mass-balance method is adopted to estimate groundwater recharge in the study area. Measurements of chloride in groundwater and rainfall were made during 8-month period of the raining season beginning with the first rain on 5th March 2016 and the last rain on 10th October 2016. The main source of recharge considered was estimated from rainfall. The results are presented in the form of a map showing the spatial distribution recharge rate of the study area, which ranges from 1308.9 to 1683.3 mm/year and the recharge percentage of the total rainfall varies from 81.5 to 95.8%. The study area is characterized by moderate groundwater recharge due to the presence of high permeable underlying lithologies which associated with high porosity. Errors in the estimated recharge rate in work maybe large because of the limited data used in this analysis.