Plastic ingestion by estuarine mullet Mugil cephalus (Mugilidae) in an urban harbour,KwaZulu-Natal,South Africa     

T Naidoo  AJ Smit  D Glassom 《African Journal of Marine Science》2016,38(1):145-149

Coastal urban environments have high plastic pollution levels, and hence interactions between plastic debris and marine life are frequent. We report on plastic ingestion by mullet Mugil cephalus in Durban Harbour, KwaZulu-Natal, South Africa. Of 70 mullet (13.0–19.5?cm total length), 73% had plastic particles in their guts, with a mean of 3.8 particles per fish (SD 4.7). Plastic ingestion showed no relation to digestive tract content or fish length. White and clear plastic fibres were ingested most commonly. This urban population of M. cephalus had a higher incidence of plastic ingestion than has been reported in studies on fish from other coastal areas or the oceanic environment.  相似文献   

On the Discrepancy in Simultaneous Observations of the Structure Parameter of Temperature Using Scintillometers and Unmanned Aircraft     

Miranda Braam  Frank Beyrich  Jens Bange  Andreas Platis  Sabrina Martin  Björn Maronga  Arnold F. Moene 《Boundary-Layer Meteorology》2016,158(2):257-283

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Regional and Global Tropopause Fold Occurrence and Related Ozone Flux Across the Tropopause     

M. Beekmann  G. Ancellet  S. Blonsky  D. De Muer  A. Ebel  H. Elbern  J. Hendricks  J. Kowol  C. Mancier  R. Sladkovic  H. G. J. Smit  P. Speth  T. Trickl  Ph. Van Haver 《Journal of Atmospheric Chemistry》1997,28(1-3):29-44

This paper gives a synthesis of three algorithms to detect the presenceof tropopause folds from vertical ozone/radio-sounding profiles and frommeteorological analysis. Also an algorithm to identify injection ofstratospheric air into the lower troposphere fromozone/⁷beryllium time series is presented. Differences in theresults obtained from the algorithms are observed and discussed with respectto the criteria for fold detection and input data used. Spatial gradients inthe obtained folding frequencies are made evident on a global scale from thealgorithm based on meteorological analysis (Q-vector/potential vorticity)and probably also on a regional European scale from algorithms both basedmeteorological analyses and on ozone/PTU soundings. The observed seasonalvariation of folding occurrence is rather flat except during summer whenalso some differences appear between the algorithms. By combining thefolding frequencies with literature estimates of the cross-tropopause ozonetransfer in single folding events, an average stratospheric ozone influxinto the troposphere of 5.7 ± 1.3× 10¹⁰ mol.cm^-2 s^-1 is obtained for the Northern hemisphereand 12± 2.7× 10¹⁰ mol. cm^-2s^-1 for Western Europe. Potential additional contributions dueto other stratosphere-troposphere exchange processes than folds are not yetincluded in these estimates. Finally, the link between statistics fromozone/⁷beryllium data and folding statistics is brieflydiscussed.  相似文献   

A conceptual model of vegetation dynamics in the semiarid Highland savanna of Namibia, with particular reference to bush thickening by Acacia mellifera     

D.F. Joubert  A. Rothauge  G.N. Smit   《Journal of Arid Environments》2008,72(12):2201-2210

Namibian rangelands are encroached with Acacia mellifera, partially resulting from a poor understanding of vegetation dynamics. A conceptual state-and-transition model of vegetation dynamics in the semiarid Highland savanna in central Namibia, emphasising bush thickening by A. mellifera, is described. Two main states, a grassy and a bushy state, are identified. These are further subdivided, and 11 transitions are identified. The key transition initiating a change from grassy to bushy state can be termed a “leap” (an occasional, infrequent mass recruitment event) following a long “sleep” (no or little change in A. mellifera density). It is rare because it requires three consecutive years of above-average rainfall for seedling establishment. Fire, coinciding with seedling establishment, can interrupt it, while a low biomass grass sward facilitates it. The phenology and physiology of the encroaching species, seed predation and sapling herbivory influence this transition. The model proposes opportunistic management interventions, particularly the use of fire, to minimise the risk of further landscape-scale transitions to a bushy state. It highlights areas where understanding of vegetation dynamics is lacking and recommends crucial research foci. Conceptual models of bush-thickening processes need to account for differences in climate and phenological details of encroaching species.  相似文献   

A GIS approach to seismic risk assessment with an application to mining-related seismicity in Johannesburg,South Africa     

Keagen Liebenberg  Ansie Smit  Serena Coetzee  Andrzej Kijko 《Acta Geophysica》2017,65(4):645-657

