Stable Isotope Analysis In R Research Articles

Tracing nitrogen and phosphorus pollution in urban runoff: Insights from isotopic tracers and SWMM modeling

Water contamination in certain rivers during rainfall necessitates the evaluation of pollutant levels within pipelines and the identification of their sources to ensure effective pollution control. In this study, we assess pollutant concentrations during runoff from surfaces, pipelines, and channels, identify pollutant sources within pipelines, and analyze sewage leakage contributions to channel pollution in residential areas in Wuxi City, China. The results showed that the event mean concentrations of total nitrogen (TN), total phosphorus (TP), ammonium (NH4+-N), and nitrate (NO3−-N) in the drainage outlet runoff were 3.4, 1.1, 8.8, and 14.9 times higher than in impervious surface runoff. The predominant forms of nitrogen and phosphorus in runoff shift from organic to inorganic as they move from the surface to pipelines. The pipeline load and contribution were further estimated by combining water quantity calculations from the calibrated and verified Storm Water Management Model (SWMM) with measured nitrogen and phosphorus concentrations in the runoff. TN, NH4+-N, NO3−-N, and PO43--P within the pipelines accounted for 59%, 83%, 90%, and 77% of the discharge loads, respectively. The application of the Stable Isotope Analysis in R (SIAR) package (MixSIAR) revealed that the domestic sewage and soil organic N were the predominant sources of pollutants within drainage pipelines, contributing 23.7% and 32.6% of NO3−-N, respectively. Additionally, the sewage leakage accounted for 33.7% and 66.9% of NO3−-N in drainage runoff and channels, respectively. Unlike existing methods, this study quantitatively highlights the significant impact of pipeline pollutants and sewage leakage on urban river water quality, providing essential insights for developing effective strategies to mitigate non-point source water pollution.

Continental Emissions Influence the Sources and Formation Mechanisms of Marine Nitrate Aerosols in Spring Over the Bohai Sea and Yellow Sea Inferred From Stable Isotopes

AbstractThe influence of continental emissions on the origin and formation mechanisms of atmospheric particulate nitrate (ρ‐NO3−) aerosols in the marine boundary layer remains unclear. Here, synchronous observations of nitrogen isotope ratios (δ15N–NO3−) and oxygen isotope anomaly (Δ17O–NO3−) in ρ‐NO3− were conducted across the Yellow Sea and Bohai Sea in Eastern China. Nitrate concentrations, δ15N–NO3− and Δ17O–NO3− exhibited a pronounced north‐to‐south latitudinal gradient. Combined with backward air mass trajectory analysis, the high nitrate concentration and isotopic characteristics in the northern sea area were found to be affected by the continental outflow near China while the low values in the southern sea area were more related to the oceanic inflow. Stable isotope analysis in R (SIAR) indicated that near the northern sea area, the nitrate radicals (NO3) reacted with hydrocarbons (HC) or dimethyl sulfides (DMS) pathway (NO3 + HC/DMS) played a leading role in nitrate production, whereas the NO2 + OH pathway dominated near the southern sea area. Nitrate in the northern seas originated mainly from nitrogen oxides (NOx = NO + NO2, the gaseous precursor of nitrate) emitted from continental sources, especially coal combustion and biomass burning. While closer to the southern seas, the proportion of NOx generated in the marine environment (from ship and biogenic emissions) increased. Overall, the differential relative contributions of continental and marine atmospheric chemistry and NOx sources lead to the spatial distribution characteristics of atmospheric nitrate concentrations and isotopic values over the Yellow and Bohai Seas.

