Groundwater Nitrate Pollution Research Articles

A novel artificial intelligence-based approach for mapping groundwater nitrate pollution in the Andimeshk-Dezful plain, Iran

This study tested three multilayer Markov random-fields (MRFs) models – multicue MRF (MMRF), conditional mixed MRF (CMMRF), and fusion MRF (FMRF) – to produce groundwater nitrate pollution maps for the first time. Random forest (RF) was also used as a baseline model. Several cutoff-dependent and cutoff-independent evaluation metrics were used to assess the goodness-of-fit and predictive performance aspects of the models. Validation results indicated that the conditional mixed MRF (with AUC = 0.805, TSS = 0.692, MCC= 0.692, F-score= 0.846, E = 0.846, MR = 0.153) outperformed the other models when producing groundwater nitrate pollution maps. The next best model was RF. All models identified hydraulic conductivity(with > 50%) as the most important variable for investigating groundwater nitrate pollution, whereas lineament density (with <7%) was the least important. Since the goodness-of-fit of all applied models ranged from very good (0.7 < AUC < 0.8) to excellent (0.9 < AUC < 1) based on AUC, SO this study revealed a promising method to accurately map groundwater nitrate pollution in support of more effective water quality management.

Evaluation of pollution swapping phenomena from a woodchip denitrification wall targetting removal of nitrate in a shallow gravel aquifer

Woodchip denitrification walls offer a potentially useful way for passive in situ remediation of groundwater nitrate pollution, yet because of the low redox state they induce on the subsurface environment there is an inherent risk they can promote pollution-swapping phenomena. We evaluated pollution-swapping phenomena associated with the first two operational years of a woodchip denitrification wall that is being trialled in a fast-flowing shallow gravel aquifer of quartzo-feldspathic mineralogy. Following burial of woodchip below the water table there was immediate export of dissolved organic carbon (DOC), phosphorus and ammonium into the groundwater. Under the low redox state sustained by labile DOC, the wall initially provided 100% nitrate removal at the expense of acute and localised pollution that occurred in the form of a plume of dissolved iron, manganese and arsenic that were mobilised from the aquifer sediments, in conjunction with methane gas emission. Within one year however, the reactivity of the woodchip wall subsided to support a steady state condition in which nitrate reduction was the terminal electron acceptor process with no measurable methane emission. Having initially functioned as a sink for the potent greenhouse gas nitrous oxide (N2O), evidence is that the woodchip wall is now exporting N2O, albeit at rates less than those associated with productive agricultural land.

Groundwater Nitrate Pollution Sources Assessment for Contaminated Wellfield

Nitrates are one of the most common groundwater contaminants and they come from different sources. The paper presents a study of groundwater quality at Varaždin wellfield in the north part of Croatia. The nitrate concentration at this location has been above the maximum allowed concentration for several decades, which has made the opening of new wellfields costly. Based on the previously developed groundwater flow model, a model that covers the narrow area of the wellfield is developed. The influential zone of the observed wellfield in working conditions is determined. Based on the developed model, the sources of nitrate pollution are located, which can be generally divided into non-point and point sources. Considering the time of groundwater retention in the horizontal flow, it is concluded that the water protection zones are marked following the applicable ordinance. Based on the developed groundwater flow model at the observed wellfield, a simulation of nitrate pollution propagation by advection and dispersion processes is performed. The simulation results point out the location of the poultry landfill as the largest source of nitrate pollution. However, poultry farms, which are located in the influence area of the wellfield, also contribute significantly to the nitrate concentration at the wellfield.

Identification and apportionment of shallow groundwater nitrate pollution in Weining Plain, northwest China, using hydrochemical indices, nitrate stable isotopes, and the new Bayesian stable isotope mixing model (MixSIAR)

