Stable Isotopes of Water and Nitrate for the Identification of Groundwater Flowpaths: A Review

Nitrate contamination in stream water and groundwater is a serious environmental problem that arises in areas of high agricultural activities or high population density. It is therefore important to identify the source and flowpath of nitrate in water bodies. In recent decades, the dual isotope analysis (δ15N and δ18O) of nitrate has been widely applied to track contamination sources by taking advantage of the difference in nitrogen and oxygen isotope ratios for different sources. However, transformation processes of nitrogen compounds can change the isotopic composition of nitrate due to the various redox processes in the environment, which often makes it difficult to identify contaminant sources. To compensate for this, the stable water isotope of the H2O itself can be used to interpret the complex hydrological and hydrochemical processes for the movement of nitrate contaminants. Therefore, the present study aims at understanding the fundamental background of stable water and nitrate isotope analysis, including isotope fractionation, analytical methods such as nitrate concentration from samples, instrumentation, and the typical ranges of δ15N and δ18O from various nitrate sources. In addition, we discuss hydrograph separation using the oxygen and hydrogen isotopes of water in combination with the nitrogen and oxygen isotopes of nitrate to understand the relative contributions of precipitation and groundwater to stream water. This study will assist in understanding the groundwater flowpaths as well as tracking the sources of nitrate contamination using the stable isotope analysis in combination with nitrate and water.

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Nitrogen Cycle Dynamics Revealed Through δ18O-NO3− Analysis in California Groundwater

Geosciences ◽

10.3390/geosciences9020095 ◽

2019 ◽

Vol 9 (2) ◽

pp. 95

Author(s):

Nate Veale ◽

Ate Visser ◽

Bradley Esser ◽

Michael Singleton ◽

Jean Moran

Keyword(s):

United States ◽

Land Use ◽

Oxygen Isotope ◽

Nitrogen Cycle ◽

The United States ◽

Nitrate Contamination ◽

Nitrate Sources ◽

Oxygen Isotope Fractionation ◽

Dual Isotope ◽

Quality Issue

Nitrate is a significant water-quality issue in California, the United States as a whole, and the world. Critical to addressing nitrate contamination is understanding the presence and extent of denitrification, and further refining the techniques used to identify nitrate sources. The use and understanding of nitrate isotopic signatures to identify nitrate sources have advanced tremendously; however, knowledge gaps remain concerning specific fractionation pathways and the role of denitrification in altering source values. Using a large unique database of California groundwater nitrate isotopic compositions, we explored the utility of nitrate–oxygen isotope ratios in determining specific nitrate origins. Lawrence Livermore National Lab (LLNL) samples were supplemented by United States Geological Society (USGS) data to create a dataset of over 1200 dual-isotope results. Methods used at LLNL allowed for the determination of δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δ2H-H2O, excess air, major dissolved gases, and excess N2. Results were examined for the degree to which δ18O-NO3− conforms to the model of nitrification in which two atoms of oxygen are sourced from ambient water and one from the atmosphere. Almost 80% of the results fall within one standard deviation of predicted values. However, 19% of samples had significantly higher values, suggesting the preservation of a synthetic nitrate source signature, mixing of sources, or widespread denitrification. Results were examined with respect to general land-use classifications and, while nitrate concentrations followed the expected pattern of being higher in agricultural settings, δ18O-NO3−patterns are complicated by application of N-fertilizer in various forms, and subsequent N cycling in the soil zone. We found that the current understanding of oxygen isotope-fractionation mechanisms cannot yet explain the prevalence of oxygen-isotope compositions with higher than predicted δ18O values, but when paired with related data such as land use and indicators of denitrification, oxygen-isotope compositions of nitrate can help to assess nitrogen cycle dynamics.

