Spatial Variation in the Optical Properties of Dissolved Organic Matter (DOM) in Lakes on the Canadian Precambrian Shield and Links to Watershed Characteristics   总被引：1，自引：0，他引：1  

Kristin K. Mueller  Claude Fortin  Peter G. C. Campbell 《Aquatic Geochemistry》2012,18(1):21-44

In the present study, we explored the use of various optical parameters to detect differences in the composition of the dissolved organic matter (DOM) in a set of lakes that are all located on the Canadian Precambrian Shield, but within which Cu and Ni speciation predictions were previously shown to diverge from measured values in some lakes but not in others. Water samples were collected with in situ diffusion samplers in 2007 (N = 18 lakes) and 2008 (N = 8 lakes). Significant differences in DOM quality were identified between the sampling regions (Rouyn-Noranda, Québec and Sudbury, Ontario) and among lakes, based on dissolved organic carbon concentrations ([DOC]), specific UV absorbance (SUVA₂₅₄), fluorescence indices (FI), and excitation–emission matrix (EEM) fluorescence measurements. Parallel factor analysis (PARAFAC) of the EEM spectra revealed four components, two of which (C3, oxidized quinone fluorophore of allochthonous origin, and C4, tryptophan-like protein fluorescence of autochthonous origin) showed the greatest inter-regional variation. The inter-lake differences in DOM quality were consistent with the regional watershed characteristics as determined from satellite imagery (e.g., watershed-to-lake surface area ratios and relative percentages of surface water, rock outcrops vegetative cover and urban development). Source apportionment plots, built upon PARAFAC components ratios calculated for our lakes, were used to discriminate among DOM sources and to compare them to sources identified in the literature. These results have implications for other areas of research, such as quantifying lake-to-lake variations in the influence of organic matter on the speciation of trace elements in natural aquatic environments.  相似文献   

Terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest Ohio, USA     

Melinda C. Campbell  Timothy G. Fisher  Ronald J. Goble 《Quaternary Research》2011,75(3):411-416

Lower slopes of the Sandia Mountains are characterized by granitic corestone topography and weathering-limited slopes with thin grusy colluvium and weakly developed soils. In contrast, thick soils with illuvial clay and pedogenic carbonate have developed below aplite outcrops. Aplite is resistant to chemical decomposition, but physically weathers to blocky clasts that enhance surface roughness and erosional resistance of colluvium, promoting accumulation of eolian fines. Thick B horizons on aplite slopes indicate limited erosion and prolonged periods of stability and soil development. Accretion of eolian material limits runoff and prevents attainment of a steady-state balance between soil production and downslope transport.  相似文献   

Differences in the neighborhood: Structural variations in the carapace of shore crabs Carcinus maenas (Decapoda: Portunidae)     

Allan T. Souza  Martina I. Ilarri  Joana Campos  João C. Marques  Irene Martins 《Estuarine, Coastal and Shelf Science》2011

The present study compared the carapace structure of Carcinus maenas in two nearby sites (2 km apart) within Minho estuary, submitted to different physicochemical and ecological conditions (water temperature, pH, crabs’ density and sex ratio). The carapace structure of the carapace and chelae of the crabs presented significant differences between sampling sites (t-test; p < 0.01). The SIMPER analysis revealed that the Weight/CW and Thickness/CW ratios explained all the dissimilarities found among sites. Overall, the male carapace was proportionally thicker at station 2 (t-test; p < 0.01), while the female carapace was proportionally thicker at station 1 (t-test; p < 0.001). A thicker carapace can be advantageous when competing for food or a sexual partner. We hypothetized that, since at station 2, the density of individuals was twice higher than at station 1, it is likely that agonistic encounters are more frequent, thus favouring a thicker carapace.  相似文献   

Petrography,mineral chemistry,and crystallization history of olivine‐phyric shergottite NWA 6234: A new melt composition     

Juliane Gross  Justin Filiberto  Christopher D. K. Herd  Mohit Melwani Daswani  Susanne P. Schwenzer  Allan H. Treiman 《Meteoritics & planetary science》2013,48(5):854-871