Groundwater nitrate (NO3−) pollution is a worldwide environmental problem. Therefore, identification and partitioning of its potential sources are of great importance for effective control of groundwater quality. The current study was carried out to identify the potential sources of groundwater NO3− pollution and determine their apportionment in different land use/land cover (LULC) types in a traditional agricultural area, Weining Plain, in Northwest China. Multiple hydrochemical indices, as well as dual NO3− isotopes (δ15N–NO3 and δ18O–NO3), were used to investigate the groundwater quality and its influencing factors. LULC patterns of the study area were first determined by interpreting remote sensing image data collected from the Sentinel-2 satellite, then the Bayesian stable isotope mixing model (MixSIAR) was used to estimate proportional contributions of the potential sources to groundwater NO3− concentrations. Groundwater quality in the study area was influenced by both natural and anthropogenic factors, with anthropological impact being more important. The results of LULC revealed that the irrigated land is the dominant LULC type in the plain, covering an area of 576.6 km2 (57.18% of the total surface study area of the plain). On the other hand, the results of the NO3− isotopes suggested that manure and sewage (M&S), as well as soil nitrogen (SN), were the major contributors to groundwater NO3−. Moreover, the results obtained from the MixSIAR model showed that the mean proportional contributions of M&S to groundwater NO3− were 55.5, 43.4, 21.4, and 78.7% in the forest, irrigated, paddy, and urban lands, respectively. While SN showed mean proportional contributions of 29.9, 43.4, 61.5, and 12.7% in the forest, irrigated, paddy, and urban lands, respectively. The current study provides valuable information for local authorities to support sustainable groundwater management in the study region.

ГЕОДИНАМІКА УРАНОВОРУДНИХ ПОЛІВ ЗАХІДНОЇ ЧАСТИНИ ІНГУЛЬСЬКОГО МЕГАБЛОКУ УКРАЇНСКОГО ЩИТА

The Ingul megablock of the Ukrainian Shield contains a number of endogenous deposits of the sodium-uranium formation, which have been developed for more than 55-60 years. With the exception of the Kirovograd uranium ore region, the deposits of which are controlled by discontinuities in the fault zone of the same name, the Vatutinske and Novokostiantynivske ore fields occupy positions within the Novoukrainsky granite-gneiss dome and in close proximity to the later geostructural formation, the Korsun-Novomyrgorod pluton. Paying attention to the high degree of saturation of the Ingul megablock with endogenous uranium deposits, it is emphasized that they also contain an increased content of thorium minerals and, in combination with uranium, they produce ascending gas flows of radon. Therefore, studies of the dynamics of the upper horizons of the lithosphere and the closely related dynamics of the hydrosphere (underground and surface), as well as the gas sphere, are especially relevant both in the regions of uranium ore fields and in areas adjacent to mining enterprises. Beyond the direct influence on the radioecological situation of uranium mining enterprises, special attention should be paid to the study of the dynamics of the lithospheric surface, including fault-block structures and the kinematics of ruptures, affecting the spread of groundwater and, as a result, surface waters contaminated with uranium in the environment. In the areas of uranium ore fields, the kinematic characteristics of disjunctivals contribute to a more correct forecast of radon accumulation in natural weakly insulated underground decompressed structures and the accumulation of more long-lived products of its decay Po, Bi, and Pb with long periods of removal of biological objects from organisms. It is emphasized that in the mine workings of mining enterprises, the technological process is accompanied by nitrate pollution of groundwater due to the use of nitrate-based explosives. Thus, for the predictive assessment of radiation and nitrate pollution of the environment of industrial sites of mining enterprises and adjacent territories, the technological process of which also affects the dynamics of the litho-hydro- and gas sphere, the structural-geological, paleogeomorphological, lithological, hydrogeological, hydrographic and topographic features of the Vatutinske and Novokostiantynivske uranium ore fields. The directions of the advancement of the groundwater fronts from directly uranium mines to the nearest drains have been established. The levels of uranium pollution of surface and underground (well) waters within the Novokostiantynivske uranium ore field, as the most promising for increasing uranium mining in the coming decades, have been determined. The proposed areas and terms of complex radioecological monitoring of the Novokostiantynivske uranium ore field in order to take preventive measures to prevent the withdrawal of existing local recreational areas and water areas into the category of ecologically hazardous. On the example of the Novokostiantynivske uranium deposit, as one of the richest endogenous deposits in Ukraine, through the production shafts, which is planned to rise to the surface of uranium ore from the same type of deposits of the uranium ore field of the same name (Lisne, Litniy and Dokuchaivske) by transporting it by main drifts, the proposed optimal complex of geodynamic studies in the system of radio and general ecological monitoring of the state of the environment of such territories.

