Nitrate In Water Research Articles

Nutrient dynamics in small west-flowing tropical mountainous rivers of India

In this study, the distribution of dissolved inorganic nitrate (DIN), phosphorus (DIP), and silicate (DSi) in surface waters of 70 coastal rivers in India's Western Ghats (WG) has been determined. The nutrient concentrations in individual rivers appear to be influenced by catchment geology, land use, and climate. The entire WG region contributes 0.31 Tg of DIN, 0.03 Tg of DIP, and 5.65 Tg of DSi annually to the coastal Arabian Sea. The annual ratios of N:P, Si:N, and Si:P suggest that most of these rivers are limited by P rather than N, and there is an excess supply of Si, primarily from natural sources. P limitation is severe during monsoon periods, while N limitation is observed in the Deccan Traps region. The annual export of 0.31 Tg of DIN from WG rivers could support 2.05 Tg of carbon (new production) on the Arabian Sea coast, indicating that the riverine export of DIN can significantly remove atmospheric CO2 through biological pumps in the Arabian Sea. The study also confirms that the excess input of Si from natural processes relative to the anthropogenic supply of limited P and N further supports the idea that riverine nutrient inputs from small west-flowing tropical mountainous rivers do not contribute to coastal eutrophication along the Eastern Arabian Sea coast.

Serotonin improves plant growth, foliar functions and antioxidant defence system in Ethiopian mustard (Brassica carinata A. Br.)

Every year, high salinity reduces agricultural crop yields by a substantial amount due to osmotic and ionic impacts that prevent plants from absorbing the required water and promote the hyperaccumulation of ions, which enter the transpiration stream and injure plant cells. Thus, in general, the effects of salinity stress on plant physio-chemicals functions are well known, but little has been explored on how serotonin combats abiotic stress in Ethiopian mustard (Brassica carinata). In this study, the effect of serotonin (SR; 200 µmol L−1) on Ethiopian mustard under salt stress (SS; 0, 50, 100 and 150 mM) was examined. Results exhibited that all SS levels tested in this trial were able to offer a significant reduction of plant growth parameters, chlorophyll contents, gas exchange, water use efficiency, fv/fm and nitrate reductase activity (NR) and increased the antioxidants and proline contents. However, the foliar application of SR significantly ameliorated the influence of all SS levels by improving gas exchange parameters, chlorophyll contents, PSll photochemical efficiency, antioxidant activities, proline, NR, water use efficiency and growth parameters. Based on these results, it is recommended that SR application is useful to uplift the growth, yield and physio-chemical mechanisms of Ethiopian mustard. Furthermore, the SR application can be carried out on various traditional crops under different climate conditions for sustainable agriculture production.

High-Resolution Estimates of N2O Emissions from Inland Waters and Wetlands in China.

Inland waters (rivers, lakes, and reservoirs) and wetlands (marshes and coastal wetlands) represent large and continuous sources of nitrous oxide (N2O) emissions, in view of adequate biomass and anaerobic conditions. Considerable uncertainties remain in quantifying spatially explicit N2O emissions from aquatic systems, attributable to the limitations of models and a lack of comprehensive data sets. Herein, we conducted a synthesis of 1659 observations of N2O emission rates to determine the major environmental drivers across five aquatic systems. A framework for spatially explicit estimates of N2O emissions in China was established, employing a data-driven approach that upscaled from site-specific N2O fluxes to robust multiple-regression models. Results revealed the effectiveness of models incorporating soil organic carbon and water content for marshes and coastal wetlands, as well as water nitrate concentration and dissolved organic carbon for lakes, rivers, and reservoirs for predicting emissions. Total national N2O emissions from inland waters and wetlands were 1.02 × 105 t N2O yr-1, with contributions from marshes (36.33%), rivers (27.77%), lakes (25.27%), reservoirs (6.47%), and coastal wetlands (4.16%). Spatially, larger emissions occurred in the Songliao River Basin and Continental River Basin, primarily due to their substantial terrestrial biomass. This study offers a vital national inventory of N2O emissions from inland waters and wetlands in China, providing paradigms for the inventorying work in other countries and insights to formulate effective mitigation strategies for climate change.

