In April 2010, approximately 4.9 million barrels of oil were accidentally released into the Gulf of Mexico during the Deepwater Horizon Macondo Mc252 Oil Spill. Some of the surface oil was carried by prevailing winds and currents and reached the coast of Louisiana impacting marsh and marine ecosystems. One and a half years after this incident, a set of oiled marsh samples (2 grab samples) coupled with nearby subtidal and intertidal cores (12 cores) were collected from Barataria Bay, Louisiana to determine the probable source of petroleum residues present and to characterize the chemical composition of the oil. Plus, pre-spill core which was collected from Barataria Bay in 2007 was analyzed to identify the background hydrocarbon composition of the area. Polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), biomarker, and stable carbon isotope compositions of selected samples were detected using a GC-MS and an elemental analyzer Conflo system coupled to a DeltaPlusXP isotope ratio mass spectrometer. The comprehensive chemical data allowed us to classify the pre and post-spill samples into 4 Groups. According to this classification, Group 1 and Group 2 samples had the highest concentrations of petroleum-derived hydrocarbons. Group 3 and background samples, on the other hand, was dominated by biogenic signatures. Although a direct connection between the detected and spilled Macondo oils results are complicated due to confounding factors (e.g., already present hydrocarbons and weathering processes), our biomarker data indicates that both oils have similar signatures. This close genetic relationship was also identified by stable carbon isotope analysis. The impact of the Macondo Mc252 Oil Spill in Barataria Bay appears to be limited to areas closer to the source. The oil has undergone moderate weathering and has penetrated into, the at least, the top 9 cm sediments. Additionally, to examine the decadal-scale history of sedimentation in these marshes, a sediment core was analyzed for the radioisotope 137Cs. The observed sedimentation rate of 0.39 cm/yr shows that oil pollutant input into Barataria Bay has been ongoing for at least 50-60 years.

Igneous intrusion can change the geochemical and petrographic properties of sedimentary organic matter (such as coals and organic-rich clays or shales) including vitrinite reflectance, maceral petrographic composition, mineralogy, stable isotope composition, trace element composition, and bulk geochemistry. Igneous intrusions into coals and organic-rich rocks may have contributed to global warming in the geologic past by causing the release of greenhouse gases. Evidence for the release of large amounts of thermogenic CH4 from the organics would include significant;13Corg enrichment in the residual organic matter. However, 13Corg of thermally altered organic matter in coals and shales adjacent to intrusions often show negative shifts and, in some cases, ambiguous or positive trends. Previous studies have evaluated 13Corg of bulk samples rather than that of individual components, or macerals. As different macerals have different isotopic compositions, maceral-specific trends may be masked by variations in maceral composition of the whole-coal samples. It is important to explain the evolution of different geochemical and petrographic signatures in coals, coals macerals, and organic-rich sedimentary rocks close to an intrusion. This study evaluates the following three hypotheses: (1) thermally altered coals show different geochemical trends compared with coals that have undergone normal burial maturation; (2) if a large-scale release of 13C-depleted thermogenic CH4 resulted from intrusion of the coal, then it should have produced 13C-enriched coal and vitrinite macerals (the most abundant components of the coal) adjacent to the intrusion due to the release of light gases; and (3) 13Corg gets heavier with the increase in heat alteration approaching an intrusion due to the release of isotopically light gases. The current study reports petrographic, bulk geochemical (proximate, and ultimate), 13Corg data (whole-coal/shale samples and vitrinite macerals separated via density-gradient centrifugation, (DGC)), density data (vitrinite macerals), and Rock-Eval pyrolysis data for occurrences of thermally altered Springfield (No. 5) Coal (Pennsylvanian), Danville (No. 7) Coal (Pennsylvanian), and an organic-rich shale in the southern part of the Illinois Basin. Petrographic analysis shows an increase in vitrinite reflectance (Rm) from background levels of 0.55% up to ~4.80% in the Springfield (No. 5) Coal, 0.66% to 4.40% in the Danville (No. 7) Coal, and 0.71% to 4.78% for organic-rich shale; a loss of liptinite macerals, formation of isotropic coke and, at the intrusion contact, even development of fine-grained mosaic anisotropic coke texture. Volatile matter (VM) content decreases and fixed carbon (FC) content, ash, and mineral matter increase approaching the coal/intrusion contact. Carbon increases whereas nitrogen, hydrogen, and oxygen decrease approaching the intrusions. The presence of carbonate minerals (confirmed by X-ray diffraction and petrographic analysis) has a significant impact on proximate and ultimate data. However, even after removal of carbonates, trends for VM vs. vitrinite reflectance, %C vs. Rm, and H vs. C do not follow typical trends associated with normal burial coalification. Approaching the contacts, free oil content (S1), remaining hydrocarbon potential (S2), carbon dioxide from pyrolysis of the organic matter (S3), and hydrogen (HI) and oxygen (OI) indices decrease whereas thermal maturity (Tmax, ⁰C) increases. In addition, HI vs. VM, S2 vs. Rm, and Tmax vs. Rm diverge from pathways seen in previous studies. Trends in most of the Rock-Eval parameters in the organic-rich shale studied here are less clear due to the degree of variation in organic matter content, but a clear increase in thermal maturity (Tmax, C) is seen. There are no significant changes in 13Corg in the whole-coal samples (WCM) of the Springfield (No. 5) Coal (-25.28 / to -24.88 /), Danville (No. 7) whole coals (-25.37 / to -24.76 /), and in the DGC-separated vitrinites (-25.33 / to -24.96 /) of the Springfield (No. 5) Coal approaching the intrusion. However, the organic-rich shale transect shows a 1.31 / positive shift in 13C (from -25.06 / to -23.87 /) approaching the intrusion. DGC-separated vitrinite densities range from 1.268 g/mL in the unaltered coal to 1.523 g/mL at the coal/intrusion contact. For the vitrinite concentrates, density shows a clear correlation with Rm, %Cdaf, Hdaf, H/C, TOC, and 13Corg. These geochemical data suggest that these coals may have followed a different maturation track because of the geologically rapid heating associated with the intrusive event. It is also suggested here that the natural coke textures produced by such rapid geological heating may differ from those observed for metallurgical cokes produced under standard industrial coking conditions. Typically, in an industrial coke oven, a coal of this initial rank (Ro = ~ 0.6%) would produce an isotropic coke, rather than the fine-grained circular anisotropic coke seen here. The development of this texture may reflect differences due to heating rates or, alternatively, may indicate "pre-heating" of the coal during the intrusion event. Changes in the isotopic signatures are not of a magnitude that would be expected if significant thermogenic CH4 had been generated by the intrusive event. Moreover, there is no petrographic evidence for condensed or immobilized thermal products due to rapid pyrolysis (12C-rich pyrolytic carbon) close to the intrusion. These geochemical and petrographic data suggest there was only minimal CH4 generation associated with the rapid heating of the coals and organic-rich sedimentary rocks by the intrusion. In addition, there is no evidence for 13C-depleted condensed gas or pyrolytic carbon at the intrusion contact that could have moderated the isotopic signature. These data agree with previously reported data from this laboratory (Rahman et al., 2014, in review) and others (Gröcke et al., 2009; Yoksoulian, 2010) that indicate no clear evidence for large-scale CH4 generation due to the rapid heating or igneous intrusion in coals or sedimentary rocks.

