Chemical composition of the graphitic black carbon fraction in riverine and marine sediments at sub-micron scales using carbon X-ray spectromicroscopy     

Paul R. Haberstroh  Jay A. Brandes  Angela F. Dickens  George Cody 《Geochimica et cosmochimica acta》2006,70(6):1483-1494

The chemical composition of the graphitic black carbon (GBC) fraction of marine organic matter was explored in several marine and freshwater sedimentary environments along the west coast of North America and the Pacific Ocean. Analysis by carbon X-ray absorption near-edge structure spectroscopy and scanning transmission X-ray microscopy shows the GBC fraction of Stillaguamish River surface sediments to be dominated by more highly ordered and impure forms of graphite, together forming about 80% of the GBC, with a smaller percent of an aliphatic carbon component. Eel River Margin surface sediments had very little highly ordered graphite, and were instead dominated by amorphous carbon and to a lesser extent, impure graphite. However, the GBC of surface sediments from the Washington State Slope and the Mexico Margin was composed almost solely of amorphous carbon. Pre-anthropogenic, highly oxidized deep-sea sediments from the open Equatorial Pacific Ocean contained over half their GBC in different forms of graphite as well as highly aliphatic carbon, low aromatic/highly acidic aliphatic carbon, low aromatic/highly aliphatic carbon, and amorphous forms of carbon. Our results clearly show the impact of graphite and amorphous C phases in the BC fraction in modern riverine sediments and nearby marine shelf deposits. The pre-anthropogenic Equatorial Pacific GBC fraction is remarkable in the existence of highly ordered graphite.  相似文献   

Confronting hysteresis: Wood based river rehabilitation in highly altered riverine landscapes of south-eastern Australia   总被引：1，自引：1，他引：1  

Andrew P. Brooks  Timothy Howell  Tim B. Abbe  Angela H. Arthington 《Geomorphology》2006,79(3-4):395

This study evaluates an experiment in river rehabilitation which uses large wood to stimulate and emulate natural system processes in an effort to reverse channel degradation, excess sediment transport and habitat simplification that has resulted from two centuries of human induced disturbances, particularly desnagging. The experiment involved the reintroduction of 436 logs (350 t) within 20 engineered log jams (ELJs) over an 1100 m reach. Commencing in 1999, the experiment was set up as a standard BACI design, with a control reach 3 km upstream. In the 5 years since implementing the rehabilitation strategy, the study reach has experienced five floods greater than the mean annual, and a further five events capable of mobilising the gravel bed. Five surveys of channel terrain have been completed since treatment implementation, and the changes to net sediment storage and morphologic diversity assessed in comparison to the control reach. Seven surveys of the fish population in the reach have also been undertaken during the project to measure the ecological response to the introduced wood. The experiment has demonstrated the effectiveness of ELJ technology in achieving engineering and geomorphic goals. To date, the treatment has halted further degradation of the river and increased sediment storage, with the test reach now storing, on average, 40 m³/1000 m² more sediment than in the control. These values, it would appear, represent a new reach-scale dynamic equilibrium storage level over decadal timescales. Additional sediment storage amounts to 3.5 m³/m³ of wood added. At the reach scale this additional storage represents a reduction of just 2% or less of the post-European expansion in channel capacity, suggesting far greater efforts are required than those employed here to reverse the cumulative effects of 180 years of channel erosion and simplification.Pool and bar area in the test reach increased by around 5% and 3.5%, respectively, while the corresponding values in the control were around 1.5% and 1%, respectively. Two indices of morphologic diversity were measured for each bed survey: the standard deviation of 3D residuals of change compared with the baseline survey (SD_iΔ3D); and the standard deviation of thalweg residuals from the line of best fit (SD_iTR). The SD_iΔ3D index shows both reaches increased in complexity through the study with the treatment increasing more than the control (0.37 and 0.29, respectively). The SD_iTR index does not detect clear changes because of the low signal to noise ratio, however, it does suggest the test reach was more complex than the control at the outset. The observed increase in fish abundance after the first 12 months of monitoring, reported previously, is now far less distinct 4 years on — a pattern seemingly reflecting the relatively minor increases in critical pool habitat and habitat diversity over the same period. Although no significant differences were detectable in fish species richness or total abundance from the reach aggregate data after 4 years, analysis of individual structures show them to be high quality habitat for native fish compared to the rest of the reach and the upstream control.These results highlight the challenges river managers face in achieving measurable improvements in the health of aquatic ecosystems in highly altered rivers. Managers must confront hysteresis in a biophysical and institutional sense when attempting to reverse the degradation of rivers. The scale of treatment implemented in this experiment was at the upper end of the spectrum of rehabilitation efforts currently being undertaken in Australia, suggesting that far greater resources and longer timescales are required to achieve the levels of improvement in the diversity of stream habitat expected by the community. The study also highlights problems with the strategy of attempting to meet multiple objectives within a reach scale rehabilitation project. While this treatment successfully met some geomorphic study objectives, maximising the benefits for fish habitat would require a strategy focused primarily on the creation of complex woody habitat within deeper pools, particularly pools immediately below riffles.  相似文献   