A violet light-emitting diode-based gas-phase molecular absorption device for measurement of nitrate and nitrite in environmental water

A simple and sensitive device for the detection of nitrite and nitrate in environmental waters was developed based on visible light gas-phase molecular absorption spectrometry. By integrating a detection cell (DC), semiconductor refrigeration temperature-controlling system (SRTCY), and nitrite reactor into a sequential injection analysis system, trace levels of nitrite and nitrate in complex matrices were successfully measured. A low energy-consuming light-emitting diode (violet, 400–405 nm) was coupled with a visible light-to-voltage converter (TSL257) to measure the gas-phase molecular absorption. To reduce the interference of water vapor, an SRTCY was used to condense the water vapor on-line before the gas-phase analyte entered the DC. The DC was radiatively heated by the SRTCY to avoid water vapor condensation in the light path. As a result, the obtained baseline noise reduced 3.75 times than that of without SRTCY. Under the optimized conditions, the device achieved limits of detection (3σ/k) of 0.055 and 0.36 mmol/L (0.77 and 5.04 mg N/L) for nitrite and nitrate, respectively, and the linear calibration ranges were 0.1–15 mmol/L (R2 = 0.9946) and 1–10 mmol/L (R2 = 0.9995), respectively. Precisions of 5.2 % and 9.0 % were achieved for ten successive determinations of 0.3 mmol/L nitrite and 1.0 mmol/L nitrate, and the analytical times for nitrite and nitrate determination were 5 and 13 min, respectively. This method was validated against standard methods and recovery tests, and it was applied to the measurement of nitrite and nitrate in environmental waters. Moreover, a device was designed to enable the field measurement of nitrite and nitrate in complex matrices.

The value of instream stable water isotope and nitrate concentration data for calibrating a travel time‐based water quality model

AbstractTransit time‐based water quality models using StorAge Selection (SAS) functions are crucial for nitrate (NO3−) management. However, relying solely on instream NO3− concentration for model calibration can result in poor parameter identifiability. This is due to the interaction, or correlation, between transport parameters, such as SAS function parameters, and denitrification rate, which challenges accurate parameters identification and description of catchment‐scale hydrological processes. To tackle this issue, we conducted three Monte‐Carlo experiments for a German mesoscale catchment by calibrating a SAS‐based model with daily instream NO3− concentrations (Experiment 1), monthly instream stable water isotopes (e.g. δ18O) (Experiment 2) and both datasets (Experiment 3). Our findings revealed comparable ranges of SAS transport parameters and median water transit times (TT50) across the experiments. This suggests that, despite their distinct reactive or conservative nature, and sampling strategies, the NO3− and δ18O time series offer similar information for calibration. However, the absolute values of transport parameters and TT50 time series, as well as the degree of parameter interaction differed. Experiment 1 showed greater interaction between certain transport parameters and denitrification rate, leading to greater equifinality. Conversely, Experiment 3 yielded reduced parameters interaction, which enhanced transport parameters identifiability and decreased uncertainty in TT50 time series. Hence, even a modest effort to incorporate only monthly δ18O values in model calibration for highly frequent NO3−, improved the description of hydrological transport. This study showcased the value of combining NO3− and δ18O model results to improve transport parameter identifiability and model robustness, which ultimately enhances NO3− management strategies.

Spatiotemporal Interpolation of Water Quality Index and Nitrates using ArcGIS Pro for Surface Water Quality Modeling in the Oum Er-Rabia Watershed

Spatiotemporal Interpolation of Water Quality Index and Nitrates using ArcGIS Pro for Surface Water Quality Modeling in the Oum Er-Rabia Watershed