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Assessing Seasonal Nitrate Contamination by Nitrate Dual Isotopes in a Monsoon-Controlled Bay with Intensive Human Activities in South China

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph17061921 ◽

2020 ◽

Vol 17 (6) ◽

pp. 1921

Author(s):

Jiacheng Li ◽

Ruixue Cao ◽

Qibin Lao ◽

Fajin Chen ◽

Chunqing Chen ◽

...

Keyword(s):

River Basin ◽

South China ◽

Human Activities ◽

Isotope Analysis ◽

N Fertilizer ◽

Nitrate Contamination ◽

Local Source ◽

Biological Processes ◽

Soil N ◽

Dual Isotope

Nitrate (NO3−) dual isotope analysis was performed in Zhanjiang Bay, which is a closed bay with intensive human activities in South China, to investigate seasonal changes in the main NO3− sources and their biogeochemical processes in the monsoon-controlled climate. The relatively low N/P ratios in Zhanjiang Bay suggests that nitrogen (N) is a limiting nutrient, which indicates that the increase of N is favorable for phytoplankton proliferation. However, a sufficient amount of ammonium was found in our study area owing to intensive human activities, which can support biological processes. Thus, less NO3− biological processes were found, indicating that NO3− isotopic characteristics may reveal details of the mixing from various sources. The Bayesian mixing model showed that NO3− in the upper bay originated from manure (43%), soil N (30%), N fertilizer (17%), and N precipitation (10%) during winter, which reflects the local human activities; while NO3- sources during summer were mainly N fertilizer (36%), soil N (32%), and manure (31%), indicating the source as the runoff from the upper river basin. Our results suggest that nitrate dual-isotope was very useful for tracing the main NO3− sources in the condition of the sufficient ammonium, and runoff exerted an important impact on the shift in NO3− sources between both the local source and the source from the upper river basin during the two seasons in this monsoon-controlled bay.

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An Optimized Snowmelt Lysimeter System for Monitoring Melt Rates and Collecting Samples for Stable Water Isotope Analysis

Journal of Hydrology and Hydromechanics ◽

10.2478/johh-2018-0007 ◽

2019 ◽

Vol 67 (1) ◽

pp. 20-31 ◽

Cited By ~ 9

Author(s):

Andrea Rücker ◽

Massimiliano Zappa ◽

Stefan Boss ◽

Jana von Freyberg

Keyword(s):

Isotopic Composition ◽

Isotope Analysis ◽

Ground Level ◽

Isotopic Signature ◽

Small Scale ◽

Spatial And Temporal Variability ◽

Environmental Tracers ◽

Hydrograph Separation ◽

Stable Water Isotopes ◽

Restricted Volume

Abstract The contribution of snow meltwater to catchment streamflow can be quantified through hydrograph separation analyses for which stable water isotopes (18O, 2H) are used as environmental tracers. For this, the spatial and temporal variability of the isotopic composition of meltwater needs to be captured by the sampling method. This study compares an optimized snowmelt lysimeter system and an unheated precipitation collector with focus on their ability to capture snowmelt rates and the isotopic composition of snowmelt. The snowmelt lysimeter system consists of three individual unenclosed lysimeters at ground level with a surface of 0.14 m2 each. The unheated precipitation collector consists of a 30 cm-long, extended funnel with its orifice at 2.3 m above ground. Daily snowmelt samples were collected with both systems during two snowfall-snowmelt periods in 2016. The snowmelt lysimeter system provided more accurate measurements of natural melt rates and allowed for capturing the small-scale variability of snowmelt process at the plot scale, such as lateral meltwater flow from the surrounding snowpack. Because of the restricted volume of the extended funnel, daily melt rates from the unheated precipitation collector were up to 43% smaller compared to the snowmelt lysimeter system. Overall, both snowmelt collection methods captured the general temporal evolution of the isotopic signature in snowmelt.