The first Isaac carbonate (FIC) is a mixed siliciclastic-carbonate base-of-slope succession in the Neoproterozoic Windermere Supergroup (WSG). Outstanding outcrop exposure at three study areas provided an excellent opportunity to observe the stratigraphic and isotopic evolution of an ancient deepwater mixed turbidite system. Based on lithological and stratal dimensions, the FIC can be subdivided into lower and upper parts suggesting temporal changes in patterns of sediment transport and deposition. δ13Ccarb also changes from -5.2‰ at the base of the FIC to 2.5‰ in the middle and then decreases to -6.3‰ at the top. Notably, the δ13Ccarb of primary cement in FIC strata is substantially more positive than most other Neoproterozoic deep-marine sections, suggesting the retention of their original shallow-marine isotopic signature. Nevertheless, this trend potentially correlates with the EN2 excursion in China and therefore the Gaskiers glaciation (~580 Ma), although better age control of WSG is needed to corroborate this correlation.

Dissolved organic matter (DOM) is a complex mixture of organic compounds and represents the largest reservoirs of carbon (C) on earth. Particulate organic matter (POM) is another important carbon component in C cycling and controls a variety of biogeochemical processes. Estuaries, as important interfaces between land and ocean, play important roles in retaining and transforming such organic matter (OM) and serve as both sources and sinks of DOM and POM. There is a diverse array of both autochthonous and allochthonous OM sources in wetland/estuarine ecosystems. A comprehensive study on the sources, transformation and fate of OM in such ecosystems is essential in advancing our understanding of C cycling and better constraining the global C budget. In this work, DOM characteristics were investigated in different estuaries. Dissolved organic matter source strengths and dynamics were assessed in a seagrass-dominated subtropical estuarine lagoon. DOM dynamics controlled by hydrology and seagrass primary productivity were confirmed, and the primary source of DOM was quantified using the combination of excitation emission matrix fluorescence with parallel factor analysis (EEM-PARAFAC) and stable C isotope analysis. Seagrass can contribute up to 72% of the DOM in the study area. The spatial and temporal variation of DOM dynamics was also studied in a freshwated dominated estuary fringed with extensive salt marshes. The data showed that DOM was primarily derived from freshwater marshes and controlled by hydrology while salt marsh plants play a significant role in structuring the distribution patterns of DOM quality and quantity. The OM dynamics was also investigated in a mangrove-dominate estuary and a comparative study was conducted between the DOM and POM pools. The results revealed both similarity and dissimilarity in DOM and POM composition. The dynamics of both OM pools are largely uncoupled as a result of source differences. Fringe mangrove swamps are suggested to export similar amounts of DOM and POM and should be considered as an important source in coastal C budgets. Lastly, chemical characterizations were conducted on the featured fluorescence component in OM in an attempt to better understand the composition and origins of the specific PARAFAC component. The traditionally defined ‘protein-like’ fluorescence was found to contain both proteinaceous and phenolic compounds, suggesting that the application of this parameter as a proxy for amino acid content and bioavailability may be limited.