РАСПРЕДЕЛЕНИЕ БИОГЕННЫХ ЭЛЕМЕНТОВ НА ГРАНИЦЕ ВОДА–ДНО В ПОРОВЫХ И НАДДОННЫХ ВОДАХ КАРСКОГО МОРЯ И МОРЯ ЛАПТЕВЫХ

The paper presents data from the 63rd cruise of the R/V “Akademik Mstislav Keldysh” in August–October 2015. The main areas of work included the western part of the Kara Sea, the bays of Novaya Zemlya (Sedova, Oga and Tsivolki), a transect through the Voronin Trench, a transect from the Lena River delta to the continental slope of the Laptev Sea. During the cruise, a chemical analysis of pore and bottom waters was carried out for the content of nitrite, nitrate nitrogen, silicon, phosphates, total alkalinity and pH. The patterns of distribution of silicon and phosphorus concentrations at the water-bottom interface are considered. In the Kara Sea analysis of the data showed that the maximum concentrations of nutrients are located in the upper 10 cm sediment layer, below that concentrations gradually decrease. In all studied bays of Novaya Zemlya, the concentrations of nutrients in the silt waters were lower than on the adjacent shelf. In the Laptev Sea, the content of nitrates in silt waters is higher, and phosphates are lower than in the Kara Sea. Differences in the content of nutrients in the bottom and silt water are associated both with external factors (river runoff) and physical and geological features of the upper sediment layer of the studied areas.

Optimization of fuel modification parameters for effective and environmentally-friendly energy from plant waste biodiesel

Sustainable energy production from plant waste and non-edible seeds offers a promising pathway towards mitigating climate change, reducing environmental impact, promoting economic development, and enhancing energy security. Although several research works have focused on the conversion of Bauhinia seed waste to biooil as a sustainable energy, none of the studies attempted to improve its overall performance through fuel modification and parameter optimization. This study proposes a novel approach by blending water and 2-Ethylhexyl nitrate (2-EHN) into Bauhinia racemose biodiesel (BRD) to minimize emissions and enhance performance. The biodiesel properties were characterized by Fourier-transform infrared and Gas chromatography-mass spectrometry analysis. The optimum levels of fuel modification parameters, such as BRD, water, and 2-EHN in conventional diesel fuel (CD), were obtained using response surface methodology, branding it as a sustainable and greener energy source for engine applications. Box-Behnken design matrix was chosen to categorize input factors, levels, and output responses. Examination of the biodiesel reveals that carbon-based constituents make a significant contribution, and the physicochemical properties align with ASTM standards. The optimization results indicate that the optimum levels of BRD, water, and 2-EHN in CD are 20.33 %, 10.26 %, and 2.05 %, respectively. The performance and emission metrics closely match the projected values. An in-depth examination of combustion, engine vibration, life-cycle assessment, and techno-economic analysis provides further evidence to reinforce the findings and suggests possible avenues for future research.

Spatio‐Temporal Trends of the Relationships Between Surface PM2.5 and Its Chemical Constituents Across Three COALESCE Network Locations in India: A Mass Closure Investigation

AbstractCOALESCE, a collaborative network studying the impacts of carbonaceous aerosols, measured PM2.5 mass and its constituents at several regionally representative sites in India. This study reconciles the reconstructed mass (RCM) from PM2.5 chemical constituents with gravimetric PM2.5 mass measured during 2019 at three COALESCE sites (Bhopal, Mesra, and Mysuru). To evaluate the extent of mass closure, the spatiotemporal variability of organic matter/organic carbon (OM/OC), filter sampling artifacts of OC, nitrate, and aerosol liquid water (ALW) were assessed. The annual loss of total particulate OC from Teflon filters varied across Bhopal (0.46–1.35 μg m−3), Mesra (0.30–0.92 μg m−3), and Mysuru (0.16–0.68 μg m−3). Likewise, the range of nitrate volatilization was 0.7–2.7 μg m−3 at Bhopal, 0.5–2 μg m−3 at Mesra, and 1.3–2.2 μg m−3 at Mysuru. Also, the range of ALW mass was 2.6–6.8 μg m−3 at Bhopal, 3.2–9.5 μg m−3 at Mesra, and 0.8–3.8 μg m−3 at Mysuru. Seasonality was observed in the value of OM/OC with an increase during the pre‐monsoon season at all sites viz., Bhopal (2.20), Mesra (1.61), and Mysuru (2.02) compared to their annual averages, suggesting enhanced contribution of secondary organics to OC. The method developed for estimating RCM in this study resulted in better mass closure compared to using conventional RCM algorithms. Overall, this study provides a robust data validation strategy and India‐specific species coefficients for use in the RCM algorithm. The outcomes of this study can guide regional aerosol sampling, chemical analyses, and model–measurement reconciliation efforts.