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Transformations and nitrate sources in an agricultural watershed(Quanshui River, China): An investigation using hydrogeochemistry, isotopes, and a Bayesian model

10.5194/egusphere-egu21-3618 ◽

2021 ◽

Author(s):

Mingda Cao

Keyword(s):

Surface Water ◽

Bayesian Model ◽

Field Investigation ◽

Climatic Conditions ◽

Agricultural Watershed ◽

Agricultural Activities ◽

Transformation Mechanism ◽

Chemical Fertilizers ◽

Nitrate Sources ◽

The Difference

The spatiotemporal changes of nitrate in agricultural watersheds are of global concern. Although numerous studies have explained the source and transformation mechanism of nitrate in groundwater and surface water, the transformation mechanism in groundwater remains poorly understood because of different hydrogeological and climatic conditions. Based on a field investigation and sampling, this study revealed the sources and transformation mechanism of nitrogen in surface water and groundwater in a karst agricultural watershed by comprehensively using water chemistry data, isotope components, and a Bayesian model (simmr). The results indicated that:1)Local agricultural activities have controlled the changes of &#948;15N-NO3-, &#948;18O-NO3- and &#948;15N-NH4+ in groundwater. The difference is that the concentration of NO3- is significantly affected by rainfall. However, the contribution of rainfall to groundwater NO3- is relatively small (<9%), indicating that there is a dual influence mechanism of leaching in the watershed that controls the concentration of groundwater NO3-, while agricultural activities control its isotope changes;2)The study observed that after fertilization, due to the influence of ammonia volatilization and nitrification, &#948;15N-NO3-, &#948;18O-NO3- in groundwater showed a simultaneous decrease, while &#948;15N-NH4+ showed an increasing trend, which may be due to the result of incomplete nitration of NH4+ in the vadose zone;3)According to the calculation results of the simmr model, in the two main fertilization periods in October 2018 and April 2019, the contribution of chemical fertilizers to groundwater NO3-reached the peak value(65% and 69%), which is in line with the seasonal variations of &#948;15N-NO3-, &#948;18O-NO3-and &#948;15N-NH4+;4)The surface water in the watershed is mainly supplied by groundwater, and the contribution of chemical fertilizers to surface water NO3- is generally higher than that of groundwater. This may be caused by the drainage of rice fields containing chemical fertilizers into the river.

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Stable Isotope Enrichment (Δ15N) in the Predatory Flower Bug (Orius majusculus) Predicts Fitness-Related Differences between Diets

Insects ◽

10.3390/insects11040255 ◽

2020 ◽

Vol 11 (4) ◽

pp. 255

Author(s):

Marta Montoro ◽

Per M. Jensen ◽

Lene Sigsgaard

Keyword(s):

Diet Quality ◽

Isotopic Ratio ◽

Isotope Analysis ◽

Mass Rearing ◽

Isotope Enrichment ◽

Orius Majusculus ◽

Food And Feed ◽

The Difference ◽

Biochemical Analyses ◽

Δ15n And Δ13c

Mass rearing of insects, used both as biological control agents and for food and feed, is receiving increasing attention. Efforts are being made to improve diets that are currently in use, and to identify alternative diets, as is the case with the predatory flower bug (Orius majusculus) and other heteropteran predators, due to the high costs of their current diet, the eggs of the Mediterranean flour moth (E. kuehniella). The assessment of alternative diets may include measurements of the predator’s fitness-related traits (development time, weight, etc.), and biochemical analyses such as lipid and protein content in the diet and the insects. However, assessing diet quality via the predator’s fitness-related traits is laborious, and biochemical composition is often difficult to relate to the measured traits. Isotope analysis, previously used for diet reconstruction studies, can also serve as a tool for the assessment of diet quality. Here, the variation in discrimination factors or isotope enrichment (Δ15N and Δ13C) indicates the difference in isotopic ratio between the insect and its diet. In this study, we investigated the link between Δ15N and diet quality in the predatory bug Orius majusculus. Three groups of bugs were fed different diets: Ephestia kuehniella eggs, protein-rich Drosophila melanogaster and lipid-rich D. melanogaster. The isotopic enrichment and fitness-related measurements were assessed for each group. Results show a relation between Δ15N and fitness-related measurements, which conform to the idea that lower Δ15N indicates a higher diet quality.

