Applicability of the dual isotopes δ15N and δ18O to identify nitrate in groundwater beneath irrigated cropland

Spalding, Roy F.; Hirsh, Aaron; Exner, Mary E.; Little, Nolan; Kloppenborg, K.L.

doi:10.1016/j.jconhyd.2018.12.004

Cited by 28 publications

(9 citation statements)

References 42 publications

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“…The accumulated NO 3 – in the vadose zone may exist for decades or centuries owing to the low denitrification rate in the region and would gradually be transported to groundwater. In addition, the estimated groundwater residence time in the study region varied from decades to hundreds of years (Table S-5), indicating relatively slow lateral flow because of the small hydraulic gradient (generally 0.2–5‰ due to the relatively broad and flat terrain) in most parts of the region, which provides favorable conditions for NO 3 – accumulation in groundwater. , Although the vadose zone acts as a buffer to delay NO 3 – transport to the aquifer, modern fertilizer-based NO 3 – has leached into groundwater in some areas with a shallow groundwater table, resulting in NO 3 – groundwater pollution. , However, a fundamental understanding of the reactive transport process of NO 3 – in the vadose zone is still lacking, limiting the accurate estimation of N stores in regions with thick vadose zones and, subsequently, the global N stock assessment. Therefore, future terrestrial N cycle analyses should incorporate NO 3 – storage, transformation, and leakage in the vadose zone over longer timescales to allow effective N management …”

Section: Resultsmentioning

confidence: 99%

“…− has leached into groundwater in some areas with a shallow groundwater table, resulting in NO 3 − groundwater pollution. 38,68 However, a fundamental understanding of the reactive transport process of NO 3 − in the vadose zone is still lacking, 8 limiting the accurate estimation of N stores in regions with thick vadose zones and, subsequently, the global N stock assessment. Therefore, future terrestrial N cycle analyses should incorporate NO 3 − storage, transformation, and leakage in the vadose zone over longer timescales to allow effective N management.…”

Section: Influence Of Agricultural Land-use Changes On the Soil Nomentioning

confidence: 99%

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Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Niu

Jia

Yang

et al. 2022

Environ. Sci. Technol.

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Excess nitrate (NO3 –) loading in terrestrial and aquatic ecosystems can result in critical environmental and health issues. NO3 –-rich groundwater has been recorded in the Guanzhong Plain in the Yellow River Basin of China for over 1000 years. To assess the sources and fate of NO3 – in the vadose zone and groundwater, numerous samples were collected via borehole drilling and field surveys, followed by analysis and stable NO3 – isotope quantification. The results demonstrated that the NO3 – concentration in 38% of the groundwater samples exceeded the limit set by the World Health Organization. The total NO3 – stock in the 0–10 m soil profile of the orchards was 3.7 times higher than that of the croplands, suggesting that the cropland-to-orchard transition aggravated NO3 – accumulation in the deep vadose zone. Based on a Bayesian mixing model applied to stable NO3 – isotopes (δ15N and δ18O), NO3 – accumulation in the vadose zone was predominantly from manure and sewage N (MN, 27–54%), soil N (SN, 0–64%), and chemical N fertilizer (FN, 4–46%). MN was, by far, the greatest contributor to groundwater NO3 – (58–82%). The results also indicated that groundwater NO3 – was mainly associated with the soil and hydrogeochemical characteristics, whereas no relationship with modern agricultural activities was observed, likely due to the time delay in the thick vadose zone. The estimated residence time of NO3 – in the vadose zone varied from decades to centuries; however, NO3 – might reach the aquifer in the near future in areas with recent FN loading, especially those under cropland-to-orchard transition or where the vadose zone is relatively thin. This study suggests that future agricultural land-use transitions from croplands to orchards should be promoted with caution in areas with shallow vadose zones and coarse soil texture.

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Section: Resultsmentioning

confidence: 99%

Section: Influence Of Agricultural Land-use Changes On the Soil Nomentioning

confidence: 99%

Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Niu

Jia

Yang

et al. 2022

Environ. Sci. Technol.

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“…Groundwater is indispensable for daily human activities (Song et al, 2021) and more than 1.5 billion people worldwide rely on it for drinking, especially in developing countries (Shaji et al, 2021), such as China (Jia et al, 2019). However, the quality of groundwater is increasingly degraded in many areas by pollutants from sources such as runoff from agricultural activities, industrial wastewaters, and municipal wastewater treatment systems (Spalding et al, 2019;McDonough et al, 2020;Krimsky et al, 2021;He et al, 2022). Nitrate (NO 3 − ) is the most common groundwater pollutant, and its rapid increase in shallow groundwater aquifers is a major concern in many countries (Kim et al, 2019;Taufiq et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Remediation of nitrate contaminated groundwater using a simulated PRB system with an La–CTAC–modified biochar filler

Wu²,

Nie³

et al. 2022

Front. Environ. Sci.