The majority of seismic activity in South Africa is related to extensive mining operations, usually in close proximity to densely populated areas where a relatively weak seismic event could cause damage. Despite a significant decrease in mining operations in the Witwatersrand area, the number of seismic events appears to be increasing and is attributed to the acid mine drainage problem. The increased seismicity is raising concern amongst disaster management centres and in the insurance industry. A better understanding is required of the vulnerability and the size of the potential loss of people and infrastructure in densely populated Johannesburg and its surrounding areas. Results of a deterministic seismic risk, vulnerability, and loss assessment are presented by making use of a geographic information system (GIS). The results illustrate the benefits of using GIS and contribute to a better understanding of the risk, which can assist in improving disaster preparedness.  相似文献   

Modelling the distribution of hard seabed using calibrated multibeam acoustic backscatter data in a tropical,macrotidal embayment: Darwin Harbour,Australia     

P. Justy W. Siwabessy  Maggie Tran  Kim Picard  Brendan P. Brooke  Zhi Huang  Neil Smit  David K. Williams  William A. Nicholas  Scott L. Nichol  Ian Atkinson 《Marine Geophysical Researches》2018,39(1-2):249-269

Spatial information on the distribution of seabed substrate types in high use coastal areas is essential to support their effective management and environmental monitoring. For Darwin Harbour, a rapidly developing port in northern Australia, the distribution of hard substrate is poorly documented but known to influence the location and composition of important benthic biological communities (corals, sponges). In this study, we use angular backscatter response curves to model the distribution of hard seabed in the subtidal areas of Darwin Harbour. The angular backscatter response curve data were extracted from multibeam sonar data and analysed against backscatter intensity for sites observed from seabed video to be representative of “hard” seabed. Data from these sites were consolidated into an “average curve”, which became a reference curve that was in turn compared to all other angular backscatter response curves using the Kolmogorov–Smirnov goodness-of-fit. The output was used to generate interpolated spatial predictions of the probability of hard seabed (p-hard) and derived hard seabed parameters for the mapped area of Darwin Harbour. The results agree well with the ground truth data with an overall classification accuracy of 75% and an area under curve measure of 0.79, and with modelled bed shear stress for the Harbour. Limitations of this technique are discussed with attention to discrepancies between the video and acoustic results, such as in areas where sediment forms a veneer over hard substrate.  相似文献   

The effect of management choices on the sustainability and economic performance of a mixed fishery: a simulation study     

Kraak  S. B. M.; Buisman  F. C.; Dickey-Collas  M.; Poos  J. J.; Pastoors  M. A.; Smit  J. G. P.; van Oostenbrugge  J. A. E.; Daan  N. 《ICES Journal of Marine Science》2008,65(4):697-712

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Record of plate boundary metamorphism during Gondwana breakup from Lu–Hf garnet geochronology of the Alpine Schist,New Zealand          下载免费PDF全文

Sophie I. Briggs  John M. Cottle  Matthijs A. Smit 《Journal of Metamorphic Geology》2018,36(7):821-841

The Zealandia portion of the Pacific–Gondwana margin underwent widespread extension, fragmentation, separation and subsidence during the final stages in the breakup of Gondwana. Although these processes shaped the geology of New Zealand, their timing and the timing of subduction cessation in the region remain unclear. To investigate the timing of these processes, we used Lu–Hf garnet geochronology to date six samples of the Alpine Schist, which represents the metamorphic section of the former Zealandia margin. The garnet dates range from 97.3 ± 0.3 to 75.4 ± 1.3 Ma. Compositional zoning in garnet indicates that the spread in ages results from diachronous metamorphism in the upper plate at the Pacific–Gondwana margin, occurring concurrently with rifting of Zealandia from East Gondwana via opening of the Tasman Sea. Clear spatial trends in the timing of garnet growth throughout the Alpine Schist are absent, indicating that either regional age trends were offset by post‐metamorphic deformation, or that metamorphism did not result from a single regional heat source, and was instead driven by short‐duration, spatially dispersed processes such as episodic fluid‐fluxing or mechanical heating. Diachronous metamorphism of the Alpine Schist can be attributed to heat conduction from the rising upper mantle during widespread extension, progressive burial and heating of accretionary wedge sediments during ongoing horizontal shortening, or fluid‐fluxing sourced from a subducting and dehydrating Hikurangi Plateau. These results indicate that during separation of Zealandia from East Gondwana in the late Cretaceous, the crust at the Pacific–Gondwana margin remained hot, potentially facilitating the extensive thinning of the Zealandia lithosphere during this time.  相似文献   

The distinct metamorphic stages and structural styles of the 1.94–1.86 Ga Snowbird Orogen,Northwest Territories,Canada     

Eric J. Thiessen  H. Dan Gibson  Daniele Regis  Sally J. Pehrsson  Kyle T. Ashley  Matthijs A. Smit 《Journal of Metamorphic Geology》2020,38(9):963-992

