1,720,987 research outputs found
The early impact of agriculture : how humans have been affecting climate for thousands of years
No full textHumans have started shaping the environment since their very first agricultural activities. Whether this influenced climate before the industrial era is object of a lively scientific discussion. Climate changes in the Late Pleistocene – Holocene transition allowed an unprecedented geographic expansion and population growth due to the possibility of producing food. Although centers of early origin and expansion of agriculture are well documented worldwide, researchers highlight the lack of instruments and data for assessing the local and regional effects of deforestation and farming activities on climate. In this work, specific molecular markers for tracing past fire events and evaluating human and animal presence are individuated. Namely, polycyclic aromatic hydrocarbons (PAHs), monosaccharide anhydrides and fecal sterols are used as source specific and stable indicators in lacustrine environments. In the first part, specific analytical methods for detecting and quantifying the selected tracers in lake sediment cores are developed. In the second part, the proposed methods are tested and applied on target locations.
New Zealand is known to represent a particular site for the study of the ecological impacts of human settlement. It was occupied by Polynesian only 700-800 y BP and resulted in abrupt and huge landscape modifications. Here, the molecular marker methods were applied on samples from two lakes and results were compared with existing paleoecological records, proving their validity in order to confirm human presence and correlate it with intensity and frequency of fires. Results showed a dramatic increase in the fluxes of both fire and human tracers soon after the Māori arrival, consistent with intensive anthropogenic land clearance, as previously hypothesized from charcoal and pollen evidence. The European 19th century colonization is also evident in the flux of fecal sterols, that rapidly increased following the population growth.
Molecular tracers were further analyzed on test sample batches from Lake Victoria (Uganda) and Flinders Island (Tasmania). In Africa, increased fire activity is observed in correspondence with the drier periods documented by paleolimnological proxies. the influence of the eastward migration of the Bantu speaking populations in the last 2000 years is visible in the sterol record, that shows good correspondence with changes in vegetation and fire regimes. In Tasmania, fecal sterols vary in accordance with the human presence, that was intermittent along the last 10,000 years, although higher resolution would be required in order to draw more precise conclusions.
All results are presented, compared with literature data and interpreted according to paleoecological, anthropological and archaeological evidence, where possible.
This work provided a reliable and objective instrument for future studies oriented to the creation of a spatial and temporal high resolution database of the early human impact on landscape and climate
Organic Biomarkers of Fire in Tropical Australian Stalagmites of the Last Millennium
No full textFire plays a critical role in the ecology of the dry tropics of Western Australia, with ignition generated by human activities and lightning strikes. Attempts to understand temporal changes in rates of biomass burning are hampered by a sparsity of records that are continuous, provide clear evidence of fire at high temporal resolution, and span multiple centuries. Aragonite stalagmites from cave KNI-51, central Australian tropics, have been previously analyzed, with U/Th ratios providing a precise chronology and oxygen isotopic ratios providing a record of past Australian monsoon rainfall variability. We demonstrate that these stalagmites also contain polycyclic aromatic hydrocarbons (PAHs), organic molecules produced by combustion, including biomass burning, and characterized by high persistence in the environment. As such, these stalagmites may serve as a novel proxy for paleofire activity. Cave KNI-51 is shallow, contained within highly permeable rillenkarren limestone, and overlain by extremely thin, carbon-poor soils. PAH sequestration, biodegradation, or mobilization in thick soils and massive bedrock – issues that would complicate transmission of PAHs from the surface to the stalagmite - are minimized. Analysis of stalagmite mud layers, which are common in these samples and are derived from cave flooding events, reveal extremely low PAH concentrations and thus pose minimal or no risk of contamination of the aragonite carbonate. In addition, stalagmite growth rates are high (1-2 mm yr-1), and thus the stalagmites appear capable of recording fire events at ~annual scales. The analytical protocol we have developed for PAHs allows detection in stalagmites at the pg level by guaranteeing the lowest contamination. Samples are drilled from pre-cleaned stalagmite slabs and solvent-extracted in the organic cleanroom after acid digestion at cold temperature. A total of 19 different 2- to 6-ring PAH compounds are analyzed and quantified by GC-MS. Analysis of stalagmite layers deposited over the past millennium are underway, with preliminary data suggesting increased fire activity in the mid-15th century, marked in particular by the presence of fluoranthene, pyrene, benzo(e)pyrene and indeno(1,2,3-c,d)pyrene in the range 2-12 ng g-1
Multi-proxy biomarker determination in peat: Optimized extraction and cleanup method for paleoenvironmental application