Mapping of Water and Soil Quality Parameters in the Gampaha-Ihalagama East and Eldeniya East Grama Niladhari Divisions, Sri Lanka

Water and soil are important natural resources, and the study of their distribution is of great interest. The Grama Niladhari Divisions, Ihalagama-East and Eldeniya-East, located in the Gampaha district, are selected as the study areas, and this is done as a pilot study. Different water and soil quality parameters are investigated followed by the construction of contour maps. As water quality parameters, pH, conductivity, phosphate content, nitrate content, and Ca2+ hardness were determined, and as soil quality parameters, pH, nitrate, organic matter, water-soluble Na+ and K+, extractable Na+ and K+, and water-soluble Ca2+ ion contents were determined. The pH of water samples lies within the range of 4.41 - 7.11 and 3.79 – 7.18 in the Ihalagama-East and Eldeniya East divisions, respectively. Almost all the samples have acidic pH values, with some falling below the lower limit of the WHO guidelines for safe drinking water (6.5 - 8.5). Conductivity values vary from 52.0 - 277.0 µS/cm and between 54.0 – 403.0 µS/cm, respectively, which is below the WHO permissible level of 1500 µS/cm. The phosphate content varies from 1.374 - 3.986 mg/L in Ihalagama-East and water-soluble phosphate was not detected in Eldeniya-East, indicating a very low range and suggesting that the water samples are less contaminated with phosphate-containing substances. Considerably high values in the range of 1.24 - 279.00 mg/L for Ihalagama-east and 59.5 mg/L - 168.0 mg/L for Eldeniya-East, are obtained for the nitrate content where most of them are beyond the safe level of drinking water, 50 mg/L. The soil pH in all the samples falls within the acidic range, varying from 2.99 - 6.73 in Ihalagama-East and 3.07 – 6.68 in Eldeniya-East. Most of the soil samples contain high nitrate contents, indicating significant contamination. The percentage soil organic matter content varies between 0.60% and 13.27% in both areas. Many fertile agricultural soils typically have an organic matter content ranging from 3% - 6% revealing that most of the samples are beyond the standard levels. The distribution of water-soluble and extractable cations does not exhibit a wide range. According to the findings, though two Grama Niladhari Divisions are selected, they also display a huge variation. This reveals the importance of mapping to address contaminations, effects of natural disasters which lead to changes in the studied water and soil quality parameters.

Spatio-Temporal Variations in Nitrate Sources and Transformations in the Midstream of the Yellow River Determined Based on Nitrate Isotopes and Hydrochemical Compositions

Nitrate pollution is a major environmental problem threatening rivers, and nitrogen and oxygen isotopes have proved to be an effective means of analyzing the sources and transformations of nitrate in rivers. However, a low monitoring frequency cannot accurately reflect the changes in nitrate. In this study, the sources and transformations of nitrate in the middle reaches of the Yellow River and its tributaries during the dry season and the wet season were analyzed based on water quality parameters and nitrate isotopes. Stable isotope analysis conducted using the R (SIAR) model was used to estimate the proportions of different nitrate sources. The results showed that the main nitrate sources in the main stream were soil nitrogen (40.95–45.83%) and domestic sewage and manure (30.93–32.60%), respectively, with little variation between the dry season and wet season because of the large flow of the Yellow River. During the dry season, the nitrate sources of the two tributaries were mainly domestic sewage and manure (45.23–47.40%), followed by soil nitrogen (31.35–34.00%). However, the primary nitrate source of T2 (Qin River) became soil nitrogen (40.05%) during the wet season, a phenomenon that was mainly caused by the significant increase in river discharge and in soil erosion in the basin. During the wet season, the concentrations of total nitrogen (TN) and nitrate (NO3−) significantly decreased in the main stream and tributaries, and nitrification and denitrification processes occurred in both the main stream and tributaries of the Yellow River. In addition, the T2 tributary (Qin River) was also significantly affected by mixed dilution. High-frequency sampling can reflect the isotopic information of nitrate in the river more comprehensively, which helps us to understand the conversion process of nitrate more accurately.

Low-Temperature Synthesis of Bi2S3 Hierarchical Microstructures via Co-Precipitation and Digestive Process in Aqueous Medium.