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Contribution of glacial melt to river runoff as determined by stable isotopes at the source region of the Yangtze River, China

Hydrology Research ◽

10.2166/nh.2015.089 ◽

2015 ◽

Vol 47 (2) ◽

pp. 442-453 ◽

Cited By ~ 5

Author(s):

Zhaofei Liu ◽

Zhijun Yao ◽

Rui Wang

Keyword(s):

Yangtze River ◽

Meteoric Water ◽

Stream Water ◽

Source Region ◽

Upstream Region ◽

The Yangtze River ◽

Hydrograph Separation ◽

Water Line ◽

Total Runoff ◽

Meteoric Water Line

The primary objective of this study was to quantify the contribution of glacial melt to total runoff in the Gaerqu River catchment, which is located in the source region of the Yangtze River, China. The isotope hydrograph separation method was used to separate glacier melt runoff from total runoff in the catchment. The degree-day method was used to investigate temporal variations in glacial melt runoff. The results showed that the contribution of glacial melt runoff to total runoff was 15.0%. The uncertainty of the separation was ± 3.7% at the confidence level of 95%. Glacial melt runoff was mainly generated in June, July, and August. The runoff coefficient was 0.23 for the catchment. Precipitation-induced runoff constituted 19.9% of the total precipitation, meaning that precipitation loss was >80% across the study period (a hydrological year). The Local Meteoric Water Line (LMWL) of the catchment was fitted as δ2H = 7.75 δ18O + 5.93. This line has a smaller slope and intercept than the Global Meteoric Water Line. The regression-lines for the δ18O and δ2H values of stream water indicated that evaporation was greater over the entire catchment than it was for the upstream region alone.

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Tracking host use by bat ectoparasites with stable isotope analysis

Canadian Journal of Zoology ◽

10.1139/cjz-2015-0246 ◽

2016 ◽

Vol 94 (5) ◽

pp. 353-360 ◽

Cited By ~ 3

Author(s):

Ulalume Hernández-Arciga ◽

L. Gerardo Herrera M. ◽

Juan B. Morales-Malacara

Keyword(s):

Stable Isotope ◽

Isotope Analysis ◽

Enrichment Factors ◽

Host Switching ◽

Host Use ◽

Higher Ed ◽

The Difference ◽

Anoura Geoffroyi ◽

Leptonycteris Yerbabuenae ◽

Host Parasite

We used C and N stable isotopes of nectarivorous bats and their ectoparasites to determine the extent to which parasites depend on the host individual for food. The difference in stable isotope values between parasites and host tissues (Δ13C and Δ15N) was used as a proxy of host use. First, we tested the hypothesis that movement among individual Mexican long-tongued bats (Choeronycteris mexicana Tschudi, 1844) is more likely to occur in winged flies than in mites as indicated by higher host–parasite isotopic Euclidian distance (ED). Second, we tested the hypothesis that ectoparasite species in two coexisting bat species representing the C3 (Geoffroy’s tailless bat, Anoura geoffroyi Gray, 1838) and the CAM (lesser long-nosed bat, Leptonycteris yerbabuenae Martínez and Villa-R., 1940) food chains were monoxenous as indicated by their isotopic values. We also examined Δ13C and Δ15N of individual parasites in relation to 13C and 15N reference enrichment factors as an indication of host switching. In general, flies in C. mexicana had higher ED and wider ranges of individual Δ13C and Δ15N than mites, suggesting that host switching occurred to a larger extent. Most ectoparasites species collected in both coexisting bats were monoxenous, but one fly species appears to be oligoxenous. Individual Δ13C and Δ15N values varied widely in these parasite species, suggesting movements within species hosts.

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