Predictive modeling of groundwater nitrate pollution and evaluating its main impact factors using random forest

Groundwater quality in plains and basins of arid and semi-arid regions with increased agriculture and urbanization development faces severe nitrate pollution, which is affected by both climate and anthropogenic activities. Here, shallow groundwater nitrate concentrations in the Yinchuan Region in central Yinchuan Plain were modeled during 2000, 2005, 2010, and 2015 using random forest. Multiple spatial environment factors were taken as predictor variables. The relative importance of these factors was also calculated using the constructed model. Remote sensing and GIS methods were used to compile various environmental factors to generate training and test sets for training and validation of the random forest model. Mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2) between the observed and predicted groundwater nitrate concentrations were used to measure the model performance. As indicated by these metrics, the random forest model for groundwater nitrate prediction was performed well. The relative importance of the predictor variables computed by the model indicated groundwater nitrate was mainly affected by the distance to the Yellow River, meteorological elements (precipitation, evaporation, and mean air temperature), and water level elevation. Additionally, urban and arable land were the two land use/land cover types that mainly influenced groundwater nitrate concentration in the Yinchuan Region, of which urban land was more influential than arable land as a result of intense expansion of urban land from 2000 to 2015. Overall, the current study provides an approach to integrate multiple environmental factors for groundwater quality study and is also significant for sustainable groundwater management in the Yinchuan Region.

Nutrient recovery and ammonia-water production by MF-vacuum evaporation treatment of pig manure

Intensive livestock farming has negatively impacted the environment by contributing to the release of ammonia and nitrous oxide, groundwater nitrate pollution and eutrophication of rivers and estuaries. However, the nutrient rich manure has always been a major focal point of resource recovery. Microfiltration has proven to be the least complex and highly energy efficient recovery process among all the other available techniques, however, the low nutrient concentration (especially nitrogen) has always been a drawback when it comes to marketing of the final product. Here we report about the efficiency of manure microfiltration followed by the vacuum evaporation of the MF permeate to produce purified and concentrated ammonia water. MF results showed the complete removal of TSS. COD and total phosphorus removal were found above 80%. However, nearly 80% of the NH4+-N was recovered in the MF permeate. The used MF membrane could achieve 50% of the initial feed volume reduction while maintaining well the nutrient qualities in each stream. Lastly, MF permeate vacuum evaporation resulted in substantial 31 gL−1 of NH4+-N condensate concentration, which was nearly 12 times higher than the initial NH4+-N concentration of MF permeate. The vacuum evaporation of MF permeates compared to raw feed and concentrate stream have been proven to be a viable alternative to recover nutrient and produce cleaner and concentrated ammonia water. However, the evaporation system requires better mixing and temperature control tools to enable gradual thermal gradients and avoid bumping in the fluid, which led to high levels of water carry over.

Dynamic Mechanisms of Groundwater Quality by Residual Contaminants of the Tanghe Wastewater Reservoir in Xiong'an New Area

Tanghe wastewater reservoir(TWR) is located on the west side of Baiyangdian Lake in Xiong'an New Area, where sewage infiltration and irrigation has been taking place for 40 years, and a large number of contaminants have accumulated in the unsaturated zone. Identifying the mechanisms by which this combined system contributes to groundwater hydrochemical dynamics is important for the protection of the water environment in the area. Hydrogeochemical methods such as tracing and improved chlor-alkali index are used to analyze the spatial and temporal characteristics and evolution mechanisms of shallow groundwater. The study shows that the groundwater chemistry in the sewage reservoir area is SO4·HCO3-Na type, with an average sewage fraction of 48.4%, and the contribution of Na+ from ion exchange and halite dissolution is 29.9% and 8.6%, respectively. The chemical type of groundwater in the sewage irrigation area is SO4·HCO3-Na·Mg, the average sewage fraction is 58.3%, and Na+ consumption of ion exchange is 8.1%. The mix dilution of precipitation and irrigation leads to a reduction in the effluent fraction and saturation index in the groundwater, and promotes the adsorption of Na+ from groundwater into the soil. Denitrification in aquifers can effectively reduce groundwater nitrate pollution. In addition, the sewage fraction before and after the restoration of the reservoir was 61.5% and 49.3%, respectively. Pollutants retained in the sewage infiltration and irrigation combined system will continue to affect the quality of shallow groundwater with varying degrees of mixing and water-rock interaction driven by rainfall and irrigation.