Bismuth sulfide (Bi2S3) nanostructures have gained significant attention in the fields of catalysis, optoelectronics, and biomedicine due to their unique physicochemical properties. This paper introduces a simple and cost-effective method for producing Bi2S3 microstructures at low temperatures (25 and 70 °C). These microstructures are formed by the hierarchical self-assembly of Bi2S3 nanoparticles, which are typically 15-40 nm in size. The nanoparticles are synthesized by the co-precipitation of thioglycolic acid, thioacetamide, and bismuth nitrate in water. The study delves into the phase composition and morphological evolution of the microstructures, concerning the chemical composition of the solution and the synthesis temperature. X-ray analysis has confirmed the formation of single-phase bismuthinite Bi2S3. The synthesis process generates primary building blocks in the form of 15-40 nm Bi2S3 nanocrystals, which then go through a hierarchical self-assembly process to produce a range of micrometer-sized structures. A scanning electron microscopy examination revealed that the primary nanoparticles self-assemble into quasi-1D worm-like nanostructures, which then self-assemble to create sponge-shaped microstructures. These structures subsequently self-organize and refine into either flower- or dandelion-like microstructures, mostly depending on the synthesis temperature and the chemistry of the digestion medium.

Effect of Different Nitrogen Levels on Water and Nitrate Distribution in Aeolian Sandy Soil under Drip Irrigation

Understanding the distribution of water and nitrate nitrogen in the soil profile is crucial for the reasonable operation of fertigation, and it is also fundamental for controlling and regulating nitrate nitrogen in the root zone, thereby meeting a crop’s requirements. The application rates of fertilizer and water directly influence this distribution of water and nitrate nitrogen. However, the effects in Aeolian sandy soil, a type of developing soil bordering deserts, remain ambiguous. In this study, field experiments for different drip fertigation treatments in Aeolian sandy soil were conducted to investigate the soil water distribution, as well as that of nitrate nitrogen. A completely randomized experimental design was implemented, encompassing three levels of irrigation amount: low (W1), medium (W2), and high (W3), and three levels of nitrogen application rate: low (F1), medium (F2), high (F3). After the completion of each irrigation treatment, soil samples were extracted at 10–20 cm intervals. The soil water and nitrate nitrogen contents in the profiles of these samples were measured. The experimental results revealed that increasing the nitrogen application rate facilitated the retention of greater amounts of water and nitrate nitrogen in the soil profile. However, with an increase in the nitrogen application rate, both soil water and nitrate nitrogen exhibited a radial tendency to move away from the drip emitter. Some moved upward and accumulated in surface soil near a ridge furrow, while some moved downward and remained in a deeper area approximately 30 cm horizontally from the emitter at depths of 40–60 cm. The uniformity of the water distribution decreased with increasing nitrogen application under low water conditions, with a reversal of this trend observed in medium and high water treatments. The effect of nitrogen application level on the uniformity of the nitrate nitrogen distribution was not significant. There was no significant correlation between the average soil water content and nitrate nitrogen content along the horizontal direction, however, a positive correlation existed in the vertical direction. In the whole profile, increasing the nitrogen application enhanced the correlation under low water conditions, but under medium and high water conditions, this trend was the opposite. This implies that, to avoid nitrate nitrogen leaching or limiting in a specific area, a moderate nitrogen application level is advisable. Under low water conditions, nitrogen application showed a positive effect on the nitrate nitrogen content, and a higher application is recommended. In cases of substantial water irrigation or rainy years, the nitrogen application rate should be decreased.

Direct detection of nitrite and nitrate in water on three-dimensional composite surface-enhanced raman scattering substrate

To solve the problem of the low sensitivity of the direct detection of nitrite and nitrate in water using Raman spectroscopy, we propose a three-dimensional composite surface-enhanced Raman spectroscopy (SERS) substrate. In addition, this cysteamine/gold/cysteamine composite structure is self-assembled onto anodic aluminum oxide and has a three-dimensional porous structure. Experimental results determined that the substrate’s detection limits for nitrite and nitrate are 0.1 mg l−1 and 1 mg l−1, respectively. Moreover, these meet environmental groundwater quality class II (nitrite, ≤0.1 mg l−1) and class I (nitrate, ≤1 mg l−1), respectively. The relative standard deviations calculated for nitrite and nitrate were 6.19% and 4.93%, respectively. Furthermore, the SERS substrate achieved equivalent detection limits for mixed nitrite and nitrate solution compared to separate nitrite and nitrate solutions, albeit with a weaker Raman signal. Therefore, this SERS substrate is capable of the sensitive and rapid determination of nitrite and nitrate at low concentrations without any treatment.

