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991.
Andrew S. Carr Arnoud Boom Brian M. Chase David L. Roberts Zoë E. Roberts 《Journal of Paleolimnology》2010,44(4):947-961
Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter.
In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic
matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon
(TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape
coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this
semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence
analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation.
Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and
are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface
sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers,
plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by
distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs
of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ13C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated
with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated
with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio
are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has
potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental
proxy variables in sediments may be lacking or equivocal. 相似文献
992.
Francesca Mietta Claire Chassagne Andrew J. Manning Johan C. Winterwerp 《Ocean Dynamics》2009,59(5):751-763
The purpose of this paper is to establish a relation between a few measurable quantities (the so-called ζ potential, organic matter content, and shear rate) and the flocculation behavior of mud. The results obtained with small-scale
flocculation experiments (mixing jar) are compared to results of large-scale experiments (settling column). The mud used for
all experiments has been collected in October 2007 in the lower Western Schelde, near Antwerp, Belgium. From this study, it
was found that the mean floc size and the Kolmogorov microscale vary in a similar way with the shear rate for suspensions
with different pH and salt concentrations. The size of flocs at a given shear rate depends on the properties of the suspension,
which affect the electrokinetic properties of the sediment; these can be described by means of the ζ potential. The main findings of this paper are: (1) In saline suspensions at pH = 8, the mean floc size increases when the
salt concentration and the ζ potential increase. (2) For a given ζ potential, the mean floc size at low pH is larger than observed at pH = 8 for any added salt. (3) The mean floc size increases
with increasing organic matter content. (4) Mud with no organic matter at pH = 8 and no added salt flocculates very little.
The response of mud suspensions to variations in salinity and pH is similar to that of kaolinite. This suggests that a general
trend can be established for different and complex types of clays and mud. This systematic study can therefore be used for
further development of flocculation models. 相似文献
993.
Danny Redo J.O. Joby Bass Andrew C. Millington 《Applied geography (Sevenoaks, England)》2009,29(1):91-110
Analyses of landscape change using remotely sensed satellite imagery constitute a large component of forest transition research, allowing for assessments of large areas. In the western highlands of Honduras is an area of complex forest dynamics (~45,000 ha) that has seen significant forest regeneration in recent years. However, analysis of the larger region (~500,000 ha) shows net forest loss. The comparative aspects highlight the importance of site selection and scale in forest transition analysis, a process often ignored in the land-use and land-cover change (LULCC) and forest transition literature. Results also highlight the importance of analyzing human-induced fragmentation at a variety of selected sites and a range of spatial scales, and producing quality, accurate forest cover and change maps. 相似文献
994.
Lake sediments can be significantly impacted by industrial activities. These impacts vary among sites and include both local
point sources and atmospherically-derived pollution. Here we present results of a lake sediment pollution record from Ullswater,
UK, where lead mining activities have taken place within the catchment since 1690, although large-scale mining did not begin
until 1840. Metal concentration data from 12 cores taken along a lake bed transect illustrate that lead mining at Greenside
Mine had a significant impact on the lake sediments. High Pb concentrations were identified throughout Ullswater, and exhibited
a spatial gradient from south to north, with concentrations decreasing with greater distance from the main source of input
at Glenridding. Furthermore, inter-element correlations exhibit spatial variation that reflects the processes by which they
are incorporated into the lake sediment record. Together, these observations illustrate potential shortcomings in palaeoenvironmental
reconstructions and pollution studies based on single cores from large and morphologically variable lakes. Sedimentation rates
were estimated by matching this pollution record with the historical record of mining activities. Within Ullswater, sedimentation
rates from 1840 to the present varied from 0.67 to 2.33 mm year−1 with a mean of 1.4 mm year−1; highest sedimentation rates were observed in the deepest section of the lake and close to the main inputs, and lowest sedimentation
rates were observed in the northern part of the lake, furthest from the main input. Despite the considerable changes in mining
techniques and production, there is little evidence to suggest significant changes in sedimentation rates over time. 相似文献
995.
Mengnjo Jude Wirmvem Takeshi Ohba Linus Anye Nche Brice Tchakam Kamtchueng Wiylahnyuy Edith Kongnso Mumbfu Ernestine Mimba Tasin Godlove Bafon Muga Yaguchi Gloria Eneke Takem Wilson Yetoh Fantong Ako Andrew Ako 《Environmental Earth Sciences》2017,76(9):354
High water demand for domestic use in Douala with over 3 million inhabitants is met mainly by shallow groundwater. Field measurements and water sampling in January 2015 were carried out to examine the major controls on the groundwater composition and spatial view of ions in the water, timing of recharge and link between the recharge process and quality of the water. Fifty-two water samples were analysed for major ions and stable hydrogen and oxygen isotopes. Low pH values (3.61–6.92) in the groundwater indicated an acidic aquifer; thus, prone to acidification. The dominant water type was Na–Cl. Nitrate, which exceeded the WHO guide value of 50 mg/l in 22% of the groundwater, poses a health problem. Mass ratios of Cl?/Br? in the water ranged from 54 to 3249 and scattered mostly along the mixing lines between dilute waters, septic-tank effluent and domestic sewage. A majority of the samples, especially the high NO3 ? shallow wells, clustered around the septic-tank effluent-end-member indicating high contamination by seepage from pit latrines; hence, vulnerable to pollution. Stable isotopes in the groundwater indicated its meteoric origin and rapid infiltration after rainfall. The δ18O values showed narrow ranges and overlaps in rivers, springs, open wells and boreholes. These observations depict hydraulic connectivity, good water mixing and a homogeneous aquifer system mainly receiving local direct uniform areal recharge from rainfall. The rapid and diffused recharge favours the leaching of effluent from the pit toilets into the aquifer; hence, the high NO3 ? and Cl? in shallow wells. Silicate weathering, ion exchange and leaching of waste from pit toilets are the dominant controls on the groundwater chemistry. Drilling of deep boreholes is highly recommended for good-quality water supply. However, due the hydraulic connection to the shallow aquifer, geochemical modelling of future effects of such an exploitation of the deeper aquifer should support groundwater management and be ahead of the field actions. 相似文献
996.