Darwinian origin of landforms     

Dov Corenblit  Johannes Steiger  Angela Gurnell  Eric Tabacchi 《地球表面变化过程与地形》2007,32(13):2070-2073

Whilst earth surface landforms evolve largely as a result of the activity of certain living organisms, the biologically driven geomorphic changes have evolutionary consequences on organisms and ecological communities. Recognition of complex biotic–abiotic feedbacks may lead to deep changes in our understanding of geomorphology. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Spatial Distribution and Long-term Movement Patterns of Cownose Rays Rhinoptera bonasus Within an Estuarine River     

Angela B. Collins  Michelle R. Heupel  Colin A. Simpfendorfer 《Estuaries and Coasts》2008,31(6):1174-1183

Passive acoustic telemetry was used to monitor the movements of cownose rays (Rhinoptera bonasus) within the Caloosahatchee River estuary in Southwest Florida. Twelve rays were tracked within the river between January 2004 and May 2005 for periods up to 234 days. Linear home range was calculated for all individuals and ranged between 0 and 18.4 km (daily) and 1 and 22.3 km (overall). Ray position within the river was compared to changing water quality parameters throughout the study. Although home range size did not increase with increasing salinity, individuals did occur farther upriver with decreasing flow rates and increasing salinity. There were no differences detected between day and night distribution patterns. Movement and presence patterns demonstrated significant use of the estuarine river over all months, indicating that cownose rays in southwest Florida may not undertake long seasonal migrations as established for other parts of their range.  相似文献   

Heathland vegetation,soil moisture and dynamic contributing area     

Angela M. Gurnell 《地球表面变化过程与地形》1981,6(6):553-570

Gurnell (1978) demonstrated the potential of the composition of wet heathland vegetation as an indicator of hydrological processes in a small heathland catchment. The present paper investigates this potential and demonstrates that on a hillslope in the study catchment simple prediction equations for pressure head based entirely on position on the slope can be substantially improved by the inclusion of vegetation related variables. It is suggested that in this context the vegetation composition is largely reflecting soil permeability and that the remaining scatter around the prediction equations results from other factors controlling micro-scale variations in the vegetation pattern.  相似文献   

Nephelines from the Somma-Vesuvius volcanic complex (Southern Italy): crystal-chemical,structural and genetic investigations     

Giuseppina Balassone  Volker Kahlenberg  Angela Altomare  Angela Mormone  Rosanna Rizzi  Michele Saviano  Nicola Mondillo 《Mineralogy and Petrology》2014,108(1):71-90

Sixteen nephelines from different geological occurrences were sampled at the type-locality, the Somma-Vesuvius volcanic complex (southern Italy), and investigated for their chemistry and crystal structure obtained by both single-crystal and powder X-ray diffraction. Nepheline-bearing samples are metamorphic or from magmatic ejecta and pumice deposits. The lower K contents characterize the pumice- and some metamorphic-derived nephelines, whereas the higher ones are found in some samples from magmatic nodules. The amount of the anorthite molecule, quite low on average, can be more variable in the metamorphic nephelines. The crystal-structure investigations on Somma-Vesuvius samples compare well with previous studies of natural nephelines. All 16 nepheline samples adopt space group P6₃. The observed lattice parameters vary between 9.9768–9.9946 Å (for a) and 8.3614–8.3777 Å (for c), respectively. Furthermore, chemical analysis revealed that all specimens exhibit an excess of Si relative the ideal Si:Al ratio of 1:1. The analysis of the T-O distances in our samples clearly indicates a distinct ordering process of aluminium and silicon on the tetrahedral sites which is an agreement with Loewenstein’s rule. A linear correlation between the distance of symmetry equivalent split atoms O(1)-O(1)’ and the T(1)-O(1)-T(2) tilt angle was observed. The average <B-O> (B = Na) distances of all crystals are very similar which is consistent with the outcome of the site population refinement indicating full occupancy with sodium. Oriented precession-type sections of reciprocal space indicated the presence of at least the most intense family of satellite peaks, demonstrating that this group of satellite reflections can occur not only in nephelines from pegmatites and ijolites but also in rocks from completely different petrological settings.  相似文献   