Nitrate in groundwater of the west side Magelang Regency, Central Java, Indonesia

Nitrate (NO3-) pollution in groundwater is generally caused by chemical fertilizers from the agricultural sector and wastewater from onsite sanitation. Magelang Regency, Central Java, Indonesia, is a large food estate that has 206 km2 paddy fields. In addition, this area is inhabited by 1.3 million people who produce onsite sanitary waste every day. Due to the concentration and intensity of fertilization and sanitary waste, which are quite high, Magelang Regency is susceptible to groundwater pollution by nitrate. This study aims to determine the characteristics of nitrate in the groundwater of the west side Magelang Regency, Central Java, Indonesia. The research was carried out by testing groundwater samples taken from several springs, dug wells, and drilled wells used by society for their daily needs. Groundwater sampling was carried out in the wet season and tested using the ion chromatography method to determine the level of nitrate in groundwater and know the chemical characteristics to analyze dominant ions in groundwater. The results showed that the average nitrate was 3.9 mg/l; the deviation standard was 5.12; minimum nitrate was 0 mg/l; and maximum nitrat was 20.78 mg/l. The origin of nitrate content may come come from feces but still in small quantities. Facies of groundwater are Ca-HCO3 and Na-Cl. It can be concluded that the groundwater of the west side Magelang Regency is not yet polluted by nitrate. However, there is still a possibility in the future, so that necessary to apply for groundwater protection immediately.

Insights into the mechanism of Mn(II)-based autotrophic denitrification: Performance, genomic, and metabonomics

The technologies for groundwater nitrate pollution treatment have drawn increasing global attention. As for autotrophic denitrification (AD), most researches aimed to the mixed microbial culture bioreactors, the mechanism of AD by purely cultured bacteria has not been fully investigated yet. Here, denitrification ability, bacterial activity, and dissolved organic matter evolution of Cupriavidus sp. HY129 in both AD and heterotrophic denitrification (HD) were studied. Genomic analysis and microbial metabolomic analysis were applied to explore the mechanism of AD and the difference and intrinsic factors in AD and HD. The results revealed that HD resulted in higher denitrification efficiency and biomass compared to AD and the bacteria preferred to synthesize humic-like proteins to maintain the progress of AD. Bacteria carry out Mn oxidation outside the bacteria cell and transfer electrons into the cell for AD. Cupriavidus sp. HY129 genome has critical metabolic pathways in both autotrophic and heterotrophic conditions, as well as the MCO gene for mediating the Mn oxidation. Energy metabolism pathways were the most significantly differences between AD and HD. Moreover, sphingolipid metabolism and mineral absorption metabolism were the most essential pathways in the autotrophic process to maintain the normal physiological activities and Mn transfer. The results explored the differences between AD and HD pathways in the same bacteria for the first time and provided new insight into understanding the metabolic characteristics of different denitrification, which provide useful information to the global nitrogen cycle and nitrate pollution treatment.

Geochemical Characteristics and Driving Factors of NO3-Type Groundwater in the Rapidly Urbanizing Pearl River Delta

