Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China

Eutrophication in coastal waters has been increasing remarkably,severely impacting the water quality in mariculture bays.In this study,we conducted multiple isotopic measurements on suspended particulate nitrogen(δ^(15)N-PN) and dissolved nitrate(δ^(15)N-NO_(3)^(-)and δ^(18)O-NO_(3)^(-)) in Zhanjiang Bay,a typical mariculture bay with a high level of eutrophication in South China,to investigate the changes in nitrogen sources and their cycling between the rainy and dry seasons.During the rainy season,the study found no significant relation between δ^(15)NPN and δ^(15)N-NO_(3)^(-)due to the impact of heavy rainfall and terrestrial erosion.In the upper bay,a slight nitrate loss and slightly higher δ_(15)N-NO_(3)^(-)and δ^(18)O-NO_(3)^(-)values were observed,attributed to intense physical sedimentwater interactions.Despite some fluctuations,nitrate concentrations in the lower bay mainly aligned with the theoretical mixing line during the rainy season,suggesting that nitrate was primarily influenced by terrestrial erosion and that nitrate isotopes resembled the source.Consequently,the isotopic values of nitrate can be used for source apportionment in the rainy season.The results indicated that soil nitrogen(36%) and manure and sewage(33%) were the predominant nitrogen sources contributing to nitrogen loads during this period.In contrast,the dry season saw a deficient ammonium concentration(<0.2 μmol/L) in the bay,due to nearly complete consumption by phytoplankton during the red tide period.Additionally,the significant loss of nitrate and simultaneous increase in the stable isotopes of dissolved and particulate nitrogen suggest a strong coupling of assimilation and mineralization during the dry season.More active biogeochemical processes during the dry season may be related to decreased runoff and increased water retention time.Overall,our study illustrated the major seasonal nitrogen sources and their dynamics in Zhanjiang B ay,providing valuable insights for formulating effective policies to mitigate eutrophication in mariculture bays.

Spatial distributions of organic carbon and nitrogen and their isotopic compositions in sediments of the Changjiang Estuary and its adjacent sea area

The spatial distribution patterns of total organic carbon and total nitrogen show significant correlations with currents of the East China Sea Shelf. Corresponding to distributions of these currents, the study area could be divided into four different parts. Total organic carbon, total nitrogen, and organic carbon and nitrogen stable isotopes in sediments show linear correlations with mean grain size, respectively, thus ＂grain size effect＂ is an important factor that influences their distributions. C/N ratios can reflect source information of organic matter to a certain degree. In contrast, nitrogen stable isotope shows different spatial distribution patterns with C/N and organic carbon stable isotope, according to their relationships and regional distributions. The highest contribution （up to 50%） of terrestrial organic carbon appears near the Changjiang Estuary with isolines projecting towards northeast, indicating the influence of the Changjiang dilution water. Terrestrial particulate organic matter suffers from effects of diagenesis, benthos and incessant inputting of dead organic matter of plankton, after depositing in seabed. Therefore, the contribution of terrestrial organic carbon to particulate organic matter is obviously greater than that to organic matter in sediments in the same place.

Analyzing biases of nitrogen contents and δ^(15)N values arising from acidified marine sediments with different CaCO_3 concentrations

In some studies, the researchers pretreated and measured organic carbon, nitrogen and their isotopes（δ^（13）C and δ^（15）N） of marine sediment together, to save costs and resources of analysis. However, the procedure of acidification to remove inorganic carbon for analysing δ^（13）C can affect the values of nitrogen and δ^（15）N, and the biases vary a lot depending on the CaCO_3 contents of sediments. In this study, the biases of total nitrogen（TN）and δ^（15）N values arising from acidified sediments were compared between the CaCO_3-poor（1%–16%） and CaCO_3-rich（20%–40%） samples. TN and δ^（15）N values were altered during acid treatment（without centrifugation） that possibly led to N-containing compounds volatilization. For CaCO_3-poor samples, acidification led to a range of 0%–40% TN losses and 0‰–2‰ shift in δ^（15）N values; and 10%–60% TN losses and 1‰–14‰ shift in δ^（15）N values for CaCO_3-rich samples. The biases from most samples exceeded the precision of the instrument（0.002% for TN and 0.08‰ for δ^（15）N）, and high biases could mislead our judgment for the environmental implication of the data. Thus,avoiding co-analysis of organic carbon, nitrogen and their isotopes（δ^（13）C and δ^（15）N） in sediments, even for CaCO_3-poor marine sediments, is necessary.