A depositional model for offshore deposits of the lower Blue Gate Member,Mancos Shale,Uinta Basin,Utah, USA          下载免费PDF全文

Lauren P. Birgenheier  Brendan Horton  Andrew D. McCauley  Cari L. Johnson  Angela Kennedy 《Sedimentology》2017,64(5):1402-1438

Depositional models that use heterogeneity in mud‐dominated successions to distinguish and diagnose environments within the offshore realm are still in their infancy, despite significant recent advances in understanding the complex and dynamic processes of mud deposition. Six cored intervals of the main body of the Mancos Shale, the lower Blue Gate Member, Uinta Basin, were examined sedimentologically, stratigraphically and geochemically in order to evaluate facies heterogeneity and depositional mechanisms. Unique sedimentological and geochemical features are used to identify three offshore environments of deposition: the prodelta, the mudbelt and the sediment‐starved shelf. Prodelta deposits consist of interlaminated siltstone and sandstone and exhibit variable and stressed trace fossil assemblages, and indicators of high sedimentation rates. The prodelta was dominated by river‐fed hyperpycnal flow. Mudbelt deposits consist of interlaminated siltstone and sandstone and are characterized by higher bioturbation indices and more diverse trace fossil assemblages. Ripples, scours, truncations and normally graded laminations are abundant in prodelta and mudbelt deposits indicating dynamic current conditions. Mudbelt sediment dispersal was achieved by both combined flow above storm wave base and current‐enhanced and wave‐enhanced sediment gravity flows below storm wave base. Sediment‐starved shelf deposits are dominantly siltstone to claystone with the highest calcite and organic content. Bioturbation is limited to absent. Sediment‐starved shelf deposits were the result of a combination of shelfal currents and hypopycnal settling of sediment. Despite representing the smallest volume, sediment‐starved shelf deposits are the most prospective for shale hydrocarbon resource development, due to elevated organic and carbonate content. Sediment‐starved shelf deposits are found in either retrogradational to aggradational parasequence sets or early distal aggradational to progradational parasequence sets, bounding the maximum flooding surface. An improved framework classification of offshore mudstone depositional processes based on diagnostic sedimentary criteria advances our predictive ability in complex and dynamic mud‐dominated environments and informs resource prospectivity.  相似文献   

Chadian faunas and flora from dyserth: Depositional environments and palaeogeographic setting of Viséan strata in northeast wales     

Ian D. Somerville  Angela R. E. Strank  Anthony Welsh 《Geological Journal》1989,24(1):49-66

New floral and faunal data from the oldest Dinantian limestones (Foel Formation) in the Dyserth area, suggest that these sediments are of Chadian age, rather than the Asbian age concluded by earlier workers. The basal late Chadian limestones rest conformably on Dinantian Basement Beds of ?Chadian age or older. The initial inundation of St. George's Land occurred during Chadian times, when shallow-water marine limestones accumulated in the Dyserth area and further to the south, together with terrestrially derived siliciclastics, containing drifted plant fragments. Periodically, a restricted hypersaline lagoonal environment was established but an open marine, neritic environment with abundant stenohaline fauna prevailed in this area. These Chadian sediments accumulated on the proximal part of a carbonate ramp and are presumed to have passed laterally downslope into deeper water basinal facies with Waulsortian buildups of the Irish Sea Basin. In the later Arundian, a carbonate ramp–to–platform transition occurred, with widespread deposition of shallow-water carbonates. In the Asbian this platform developed a rimmed margin, with buildups forming a linear belt between platform and basin. An almost complete Chadian to Brigantian Lower Carboniferous sequence can now be recognized in North Wales. This succession is comparable with the shelf succession in south Cumbria on the northern margin of the Irish Sea Basin.  相似文献