In response to rapid economic development, nitrate pollution of groundwater is becoming a serious issue in many parts of China. Urbanization and industrialization are the main drivers of NO3-type groundwater expansion. Focusing on the Pearl River Delta, the occurrence and driving factors of shallow nitrate groundwater are discussed. Overall, groundwater nitrate concentrations are generally high in this region. Of 1538 groundwater samples, 5.7% had nitrate concentrations higher than the groundwater quality standard(88.6 mg·L-1) and 18.5% were classified as NO3-type waters, which are mainly distributed in the hilly and piedmont areas. Guangzhou, Dongguan, Foshan, Zhuhai and other areas show high total dissolved solid(TDS)-concentration NO3-type waters, which are affected by urbanization and industrialization. In comparison, low-TDS NO3-type waters are distributed in the hilly and valley areas. In the Xijiang and Dongjiang plains, the TDS concentrations on groundwater increased significantly due to inputs of industrial wastewater and saline seawater. The NO3- concentration in the groundwater in this area exceeded the class III water standard but did not change the hydrochemical type classification. However, industrialization has led to the frequent appearance of SO4-type water in this area. The NO3-type water occurs in acidic or weakly acidic environments, typically characterized by low TDS and total hardness concentrations, and high Cl-, SO42-, and K+ concentrations. The formation of NO3-type water is mainly affected by domestic sewage, industrial wastewater, agricultural nitrogen fertilizer, septic tank outflows, and landfill leachate leakage. Generally, the pollution loads of high-TDS NO3-type waters are higher than low-TDS NO3-type waters. The delineation of NO3-type waters, especially the low-TDS type, is helpful for identifying groundwaters posing greater risks for human activities, and those with low nitrate concentrations but potential pollution risk, which is of great significance in the prevention and control of groundwater pollution.

Elucidating the Pollution Sources and Groundwater Evolution in Typical Seawater Intrusion Areas Using Hydrochemical and Environmental Stable Isotope Technique: A Case Study for Shandong Province, China

Abstract Seawater intrusion has a serious impact on industry, agriculture, and people’s daily life. Thus, the present study was designed to elucidate the pollution sources and groundwater evolution in typical intrusion areas of Shandong Province by hydrochemistry and environmental isotope techniques. The water samples were collected to analyze the groundwater evolution under different intrusion, and groundwater evolution in the south of Laizhou Bay from 2005 to 2019. The findings indicated that the groundwater level dropping funnel caused by overexploitation was the direct causation of seawater intrusion in the three typical intruded areas. The groundwater evolution paths demonstrated that the groundwater in the south of Laizhou Bay had the fastest evolution rate and the highest degree of evolution, followed by the Dagu River Basin. The groundwater evolution extent and fitting of mixing lines indicated that the groundwater in the south of Laizhou Bay, Longkou, and Dagu River Basin was dominated by palaeosaltwater intrusion, modern seawater intrusion, and sea-saltwater mixed intrusion, respectively. Palaeosaltwater mixing produces a more severe salinization effect compared to seawater mixing. Meanwhile, the isotopes are gradually enriched with the deepening of intrusion, while the decrease of isotopes is delayed compared with the saltwater retreat. This is caused by that the stable isotopes enriched in the aquiclude due to the chemical permeation effect will be released into the aquifer after the salinity attenuates in the aquifer. The palaeosaltwater intrusion caused by anthropogenic activities has promoted serious fluorine pollution in the south of Laizhou Bay, while the groundwater nitrate pollution in Longkou was the most serious, followed by the Dagu River Basin due to high-density agricultural and domestic activity.

Short-Term Changes in Erosion Dynamics and Quality of Soils Affected by a Wildfire and Mulched with Straw in a Mediterranean Forest

Wildfire heavily impacts the quality of forest soils, and the precipitation occurring immediately after fire can determine high runoff and erosion rates, which may lead to noticeable soil degradation. Mulching is commonly used to limit the hydrological impacts of wildfire and climate, but this post-fire management technique may alter the erosion–deposition dynamics at the hillslope scale and, consequently, alter soil quality. In order to explore the magnitude and significance of these changes (little was studied in the literature until now), this communication reports the first results of a field activity that evaluated the changes in soil quality in areas affected by a wildfire and subjected to different post-fire treatments in Mediterranean forests. The main properties of sediments eroded from burned and untreated soils, and mulched soils (using a straw dose of 0.2 kg/m2 of dry weight), were measured after the first rainstorm (height of 37 mm and maximum intensity of 11.6 mm h−1) occurring two months after a wildfire (occurred on 30 June 2016) in a pine forest of Castilla-La Mancha (Spain). This event produced a runoff volume of 0.07 ± 0.02 mm in mulched soils and 0.10 ± 0.10 mm in non-mulched soils; soil loss was 0.20 ± 0.06 g/m2 in the mulched area and 0.60 ± 0.60 g/m2 in the non-mulched area. In comparison to burned and non-treated areas, this study showed: (i) increases in salinity, and reductions in organic matter, nutrients, nitrates, and micro-elements in burned and untreated soils; (ii) reductions in runoff (−20%) and in soil erosion (−60%) as a result of mulch cover; (iii) effectiveness of mulching in limiting the declines in soil quality detected in burned and eroded areas; and (iv) transport of low amounts (less than 10–15%) of some compounds (organic matter and nutrients) downstream of the fire-affected areas (both mulched and untreated). Phosphorous runoff toward valley areas and nitrate incorporation into the soil, detected in both mulched and untreated areas, require attention, since these processes may cause eutrophication of water bodies or nitrate pollution in groundwater.