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In the present study, the Erigeron canadensis L., a typical invasive plant in Southwest China, was utilized as the raw material to prepare original biochar (ECL), a rare earth element La–modified biochar (La–ECL), and a rare earth element La coupling cationic surfactant [cetyltrimethylammonium chloride (CTAC)]–modified biochar (La/CTAC–ECL). These materials were then added to simulated permeable reactive barriers (PRBs) and their nitrate (NO3−) contaminant remediation performances were evaluated in groundwater. The results show that the breakthrough time for NO3− in a simulated PRB column increases as the concentration of the influent NO3− and the flow rate decreases, whereas with the increases of filler particle size and the height of the filler in the column initially increases, and then decreases. Considering an initial NO3− concentration of 50 mg L−1, and a filler particle size range of 0.8–1.2 mm, the maximum adsorption capacity of the La/CTAC–ECL column for NO3− is 18.99 mg g−1 for a filler column height of 10 cm and an influent flow rate of 15 ml min−1. The maximum quantity of adsorbed NO3− of 372.80 mg is obtained using a filler column height of 15 cm and an influent flow rate of 10 ml min−1. The Thomas and Yoon–Nelson models accurately predict the breakthrough of NO3− in groundwater in the simulated PRB column under different conditions, and the results are consistent with those from dynamic NO3− adsorption experiments. TEM, XRD, FTIR, and XPS analyses demonstrate that the modification using the La and CTAC improves the surface structure, porosity, permeability, and configuration of functional groups of the biochar. The mechanisms of NO3− removal from groundwater using the La/CTAC–ECL include pore filling, surface adsorption, ion exchange, and electrostatic adsorption. The composite La/CTAC–ECL exhibits a superior potential for the remediation of NO3− contaminated groundwater.

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“…microbial reduction of nitrate) (e.g. Kendall, 1998;Wexler et al, 2014;Park et al, 2018;Spalding et al, 2019). Understanding the sources of nitrate is important for remediation of excessive nitrate concentrations as at Tinwald (Aitchison-Earl, 2019).…”

Section: Introductionmentioning

confidence: 99%

Irrigation return flow causing a nitrate hotspot and denitrification imprints in groundwater at Tinwald, New Zealand

Stewart

Aitchison-Earl

2020

Hydrol. Earth Syst. Sci.

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Abstract. Nitrate concentrations in groundwater have been historically high (N≥11.3 mg L−1) in an area surrounding Tinwald, Ashburton, since at least the mid-1980s. The local community is interested in methods to remediate the high nitrate in groundwater. To do this, they need to know where the nitrate is coming from. Tinwald groundwater exhibits two features stemming from irrigation with local groundwater (i.e. irrigation return flow). The first feature is increased concentrations of nitrate (and other chemicals and stable isotopes) in a “hotspot” around Tinwald. The chemical concentrations of the groundwater are increased by recirculation of water already relatively high in chemicals. The irrigation return flow coefficient C (irrigation return flow divided by irrigation flow) is found to be consistent with the chemical enrichments. The stable isotopes of the groundwater show a similar pattern of enrichment by irrigation return flow of up to 40 % and are also enriched by evaporation (causing a loss of about 5 % of the original water mass). Management implications are that irrigation return flow needs to be taken into account in modelling of nitrate transport through soil–groundwater systems and in avoiding overuse of nitrate fertiliser leading to greater leaching of nitrate to the groundwater and unnecessary economic cost. The second feature is the presence of “denitrification imprints” (shown by enrichment of the δ15N and δ18ONO3 values of nitrate) in even relatively oxic groundwaters. The denitrification imprints can be clearly seen because (apart from denitrification) the nitrate has a blended isotopic composition due to irrigation return flow and N being retained in the soil–plant system as organic N. The nitrate concentration and isotopic compositions of nitrate are found to be correlated with the dissolved oxygen (DO) concentration. This denitrification imprint is attributed to localised denitrification in fine pores or small-scale physical heterogeneity where conditions are reducing. The implication is that denitrification could be occurring where it is not expected because groundwater DO concentrations are not low.

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Applicability of the dual isotopes δ15N and δ18O to identify nitrate in groundwater beneath irrigated cropland

Cited by 28 publications

References 42 publications

Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Remediation of nitrate contaminated groundwater using a simulated PRB system with an La–CTAC–modified biochar filler

Irrigation return flow causing a nitrate hotspot and denitrification imprints in groundwater at Tinwald, New Zealand

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Applicability of the dual isotopes δ15N and δ18O to identify nitrate in groundwater beneath irrigated cropland

Cited by 28 publications

References 42 publications

Tracing the Sources and Fate of NO3– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Tracing the Sources and Fate of NO3– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Remediation of nitrate contaminated groundwater using a simulated PRB system with an La–CTAC–modified biochar filler

Irrigation return flow causing a nitrate hotspot and denitrification imprints in groundwater at Tinwald, New Zealand

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Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region

Tracing the Sources and Fate of NO₃^– in the Vadose Zone–Groundwater System of a Thousand-Year-Cultivated Region