Nitrogen sources and cycling revealed by dual isotopes of nitrate in a complex urbanized environment

Asundi, Anand; Thibodeau, Benoît; Geeraert, Naomi; Xu, Meixiang; Kao, Shuh-Ji; Baker, David M.

doi:10.1016/j.watres.2018.06.004

Cited by 121 publications

(49 citation statements)

References 25 publications

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“…The east-west isotopic gradient observed today is reversed, with CS-δ 15 N being ~2‰ lower toward the Pearl River estuary compared to eastern values (Figure 7c). The presence of anomalously low-δ 15 N DIN sources to the Pearl River estuary has been observed in NO 3 δ 15 N (Archana et al, 2018;Ye et al, 2015) and in Porites tissue δ 15 N . This indicates that low-δ 15 N N is being discharged directly into the estuary, bypassing the upstream isotopic homogenization described earlier (Figure 7c).…”

Section: Anthropogenic N Footprint In the Pearl River Estuary In Thmentioning

confidence: 95%

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

Duprey

Wang

Kim

et al. 2020

Global Change Biology

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Historical coral skeleton (CS) δ18O and δ15N records were produced from samples recovered from sedimentary deposits, held in natural history museum collections, and cored into modern coral heads. These records were used to assess the influence of global warming and regional eutrophication, respectively, on the decline of coastal coral communities following the development of the Pearl River Delta (PRD) megacity, China. We find that, until 2007, ocean warming was not a major threat to coral communities in the Pearl River estuary; instead, nitrogen (N) inputs dominated impacts. The high but stable CS‐δ15N values (9‰–12‰ vs. air) observed from the mid‐Holocene until 1980 indicate that soil and stream denitrification reduced and modulated the hydrologic inputs of N, blunting the rise in coastal N sources during the early phase of the Pearl River estuary urbanization. However, an unprecedented CS‐δ15N peak was observed from 1987 to 1993 (>13‰ vs. air), concomitant to an increase of NH4+ concentration, consistent with the rapid Pearl River estuary urbanization as the main cause for this eutrophication event. We suggest that widespread discharge of domestic sewage entered directly into the estuary, preventing removal by natural denitrification hotspots. We argue that this event caused the dramatic decline of the Pearl River estuary coral communities reported from 1980 to 2000. Subsequently, the coral record shows that the implementation of improved wastewater management policies succeeded in bringing down both CS‐δ15N and NH4+ concentrations in the early 2000s. This study points to the potential importance of eutrophication over ocean warming in coral decline along urbanized coastlines and in particular in the vicinity of megacities.

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Section: Anthropogenic N Footprint In the Pearl River Estuary In Thmentioning

confidence: 95%

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

Duprey

Wang

Kim

et al. 2020

Global Change Biology

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“…Hence, identifying and quantifying the sources and biogeochemical processing of nitrate in aquatic systems are key to informing water resource management, agricultural nutrient optimization strategies, and urban pollutant mitigation . Stable isotopes are proven tools in this regard, as the δ 15 N, δ 18 O and δ 17 O isotopic composition of NO 3 − provides essential information about nitrogen (N) sources and biogeochemical sinks, allowing one to distinguish between organic waste, fertilizers, and atmospheric N sources . Furthermore, isotopic time series and geospatial depictions of nitrate in ground and surface water reveal important changes in agricultural land use, inform optimization of fertilization practices not achievable based on NO 3 − concentrations alone, and allow for detection of natural bioremediation processes such as bacterial denitrification .…”

Section: Introductionmentioning

confidence: 99%

A Ti(III) reduction method for one‐step conversion of seawater and freshwater nitrate into N₂O for stable isotopic analysis of ¹⁵N/¹⁴N, ¹⁸O/¹⁶O and ¹⁷O/¹⁶O