Long term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding potential nutrient impacts of increased freshwater delivery on coastal biogeochemistry. The present study sought to increase understanding of the coastal marine system of South Florida under modern conditions and through the anthropogenic changes in the last century, on scales ranging from individual nutrient cycle processes to seasonal patterns in organic material (OM) under varying hydrodynamic regime, to century scale analysis of sedimentary records. In all applications, carbon and nitrogen stable isotopic compositions of OM were examined as natural recorders of change and nutrient cycling in the coastal system. High spatial and temporal variability in stable isotopic compositions were observed on all time scales. During a transient phytoplankton bloom, ä15N values suggested nitrogen fixation as a nutrient source supporting enhanced productivity. Seasonally, particulate organic material (POM) from ten sites along the Florida Reef Tract and in Florida Bay demonstrated variable fluctuations dependent on hydrodynamic setting. Three separate intra-annual patterns were observed, yet statistical differences were observed between groupings of Florida Bay and Atlantic Ocean sites. The POM ä15N values ranged on a quarterly basis by 7‰, while ä13C varied by 22‰. From a sediment history perspective, four cores collected from Florida Bay further demonstrated the spatial and temporal variability of the system in isotopic composition of bulk OM over time. Source inputs of OM varied with location, with terrestrial inputs dominating proximal to Everglades freshwater discharge, seagrasses dominating in open estuary cores, and a marine mixture of phytoplankton and seagrass in a core from the boundary zone between Florida Bay and the Gulf of Mexico. Significant shifts in OM geochemistry were observed coincident with anthropogenic events of the 20th century, including railroad and road construction in the Florida Keys and Everglades, and also the extensive drainage changes in Everglades hydrology. The sediment record also preserved evidence of the major hurricanes of the last century, with excursions in geochemical composition coincident with Category 4-5 storms.

Cette thèse visait (i) à quantifier la variabilité de l’efficience d’utilisation de l’eau (WUE) chez le peuplier noir (Populus nigra L.), (ii) à juger de sa plasticité phénotypique en réponse à des contraintes hydrique et thermique et (iii) à juger des liens entre WUE, croissance et survie. A cette fin, des études à partir de semis, en chambre de croissance et en milieu naturel, ainsi qu’à partir de populations installées en dispositifs de pépinière ont été réalisées. Nos travaux ont permis de montrer une importante variabilité et une importante plasticité du caractère ‘efficience d’utilisation de l’eau’ quels que soient l’échelle d’étude, le fond génétique et les conditions de croissance. Une diminution de WUE a été observée en réponse à la contrainte thermique alors qu’une augmentation de WUE a été observée en réponse à un déficit hydrique modéré. Nos travaux démontrent également un lien entre WUE et la survie sous de fortes températures suggérant que sous ces conditions, une faible efficience d’utilisation de l’eau conférerait un avantage pour les individus. De plus in situ, un lien négatif entre WUE et la densité de régénération a été observé démontrant que les plus faibles valeurs de WUE sont observées pour les plus fortes densités. Le caractère ‘efficience d’utilisation de l’eau’ pourrait donc s’avérer un caractère limitant de la régénération de l’espèce dans des conditions d’augmentation de température ; une telle augmentation pourrait alors avoir une conséquence directe sur la structuration génétique des populations futures. Ces travaux suggèrent enfin une structuration géographique de la variabilité de WUE qui reste à confirmer à partir d’un plus grand nombre de populations. Ce travail ouvre des perspectives intéressantes pour l’identification des bases physiologiques à l’origine des variations de WUE, de sa plasticité et de sa structuration géographique. / This work aimed (i) to quantify variability of water-use efficiency (WUE) on black poplar (Populus nigra L.), (ii) to quantify the phenotypic plasticity in response to water deficit and increase of temperature and (iii) to precise the relationships between WUE, growth and leaf survival. Studies on seedlings in growth chambers and in natural conditions, and on populations established in common garden studies were realized. Significant variations and significant plasticity of water-use efficiency were observed on seedlings and adults whatever growth conditions and genetic background. A significant decrease of WUE was observed in response to increase of temperature while an increase of WUE was observed in response to moderate water deficit. Under elevated temperature a significant relationship was observed between WUE and leaf survival suggesting that low WUE confers an advantage for individuals under these conditions. Moreover in situ, a negative relationship between WUE and seedlings density was detected suggesting that low WUE are observed under high seedlings densities. The complex trait ‘water-use efficiency’ should be a limiting character of species establishment under increase of temperatures; this temperature elevation should have consequences on genetic structuration of populations in the future. Our results suggest a geographical structuration of WUE variability but results must be confirmed on several others populations. This present work opens prospects for identification of physiological bases of WUE variations, its plasticity and its geographical structuration.

