Compound-specific isotopes of fatty acids as indicators of trophic interactions in the East China Sea ecosystem

The composition and compound-specific isotopes of fatty acids were studied within food webs in the East China Sea.Lipid-normalized stable carbon isotopes of total organic carbon had a good correlation with trophic level.Variations in fatty acid compositions among different species were observed but were unclear.Different dietary structures could be traced from molecular isotopes of selected fatty acids in the Shiba shrimp(Matapenaeus joyneri),the coastal mud shrimp(Solenocera crassicomis) and the northern Maoxia shrimp(Acetes chinensis).Both M.joyneri and S.crassicomis are mainly benthos feeders,while A.chinensis is a pelagic species,although they have a similar fatty acid composition.There was a good correlation for isotopes of arachidonic acid(C20:4n6;ARA) and docosahexaenoic acid(C22:6n3;DHA)among pelagic species from higher trophic levels.The isotopic compositions of DHA in benthic species were more negative than those of pelagic species at the same trophic level.The fact that the diet of benthic species contains more degraded items,the carbon isotopes of which are derived from a large biochemical fraction,may be the reason for this variation.A comparative study of benthic and pelagic species demonstrated the different carbon sources in potential food items and the presence of a more complex system at the watersediment interface.

Compound-specific hydrogen isotopes of long-chain n-alkanes extracted from topsoil under a grassland ecosystem in northern China

To investigate characteristics of H isotope variation in long-chain n-alkanes （δDn-alkanes） from higher plants in surface soils under a single ecosystem, 12 samples from a basalt regolith were randomly collected from Damaping in Wanquan County of Zhangjiakou in North China. Molecular distribution and C （δ^13Cn-alkanes） and H isotopes of long-chain n-alkanes, as well as C isotopes of TOC （δ^13CTOC）, were analyzed. Both δ^13CTOC and δ^13Cn-alkanes values from four representative dominant long-chain n-alkanes （n-C27, n-C29, n-C31, n-C33） derived from terrestrial higher plants show minor variations among the 12 samples, indicating the major contributor is from local grasses with a uniform C3 photosynthetic pathway. In contrast, variations in δ^13Cn-alkanes values of the four long-chain n-alkanes are relatively large, with the more abundant homologs generally showing more negative δDn-alkanes values and less variation. However, variation of 〈30‰ among weighted averaged δDn-alkanes values of the four long-chain n-alkanes is not only less than that among δDn-alkanes values for different modern terrestrial C3 grasses from the specific locations, but also less than the literature values of δDn-alkanes of long-chain n-alkanes for single species over different seasons. Thus, because the sources of long-chain n-alkanes in surface soils and sediments are similarly from multiple individual plants, our results are significant in confirming that paleoclimatic, paleoenvironmental and paleohydrological information can be interpreted more accurately from δDn-alkanes values of long-chain n-alkanes from sediments, particularly terrestrial sediments with organic matter derived from in-situ plants.

Variation in Solvent-Extractable Lipids and n-Alkane Compound-Specific Carbon Isotopic Compositions with Depth in a Southern China Karst Area Soil

Because literatures about the lipid compositions of modern soils in karst areas are scarce, we have studied the soil horizons overlying the Heshang （和尚） Cave that has provided paleoclimate records from speleothem lipid contents. Our analysis reveals a series of n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones distribution and relative abundance changing with the depth, and in which the ratios of the lower molecular weight to higher molecular weight n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones have a peak at a subsurface depth of 5 to 10 cm. An accompanying peakin 17β（H）, 21β（H）-hop-22（29）-ene （diploptene） and a shift to less negative n-alkane carbon isotopic values also identify this layer in the karst soil. This pattern indicates the existence of a subsurface soil layer in which the microorgan- isms that produce these compounds are espe- cially abundant. The carbon isotopic values of individual plant wax n-alkanes are about 3%0 greater at the base of the 30- to 40-cm soil profile than in the surface layer, probably as a result ofselective microbial degradation of n-alkanes from different primary sources. The lipids and carbon iso- topic values of individual plant wax n-alkanes study of the overlying soil show a strong microbial activity in this karst soil and help in interpreting the lipid compositions and specific carbon isotopic value of n-alkanes of the stalagmites of the Heshang Cave for paleoenvironmental reconstructions.