Determination of the geographical origin of Chinese teas based on stable carbon and nitrogen isotope ratios

The objective of this study was to investigate the geographical origin of Chinese teas using carbon and nitrogen stable isotope ratio technology.The results showed that inter-provincial dispersion of teas in Guangdong(GD),Guangxi(GX),Hainan(HA),Fujian(FJ),Shandong(SD),Sichuan(SC),Chongqing(CQ),and Henan(HN) provinces was high,while in Zhejiang(ZJ),Hubei(HB),Yunnan(YN),and Anhui(AH) provinces,it was low.Tea samples from GD,GX,HA,and FJ provinces were clustered in one group and separated from those from AH and HB provinces.Thus,carbon and nitrogen stable isotope ratio technology could discriminate teas from among some provinces of China,but not from among others.Better separation might be obtained with a combination of isotopic ratios and other indexes,such as elemental data and organic components.

The subsistence patterns of the Shengedaliang site(-4,000 yr BP)revealed by stable carbon and nitrogen isotopes in northern Shaanxi,China

In order to explore subsistence patterns in northern Shaanxi Province around 4,000 yr BP,28 human and 24 animal bones from the Shengedaliang site were sampled for stable carbon and nitrogen isotope ratio analysis.The results show that most people primarily subsisted on C_4 resources,e.g.millet and millet-related animal products,despite the fact that there was some intake of C_3 plants by some individuals.Stable nitrogen isotope values indicate that there were differences in meat consumption between individuals at the site.Pigs were mainly foddered with millet and millet byproducts,as well as some cattle,according to their highδ^(13)C values.However,most cattle and the sheep/goats consumed wild C_3 plants at Shengedaliang.Our above findings indicates that subsistence patterns in northern Shaanxi around 4,000 yr BP were characterized by millet farming,while the grassland animal husbandry,e.g.cattle and sheep/goats raising,displayed very little contribution to local economy.The intensive millet farming in northern Shaanxi provided enough food for population growth,ensured the accumulation of wealth,and consequently accelerated social differentiation and complexity.

The influence of agriculture in the process of population integration and cultural interaction during the Eastern Zhou Period in central-south, Inner Mongolia: Carbon and nitrogen stable isotope analysis of human bones from the Dabaoshan cemetery, Helingee

Central-south Inner Mongolia, China, is highly sensitive to the cultural interactions between sedentary agriculturalists and nomadic pastoralists during the Eastern Zhou Period(770–256 BC). The previous pattern of multiple cultures and diverse ethnic groups has been transformed to the increasingly dominated cultural system of Central Plain since the middle and late Warring States Period, when the states of Zhao and Qin have conquered the most parts of central-south Inner Mongolia.However, the variation of subsistence strategies during this historical process has never been evaluated. Particularly, as the typical representative of Central Plain cultures, the effect of intensive millet agriculture is still unknown in the process of population integration and culture interaction. Thus, to explore the shift of subsistence pattern, carbon and nitrogen stable isotope analysis of bone collagen from Dabaoshan site(410–180 BC) have been performed. The isotopic result indicates a large amount of C_4-based animal protein consumed by Dabaoshan humans. According to the archaeological backgrounds, we propose the Dabaoshan persons intensively relied on the millet agriculture and developed the agro-pastoral economy, which hinted the comprehensive influences from Central plain civilizations in late Warring States Period. Further compared with other published isotopic data in the same region during different periods, we suggest the millet agriculture has played the positive role in the process of population integration and culture fusion in central-south Inner Mongolia during the Eastern Zhou Period.

Sewage pollution in Negril, Jamaica: effects on nutrition and ecology of coral reef macroalgae

Coral reefs in the Negril Marine Park （NMP）, Jamaica, have been increasingly impacted by nutrient pollution and macroalgal blooms following decades of intensive development as a major tourist destination. A baseline survey of DIN and SRP concentrations, C：N：P and stable nitrogen isotope ratios （δ^15N） of abundant reef macroalgae on shallow and deep reefs of the NMP in 1998 showed strong P-limitation and evidence of increasing sewage pollution. In 1999, a sewage collection and treatment project began diverting wastewater from the resort and urban areas to a pond system that discharged partially-treated effluent into the South Negril River （SNR）. These sewage discharges significantly increased concentrations of NH2 and SRP （N：P -13） in the SNR, which flows into Long Bay and around Negril＇s ＂West End＂. Concentrations of SRP, the primary limiting nutrient, were higher on shallow reefs of the West End in 2001 compared to 1998. Stable nitrogen isotope ratios （δ^15N） of abundant reef macroalgae on both shallow and deep reefs of the West End in 2002 were significantly higher than baseline values in 1998, indicating an escalating impact of sewage nitrogen pollution over this timeframe. The increased nutrient concentrations and δ^15N enrichment of reef macroalgae correlated with blooms of the chlorophyte Chaetornorpha linum in shallow waters of Long Bay and Codium isthrnocladum and Caulerpa cupressoides on deep reefs of the West End. Sewage treatment systems adjacent to coral reefs must include nutrient removal to ensure that DIN and SRP concentrations, after dilution, are below the low thresholds noted for these oligotrophic ecosystems.