Current Central American agricultural practices are environmentally and economically unsustainable, yet the ancient Maya who lived in the same region thrived for thousands of years. Archaeologists have attempted to understand the factors enabling the prolonged success and ultimate collapse of the Maya societies. Some have proposed that the karst seasonal wetlands, called bajos, that border many Maya sites in the region were an influential factor in the Maya's ability to flourish. For the past decade, researchers have used carbon isotope analyses to identify areas of ancient maize agriculture at Maya archaeological sites. In this study, we collected soil samples from bajos and upland areas at Tikal, one of the most prominent Maya sites, located in northern Guatemala, and analyzed the samples for evidence of past C4 vegetation. Our results confirm that bajos were utilized by the ancient Maya for long-term maize cultivation. Additionally, they suggest that modern agricultural methods in Guatemala that strategically utilize bajos may improve productivity and sustainability.

No description available.

Perennial ryegrass (Lolium perenne L.) is a cool-season turfgrass susceptible to low temperature injury. Wilt-based (WB) irrigation is a common practice in scheduling turf irrigation as an alternative to well-watered (WW). Moisture stress has been shown to promote cold hardiness but this has not been investigated in response to WB irrigation. Measurements of 13C isotope discrimination (DELTA) are useful predictors of water use efficiency (WUE), drought resistance, evapotranspiration (ET) and salinity tolerance but the relevance to turfgrass cold hardiness has not been determined. DELTA analyses may enable more efficient screening protocols in breeding for improved cold hardiness. Objectives of this study were to examine perennial ryegrass genotypes in relation to cold hardiness, DELTA and WUE in response to WW and WB irrigation schedules, to compare genetic diversity between top-performing (TP) and bottom-performing (BP) perennial ryegrass genotypes, and to assess the predictive value of DELTA of for cold hardiness. Six genotypes were selected based on turf quality from the most northern NTEP location (Orono, ME) and included three TP (‘All Star 2’, ‘Mach I’ and ‘Sunkissed’) and three BP (‘APR-1234’, ‘Buccaneer’ and ‘WVPB-R-82’) genotypes. ET, yield, WUE, shoot water content, rooting potential, wilting tendency, DELTA and median lethal temperatures (LT50) using whole-plant survival were measured from greenhouse samples grown in weighing lysimeters in 2007 and 2008. Plant measurements in both years were based on sampling conducted at the last cycle after 68-d of irrigation with 100% of ET applied at leaf-roll (WB) versus ET replacement every 4-d (WW). Lower LT50 values were generally associated with low yield, low WUE and low shoot water content, whether the result of irrigation treatment or genotypic variation. TP genotypes demonstrated significantly lower LT50 temperatures (greater cold hardiness) in comparison to BP genotypes in both years. Modest cold hardiness enhancement with WB irrigation was highest for TP genotypes. Wilting tendency and DELTA were not reliable predictors of cold hardiness, although individual TP genotypes exhibited responses distinctly different than some BP genotypes. Further research is needed to investigate the physiological mechanisms of enhanced turfgrass cold hardiness in response to moisture stress.

Yes / Cattle (Bos taurus) are biologically able to breed year-round, potentially giving farmers the freedom to choose a calving strategy to best meet their economic goals. Thus, an accurate method to determine cattle birth seasonality from archaeological remains would prove to be a valuable tool when investigating a prehistoric farming community. This paper presents the results of intra-tooth isotope ratio analysis (δ18O, δ13C) of first, second and third molars from 15 cattle. The principal outcome is a possible new approach to determining cattle birth seasonality utilizing both carbon and oxygen isotope ratio measurements of first molar enamel. Although this technique requires verification through more extensive testing, particularly of modern material, initial results suggest that it may produce more accurate predictions of birth seasonality than techniques based on intra-tooth δ18O measurements of second and third molars.