No full textOrganic compounds stored in sedimentary archives, such as peat bogs, can provide information on numerous processes related to paleoenvironmental changes. The application of multi-proxy methods permits to overcome the limits imposed by reduced sample size, although complex matrices need particular attention to some analytical aspects. Here, we developed and validated a method for the simultaneous determination of 27 n-alkanes, 18 polycyclic aromatic hydrocarbons and 6 sterols in peat by optimizing the extraction and cleanup procedures. The method was evaluated in terms of accuracy, recovery, detection limits and according to green chemistry assessments. In the view of future application in high-resolution multi-proxy geochemical paleoenvironmental studies, it was applied to a test batch of eight samples from the Coltrondo ombrotrophic peatland, located in northern Italy. The multi-proxy approach allowed extracting less than 1 g of dry sample. The stability of proxies over time was assessed by analyzing samples in a wide time and depth range. Results were in agreement with existing historical records and represent the first peat biomarker data for the area
GC-MS method for determining faecal sterols as biomarkers of human and pastoral animal presence in freshwater sediments
No full textIn order to determine sterols and stanols in freshwater sediments to reconstruct the past presence of humans and pastoral animals, we developed an analytical method based on pressurised liquid extraction (PLE), clean-up performed using solid phase extraction (SPE) and sterol determination using gas chromatography–mass spectrometry (GCMS)analysis.PLEextractionconditionswereoptimisedusing dichloromethane (DCM) and DCM/methanol mixtures. Clean-up was performed with 2 g silica SPE cartridges, and the concentrated extracts were eluted with 70 mL DCM. Extraction yield was evaluated using an in-house reference material spiked with 13C-labelled cholesterol and aged for 10 days. In comparison with pre-extraction, where the sediment is extracted and then spiked with a known analyte concentration,thisapproachpreservestheoriginalcompositionof the sediment. DCM and DCM/methanol mixtures resulted in high extraction yields ranging from 86 to 92 % with good reproducibility (relative standard deviation (RSD) 5–8 %). PLE extraction yields obtained with DCM as the extracting solvent were about 1.5 times higher than extractions using an ultrasonic bath. The solvent extraction mixture and matrix composition stronglyaffectedthe solvent extractioncompositionwhere higheroverall recoveries (70–80%)for eachcompound were obtained with DCM. The extraction mixture and
matrix composition also affected the analyte concentrations, resulting in a method precision ranging from 1 to 18 %. Diatomaceous earth spiked with 10 to 100 ng of sterols, and environmental samples fortified with suitable amounts of sterols provided apparent recovery values ranging from 90 to 110%.Weappliedthemethodtoenvironmentalsamplesboth close to and upstream from sewage discharge zones, resulting in substantially higher faecal sterol(FeSt)concentrations near the sewage. In addition, we also applied the method to a 37cm freshwater sediment core in order to evaluate its applicability for obtaining vertical sterol profiles
Fire and human record at Lake Victoria, East Africa, during the Early Iron Age: Did humans or climate cause massive ecosystem changes?
Full text linkOrganic molecular markers determined in a sediment core (V95-1A-1P) from Lake Victoria (East Africa) were used to reconstruct the history of human
impact and regional fire activity during the Early Iron Age (~2400 to ~1100 yr BP). Fire history was reconstructed using levoglucosan and polycyclic
aromatic hydrocarbons (PAHs) as markers for biomass burning that demonstrate two distinct fire periods peaking at 1450–1700 and 1850–2050 cal. yr
BP. A partial correlation between levoglucosan and PAHs is interpreted as different transport behaviors and burn temperatures affecting the proxies. A
fecal sterol index (CoP-Index) indicates the presence of humans near the lakeshore, where the CoP-Index lags a few centuries behind the fire peaks. The
CoP-Index peaks between 1850 and1950 cal. yr BP and between 1400 and 1500 cal. yr BP. Retene, a PAH that indicates softwood combustion, differs
from other PAHs and levoglucosan by abruptly increasing at ~1650 cal. yr BP and remaining high until 1200 cal. yr BP. This increase may potentially signal
human activity in that the development of metallurgy and/or ceramic production requires highly efficient fuels. However, this increase in retene occurs
at the same time as severe drought events centered at ~1500 and ~2000 yr BP where the droughts and associated woodland to grassland transition may
have resulted in more intense fires. The grassland expansion could have created favorable conditions for human activities and triggered settlement growth
that in turn may have created a positive feedback for further landscape opening
Multi-biomarker analysis of sediments for paleoclimate research
Full text linkLacustrine sedimentary cores provide continuous records of large-scale and local environmental modifications, intelligible thanks to specific organic markers that accumulated in these archives during past millennia. In order to improve our knowledge on ecosystem changes due to biomass burning events and human presence during the Holocene, an effective analytical method to detect organic compounds contained in sediment samples is needed.