Quantification of Nitrate Sources and Its Spatial Heterogeneity by Dual Isotopes

Nitrate source allocation is important for watershed environmental management. In this paper, 59 surface water samples were collected in late July 2022 in the Erhai Basin of the Yunnan–Guizhou Plateau in southwestern China, where the source of nitrate pollution in surface water is still unknown. The potential sources of nitrate were identified and estimated using hydrochemistry indicators, the δ 15 N / δ 18 O − NO 3 − and the Stable Isotope Analysis in R (SIAR) model. The results showed that the various forms of nitrogen compounds, transport and transformation processes, and their sources in the Erhai Basin were characterized by obvious spatial scale differentiation. First, the mean values of NO 3 − , NO 2 − , and NH 4 + in the watershed were 1.14 ± 1.49 mg/l, 0.11 ± 0.06 mg/l, and 0.14 ± 0.09 mg/l, respectively, while the differences among the three in the secondary zoning scale were mainly reflected in the ES region. Second, both δ 15 N − NO 3 − (−0.64‰ to +17.67‰) and δ 18 O − NO 3 − (−1.87‰ to +24.42‰) had some differences in primary and secondary zoning. Third, nitrification was the dominant process of nitrate transport and transformation in the watershed, but it was also characterized by spatial differentiation. Fourth, the output of the SIAR model showed that the proportion of nitrate pollution sources in the basin was soil nitrogen (37.16%), domestic sewage (36.06%), livestock manure (13.49%), and chemical fertilizer (13.29%), and there was also obvious spatial differentiation. This study provides a new perspective for the spatial heterogeneity analysis of nitrate pollution sources and the corresponding pollution control.

Diet During the Late Initial Period (1100–800 BC) in the Chavín Heartland: New Data from Canchas Uckro (North-Central Peru)

During the late Initial Period (c. 1100-800 BC), the Conchucos region of highland Peru witnessed the formation of the ceremonial and “proto-urban” center of Chavín de Huántar (c. 1000-500/400 BC). An important question regarding Chavín de Huántar centers on the nature of its subsistence economy during the time when it was first founded. In this paper, we present new results from zooarchaeological, starch granule, and stable isotope (δ13C and δ15N) analyses to reconstruct diet from Canchas Uckro, a settlement located in Chavín de Huántar's heartland region. Founded c. 1100 BC and abandoned just after 800 BC, Canchas Uckro provides insight into socioeconomic processes during the early phases of Chavín de Huántar. Extant faunal remains suggest deer comprised an important component of the diet, while camelids constitute a minor proportion of the assemblage. Starch granules recovered from the pottery indicate that domesticated cultigens (maize, potato, and manioc) were obtained from different highland production zones. δ13C and δ15N analysis of a sample of human skeletal remains, coupled with Stable Isotope Analysis in R (SIAR) mixing models, demonstrate that C3plants constitute most of the diet, while maize was not intensively consumed. δ13C and δ15N further indicate that deer made up 25-50% of the diet. The results of this study add to a gro wing corpus of data on subsistence practices in the north-central and northern highlands of Peru prior to the widespread adoption of domesticated camelids.

Using a Multi-isotope Approach and Isotope Mixing Models to Trace and Quantify Phosphorus Sources in the Tuojiang River, Southwest China.

Identifying phosphorus (P) sources is critical for solving eutrophication and controlling P in aquatic environments. Phosphate oxygen isotopes (δ18Op) have been used to trace P sources. However, the application of this method has been greatly restricted due to δ18OP values from the potential source having wide and overlapping ranges. In this research, P sources were traced by combining δ18Op with multiple stable isotopes of nitrogen (δ15N), hydrogen (δD), and dissolved inorganic carbon (δ13C). Then, a Bayesian-based Stable Isotope Analysis in R (SIAR) model and IsoSource model were used to estimate the proportional contributions of the potential sources in the Tuojiang River. δ18Op was not in equilibrium with ambient water, and statistically significant differences in the δ18Op values were found between the potential sources, indicating that δ18Op can be used to trace the P sources. δ15N, δD, and δ13C could assist δ18Op in identifying the main sources of P. The SIAR and IsoSource models suggested that industrial and domestic sewage was the largest contributor, followed by phosphate rock and phosphogypsum and agricultural sewage. The uncertainty of the calculation results of the SIAR model was lower than that of the IsoSource model. These findings provide new insights into tracing P sources using multiple stable isotopes in watersheds.