Quantifying nitrate pollution sources of the drinking water source area using a Bayesian isotope mixing model in the northeastern suburbs of Beijing, China

ABSTRACT Nitrate pollution has become an environmental problem of global concern. One effective way for controlling the nitrate pollution of water is to identify the pollution source and reduce the input of nitrate. This study traces and quantifies the sources of nitrate contamination to groundwater and surface water in the northeastern suburbs of Beijing, where an emergency groundwater source zone is located. Nitrogen and oxygen stable isotope analysis, geospatial analysis techniques, principal component analysis, correlation analysis, and a Bayesian isotope mixing model were used to achieve our goals. The results show that the main sources of nitrate pollution in groundwater were manure and sewage (M&S) (42.6 %) > soil nitrogen (SN) (26.6 %) > in fertilizer and rain (NHF&R) (24.5 %) > fertilizer (NOF) (5.0 %) > in atmospheric deposition (NAD) (1.3 %), and main sources of nitrate in surface water were M&S (28.8 %) > SN (20.4 %) > NAD (19.8%) > NOF (16.5%) > NHF&R (14.5 %). Due to the high permeability of the aquifer in the study area, there was a strong hydraulic connection between groundwater and surface water. The discharge of treated wastewater (reclaimed water) into the mostly dried river channel in the study area might aggravate nitrate pollution in the groundwater.

Determining hydrogeological and anthropogenic controls on N pollution in groundwater beneath piedmont alluvial fans using multi-isotope data

Piedmont alluvial fans have, for a long time, supported clean groundwater for human development worldwide. Rapid urbanization in China has over-exploited groundwater and resulted in severe groundwater nitrate pollution in piedmont alluvial fans, which has led to both human health concerns and clean water shortages, especially in rural residential areas where drinking water is mainly derived from shallow groundwater. However, sources of nitrate in groundwater and their pathways are still unclear. In this study, we hypothesized that untreated manure and domestic sewage are the primary nitrate sources in a residential area, and that an unconfined aquifer would be more vulnerable to nitrate pollution than a confined aquifer due to nitrate infiltration via the vadose zone. To verify this hypothesis, groundwater nitrate pollution in a well-characterized piedmont alluvial fan was studied through hydrochemical composition and multi-isotope (δ15NNO3, δ34SSO4, δ18OSO4, δ13CDIC) data over four seasons. Seasonal variations for both NO3− concentrations and δ15NNO3 values in unconfined groundwater (UGW) and confined groundwater (CGW) were observed. Mixing of nitrate sourced from manure/sewage, precipitation, soil nitrogen, and synthetic fertilizer controlled the groundwater nitrate level, and manure/sewage contributed 52.4%, 32.4%, and 33.7% nitrate to UGW, CGW, and surface water (SFW), respectively, based on Stable Isotope Mixing Models in R (SIMMR) analysis. Denitrification had a minor effect on groundwater nitrate levels in a residential area, and nitrate pollution in CGW was partly due to nitrate migration through geological faults and fracture zones in a piedmont alluvial fan. Nitrate pollution sources and pathways in residential areas were confirmed through multiple isotopes (δ15NNO3, δ13CDIC, δ34SSO4, and δ18OSO4). Collectively, these results highlight the roles of the hydrogeological setting and anthropogenic activities in groundwater N pollution beneath piedmont alluvial fans.