Synthesis of Triamine on OMS-2 Support for Removal of Nitrate and Phosphate in Water

Synthesis of Triamine on OMS-2 Support for Removal of Nitrate and Phosphate in Water

Synthesis of Hydroxylamine via Ketone-Mediated Nitrate Electroreduction.

Hydroxylamine (HA, NH2OH) is a critical feedstock in the production of various chemicals and materials, and its efficient and sustainable synthesis is of great importance. Electroreduction of nitrate on Cu-based catalysts has emerged as a promising approach for green ammonia (NH3) production, but the electrosynthesis of HA remains challenging due to overreduction of HA to NH3. Herein, we report the first work on ketone-mediated HA synthesis using nitrate in water. A metal-organic-framework-derived Cu catalyst was developed to catalyze the reaction. Cyclopentanone (CP) was used to capture HA in situ to form CP oxime (CP-O) with C═N bonds, which is prone to hydrolysis. HA could be released easily after electrolysis, and CP was regenerated. It was demonstrated that CP-O could be formed with an excellent Faradaic efficiency of 47.8%, a corresponding formation rate of 34.9 mg h-1 cm-2, and a remarkable carbon selectivity of >99.9%. The hydrolysis of CP-O to release HA and CP regeneration was also optimized, resulting in 96.1 mmol L-1 of HA stabilized in the solution, which was significantly higher than direct nitrate reduction. Detailed in situ characterizations, control experiments, and theoretical calculations revealed the catalyst surface reconstruction and reaction mechanism, which showed that the coexistence of Cu0 and Cu+ facilitated the protonation and reduction of *NO2 and *NH2OH desorption, leading to the enhancement for HA production.

Application of a portable ion chromatograph for real-time field analysis of nitrite and nitrate in soils and soil pore waters

Real-time monitoring of nitrite and nitrate is crucial for maintaining soil health and promoting plant growth. In this study, a portable ion-chromatograph (IC, Aquamonitrix) analyser, coupled with a field-applicable ultrasonic-assisted extraction method, was utilised for in-field determination of nitrate and nitrite in soils. This is the first application of this type of analyser to soil nutrients. On-site analysis of soil from a local sports field showed 94.8 ± 4.3 μg g−1 nitrate, with LODs of 32.0 μg g−1 for nitrate and 5.4 μg g−1 for nitrite. The results were in close agreement with those obtained using a conventional lab-based IC. Relative standard deviations (%RSDs) for soil analysis using Aquamonitrix were consistently below 10%. The obtained average recoveries of samples spiked with nitrite were 100% and 104% for the portable IC and conventional IC, respectively. Furthermore, to assess the suitability of portable IC for samples with high organic matter content, various natural organic fertilisers were extracted and analysed. The results showed 16.2 ± 0.7 μg g−1 nitrite and 28.5 ± 5.6 μg g−1 nitrate in sheep manure samples with LODs of 2.0 μg g−1 for nitrite and 12.0 μg g−1 for nitrate. The portable IC system was further demonstrated via real-time on-site analysis of soil pore-water acquired using a portable battery-based ceramic pore-water sampler. A continuous increase in nitrate concentration over time was observed (from 80 to 148 μg mL−1) in the soil pore-water in a vegetable garden four days after heavy rain. Unlike conventionally sampled natural waters, 7-day storage of the studied pore water samples revealed no changes in nitrate concentrations. An average of 558 ± 51 μg mL−1 nitrate was detected in the soil pore-water samples analysed on a spinach farm, immediately after irrigation.

Spatial distribution, sources, and human health risk assessment of elevated nitrate levels in groundwater of an agriculture-dominant coastal area in Hainan Island, China