Determination of nitrate sources in a karst plateau reservoir based on nitrogen and oxygen isotopes

ABSTRACT Investigating the sources, migration and proportional contribution of nitrate is essential to effectively protect water quality. δ 15N-NO3 –, δ 18O-NO3 – and Stable Isotope Analysis in R (SIAR) were used to qualitatively and quantitatively analyse nitrate sources in the Pingzhai Reservoir water body. The values of δ 15N-NO3 – and δ 18O-NO3 – in water vary with season. Soil organic nitrogen and chemical fertilisers are the main sources of nitrate in autumn, while domestic sewage and livestock manure are the primary sources of nitrate in winter and spring. The SIAR results showed that chemical fertilisers, livestock manure, sewage, and soil organic nitrogen had the highest proportional contribution. In autumn, the proportional contribution of chemical fertilisers to river and reservoir were 47 and 51 %. During winter, the proportional contributions of livestock manure and sewage to river and reservoir were 53 and 68 %, respectively, and in spring 49 and 68 %, respectively. Considering the fragility of karst ecosystems, strict measures should be formulated for the use of chemical fertilisers and standards for sewage discharge should be raised. Control nitrogen input from agricultural activities and prevent water quality deterioration.

Quantifying the formation pathways of nitrate in size-segregated aerosols during winter haze pollution

Nitrate (NO3−) is an important acidic component in haze pollution. The NO3− formation pathways for bulk aerosols have been studied thoroughly, leaving the size-segregated NO3− formation mechanisms underexplored. By coupling nitrate dual isotopes with aerosol chemical compositions, we studied size-segregated aerosols collected during winter haze pollution events at Chengdu, China. Different formation mechanisms for the size-segregated NO3− were analyzed. For fine particles (0.43–2.1 μm), NO3− was dominantly formed under NH4+ enriched conditions, during which the SIAR (stable isotope analysis in R) model suggested that N2O5 hydrolysis, NO3 + VOCs (volatile organic compounds) and NO2 + OH homogeneous reactions contributed 38–42 %, 32–38 %, and 22–30 % of NO3− production, respectively. For coarse particles (>3.3 μm), majority of NO3− was produced through the reaction of gas-phase HNO3 with CaCO3 (63–71 %). This work revealed differential formation pathways of size-segregated NO3− and provided quantitative insights on information on NO3− formation during the haze pollution.

Assessment of sources variability of riverine particulate organic matter with land use and rainfall changes using a three-indicator (δ13C, δ15N, and C/N) Bayesian mixing model

In intensive agricultural watersheds, riverine particulate organic matter (POM) may be transported from many sources such as rice paddies, crop uplands, forests, and livestock farming areas during rainy seasons. However, the impacts of land-use and rainfall changes on the POM sources are not well understood. In this study, changes in the sources of riverine POM were investigated in an agricultural area of Korea between 2014 and 2020/21. During this period, land-use and rainfall patterns changed dramatically. The δ13C, δ15N, and C/N of the POM sources as well as those of riverine POM were analyzed, and a stable isotope analysis in R (SIAR) model was utilized for source apportionment. There were differences in δ13C, δ15N, and C/N among the sources. For example, manure had higher δ13C (−22.6 ± 3.3‰) and δ15N (+10.6 ± 5.9‰) than soils (from −28.0 ± 0.8‰ to −25.1 ± 1.2‰ for δ13C and +3.6 ± 1.7‰ to +9.8 ± 1.4‰ for δ15N). For soils, the δ13C and δ15N were higher for upland soils, while C/N was greater for forest soils than for others. For riverine POM, the δ15N marginally changed; however, the δ13C and C/N increased from −26.1 ± 0.9‰ to −20.8 ± 5.3‰ and from +7.7 ± 1.7 to +18.8 ± 8.3 between 2014 and 2020/21, respectively. The SIAR model showed that the contributions of paddy (from 41.0% to 14.9%) and upland fields (from 48.1% to 23.7%) to riverine POM decreased between the periods due to decreased paddy area and the implementation of best management practice on upland fields, respectively. However, the contribution of forests (from 3.5% to 28.0%) and manure (from 7.4% to 33.5%) increased probably due to improper management of forest clear-cutting sites and livestock manure storage sites. The contributions of agricultural soils to riverine POM decreased in drier years. Our study suggests that land management rather than land-use area is critical in riverine POM management, particularly in wetter years.