Knowledge of Martian igneous and mantle compositions is crucial for understanding Mars' mantle evolution, including early differentiation, mantle convection, and the chemical alteration at the surface. Primitive magmas provide the most direct information about their mantle source regions, but most Martian meteorites either contain cumulate olivine or crystallized from fractionated melts. The new Martian meteorite Northwest Africa (NWA) 6234 is an olivine‐phyric shergottite. Its most magnesian olivine cores (Fo₇₈) are in Mg‐Fe equilibrium with a magma of the bulk rock composition, suggesting that it represents a melt composition. Thermochemical calculations show that NWA 6234 not only represents a melt composition but is a primitive melt derived from an approximately Fo₈₀ mantle. Thus, NWA 6234 is similar to NWA 5789 and Y 980459 in the sense that all three are olivine‐phyric shergottites and represent primitive magma compositions. However, NWA 6234 is of special significance because it represents the first olivine‐phyric shergottite from a primitive ferroan magma. On the basis of Al/Ti ratio of pyroxenes in NWA 6234, the minor components in olivine and merrillite, and phosphorus zoning of olivine, we infer that the rock crystallized completely at pressures consistent with conditions in Mars' upper crust. The textural intergrowths of the two phosphates (merrillite and apatite) indicate that at a very last stage of crystallization, merrillite reacted with an OH‐Cl‐F‐rich melt to form apatite. As this meteorite crystallized completely at depth and never erupted, it is likely that its apatite compositions represent snapshots of the volatile ratios of the source region without being affected by degassing processes, which contain high OH‐F content.  相似文献   

From mush to eruption in centuries: assembly of the super-sized Oruanui magma body     

Aidan S. R. Allan  Daniel J. Morgan  Colin J. N. Wilson  Marc-Alban Millet 《Contributions to Mineralogy and Petrology》2013,166(1):143-164

The magmatic systems that give rise to voluminous crystal-poor rhyolite magma bodies can be considered to operate on two contrasting timescales: Those governed by longer-term processes by which a magma acquires its chemical and isotopic characteristics (e.g., fractional crystallisation and assimilation), and those operating at shorter timescales during the physical accumulation of the melt-dominant magma body that finally erupts. We explore the compositional and textural relationships between amphibole and orthopyroxene crystals from the 25.4 ka, 530 km³ (magma) Oruanui eruption products (Taupo volcano, New Zealand) to investigate how processes related to the physical assembly of the pre-eruptive magma body are represented in the crystal record. Over 90 % of orthopyroxenes from the volumetrically dominant high-SiO₂ (>74 wt%) rhyolite pumices record textural evidence for a significant disequilibrium event (partial dissolution ± resorption of cores and interiors) prior to the growth of 40–500 μm thick rim zones. This dissolution/regrowth history of orthopyroxene is recorded in the chemistry of co-crystallising amphiboles as a prominent inflection in the concentrations of Mn and Zn, two elements notably enriched in orthopyroxene relative to amphibole. Textural and chemical features, linked with in situ thermobarometric estimates, indicate that a major decompression event preceded the formation of the melt-dominant body. The decompression event is inferred to represent the extraction of large volumes of melt plus crystals from the Oruanui crystal mush/source zone at pressures of 140–300 MPa (~6–12 km depth). Orthopyroxene underwent partial dissolution during ascent before reestablishing in the melt-dominant magma body at pressures of 90–140 MPa (~3.5–6 km). We model Fe–Mg diffusion across the core-rim boundaries along the crystallographic a or b-axes to constrain the timing of this decompression event, which marked establishment of the melt-dominant magma body. Maximum modelled ages indicate that this event did not begin until ~1,600 years before eruption, consistent with constraints from zircon model-age spectra. Once extraction began, it underwent runaway acceleration with a peak extraction age of ~230 years, followed by an apparent period of stasis of ~60 years prior to eruption. The rapidity of the extraction and accumulation processes implies the involvement of a dynamic driving force which, in the rifted continental arc setting of the Taupo Volcanic Zone, seems likely to be represented by magma-assisted extensional tectonic processes.  相似文献   

Geological and thermochronological studies of the Dashui gold deposit, West Qinling Orogen, Central China   总被引：3，自引：0，他引：3  

Qingtao Zeng  Noreen J. Evans  Brent I. A. McInnes  Geoffrey E. Batt  Campbell T. McCuaig  Leon Bagas  Eric Tohver 《Mineralium Deposita》2013,48(3):397-412