Altabet

Wassenaar

Douence

et al. 2019

Rapid Comm Mass Spectrometry

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Rationale: The nitrogen and oxygen (δ 15 N, δ 18 O, and δ 17 O values) isotopic compositions of nitrate (NO 3 − ) are crucial tracers of nutrient nitrogen (N) sources and dynamics in aquatic systems. Current methods such as bacterial denitrification or Cd-azide reduction require laborious multi-step conversions or toxic chemicals to reduce NO 3 − to N 2 O for 15 N and 18 O isotopic analyses by isotope ratio mass spectrometry (IRMS). Furthermore, the 17 O composition of N 2 O cannot be directly disentangled using IRMS because 17 O contributes to mass 45 ( 15 N). Methods: We describe a new one-step chemical conversion method that employs Ti(III) chloride to reduce nitrate to N 2 O gas in septum sample vials. Sample preparation takes only a few minutes followed by a 24-h reaction producing N 2 O gas (65-75% recovery) which partitions into the headspace. The N 2 O headspace was measured for 15 N, 18 O and 17 O by IRMS or laser spectrometry. Results: IRMS and laser spectrometric analyses gave accurate and reproducible N and O isotopic results down to 50 ppb (3.5 μM) NO 3 -N, similar in precision to the denitrifier and Cd-azide methods. The uncertainties for dissolved nitrate reference materials (USGS32, USGS34, USGS35, IAEA-NO 3 ) were ±0.2‰ for δ 15 N values and ±0.3‰ for δ 18 O values using IRMS. For laser-based N 2 O isotope analyses the results were similar, with an δ 17 O uncertainty of ±0.9‰ without any need for 15 N correction. Conclusions: Advantages of the Ti(III) reduction method are simplicity, low cost, and no requirement for toxic chemicals or anaerobic bacterial cultures. Minor corrections may be required to account for sample nitrate concentration variance and potential chemical interferences. The Ti(III) method is easily implemented into laboratories currently using N 2 O headspace sampling apparatus. We expect that the Ti(III) method will promulgate the use of N and O isotopes of nitrate in important studies of nutrient dynamics and pollution in a wide range of aquatic ecosystems.

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“…Laboratory 15 N tracer techniques are often used as standard methods to determine the potential rates of denitrification and anammox. This technique has been successfully applied to quantify the in situ N removal rates [24].…”

Section: Potential Nitrogen Removal Rate In Urban River and Its Determentioning

confidence: 99%

“…Self-purification function of riverine ecosystems can removal N pollutants through microbial driven processes of ammonification, nitrification, denitrification and anoxic ammonium oxidation (anammox) [11]. However, N removal processes are influenced by variation of environmental factors, contaminants and microbial communities [11][12][13][14][15]. Water quality also deeply influences river ecosystem structure, food-web integrity, as well as ecosystem functions and services [16].…”

Section: Introductionmentioning

confidence: 99%

Insight into the nitrogen accumulation in urban center river from functional genes and bacterial community

Liu

Jiang

et al. 2020

PLoS ONE

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Along with urbanization, the intensified nitrogen pollution in urban rivers and the form of black-odor rivers has become one of the biggest concerns. Better understanding of the nitrogen transformations and microbial mechanisms occurring within urban rivers could help to manage their water quality. In this study, pollution characteristics, potential nitrogen removal rate, composition and function of bacterial community, and abundance of functional genes associated with nitrogen transformation were comparatively investigated in a typical urban river (FC) and a suburban river (LH). Compared with LH, FC was characterized by higher content of nutrients, lower potential nitrogen removal rate and lower abundance of functional genes associated with nitrogen transformation in both overlying water and sediment, especially in summer. Sediment dissolved organic matter characterized by excitation−emission matrix (EEM) showed that FC was more severely polluted by high nitrogen organic matter. Our results revealed that anammox was the main nitrogen removal pathway in both rivers and potential nitrogen removal rates decreased significantly in summer. Bacterial community analysis showed that the benthic communities were more severely influenced by the pollutant than aquatic ones in both rivers. Furthermore, the FC benthic community was dominated by anaerobic respiring, fermentative, sulfate reduction bacteria. Quantitatively, the denitrification rate showed a significant positive correlation with the abundance of denitrification genes, whilst the anammox rate was significantly negatively correlated with bacterial diversity. Meanwhile, NH 4 +-N had a significant negative correlation to both denitrification and anammox in sediment. Taken together, the results indicated that the increased nitrogen pollutants in an urban river altered nitrogen removal pathways and bacterial communities, which could in turn exacerbate the nitrogen pollution to this river.

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Nitrogen sources and cycling revealed by dual isotopes of nitrate in a complex urbanized environment

Cited by 121 publications

References 25 publications

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

A Ti(III) reduction method for one‐step conversion of seawater and freshwater nitrate into N₂O for stable isotopic analysis of ¹⁵N/¹⁴N, ¹⁸O/¹⁶O and ¹⁷O/¹⁶O

Insight into the nitrogen accumulation in urban center river from functional genes and bacterial community

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Nitrogen sources and cycling revealed by dual isotopes of nitrate in a complex urbanized environment

Cited by 121 publications

References 25 publications

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ15N records in the Pearl River estuary

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ15N records in the Pearl River estuary

A Ti(III) reduction method for one‐step conversion of seawater and freshwater nitrate into N2O for stable isotopic analysis of 15N/14N, 18O/16O and 17O/16O

Insight into the nitrogen accumulation in urban center river from functional genes and bacterial community

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Product

Resources

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Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ¹⁵N records in the Pearl River estuary

A Ti(III) reduction method for one‐step conversion of seawater and freshwater nitrate into N₂O for stable isotopic analysis of ¹⁵N/¹⁴N, ¹⁸O/¹⁶O and ¹⁷O/¹⁶O