Developing an authentication approach using SPME-GC-IRMS based on compound-specific δ^(13)C analysis of six typical volatiles in wine

An analytical method using gas chromatography isotope ratio mass spectrometry(GC-IRMS)combined with solid phase micro-extraction(SPME)was developed to measure the 613C values of six typical volatiles commonly occurring in wine(isoamyl acetate,2-octanone,limonene,2-phenylethanol,ethyl octanoate and ethyl decanoate)for the first time.SPME selected with a divinylbenzene/carboxen/polydimethylsiloxane fiber was combined with the GC-IRMS for pretreatment optimization.The optimized SPME parameters of extraction time,extraction temperature and salt concentration were 40 min,40℃ and 10%,respectively.The 613C values measured by SPME-GC-IRMS were in good agreement with those measured via elemental analyzer(EA)-IRMS and GC-IRMS.The differences range from 0.02‰to 0.44‰ with EA-IRMS and from 0 to 0.28‰ with GC-IRMS,indicating the high accuracy of the method.This newly established method measured the precision within 0.30‰ and was successfully validated to discriminate imported real wine samples with identical label but amazing price differences from different importers.

Identification of the sources of polycyclic aromatic hydrocarbons based on molecular and isotopic characterization from the Yangtze estuarine and nearby coastal areas

Samples of suspended particulate matters （SPMs）, surface sediment and road dust were collected from the Yangtze estuarine and nearby coastal areas, coastal rivers, and central Shanghai. The samples were analyzed for the presence of 16 polycyclic aromatic hydrocarbons （PAHs） in the USEPA priority-controlled list by GC-MS. The compound-specific stable carbon isotopes of the individual PAHs were also analyzed by GC-C-IRMS. The sources of PAHs in the SPMs and surface sediments in the Yangtze estuarine and nearby coastal areas were then identified using multiple source identification techniques that integrated molecular mass indices with organic compound-specific stable isotopes. The results revealed that 3-ring and 4-ring PAH compounds were dominant in the SPMs and surface sediments, which are similar to the PAH compounds found in samples from the Wusong sewage discharge outlet, Shidongkou sewage disposal plant, Huangpu River, coastal rivers and central Shanghai. Principal component analysis （PCA） integrated with molecular mass indices indicated that gasoline, diesel, coal and wood combustion and petroleum-derived residues were the main sources of PAHs in the Yangtze Estuary. The use of PAH compound-specific stable isotopes also enabled identification of the PAHs input pathways. PAHs derived from wood and coal combustion and petroleum-derived residues were input into the Yangtze Estuary and nearby coastal areas by coastal rivers, sewage discharge outlets during the dry season and urban storm water runoff during the flood season. PAHs derived from vehicle emissions primarily accumulated in road dust from urban traffic lines and the commercial district and then entered the coastal area via the northwest prevailing winds in the dry season and storm water runoff during flood season.

A Forensic Approach for Assessing Modes of Subsurface Petroleum Releases

Chronic petroleum discharges resulting from underground storage tank (UST) system failures may continue for months or years, whereas catastrophic releases result from structural failures or overfills that occur over shorter time periods. A forensic analytical framework is useful for distinguishing between chronic and catastrophic releases and identifying responsible parties. However, the forensic program must account for the petroleum type because identifying release modes relies on understanding the chemical evolution of petroleum through time within the context of site conditions. Here we discuss key petroleum components that aid in reconstructing the release and identifying potential responsible parties when subsurface conditions are known.