The Dashui gold deposit is a structurally controlled, Carlin-type gold deposit hosted by recrystallised limestone in the West Qinling Orogen of Central China. The major, structurally late east-trending Dashui Fault forms the hanging wall to the gold mineralisation at the Dashui mine and defines the contact between Middle Triassic limestone and a steeply dipping overlying succession of Middle Triassic argillaceous limestone, dolomite, and sandstone. Multiple carbonate veins and large-scale supergene enrichment, represented by hematite, goethite, limonite and jarosite, characterise the deposit. Detailed geochronological investigation using zircon SHRIMP U-Pb dating reveals that volcanic rocks closely associated with the Dashui gold deposit were synchronous with the Ge’erkuohe Granite and pre-date mineralisation. The igneous dyke sample from the hanging wall has the same U-Pb zircon age as the footwall, ca. 213 Ma. (U-Th)/He thermochronology on dykes in the hanging wall and footwall of the Dashui Fault yields identical (U-Th)/He zircon ages of ca. 210 Ma but distinct (U-Th)/He apatite ages of ca. 136 and 211 Ma, respectively. Therefore, the hanging wall and footwall are interpreted as having distinct post-mineralisation exhumation histories. Reverse fault movement exhumed the hanging wall ~2 to 4 km since the Late Triassic with the main component of faulting taking place between the Late Triassic and Early Cretaceous. These relationships suggest a Late Triassic to Early Cretaceous age for the primary gold mineralisation at the Dashui gold deposit, with the corollary that any ‘missing portion’ of the deposit, previously hypothesised to exist in the hanging wall of the Dashui Fault, has been eroded away. The mineralisation in the footwall may have been supergene enriched soon after the primary mineralisation was emplaced, because it has been located at shallow depth since the Late Triassic. Semi-quantitative results obtained in this study also constrain the maximum depth of formation of the Dashui gold at no more than 2 km.  相似文献   

Flow‐field and palaeogeographic reconstruction of volcanic activity in the Permian Gerringong Volcanic Complex,southern Sydney Basin,Australia   总被引：1，自引：1，他引：0  

L. M. Campbell  P. J. Conaghan  R. H. Flood 《Australian Journal of Earth Sciences》2013,60(3):357-375

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Evaluating vegetative transplant success in Posidonia australis: a field trial with habitat enhancement     

Campbell ML  Paling EI 《Marine pollution bulletin》2003,46(7):828-834

Seagrasses in Western Australia grow on open coastlines that are wave and surge exposed, which are known to reduce transplant success. This study investigated the use of habitat enhancement procedures to improve the survival and expansion of Posidonia australis transplants. Limited success transplanting P. australis vegetative propagules (plugs) was achieved after habitat enhancement was implemented, using artificial seagrass (ASG) mats to emulate a "surrogate" seagrass meadow. The ASG mats enhanced one aspect of the habitat (stabilised sediment grain size) but did not suitably stabilise erosion and accretion. Transplant survival was significantly increased (up to 50% survival) in 60% of the sites where ASG mats were present. However, only 8% of the total transplant population exhibited rhizome extension (3.2+/-0.11 mmd(-1)).  相似文献   

Quantifying preferential flow in soils: A review of different techniques   总被引：19，自引：0，他引：19  

Suzanne E. Allaire  Stphanie Roulier  Allan J. Cessna 《Journal of Hydrology》2009,378(1-2):179-204

Preferential flow (PF) in soil has both environmental and human health implications since it favours contaminant transport to groundwater without interaction with the chemically and biologically reactive upper layer of soil. PF is, however, difficult to measure and quantify. This paper reviews laboratory and field techniques, such as breakthrough curves, dye tracing, and scanning techniques, for evaluating PF in soil at different scales. Advanced technologies, such as scanning techniques, have increased our capability to quantify transport processes within the soil with minimal soil disturbance. Important issues with respect to quantifying PF concern large-scale studies, frozen soil conditions, tracing techniques for particles and gases, a lack of simple mathematical tools for interpreting field data, and the lack of a systematic approach for comparing PF data resulting from different measurement techniques. Also, more research is required to quantify the relative importance of the various PF processes that occur in soil rather than the integrated result of all PF processes in soils.  相似文献   

Productivity,carbon assimilation and intra-annual change in tropical reef platform seagrass communities of the Torres Strait,north-eastern Australia     

Michael A. Rasheed  Kara R. Dew  Len J. McKenzie  Robert G. Coles  Simon P. Kerville  Stuart J. Campbell 《Continental Shelf Research》2008

Detailed data on seagrass distribution, abundance, growth rates and community structure information were collected at Orman Reefs in March 2004 to estimate the above-ground productivity and carbon assimilated by seagrass meadows. Seagrass meadows were re-examined in November 2004 for comparison at the seasonal extremes of seagrass abundance. Ten seagrass species were identified in the meadows on Orman Reefs. Extensive seagrass coverage was found in March (18,700 ha) and November (21,600 ha), with seagrass covering the majority of the intertidal reef-top areas and a large proportion of the subtidal areas examined. There were marked differences in seagrass above-ground biomass, distribution and species composition between the two surveys. Major changes between March and November included a substantial decline in biomass for intertidal meadows and an expansion in area of subtidal meadows. Changes were most likely a result of greater tidal exposure of intertidal meadows prior to November leading to desiccation and temperature-related stress.  相似文献