We used Accelerated Solvent Extraction (ASE) technique followed by analysis with gas and liquid chromatographers coupled with mass spectrometers (GC-MS, IC-MS). The extraction of the molecules of interest from the sediments is made with a mixture of DCM:MeOH 9:1 v/v and it is followed by a 3 steps purification with silica gel columns. The first fraction is eluted with HEX:DCM 9:1 v/v and contains n-alkanes, indicators of vegetation, and polycyclic aromatic hydrocarbons (PAHs) as combustion proxies. Then, a second fraction is eluted with DCM and derivatized with the silylation process, in order to get the faecal sterols and stanols (FeSts), indicators of past human and grazing animals presence. These two fractions are analysed with the GC-MS technique. The third and last fraction is eluted with MeOH and contains the monosaccharide anhydrides (MAs), specific indicators of vegetation burning processes, which are analysed with IC-MS. Internal standards labelled C13 are used for the quantification and procedural blanks are extracted every batch of 12 samples.
The method may undergo variations, on the basis of the complex sediment matrices which not always lend itself to the same kind of treatment. However, the technique was applied in different lakes from different continents and the obtained results, compared with historical and climate literature data, seem to demonstrate the potentiality of the method as a resourceful instrument to reconstruct past burning events and human-ecosystem interactions
Organic biomarkers characterisation in peat samples
No full textN-alkanes, n–alkanoic acids are synthesized as part of the epicuticular leaf wax of plants. They can be used as paleoenvironmental proxies thanks to stability and weak solubility in water, especially for the long chain n-alkanes that are present only in leaves. The study of modern plants shows a clear predominance of chains with odd carbon number in n-alkanes and of even chains in n-alkanoic acids: this information could be used as indicator of the origin of molecules (natural vs petrogenic) and of bacterial degradation. Characteristic n-alkanes fall in the range C15-C31: the distribution pattern and dominant chain lengths of n-alkanes and n- alkanoic acids can be used in a multi-proxy analysis in order to reconstruct the composition of plant population and climate fluctuations [1].\ud
Although the instrumental analysis of n-alkanes, normally performed by GC-FID, is widely employed, the characteristics of complex matrices such as peat require particular care in the extraction and purification procedures. In this work, GC-MS (Agilent 7890 – 5975c) methods for the detection of C10 to C36 n-alkanes and C11 to C24 n-alkanoic acids have been developed. The extraction was carried out by Pressurized Liquid Extraction PLE using a DCM:n-hexane mixture. Extracts were subsequently concentrated under a gentle stream of nitrogen and the clean- up was performed on silica gel SPE cartridges, collecting an apolar and a polar fraction separately, by eluting samples with a mixture of n-hexane:DCM followed by DCM:MeOH. Literature data often report palmitic and stearic acids as dominant species in samples, but rarely blank values are discussed [2]. In the present work, large amounts (ng to tens of ng) of C16 and C18 have been detected in laboratory blanks and mainly in SPE tubes, therefore requiring a strong conditioning with 40 mL of each solvent. The fractions were re-concentrated to about 100 μL and, before GC-MS analyses, the polar fraction was derivatized at 60°C. The method was finally tested on a small batch of samples from a peat bog located in the Dolomites
Organic proxies in speleothems: analytical method and first data from cave KNI-51
Full text linkSpeleothems are important archives for paleo environments thanks to their high temporal resolution and potential for precise and accurate dating. Organic biomarkers in speleothems are not widely explored because of low concentrations and high sample amount required to obtain detectable levels. The potential for paleoenvironmental reconstruction from organic molecules in speleothems is high, but low contamination and high sensitivity analytical tools are required to obtain well resolved and reliable records. We developed a method for the analysis of fire-derived polycyclic aromatic hydrocarbons (PAHs) and nalkanes in speleothems and applied it to aragonite stalagmites from cave KNI-51 in the central Australian tropics. These stalagmites have already been precisely dated by U/Th methods, and have detailed oxygen isotopic time series that provide a detailed record of past Australian monsoon rainfall variability [1]. The characteristics of the cave make it suitable for this research, thanks to the considerably high growth rates of the stalagmites (1-2 mm yr-1), that allow analysis at an annual