Diesel vehicle emission accounts for the dominate NOx source to atmospheric particulate nitrate in a coastal city: Insights from nitrate dual isotopes of PM2.5

Nitrate has long been focused due to its dominant proportion in PM2.5. In this study, PM2.5 samples were non-consecutively collected in a coastal city located in Western Pacific from March 6, 2019 to January 16, 2020. On the basis of the determination of water soluble inorganic ions and nitrogen and oxygen isotopic signatures of nitrate, its formation pathways were estimated by isotope fractionation calculation and NOx source contributions were quantified with stable isotope analysis in R (SIAR) model. Results showed that δ15N-NO3− ranged from −3.7‰ to 32.1‰, and δ18O-NO3− varied from 38.1‰ to 101.4‰. Nitrate formation was dominated by oxidation of NO2 with hydroxyl radical (OH) in spring, summer, and fall, while it was mainly controlled by N2O5 heterogeneous hydrolysis in winter. Quantitative analysis of NOx sources contributing to nitrate by using SIAR model showed that estimated annual average contributions from diesel vehicle emission, gasoline vehicle emission, biogenic soil emission, biomass burning, and coal combustion were 25.6%, 21.4%, 21.1%, 17.4%, and 14.5%, respectively. The control of diesel vehicle emission is vital to nitrate reduction and air quality improvement in spring, summer, and fall, while coal combustion is the primary NOx source to nitrate in winter. Posterior distribution of source contribution results from SIAR model presented more stable results in spring.

Invasive Apple Snail Diets in Native vs. Non-Native Habitats Defined by SIAR (Stable Isotope Analysis in R)

Invasive apple snails adversely impact the ecological function of non-native habitats, resulting in eutrophication as well as reduced biodiversity, which diminishes ecosystem goods and services, thereby [negatively] impacting human well-being. The onus here is to define the diet of an invasive apple snail (Pomacea canaliculata) in native (Maldonado, Uruguay) versus non-native habitats (Hangzhou, China, and Oahu, HI, USA). Diets for apple snails, in five sites, within both native and non-native habitats were defined via SIAR (Stable Isotope Analysis in R) with δ13C and δ15N stable isotope data collected therein. SIAR models indicate P. canaliculata shift diet from generalist (where myriad plant species comprise relatively small proportions of overall diet) to a specialist diet (where plants species constitute much larger proportions of said diet). What may be more telling is that in (anthropogenically disturbed) portions of the native habitat, and progressively more so in non-native habitats, invasive apple snail diets are increasingly composed of aquatic plants. The inherent and pronounced dietary differences amongst pristine and anthropogenically disturbed native habitats, as well as non-native habitats, provide a mechanism that may elucidate the variable ecological impacts of invasive apple snails within native and non-native habitats.

Isotopic source identification of nitrogen pollution in the Pi River in Chengdu.

This study used stable isotope (δ15 N- and δ18 O- ) ratios, modeled by means of a Bayesian stable isotope analysis in R (SIAR) approach, to identify nitrate sources in the Pi River, which flows through the megacity Chengdu. The goal was to determine where management resources should be applied to reduce nitrogen pollution. Results revealed that was the primary nitrogen species throughout the study area; that it originated in manure and sewage, as well as nitrification of fertilizer and soil nitrogen; and that the nitrogen in the main stream came primarily from the tributaries. Notably, the nitrogen concentration in the tributaries exhibited no evident seasonal variations, further demonstrating that its source was intensive anthropogenic activity. Results of Bayesian model (SIAR) estimation indicated that manure and sewage were the dominant nitrate contributors in the watershed and that the nitrate concentration decreased from 54.19% to 39.57% in response to water treatment. These results empirically demonstrate that the methodology described in this work can be used effectively in catchments affected by intensive anthropogenic activity to determine where management resources should be applied to reduce nitrogen pollution. Integr Environ Assess Manag 2022;18:1609-1620. © 2022 SETAC.

Using nitrogen and oxygen stable isotopes to analyze the major NOx sources to nitrate of PM2.5 in Lanzhou, northwest China, in winter-spring periods