Influence of the subsurface physical barrier on nitrate contamination and seawater intrusion in an unconfined aquifer

Coastal areas are facing not only environmental problems associated with seawater intrusion (SWI) but also health and ecological problems caused by excessive nitrate (NO3−) contamination. The installation of a subsurface physical barrier (SPB) is one of the common methods employed to reduce or prevent SWI, but there are few studies on the impact of SPBs on NP in groundwater. Through laboratory experiments and numerical simulations, the effects of the hydraulic gradient (HG), the nitrate concentration of the set groundwater nitrate pollution source, the relative height of the SPB (HP’) and the relative distance between the SPB and the saltwater boundary on the NP of groundwater in the presence of SWI, subsurface dams and cut-off walls were studied. Evaluation indicators were established to evaluate the degree and shape of the SWI and NP. To better describe the relationship between the velocity distribution and changes in the velocity distribution area and the degree of NP and SWI, the velocity distribution in the presence of SWI and a SPB was summarized separately. The results showed that when there was SPB, low-velocity zones were formed on both sides of the SPB, which not only slowed the migration of NO3− but also changed the shape of the NO3−-contaminated area. The closer to the SPB area the pollutants were, the more obvious the obstruction effect. The obstruction effect of adding the cut-off wall on NP was more obvious than that of adding the subsurface dam wall. The selected HG and Hp’ were important factors affecting NP and SWI. The higher HG was, the more serious the NP, the lower the HG, and the stronger the degree of SWI. Adding SPBs reduces the impact of HGs on NP and SWI. Therefore, the design of SPBs in coastal areas should focus on aspects related to these two factors.

Groundwater quality of an hard rock aquifer in the Subledu Basin of Khammam district, India

Hard rock aquifers of Indian peninsula are loaded with excess nitrate due to heavy use of fertilizers during irrigation and excess fluoride due to the geogenic contamination. This study is focused on the groundwater quality in Subledu Basin in view of the large-scale use of groundwater for both irrigation and drinking purposes as no such study was carried out earlier in the basin. The study area is located at Khammam district, Telangana state, India, which is a hard rock terrain mostly covered with granites and gneisses. Twenty-two groundwater samples were collected covering the entire basin in the month of May 2019 from running hand pumps for analyzing the major anions and cations in the groundwater. The samples were analyzed by using standard gravimetric method for evaluation of total dissolved solids; titrimetric methods to analyze carbonates, bicarbonates and chloride; UV spectrometric method for estimation of nitrate; and ion-selective electrode method for fluoride and spectrophotometer for sulfate and phosphate. These chemical constituents are used to calculate parameters, namely total hardness, sodium adsorption ratio, residual sodium carbonate, sodium percentage, Kelley’s ratio and magnesium hazard. The spatial distribution maps of important chemical constituents are prepared by using the contour maps created by utilizing the inverse distance weighted interpolation tool in the Geographical Information System. The excess fluoride values of 2.84 mg/l, 2.76 mg/l and 1.87 mg/l are observed in the villages of Pocharam, Kistapuram and Turakagudem, respectively, as against the maximum permissible concentration of 1.5 mg/l prescribed by World Health Organization. Excess use of fertilizers for agriculture is causing the nitrate pollution of groundwater in more than 50% of the samples with concentrations ranging from a minimum of 2 mg/l to a maximum of 460 mg/l in the villages of Medidapalle and Bachodu. It is identified that the total hardness is ranging between 200 and 820 mg/l which is very high when compared with the Bureau of Indian Standards. Based on sodium adsorption ratio, residual sodium carbonate, Kelley’s ratio, and sodium percentage analyses, two samples were not suitable for irrigation. Similarly, 13 samples are not suitable for drinking water purposes based on the excess presence of fluoride and nitrate. Groundwater quality maps of Subledu Basin depicting the areas suitable or not for the irrigation as well as for drinking purposes were prepared. From these maps, it is found that groundwater from large parts of the basin is not suitable for drinking purposes while for irrigation purposes it is suitable.