This study uses 3D seismic reflection dataset to investigate the time-integrated growth and degradation of fault-propagation folds and associated slump deposits in the deepwater Niger Delta. The results of the analysis showed that slump deposits are sourced almost entirely from the degradation of growing fold crests—resulting in the development of seaward-facing scarps on the forelimbs of these folds. The scarps develop parallel to fold axes and have dips that range between 4° SW and 20° SW. The constant presence of fan-shaped slump deposits downdip of these scarps suggests a direct relationship to fold crest degradation. Moreover, the spatio-temporal distribution of the slumps also shows a direct relationship with the heights of seabed scarps along the strike of growing folds. Slumps have short run-out distances (generally less than 5 km); however, they also travel long distances downslope (up to 10 km) across growing structures by exploiting relay areas between growing scarps. 相似文献
997.
John P. Craddock Suzanne D. Craddock Alex Konstantinou Andrew R.C. Kylander-Clark David H. Malone 《地学前缘(英文版)》2017,8(6):1357-1384
We report the calcite twinning strain results of a traverse across the Grenville orogen from Parry Sound, Ontario (NW) to Ft. Ann, New York (SE), including the younger, adjacent Ordovician Taconic allochthon. Fifty four carbonates (marbles, calcite veins, Ordovician limestone) were collected resulting in 68 strain analyses on mechanically twinned calcite (n = 2337 grains) across the Central Gneiss Belt (CGB; 3 samples), the Central Metasedimentary Belt (CMB; 27 samples), the Central Granulite Terrane (CGT; Adirondack's; 13 samples) and the Ottawan Orogenic Lid (OOL; 11 samples). Twinning strains in the greenschist-grade OOL marbles preserve N–S shortening and U-Pb titanite ages (~1150 Ma; n = 4) document these marbles formed during the Shawinigan (1190–1140 Ma) part of the Grenville orogen. From northwest to southeast, the Ottawan (1095–1020 Ma) twinning strain is dominantly a layer-parallel shortening fabric oriented N–S (Parry Sound), then becomes parallel to the Grenville thrust direction (NW–SE) across the CMB to the Adirondack Highlands where the sub-horizontal shortening strain becomes margin-parallel (SW–NE). Within the regional sample suite there are two areas studied in detail, the Bancroft shear zone (n = 11) and a roadcut on the southeast side of the Adirondack Mountains (Ft. Ann, NY; n = 8). Marbles from the Bancroft shear zone contain calcite grains with 2 sets of twin lamellae (e1 and e2). The better-developed e1 sets (n = 406) record a horizontal fabric oriented NW–SE whereas the younger e2 lamellae (n = 146) preserve a margin-parallel (SW–NE) horizontal fabric. Both the e1 and e2 strains record an overprint vertical shortening strain (NEV), perhaps related to extensional orogenic collapse. We also report an Ottawan orogen-aged granoblastic mylonite (1093 Ma, U-Pb zircon; 1102 Ma Ar-Ar biotite) in the Keweenaw thrust hanging wall 500 km inboard of the Grenville front and interpret the relations of Grenville-Keweenaw far-field dynamics. 相似文献
998.
Stacey C. Priestley Daniel L. Wohling Mark N. Keppel Vincent E. A. Post Andrew J. Love Paul Shand Lina Tyroller Rolf Kipfer 《Hydrogeology Journal》2017,25(7):2031-2047
The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates. 相似文献
999.
Justina M. Burns William J. Cooper John L. Ferry D. Whitney King Brian P. DiMento Kristopher McNeill Christopher J. Miller William L. Miller Barrie M. Peake Steven A. Rusak Andrew L. Rose T. David Waite 《Aquatic Sciences - Research Across Boundaries》2012,74(4):683-734
This review summarizes direct and indirect analytical methods for the detection and quantification of the reactive oxygen species (ROS): 1O2, O 2 ·? /HOO·, H2O2, HO·, and CO 3 ·? in aqueous solution. Each section briefly describes the chemical properties of a specific ROS followed by a table (organized alphabetically by detection method, i.e., absorbance, chemiluminescence, etc.) summarizing the nature of the observable (associated analytical signal) for each method, limit of detection, application notes, and reaction of the probe molecule with the particular ROS. 相似文献
1000.
Rowlands G Purkis S Riegl B Metsamaa L Bruckner A Renaud P 《Marine pollution bulletin》2012,64(6):1222-1237
We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs. 相似文献