Nitrate (NO3−) is a standout amongst the essential inorganic aerosols in the atmosphere. Stable isotopic constraint is a robust means to identify the oxidation mechanisms for atmospheric particulate nitrate (NO3−) production. However, rarely studies noted the heavily polluted environments of northwest China. In this study, fine particulate matter (PM2.5) samples were gathered starting from December 2017 till April 2018 in the urban zone of Lanzhou, northwest China, and water-soluble ions, δ15N– NO3− and δ18O– NO3−, were analysed to explore the possible sources of NO3− aerosols. The average concentration of PM2.5 was 63.1 ± 22.6 μg m−3, indicating severe fine PM pollution. The formation of secondary pollutants NO3−, SO42−, and NH4+ concentrations were higher in winter than in spring. The Ca2+, Na+, and Mg2+ concentrations were much higher in spring than in winter, and the concentration of Ca2+ was higher than those in other cities, which implies that the PM2.5 concentration is significantly affected by dust. The δ15N and δ18O values were lower in warmer months, confirming that the contribution of each nitrate source and the oxidation pathways change similarly as the season transforms from cold to warm. The nitrogen sources were analysed using stable isotope analysis in R (SIAR). The results showed that coal combustion, biomass burning, vehicle exhausts, and soil microbial emissions account for 42.2 ± 9.9%, 27.8 ± 16.2%, 22.2 ± 12.3%, and 7.7 ± 5.2% of the nitrate in PM2.5 in winter and 30.7 ± 11.4%, 28.3 ± 15.7%, 26.5 ± 14.4%, and 14.4 ± 6.9% in spring, respectively. The fractional contributions of coal combustion gradually increased in winter. These results are useful for reducing NOx emissions in urban environments and clarifying the relationship between regional NOx emissions and atmospheric NO3− pollution or deposition.

Source tracking of dissolved organic nitrogen at the molecular level during storm events in an agricultural watershed

Accelerated export of nitrogen-containing dissolved organic matter (DOM) or dissolved organic nitrogen (DON) to streams and rivers from agricultural watersheds has been reported worldwide. However, few studies have examined the dynamics of DOM molecular composition with the attention paid to the relative contributions of DON from various sources altered with flow conditions. In this study, end-member mixing analysis (EMMA) was conducted with the optical properties of DOM to quantify the relative contributions of several major organic matter sources (litter, reed, field soil, and manure) in two rivers of a small agricultural watershed. DOC and DON concentration increased during the storm events with an input of allochthonous DOM as indicated by an increase in specific ultraviolet absorbance at 254 nm (SUVA254) and a decrease in biological index (BIX), fluorescence index (FI), and protein-like component (%C3) at high discharge. EMMA results based on a Bayesian mixing model using stable isotope analysis in R (SIAR) were more accurate in source tracking than those using the traditional IsoSource program. Manure (>30%) and field soil (also termed as “manure-impacted field soil”) (>23%) end-members revealed their predominant contributions to the riverine DOM in SIAR model, which was enhanced during the storm event (up to 56% and 38%, respectively). The molecular composition of the riverine DOM exhibited a distinct footprint from the manure and manure-impacted field soil, with a larger number of CHON formulas and abundant polyphenols and condensed aromatics in peak flow samples in the studied rivers. The riverine DOM during peak flow contained many unique molecular formulas in both rivers (4980 and 2082) of which >60% originated from manure and manure-impacted field soil. Combining the EMMA with DOM molecular composition clearly demonstrated the effect of manure fertilizer on the riverine DOM of the watershed with intensive agriculture. This study provides insights into the source tracking and regulation of DON leaching from anthropogenically altered river systems worldwide.

Identifying nitrogen source and transport characteristics of the urban estuaries and gate-controlled rivers in northern Taihu Lake, China

Revealing nitrogen source and transport mechanisms are essential to achieving optimal nitrogen management in urban estuaries and gate-controlled rivers. However, in plains river networks, gate and/or dam construction make the nitrogen sources difficult to trace. In this study, seasonal water samples from typical urban estuaries and gate-controlled rivers in northern Taihu Lake were analyzed using statistical analysis and stable isotope analysis in R (SIAR). The results show that the concentrations of various nitrogen forms showed obvious spatial–temporal distribution characteristics by multiple sources. Specifically, the nitrogen concentration was lower during the wet season than the dry season (T = 6.02, p < 0.01). Gate construction had a dual effect on the water environment, because it changed both the nitrogen transport processes and the nitrogen enrichment risk between the river side and lake side. The δ18O-NO3- and δ15N-NO3- values were sensitive to anthropogenic activity intensity and urbanization process, showing the following order of δ15N-NO3- values: Countryside > Suburbs > Downtown, and Construction Land > Forest-grassland > Farmland. While, a contrary trend was observed among the variations in δ18O-NO3- values. According to the SIAR model, sewage/manure, fertilizer, and sediment nitrogen (sediment N) were the main nitrate sources, accounting for 42.68%, 23.79%, and 23.71%, respectively. The proportion of urban nitrogen discharge has surpassed that of agricultural sources, becoming the largest nitrogen source in the waterbody. Under the coupling of meteorological conditions and estuary shape, the endogenous nitrogen released from sediment became the second largest contributor in some estuaries. These findings suggest that it is necessary to strengthen the control of urban exogenous nitrogen input and sediment nitrogen endogenous release to enable future estuarine nitrogen management and habitat restoration.

