Exposure of inner-shelf reefs to nutrient enriched runoff entering the Great Barrier Reef Lagoon: post-European changes and the design of water quality targets   总被引：1，自引：0，他引：1  

Wooldridge S  Brodie J  Furnas M 《Marine pollution bulletin》2006,52(11):1467-1479

We used historical flood plume extent data (modelled) to quantify the typical spatial extent of the summer runoff-seawater mixing zone of the Great Barrier Reef (GBR) lagoon. Spatially explicit analysis of the variability of in situ chlorophyll a concentrations (observed) across the runoff-seawater mixing zone, then allowed us to explore regional differences in the nutrient enrichment impact of runoff events from the various river systems that drain the GBR catchment. We demonstrate the existence of a discernable north-south gradient along the length of the GBR, such that for equivalent runoff:seawater dilutions ratios, lower levels of nutrient enrichment (as indicated by chlorophyll alpha observations) result from the river systems that drain the relatively undisturbed northern areas of the GBR catchment, compared to more human-impacted central and south areas. We identify a strong correlation between this north-south enrichment gradient and the flood concentration of dissolved inorganic nitrogen (DIN) entrained by the various river systems. By substituting the nutrient enrichment characteristics of the human-impacted river discharges with those of the undisturbed northern rivers, we provide a means to compare the short-term enriching 'footprint' for existing runoff intrusions with those that are likely to have occurred under pre-European catchment conditions. We demonstrate that under pre-European conditions, the nutrient enriching impact from river runoff was likely to have been largely constrained within 1-2 km of the coast, whereas existing conditions support the impact of reefs some 20-30 km off the coast. By using the developed spatial relations, we show that for the heavily human-impacted river systems, reductions in the end-of-river concentrations of DIN in the order 50-80% are needed in order to restore parity with pre-European conditions. We discuss these results in regard to developing end-of-catchment water quality targets for the region.  相似文献   

Radio emission from supernova remnants: implications for post-shock magnetic field amplification & the magnetic fields of galaxies     

Todd A. Thompson  Eliot Quataert  Norman Murray † 《Monthly notices of the Royal Astronomical Society》2009,397(3):1410-1419

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Potential impact of climate change and reindeer density on tundra indicator species in the Barents Sea region     

Christoph Zöckler  Lera Miles  Lucy Fish  Annett Wolf  Gareth Rees  Fiona Danks 《Climatic change》2008,87(1-2):119-130

Climate change is expected to alter the distribution of habitats and thus the distribution of species connected with these habitats in the terrestrial Barents Sea region. It was hypothesised that wild species connected with the tundra and open-land biome may be particularly at risk as forest area expands. Fourteen species of birds were identified as useful indicators for the biodiversity dependent upon this biome. By bringing together species distribution information with the LPJ-GUESS vegetation model, and with estimates of future wild and domestic reindeer density, potential impacts on these species between the present time and 2080 were assessed. Over this period there was a net loss of open land within the current breeding range of most bird species. Grazing reindeer were modelled as increasing the amount of open land retained for nine of the tundra bird species.  相似文献   

≥3700 Ma pre-metamorphic dolomite formed by microbial mediation in the Isua supracrustal belt (W. Greenland): Simple evidence for early life?     

Allen P. Nutman  Clark R.L. Friend  Vickie C. Bennett  David Wright  Marc D. Norman 《Precambrian Research》2010