resolution. In addition, cave KNI-51 is shallow, contained within highly permeable rillenkarren limestone, and overlain by extremely thin, carbon-poor soils. Thus, the sequestration, biodegradation, or mobilization of PAHs and n-alkanes in soils and bedrock are minimized, allowing them to be easily transported from the surface to the stalagmite. In order to check for the risk of contamination of the aragonite layers during flooding episodes, we also analyzed sediments from above and inside the cave. Results show that flood sediments do not bias our analyses of carbonate material. With respect to the few existing methods for PAH analysis in speleothems [2, 3], some substantial modifications were made to the pre-analytical phase, all of which were aimed at increasing the analytical signal: our analytical protocol allows detection of analytes in stalagmites at the ng to sub-ng level by guaranteeing the lowest contamination. Samples are drilled from pre-cleaned stalagmite slabs, dissolved in HCl at low temperature, solvent-extracted and volume reduced in a class 10,000 organic cleanroom. 19 different 2- to 6-ring PAH compounds and 26 n-alkanes (C10-C35) were analyzed and quantified by GC-MS. Preliminary results suggest increased fire activity in the mid-15thcentury, marked in particular by the presence of fluoranthene, pyrene, benzo(e)pyrene and indeno(1,2,3-c,d)pyrene. Only high molecular weight n-alkanes in the range C23-C32 had significant concentrations in most samples, showing no marked odd-even predominance, likely indicating the presence of another source beside plant residues in soil
Persistent Organic Pollutants (POPs) in Antarctica: Occurrence in continental and coastal surface snow
Full text linkDespite geographical isolation and almost complete absence of human settlements, Antarctica is affected by Persistent Organic Pollutants (POPs): the traces of these impacts are recorded in the snow. Although POPs were detected in Antarctica decades ago, there are still large knowledge gaps and a comprehensive understanding of their fundamental patterns is lacking. In this study, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs, including the non-Aroclor PCB-11), polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) were measured in surface snow samples from five selected locations of Northern Victoria Land. To our knowledge this is the first study providing ground-based measurements of PCDD/Fs, PCB-11 and PBDEs in Antarctic surface snows, including the plateau. Long-range atmospheric transport (LRAT) followed by regional redistribution were hypothesized as governing sources of POPs to the Antarctic Plateau, but also local pollution from human activities was found. Sub-pg L− 1 levels of PCDD/Fs were detected in the coastal samples, while PCBs (ΣPCBs 110-580 pg L− 1) generally showed a decrease with respect to the past decades. Similar concentrations of PBDEs (ΣBDEs 130–340 pg L− 1) were found, mainly attributable to the congeners BDE-47 and BDE-99. PAHs (ΣPAHs 0.65–140 ng L− 1) were the most abundant compounds in all sites with an unexpected high value near a refueling point. Possible source areas of contamination were investigated by means of the HYSPLIT model
Plant Residues as Direct and Indirect Sources of Hydrocarbons in Soils: Current Issues and Legal Implications
No full textPlant residues are the main source of organic matter in soil; this process takes place naturally in forests and with organic amendments in farmlands. Terrestrial plants also synthesize hydrocarbons. Typically, angiosperms contain hundreds to thousands of milligrams of long chain n-alkanes per kilogram in leaf waxes. However, petroleum pollution is a worldwide issue, and different national regulations set the guideline limit for petroleum hydrocarbons in green areas at 50 mg kg-1. Focusing on the Italian legislation as a case study, we hypothesized that direct or indirect high inputs of plant residues could lead the level in the soil to exceed this limit, resulting in a false positive petroleum contamination. Therefore, we investigated the occurrence of hydrocarbons in soils with different inputs of natural or farming biomasses. The highest total petroleum hydrocarbon (TPH) concentrations were found in background soils from protected woodlands, remarkably with most samples resulting in levels above the guideline limit. Similarly, the TPH concentrations in agricultural soils amended with compost and digestate were higher than those in samples of soil in which only chemical fertilizers were used. n-Alkane carbon preference indices underlined the role of plant residues as a source of hydrocarbons in these samples, clearly distinguishing spiked petrogenic contamination. Possible revisions of the regulatory and analytical methods are then discussed
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