Water Pollution Characteristics and Source Apportionment in Rapid Urbanization Region of the Lower Yangtze River: Considering the Qinhuai River Catchment

Clarifying the current situation of regional water pollutants and the relationship between pollutants and pollution sources is considered essential for managing the water environment. Water quality identification index (WQI), cluster analysis (CA), positive matrix factorization (PMF), and stable isotope analysis in R (SIAR) were employed to interpret a large and complex water quality data set of the Qinhuai River catchment generated during 2015 to 2019 to monitor of 11 parameters at 29 different sampling sites. WQI analysis indicated that water quality in Qinhuai River catchment is considered to have "moderate pollution," and an improving trend of water quality was observed at the interannual scale. TN was the most deteriorated of all pollution parameters. CA and PMF results on the spatial scale revealed that sampling sites located at downtown of Nanjing and Lishui District or Jangling University town were highly polluted due to the sewage from domestic sewage and business service sewage (28.88%) as well as industrial wastewater (27.43%), while sampling sites located at Hushu Street Administrative District, Ergan River, and Sangan River were slightly polluted by rural domestic wastewater and garbage (28.79%), and agricultural non-point source pollution (24.3%). The middle-lower reaches (Jiangning Development Zone and Moling Street) and middle reaches (Lukou Street Administrative District) were moderately polluted by industrial wastewater (27.25%), sewage from domestic wastewater and business service wastewater (31.62%) as well as inner sources (24.76%). The SIAR results showed that NO3--N was the main nitrogen form, and the NO3--N mainly originated from sewage (61%) and soil (34%) in the Yuntaishan River sub-catchment. These results will aid in the development of measures required to control water pollution in river catchments.

Nutritional contribution of terrestrial organic carbon to four fish species in the Yellow River Estuary and adjacent coastal waters

Only a small amount of terrestrial organic carbon was found in the ocean organic carbon pool, though 0.40 Gt terrestrial organic carbon was transported to ocean via estuaries each year. This finding indicated that large quantity of terrestrial organic carbon was depleted in the estuaries and coasts, which provided additional materials and energy for the ecosystem. To investigate the material and energy supplement of terrestrial organic carbon transported by the Yellow River to the estuary and coastal system, the nutritional contribution of terrestrial organic carbon to four fish species: <italic>Acanthogobius ommaturus</italic>, <italic>Cynoglossus joyneri</italic>, <italic>Chaeturichthys stigmatias</italic>, <italic>Sardinella zunasi</italic>, was studied using multivariate analysis of similarity (MANOSIM) and stable isotope analysis in R (SIAR). In MANOSIM, the similarity carbon and nitrogen stable isotope in the temporal level was studied by the factors of species and seasons, and that in the spatial level was studied by the factors of species and stations. The similarity was judged by <italic>R</italic>. <italic>R</italic><0.25, similarity was high. 0.25≤<italic>R</italic>≤0.50, similarity was in the middle level. <italic>R</italic>>0.50, similarity was in the low level. In the study of SIAR, the nutritional sources of four fish species were considered as riverine, terrestrial and marine sources. The carbon stable isotope of riverine, terrestrial and marine source was (-30.0±0.4) ‰, (-26.0±0.4) ‰, and (-18.1±0.9) ‰ respectively. And the nitrogen stable isotope of riverine, terrestrial and marine source was (9.0±0.7) ‰, (1.0±0.7) ‰, and (6.0±1.2) ‰ respectively. Trophic enrichment factors (TEF) of carbon and nitrogen stable isotope was (1.1±1.3) ‰ and (2.8±1.4) ‰ respectively. We found that carbon and nitrogen stable isotope of four species showed no significant difference either in temporal level (<italic>R</italic>=0.08, <italic>P</italic><0.01) or in spatial level (<italic>R</italic>=0.19, <italic>P</italic><0.01) by MANOSIM. However, temporal and spatial variations of nutritional contribution of terrestrial organic carbon to four species were obvious. The nutritional contribution of terrestrial organic carbon was 8.7%, 7.3%, 4.3% and 32.0% higher in summer than that in autumn for <italic>Acanthogobius ommaturus</italic>, <italic>Cynoglossus joyneri</italic>, <italic>Chaeturichthys stigmatias</italic> and <italic>Sardinella zunasi</italic> respectively. And nutritional contribution of terrestrial organic carbon was 19.8%, 12.4%, 14.1% and 13.2% higher in estuary than that in coast for <italic>Acanthogobius ommaturus</italic>, <italic>Cynoglossus joyneri</italic>, <italic>Chaeturichthys stigmatias</italic> and <italic>Sardinella zunasi</italic> respectively. Temporal and spatial variations of Yellow River transporting terrestrial organic carbon may lead to variations.