Novel sediment source fingerprinting quantifying erosion-induced total nitrogen and total phosphorus outputs from an intensive agricultural catchment,North China

Intensive farming is a primary cause of increased sediment and associated nitrogen(N)and phosphorus(P)loads in surface water systems.Determining their contributing sources,pathways and loads present major challenges in the high-intensity agricultural catchments.Herein,we quantify the sediment sources and magnitude of sediment total N and total P from different sources using a novel application of compound-specific stable isotope(CSSI)and fallout radionuclides(FRNs)of^(137)cs and^(210)pbex in an intensive agricultural catchment in North China.Sediment sources from surface and sub-surface soils were estimated from FRNs fingerprint and accounted for 62±7%and 38±7%respectively,while surface soil from land uses that originated from hillslope were identified by CssI fingerprint.Using a novel application of FRNs and CSSI sediment fingerprinting techniques,the dominant sediment source was derived from maize farmland(44±0.1%),followed by channel bank(38±7%).The sedimentation rate(13.55±0.30 t ha^(-1)yr^(-1))was quantifed by the^(137)cs cores(0-60 cm)at the outlet of this catchment.The total N and total P in sediment were both mostly derived from maize farmland and least from channel banks.The channel banks are significant sediment sources but contribute little to the input of sediment N and P for eutrophication.It implies that chemically-applied farmlands are the main hotspots for catchment erosion control and pollution prevention.The novel application of FRNs and CSSI techniques cost-effectively quantified sediment N and P loads from different sources with a single visit to the catchment,enabling rapid assessment for optimizing soil conservation strategies and land management practices.

A New Approach to Reconstruct Paleogene Atmospheric Hydrology at High Latitudes

Reconstruction of ancient atmospheric conditions through the analysis of precipitation patterns is a novel endeavor in the study of paleoclimate. A new approach is now available for a quantitative reconstruction of Paleogene atmospheric hydrological conditions in High Arctic. It is based on 1） the discovery of exceptionally-preserved Paleogene plant fossils from the Canadian Arctic which yielded in situ labile biomolecules 2） the development of compound-specific hydrogen isotope analysis which can be applied to small amount of plant material and 3） taxon-specific apparent hydrogen isotope fractionation factors obtained from empirical measurement. A new moisture recycling model is established to explain the reconstructed paleohydrologic pattern in the High Arctic during Paleogene.

Catchment environmental change over the 20th Century recorded by sedimentary leaf wax n-alkane δ^(13)C off the Pearl River estuary

The compound-specific stable carbon isotope compositions(δ^(13)C) of leaf wax n-alkanes from two short sediment cores recovered off the Pearl River estuary(PRE) were analyzed to check for their capability of indicating decadal scale catchment environmental change. Sedimentary long-chain n-alkanes exhibited an odd-over-even predominance, with a maximum at n-C_(29) or n-C_(31), indicating their leaf wax origin was from vascular plants. The δ^(13)C values of C_(29) and C_(31) n-alkane in all the sediment samples were in the range of -28.8‰ to -31.2‰, consistent with the C_3 plant-dominated vegetation in the Pearl River catchments. The time series of δ^(13)C records from the two cores were comparable and displayed a decreasing trend from the early 20 th century to the end of the 1970s, followed by a reversal in that change leading to continued increase for ca. 15 years. After being corrected for the effect of atmospheric CO_2 rise and δ^(13)C_(atm) decline, the δ^(13)C_(29) records largely retained their raw changing pattern; the post-1980 increase being more conspicuous. The slightly decreasing trend in corrected δ^(13)C records before around 1980 may have been caused by an increase in precipitation, whereas the subsequent increase of δ^(13)C is likely associated with the observed dry climate and/or intensive anthropogenic deforestation. Our results thus demonstrate that leaf wax n-alkanes buried in the sediments off the PRE may well reflect change in the regional climate and/or human activity in the river catchments over the past century.