Palaeoproterozoic orogenesis within the Archean southeastern Rae craton is related to the initial amalgamation of Laurentia. Characterizing the accompanying tectonic processes during this time has been complicated due to polymetamorphism, which results in the obscuring of the age record of the terranes involved. To improve the knowledge of the tectonic evolution of the South Rae Craton, petrologic and structural analyses are applied in conjunction with in situ trace element chemistry, inclusion barometry, U–Pb monazite and titanite, and Lu–Hf garnet chronology. The data robustly constrain Palaeoproterozoic pressure–temperature–time paths of major deformational events along the southeastern Rae craton margin. D₁ occurred between 1.94 and 1.93 Ga in the Dodge-Snowbird domain, which included prograde burial of metasedimentary rocks, deposited at 2.2–2.0 Ga, and the development of migmatitic layering and east-southeast trending folds (S₁, F₁). Peak metamorphism is recorded in metasedimentary units at c. 1.93 Ga when rocks reached conditions of 9.0–10.5 kbar and 810–830°C. Within the Dodge-Snowbird domain, D₂ imparted north-northeast trending open folds and associated axial planar cleavage (S₂, F₂) between 1.93 and 1.90 Ga during east-west compression that appears to have been synchronous with cooling and exhumation. Later D₂ deformation, localized within the Wholdaia Lake shear zone (WLsz; S_T1), developed in the footwall of this thrust-sense structure at 1,873 ± 5 Ma at conditions of 9.5–11.0 kbar and 820–850°C. The hangingwall Dodge-Snowbird domain had already cooled to below 300°C by then, indicating a significant structural and metamorphic break across the domain's western boundary. A new phase of unroofing (D₃) involved pervasive amphibolite- to greenschist facies extensional shearing (S_T2) within the WLsz, which overprinted S_T1 foliations between 1.87 and 1.86 Ga. Continued greenschist facies shearing younger than 1.86 Ga likely ended by c. 1.83 Ga when lamprophyre dykes cut the structure, which was followed by cooling until c. 1.80 Ga. This work highlights the utility and application of multiple chronometers (zircon, monazite, titanite, garnet) along with structural and petrologic analysis that together can resolve precise orogenic cycles in polymetamorphic terranes that may otherwise be undetected. The time-resolved P–T–D histories derived here enable more robust interpretations regarding the nature and evolution of 1.9 Ga tectonism along the southeast Rae craton margin, which may be used to refine models for Laurentian terrane amalgamation.  相似文献   

Towards a Validation of Scintillometer Measurements: The LITFASS-2009 Experiment   总被引：3，自引：2，他引：1  

Frank Beyrich  Jens Bange  Oscar K. Hartogensis  Siegfried Raasch  Miranda Braam  Dani?lle van Dinther  Doreen Gr?f  Bram van Kesteren  Aline C. van den Kroonenberg  Bj?rn Maronga  Sabrina Martin  Arnold F. Moene 《Boundary-Layer Meteorology》2012,144(1):83-112

Scintillometry has been increasingly used over the last decade for the experimental determination of area-averaged turbulent fluxes at a horizontal scale of a few kilometres. Nevertheless, a number of assumptions in the scintillometer data processing and interpretation still call for a thorough evaluation, in particular over heterogeneous terrain. Moreover, a validation of the path-averaged structure parameters derived from scintillometer data (and forming the basis for the flux calculations) by independent measurements is still missing. To achieve this, the LITFASS-2009 field campaign has been performed around the Meteorological Observatory Lindenberg ?C Richard-A?mann-Observatory of the German Meteorological Service (DWD) in July 2009. The experiment combined tower-based in-situ turbulence measurements, field-scale laser scintillometers, long-range optical (large-aperture) and microwave scintillometers, and airborne turbulence measurements using an automatically operating unmanned aircraft. The paper describes the project design and strategy, and discusses first results. Daytime near-surface values of the temperature structure parameter, ${C_{T}^{2}}$ , over different types of farmland differ by more than one order of magnitude in their dependence on the type and status of the vegetation. Considerable spatial variability in ${C_{T}^{2}}$ was also found along the flight legs at heights between 50 and 100?m. However, it appeared difficult to separate the effects of heterogeneity from the temporal variability of the turbulence fields. Aircraft measurements and scintillometer data agreed in magnitude with respect to the temporal variation of the path-averaged ${C_{T}^{2}}$ values during the diurnal cycle. The decrease of ${C_{T}^{2}}$ with height found from the scintillometer measurements close to the surface and at 43?m under daytime convective conditions corresponds to free-convection scaling, whereas the aircraft measurements at 54 and 83?m suggest a different behaviour.  相似文献