Sources and transformation mechanisms of inorganic nitrogen: Evidence from multi-isotopes in a rural-urban river area

Multi-isotope tracers were applied to quantitatively reveal the sources and transformation mechanisms of inorganic nitrogen both spatially and seasonally in a complex land use area in China. Based on land use and the level of socioeconomic development, the study area was divided into four zones: the rural area, developed urban area, developing urban area and industrial urban area. The redox condition and isotope analysis results indicated that the nitrification process dominated in the Han and Rong River, which were characterized by ammonium nitrogen (NH4+-N) and oxidizing conditions, while neither nitrification nor denitrification occurred in the Lian River. The inorganic nitrogen sources of the four areas were revealed from the results of a stable isotope analysis in R (SIAR) and a two-component mixing model after determining the transformation mechanisms. In the rural area, nitrate nitrogen (NO3−-N) was mainly sourced from the increased fertilization of nitrogen fertilizer (42–56%) to farmland during the wet season, and from soil nitrogen (33–62%) related to increased nitrification during the dry season. In the urban area, the contributions of soil nitrogen, manure and sewage and industrial wastewater to the total inorganic nitrogen exhibited large seasonal and spatial differences, which were distinguished by the environmental management supported by gross domestic production (GDP). In the developed and developing urban areas, soil nitrogen contributed 41% and 47% of the NO3−-N, respectively, during the wet season, and 47% and 54%, respectively, during the dry season. The second highest contribution was from manure and sewage (30–41%) with no seasonal differences. In the industrial urban area, the dominant contribution to the NH4+-N was from manure and sewage (81%) during the wet season, but industrial wastewater (84%) in the dry season. Our findings elucidate the multiplex sources and transformation mechanisms of inorganic nitrogen, and promote the management of nitrogen tracing to control nitrogen pollution in complex land use areas.

Trophic interactions and metal transfer in marine ecosystems driven by the Peruvian scallop Argopecten purpuratus aquaculture

AbstractThis study investigates the trophic interactions and As and Cd transfer along seven marine ecosystems in Peru. Five of these ecosystems are driven by aquaculture of the Peruvian scallop Argopecten purpuratus. A southward increased gradient of δ15N was observed among the three examined regions along the Peruvian coast. The stable isotope analysis in R (SIAR)‐stable isotope mixing models helped to clarify the feeding ecology of A. purpuratus and its important predators (e.g., Bursa ventricosa, Romaleon setosum). The food items of A. purpuratus can be ranked in decreasing order of importance: seston &gt; sediment &gt; particulate organic matter (POM) &gt; brackish‐and‐fresh water POM input, while A. purpuratus itself was found to be the main prey item for predators. The highest trophic magnification factors (TMFs) were 1.46 and 1.07 for As and Cd, respectively, and were both found at the location in front of the Illescas Reserve Zone (northern Peru). Metal biomagnification and non‐biomagnification effects were found in the Peruvian marine food webs, but A. purpuratus always fitted the trophic metal magnification or bio‐dilution regression model as intermediate consumer and/or prey. The TMFs and linear metal relationships implied that As contamination is a serious concern in marine ecosystems in Peru.