Chemical (meta)sedimentary rocks in the amphibolite facies ≥3700 Ma Isua supracrustal belt (W. Greenland) are mostly strongly deformed, so there is only a small chance of the survival of features such as stromatolites or microfossils that would be direct proof of a ≥3700 Ma biosphere. Therefore the search for evidence of ≥3700 Ma life in Isua rocks has focused on chemical signatures, particularly C-isotopes. The new approach presented here is based on whole rock chemistry rather than isotopic signatures. Isua chemical sedimentary rocks have Ca–Mg–Fe bulk compositions that coincide with ferroan dolomite – siderite/Fe-oxide mixtures. Most have low Al₂O₃, TiO₂ contents (<0.5 and <0.05 wt% respectively) showing minimal contamination from terriginous materials. Identical seawater-like REE + Y shale-normalised trace element signatures with La, Ce, Eu and Y positive anomalies are found in magnetite-rich banded iron formation (BIF – such as the geochemical standard IF-G), dolomite-rich rocks and quartz–carbonate–calc-silicate rocks. Additionally from a rare, small area of low deformation in Isua, there are ∼3700 Ma pillow lava interstices consisting of quartz + tremolite + calcite derived from pre-metamorphic dolomite + silica. Thus the dolomite in the chemical sediments and the pillow interstice was part of the pre-metamorphic assemblage, and was deposited from seawater and/or low-temperature groundwater (as shown by the REE + Y chemistry). Therefore, at least some Isua carbonate rocks are sedimentary or diagenetic in origin rather than being formed by metasomatism at 600–500 °C as proposed by Rose et al. (1996. American Journal of Science 296, 1004–1044).  相似文献   

Application of uncertainty visualization methods to meteorological trajectories     

Ryan A. Boller  Scott A. Braun  Jadrian Miles  David H. Laidlaw 《Earth Science Informatics》2010,3(1-2):119-126

We present an application of uncertainty visualization to air parcel trajectories generated from a global meteorological model. We derive an approximation of advection uncertainty due to interpolation and incorporate this uncertainty into our visualization of trajectories. Our work enables efficient visual pruning of unlikely results, especially in regions of atmospheric shear, potentially reducing erroneous interpretations. Finally, we apply these methods to a real-world meteorological problem to demonstrate its use.  相似文献   

Assessing regional impacts and adaptation strategies for climate change: the Washington Climate Change Impacts Assessment     

Edward L. Miles  Marketa M. Elsner  Jeremy S. Littell  Lara Whitely Binder  Dennis P. Lettenmaier 《Climatic change》2010,102(1-2):9-27

Climate change in the twenty-first century will strongly affect the processes that define natural and human systems. The Washington Climate Change Impacts Assessment (WACCIA) was intended to identify the nature and effects of climate change on natural and human resources in Washington State over the next century. The assessment focused on eight sectors that were identified as being potentially most climate sensitive: agriculture, energy, salmon, urban stormwater infrastructure, forests, human health, coasts, and water resources. Most of these sectors are sensitive in one way or another to water availability. While water is generally abundant in the state under current climate conditions, its availability is highly variable in space and time, and these variations are expected to change as the climate warms. Here we summarize the results of the WACCIA and identify uncertainties and common mechanisms that relate many of the impacts. We also address cross-sectoral sensitivities, vulnerabilities, and adaptation strategies.  相似文献   

Fire and drought as drivers of early Holocene tree line changes in the Peruvian Andes     

Dunia H. Urrego  Brittany A. Niccum  Christopher F. La Drew  Miles R. Silman  Mark B. Bush 《第四纪科学杂志》2011,26(1):28-36

Three pollen and charcoal records from three lakes lying at 3400 m elevation in southern Peru provided a record of landscape change spanning the last ca.18 000 cal. a BP. The tree line lay close to the site between ca. 16 000 and 12 000 cal. a BP, with Polylepis woodlands growing near the lakes. Progressively drying conditions led to increased fire after 12 000 cal. a BP, coinciding with a decline in Polylepis cover and Andean forest relicts as puna grasslands expanded. A strong decrease in the rate of sediment deposition between ca. 12 000 and ca. 4400 cal. a BP was interpreted to indicate the presence of sedimentary hiatuses. With the return of wet conditions after 4400 cal. a BP, forests did not reassemble around the lakes. Instead, fire‐maintained grasslands dominated the landscape. Humans probably induced the intensified fire activity during the late Holocene and thereby deflected local successions. The modern fragmented landscape, with Polylepsis woodlands existing in fire‐resistant pockets above the general limit of the Andean tree line, resulted from the intensification of human land use practices during the last 4400 cal. a BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Effects of urbanization on streamflow in the Atlanta area (Georgia,USA): a comparative hydrological approach   总被引：1，自引：0，他引：1  