Food web structure and trophic levels in polyculture ricecrab fields

Stable carbon and nitrogen isotopes were used to investigate nutrient pathways and trophic relationships from the rice-crab system in Panjin, Liaoning Province, China. Values of 313C ranged from -27.38%±0.44%o to -18.34%±0.26%o and δ^15N ranged from 1.10%o4-0.88%o to 9.33%±0.57%. Pseudorasbora parva （Stone moroko） had the highest δ^13C and 8tSN values. The lowest δ^13C values were obtained for the macrophytes and the lowest δ^15N value was found in sediments. Stable carbon and nitrogen isotopes were used to determine the contribution of different food items to the diets of crabs. The δ^13C results indicated that the Pseudorasbora parva made the greatest contribution to the diet of Eriocheir sinensis （Chinese mitten crab）, while the δ^15N results indicated that most food items contributed more than 10% to the diet of the crab. There were three trophic levels identified in the system （Levels 0-2）. The crab Eriocheir sinensis, fish Pseudorasbora parva and Misgurnus anguillicaudatus （Oriental weatherfish）, and the oligochaete Limnodrilus hoffmeisteri （Limnodrilus worm）, were at the second level, zooplankton were at the first level and suspended particulate matter and macrophytes were at trophic position 0.

Tree-ring δ^(15)N of Qinghai spruce in the central Qilian Mountains of China:Is pre-treatment of wood samples necessary?

A knowledge of the tree-ring stable nitrogen isotope ratio(δ^(15)N)can deepen our understanding of forest ecosystem dynamics by indicating the long-term availability,cycling and sources of nitrogen(N).However,the radial mobility of N blurs the interannual variations in the long-term N records.Previous studies of the chemical extraction of tree rings before analysis had produced inconsistent results and it is still unclear whether it is necessary to pre-treat wood samples from specific tree species to remove soluble N compounds before determining theδ^(15)N values.We compared the effects of pre-treatment with organic solvents and hot ultrapure water on the N concentration andδ^(15)N of tree rings from endemic Qinghai spruce(Picea crassifolia)growing in the interior of the central Qilian Mountains,China,during the last 60 a.We assessed the effects of different preparation protocols on the removal of the labile N compounds and investigated the need to pre-treat wood samples before determining theδ^(15)N values of tree rings.Increasing trends of the tree-ring N concentration were consistently observed in both the extracted and unextracted wood samples.The total N removed by extraction with organic solvents was about 17.60%,with a significantly higher amount in the sapwood section(P<0.01).Theδ^(15)N values of tree rings decreased consistently from 1960 to 2019 in both the extracted and unextracted wood samples.Extraction with organic solvents increased theδ^(15)N values markedly by about 5.2‰and reduced the variations in theδ^(15)N series.However,extraction with hot ultrapure water had little effect,with only a slight decrease in theδ^(15)N values of about 0.5‰.Our results showed that the radial pattern in the inter-ring movement of N in Qinghai spruce was not minimized by extraction with either organic solvents or hot ultrapure water.It is unnecessary to conduct hot ultrapure water extraction for the wood samples from Qinghai spruce because of its negligible effect on the removal of the labile N.Theδ^(15)N variation trend of tree rings in the unextracted wood samples was not influenced by the heartwood-sapwood transition zone.We suggest that theδ^(15)N values of the unextracted wood samples of the climate-sensitive Qinghai spruce could be used to explore the ecophysiological dynamics while focusing on the long-term variations.

Nitrogen pollution and source identification of urban ecosystem surface water in Beijing

Nitrogen contamination of surface water is a worldwide environmental problem with intensive agricul- ture and high population densities. We assessed the spatial and seasonal variation in concentrations of total nitrogen and different nitrogen species present in surface-water in Beijing, China. Also, chemical （NO3-N/C1-） and isotopic （615Nnitrate） indicators were used to identify nitrate sources. The results showed that, during 2009 and 2010, nitrate nitrogen concentrations ranged from 0.7 to 7.6 mg· L^-1, ammonium nitrogen from 0. I to 3.4 mg· L^-1, and total nitrogen from 2.4 to 17.0mg· L^-1. Inorganic nitrogen accounted for between 60 and 100% of total nitrogen at the ten monitoring sites. Nitrate nitrogen, ammonium nitrogen, and total nitrogen concentrations at the 2 downstream monitoring sites in south-eastern Beijing were significantly higher than those at the other eight upstream monitoring sites （P 〈 0.01）. Examination of seasonal variation showed that there was a significant inverse relationship between nitrate nitrogen concentrations and precipitation, and that nitrate nitrogen concentrations peaked in the dry seasons. The information given by the 15Nnitrate values and nitrate nitrogen concentrations, combined with the NO3-N/C1- ratio distribution, showed that domestic sewage was the major source of nitrate in Beijing. Methods to control and reduce sewage pollution are urgently needed to help manage surface water quality in Beijing.