Characteristics of coastal aquifer contamination by seawater intrusion and anthropogenic activities in the coastal areas of the Bohai Sea, eastern China

• 60,000 km 2 of coastal aquifers are affected by seawater (saltwater) intrusion around Bohai Gulf. • Palaeo-saltwater intrusion strongly affected groundwater evolution in Bohai Bay and Laizhou Bay. • The seawater intrusion caused the enrichment of fluorine in coastal aquifers. • Nitrate pollution increased in the coastal areas is a consequence of anthropogenic activities. A comprehensive study was performed to identify the origins of salinity and the geochemical processes governing hydrochemistry, and to distinguish the role of evaporation, mixing, and water–rock interaction from seawater intrusion (SWI) or palaeo-saltwater intrusion (PSWI) on groundwater chemistry in the coastal aquifer around the Bohai sea in China. For these purpose, geochemical and multivariate statistical methods were applied. The results indicated that the intrusion area around the Bohai sea can be divided into: (i) the palaeo-saltwater intrusion zone (including the south of Laizhou Bay, Tianjin, and Panjin on the north of Liaodong Bay), and (ii) the modern seawater intrusion zone. The analysis of selected ions (Na + /Cl − and Br − /Cl − ) and isotopic compositions showed that the saltwater intrusion is the predominant factor of increasing salinity in groundwater, followed by water–rock interaction (e.g. mineral weathering and ion exchange), and evaporation. Sources of specific ions (Ca and F) are dominated by mineral weathering-dissolution rather than the saltwater intrusion. Furthermore, anthropogenic activities are the dominant cause of groundwater nitrate pollution in the coastal area around Bohai sea. This type of pollution is most serious in Liaodong Bay due to the industrial waste, fertilizers, pesticides, and domestic sewage. It is followed by pollution in Qinhuangdao due to agricultural and domestic factors, and pollution in Laizhou Bay due to domestic sewage. The source of high fluorine in groundwater is the dissolution of fluorine-containing minerals caused by saltwater intrusion. The degree of groundwater fluorine pollution is as follows: Liaodong Bay < Tianjin < Qinhuangdao < Laizhou Bay.

Determining nitrate and sulfate pollution sources and transformations in a coastal aquifer impacted by seawater intrusion—A multi-isotopic approach combined with self-organizing maps and a Bayesian mixing model

Over the past few decades, the La Paz aquifer system in Baja California Sur, Mexico, has been under severe pressure due to overexploitation for urban water supply and agriculture; this has caused seawater intrusion and deterioration in groundwater quality. Previous studies on the La Paz aquifer have focused mainly on seawater intrusion, resulting in limited information on nitrate and sulfate pollution. Therefore, pollution sources have not yet been identified sufficiently. In this study, an approach combining hydrochemical tools, multi-isotopes (δ2HH2O, δ18OH2O, δ15NNO3, δ18ONO3, δ34SSO4, δ18OSO4), and a Bayesian isotope mixing model was used to estimate the contribution of different nitrate and sulfate sources to groundwater. Results from the MixSIAR model revealed that seawater intrusion and soil-derived sulfates were the predominant sources of groundwater sulfate, with contributions of ~43.0% (UI90 = 0.29) and ~42.0% (UI90 = 0.38), respectively. Similarly, soil organic nitrogen (~81.5%, UI90 = 0.41) and urban sewage (~12.1%, UI90 = 0.25) were the primary contributors of nitrate pollution in groundwater. The dominant biogeochemical transformation for NO3- was nitrification. Denitrification and sulfate reduction were discarded due to the aerobic conditions in the study area. These results indicate that dual-isotope sulfate analysis combined with MixSIAR models is a powerful tool for estimating the contributions of sulfate sources (including seawater-derived sulfate) in the groundwater of coastal aquifer systems affected by seawater intrusion.

Influence of the carbon source concentration on the nitrate removal rate in groundwater

ABSTRACT At present, groundwater nitrate pollution in China is serious. The use of microorganisms for biological denitrification has been widely applied, and it is a universal and efficient in situ groundwater remediation technique, but this approach is influenced by many factors. In this study, glucose was adopted as the carbon source, four different concentrations of 0, 2, 5 and 10 g/L were considered, and natural groundwater with a nitrate concentration of 300.8 mg/L was employed as the experimental solution. The effect of the carbon source concentration on the nitrate removal rate in groundwater was examined through heterotrophic anaerobic denitrification experiments. The results showed that the nitrate removal rate could be improved by the addition of an external carbon source in the process of biological denitrification, and an optimal concentration was observed. At a glucose concentration of 2 g/L, the denitrification effect was the best.