Seth Rose  Norman E. Peters 《水文研究》2001,15(8):1441-1457

For the period from 1958 to 1996, streamflow characteristics of a highly urbanized watershed were compared with less‐urbanized and non‐urbanized watersheds within a 20 000 km² region in the vicinity of Atlanta, Georgia: in the Piedmont and Blue Ridge physiographic provinces of the southeastern USA. Water levels in several wells completed in surficial and crystalline‐rock aquifers were also evaluated. Data were analysed for seven US Geological Survey (USGS) stream gauges, 17 National Weather Service rain gauges, and five USGS monitoring wells. Annual runoff coefficients (RCs; runoff as a fractional percentage of precipitation) for the urban stream (Peachtree Creek) were not significantly greater than for the less‐urbanized watersheds. The RCs for some streams were similar to others and the similar streams were grouped according to location. The RCs decreased from the higher elevation and higher relief watersheds to the lower elevation and lower relief watersheds: values were 0·54 for the two Blue Ridge streams, 0·37 for the four middle Piedmont streams (near Atlanta), and 0·28 for a southern Piedmont stream. For the 25 largest stormflows, the peak flows for Peachtree Creek were 30% to 100% greater than peak flows for the other streams. The storm recession period for the urban stream was 1–2 days less than that for the other streams and the recession was characterized by a 2‐day storm recession constant that was, on average, 40 to 100% greater, i.e. streamflow decreased more rapidly than for the other streams. Baseflow recession constants ranged from 35 to 40% lower for Peachtree Creek than for the other streams; this is attributed to lower evapotranspiration losses, which result in a smaller change in groundwater storage than in the less‐urbanized watersheds. Low flow of Peachtree Creek ranged from 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of stormwater and the paving of groundwater recharge areas. The timing of daily or monthly groundwater‐level fluctuations was similar annually in each well, reflecting the seasonal recharge. Although water‐level monitoring only began in the 1980s for the two urban wells, water levels displayed a notable decline compared with non‐urban wells since then; this is attributed to decreased groundwater recharge in the urban watersheds due to increased imperviousness and related rapid storm runoff. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

From the Hagedoorn imaging technique to Kirchhoff migration and inversion   总被引：1，自引：0，他引：1  

Norman Bleistein  Samuel H. Gray 《Geophysical Prospecting》2001,49(6):629-643

The seminal 1954 paper by J.G. Hagedoorn introduced a heuristic for seismic reflector imaging. That heuristic was a construction technique – a 'string construction' or 'ruler and compass' method – for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace. Later, Kirchhoff migration was developed. This method is based on an integral representation of the solution of the wave equation. For decades Kirchhoff migration has been one of the most popular methods for imaging seismic data. Parallel with the development of Kirchhoff wave-equation migration has been that of Kirchhoff inversion, which has as its objectives both structural imaging and the recovery of angle-dependent reflection coefficients. The relationship between Kirchhoff migration/inversion and Hagedoorn's constructive technique has only recently been explored. This paper addresses this relationship, presenting the mathematical structure that the Kirchhoff approach adds to Hagedoorn's constructive method and showing the relationship between the two.  相似文献   

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana,California     

Ronald I. Dorn  Norman Meek 《地球表面变化过程与地形》1995,20(6):547-560

Manganiferous rock varnish, silica glaze and iron skins have formed on 20- to 40-year-old slag piles near Fontana, southern California. Rapid rock-varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments, combined with the likelihood that Mn-rich solutions flow over slag surfaces. A new model is proposed for the formation of silica glaze, involving soluble Al-Si complexes and the nature of wetting films. Iron skins occur where runoff is concentrated, and where iron bacteria grow. Observations indicate: (i) substrate can be important in supplying Mn, as well as maintaining a stable surface and channelling runoff to microspots where varnish grows; (ii) ignorance of boundary layer pH/Eh conditions makes chemical-physical models of varnish formation speculative; (iii) the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood, but is probably an important limiting factor on varnish growth rates; and (iv) there must be at least two steps in biotic varnishing-accretion of Mn-Fe in casts, followed by cementation of clays by either in situ cast residue or Mn-Fe remobilized from casts. Varnish accretion may be limited by the rate at which both steps occur. Rapid development of readily distinguishable manganiferous rock varnishes at this post-1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock-varnish coatings.  相似文献