Resorption-related nitrogen changes in the leaves and roots of Larix kaempferi seedlings under nutrient-sufficient and nutrient-starvation conditions

Aims Larch is the dominant timber species in Northeast China.However,compared with the adjacent secondary forests,soil available ni-trogen(N)significantly declined in~40-year-old larch plantations.Thus,it is of great importance to determine how N use strategies in larch change in response to declining soil N availability.Methods We investigated the changes in N concentration and ^(15)N natural abundance(δ^(15)N)from 18 August to 25 October in the leaves,stems,branches and roots of 1-year-old Larix kaempferi seedlings under nutrient-sufficient(NSu)and nutrient-starvation(NSt)condi-tions with a pot experiment in Northeast China.Important Findings Stem and branch N concentrations exhibited upward trends,and leaf N concentration exhibited a downward trend.Root N concentration exhibited an upward trend under NSu conditions,but a downward trend under NSt conditions.These results suggested that stems and branches were served as N storage organs,but roots shifted from storage to resorption organs when switched from NSu to NSt.Leaf nutrient resorption was intensely occurred on 11 October,as indi-cated by the sharply decreased leaf N concentration and increased stem,root and branch N concentrations.Theδ^(15)N of roots,branches and leaves overlapped between NSu and NSt approximately on 11 October,which may be regulated by isotope discrimination dur-ing N resorption.Leaf N resorption efficiency under NSt(76.33%)was significantly higher than that of NSu(56.76%),indicating that nutrient stress stimulates leaf N resorption.Taken together,larch seedlings enhance leaf nutrient resorption and shift roots from nu-trient storage to nutrient resorption to adapt to NSt conditions.These changes might relieve the adverse effects of declining soil nutrient availability on seedling survival and regeneration.

Distribution and Sources of Organic Matter in Surface Sediments of the Karachi Coast,Pakistan

Under the steadily intensifying human activities in coastal areas,it is crucial to distinguish the sources of organic matter(OM)in sediments for better understanding of the environmental change.In this study,25 surface sediments collected along the harbor and creeks areas off Karachi coast were used for total organic carbon(TOC),total nitrogen(TN),stable carbon(δ^(13)C)and nitrogen(δ^(15)N)isotopic compositions,phytoplankton biomarkers(brassicasterol,dinosterol and cholesterol)and glycerol dialkyl glycerol tetraethers(GDGTs)analyses,to trace the distribution of OM and identify its sources.TOC,TN,δ^(13)C,and δ^(15)N are in the range of 0.04% to 5.28%,0.01% to 0.57%,-17.55‰ to -26.31‰,and 2.83‰ to 6.04‰,respectively.C/N values range from 4.24 to 21.04.The δ^(13)C,δ^(15)N,C/N,BIT(Branched Isoprenoid Tetraether)index together with phytoplankton biomarkers show both marine and terrestrial OM input to the creeks and Harbor stations.In contrast,the stations from Western Coast indicate a marine source predominance.A clearly impact of human activities is seen from sediments near river mouths.

Ammonia in urban atmosphere can be substantially reduced by vehicle emission control:A case study in Shanghai, China

To investigate the impact of emission controls on ammonia(NH_(3)) pollution in urban atmosphere, observation on NH_(3)(1 hr interval) was performed in Shanghai before, during and after the 2019 China International Import Expo (CIIE) event, along with measurements on inorganic ions, organic tracers and stable nitrogen isotope compositions of ammonium in PM_(2.5). NH_(3)during the CIIE period was 6.5±1.0μg/m^(3), which is 41% and 32% lower than that before and after the event, respectively. Such a decrease was largely ascribed to the emission controls in nonagricultural sources, of which contribution for measured NH_(3)in control phase abated by ~20% compared to that during uncontrol period. Molecular compositions of PAHs and hopanes further suggested a dominant role of the reduced vehicle emissions in the urban NH_(3)abatement during the CIIE period. Our results revealed that vehicle exhaust emission control is an effective way to mitigate NH_(3)pollution and improve air quality in Chinese urban areas.