In order to comprehend the groundwater nitrate contamination in Hainan Island, which is recognized as China's sole “tropical agricultural production base,” the distribution characteristics of nitrate in different aquifers and land-use types were elucidated through hydrochemical and geostatistical analysis methods. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and absolute principal component score-multiple linear regression (APCS-MLR) were employed for qualitative and quantitative analysis of the nitrate source. The results showed that NO3−-high (>88.57 mg/L) groundwater accounted for about 10 % of the total distribution area of the western coastal area in Hainan Island. Moreover, the proportions of NO3−-high groundwater in pore water and fissure water were 10 % and 7 %, respectively. The order of groundwater nitrate concentration in different land-use types was as follows: bare land, cultivated land, construction land, grassland, and woodland. The main sources of elevated nitrate concentrations in pore water were animal feces and nitrogen/potassium fertilizers, accounting for 45.4 % of the overall contribution. These substances infiltrated through the vadose zone, leaching out and mobilizing selenium within this zone, ultimately leading to the characteristic enrichment patterns observed in pore water, including nitrate, arsenic, potassium, and selenium. Furthermore, the occurrence of high nitrate in fissure water was mainly attributed to the leaching of cultured manure, septic tank leakage, and infiltration of domestic sewage, accounting for a contribution rate of 32.9 %. Simultaneously, under oxidizing conditions, selenium became activated and entered groundwater through water flow, thereby exhibiting common enrichment characteristics with nitrate and potassium in fissure water. In addition, the assessment of human health risks revealed that 16 % and 40 % of groundwater samples posed unacceptable non-carcinogenic risks to adults and children respectively, with a higher risk for local children. The study recommends the reasonable application of chemical fertilizers, as well as the strengthening of sewage treatment capacity and standardized disposal of manure and feces, to reduce nitrate contamination of groundwater at source and ensure the safety of drinking water.

Far-UVC Photolysis of Peroxydisulfate for Micropollutant Degradation in Water.

Increasing radical yields to reduce UV fluence requirement for achieving targeted removal of micropollutants in water would make UV-based advanced oxidation processes (AOPs) less energy demanding in the context of United Nations' Sustainable Development Goals and carbon neutrality. We herein demonstrate that, by switching the UV radiation source from conventional low-pressure UV at 254 nm (UV254) to emerging Far-UVC at 222 nm (UV222), the fluence-based concentration of HO• in the UV/peroxydisulfate (UV/PDS) AOP increases by 6.40, 2.89, and 6.00 times in deionized water, tap water, and surface water, respectively, with increases in the fluence-based concentration of SO4•- also by 5.06, 5.81, and 55.47 times, respectively. The enhancement to radical generation is confirmed using a kinetic model. The pseudo-first-order degradation rate constants of 16 micropollutants by the UV222/PDS AOP in surface water are predicted to be 1.94-13.71 times higher than those by the UV254/PDS AOP. Among the tested water matrix components, chloride and nitrate decrease SO4•- but increase HO• concentration in the UV222/PDS AOP. Compared to the UV254/PDS AOP, the UV222/PDS AOP decreases the formation potentials of carbonaceous disinfection byproducts (DBPs) but increases the formation potentials of nitrogenous DBPs.

Tracing the contributions of different nitrate sources associated with submarine groundwater discharge in coastal seawaters off Jeju Island, Korea

We measured the concentrations of dissolved inorganic nutrients and the dual isotopic composition of nitrate (δ15N-NO3− and δ18O-NO3−) in coastal waters off Jeju, a volcanic island in Korea, to trace its main sources. Sampling of seawater and fresh groundwater was conducted in four different coastal areas of Jeju Island: Haengwon (HW), Pyoseon (PS), Ilgwa (IG), and Sagye (SG) in May 2020 and 2021. The significant negative correlations between NO3− and salinity in the four areas indicate that the main source of NO3− is fresh submarine groundwater discharge (FSGD), with the extrapolated fresh groundwater endmember values ranging from 170 to 300 μM (δ15N-NO3−: 4.1–10.8 and δ18O-NO3−: 1.7–6.4). The actual sources of SGD-driven NO3− in these coastal waters were determined using a bi-plot diagram (δ15N-NO3− vs. δ18O-NO3−) and a Bayesian stable isotope mixing model (MixSIAR). The results showed that, besides the background contribution from open-ocean waters, the main sources of NO3− in HW were fertilizer (69 ± 5%) and manure and sewage (24 ± 7%) and those in PS, IG, and SG were manure and sewage (PS: 53 ± 11%, IG: 57 ± 12%, SG: 63 ± 13%) and fertilizer (PS: 27 ± 8%, IG: 24 ± 5%, SG: 22 ± 5%). Our extrapolation approach for NO3− dual isotopes provides a better way to evaluate the main sources of NO3− in coastal waters off volcanic islands where SGD-driven NO3− is significant, but its actual source groundwater cannot be located.