Coupling stable isotopes to evaluate sources and transformations of nitrate in groundwater and inflowing rivers around the Caohai karst wetland, Southwest China

Nitrate is one of the most common pollutants in aquatic ecosystems, particularly in highly vulnerable karst aquifers. In Caohai Lake, an important karst wetland in southwestern China, karst surface water and groundwater are important recharge water sources, and nitrates flow into the wetland along with the surface water and groundwater, degrading the wetland water quality. Therefore, identifying the sources of nitrate in the surface water and groundwater in the Caohai catchment is of great significance to the protection of the wetland water environment. In this study, the nitrate concentrations, hydrochemistry and multiple stable isotope ratios (δ18O-H2O, δD-H2O, δ15N-NO3- and δ18O-NO3-) were used to identify the sources and fate of the NO3- in the groundwater and inflowing rivers around the Caohai wetland. The results showed that the NO3- concentrations in the groundwater samples from the southern side exceeded the WHO limit during the wet season, while other samples did not exceed the limit. The mean concentrations of NO3- in groundwater were higher than those in the inflowing river water, and NO3- concentrations decreased in the order of wet season>dry season>normal season in the groundwater and inflowing rivers. The hydrochemistry and multiple isotope ratios suggest that the nitrate transformation was dominated by nitrification processes, while denitrification had an influence on the transformation of NO3- (as evidenced by isotopes) in groundwater during the dry season. According to the analyses based on a stable isotope analysis in R (SIAR), sewage and manure were the main sources of NO3- in the groundwater, while sewage, manure and chemical fertilizer were the major sources of NO3- in the inflowing river water; therefore, the scientific use of farmland fertilizers and the treatment of domestic sewage should be strengthened to safeguard groundwater quality and control the NO3- concentrations in rivers.

Identify the Nitrate Sources in Different Land Use Areas Based on Multiple Isotopes

Different land uses have different impacts on the water quality of the region. Multiple isotopes (δD-H2O, δ18O-H2O, δ15N-NO3-, and δ18O-NO3-) and the SIAR (stable isotope analysis in R) model were applied to identify the nitrate sources and estimate the proportional contributions of multiple nitrate sources in a river in a typical urban area (the Grand Canal, Hangzhou) and a river in a typical forest and agricultural area (Yuying Riveri). The results indicated that there were different degrees of nitrogen pollution in the Grand Canal and Yuying River; NO3--N and NH4+-N are the predominant forms of nitrogen in the Grand Canal, and the primary form of nitrogen in Yuying River was NO3--N. There was an obvious linear relationship between the hydrogen and oxygen isotopes (R2=0.78). The δD-H2O and δ18O-H2O values for the Grand Canal and Yuying River were distributed along the local meteoric waterline, indicating that precipitation served as the primary water source in these rivers. All of the δ18O-NO3- values of the Grand Canal and Yuying River were lower than 15 ‰. It was revealed that nitrification, rather than denitrification, was the primary N cycling process in the two rivers. The δ15N-NO3-/δ18O-NO3- ratios of some of the samples from the Grand Canal ranged from 1.3 to 2.1, accompanied by low concentrations of DO and NO2-, indicating that denitrification existed in some sections of the Grand Canal. The δ15N-NO3- values of the samples from the Grand Canal (average:6.1‰) were higher than those from the Yuying River (average:2.3‰). The NO3- source contributions differed significantly between the Grand Canal and Yuying River. The contributions of NO3- sources in the Grand Canal were sewage/manure (37.0%) > soil nitrogen (35.7%) > chemical fertilizer (19.1%) > precipitation (8.2%), and those in the Yuying River were chemical fertilizer (46.1%) > soil nitrogen (22.8%) > precipitation (17.3%) > sewage/manure (13.8%). The contribution of the sewage/manure was substantially increased in the Grand Canal in the urban area with stronger human activities primarily due to the sporadic discharge of domestic sewage and urban runoff. Chemical fertilizer is the main NO3- source in the Yuying River near the forest and agricultural area, suggesting that the nitrogen pollution caused by agricultural non-point sources was extremely serious. The contribution of precipitation decreased in the areas of substantial human activities. The isotopic fractionation produced by denitrification was affected by the contributions of the NO3- sources, which were calculated by SIAR model. Sewage/manure and chemical fertilizer produced significant impacts, followed by soil nitrogen and precipitation.