The Effects of Reduced Tidal Flushing on Mangrove Structure and Function Across a Disturbance Gradient     

Rachel J. Harris  Eric C. Milbrandt  Edwin M. EverhamIII  Brian D. Bovard 《Estuaries and Coasts》2010,33(5):1176-1185

The effects of reduced tidal flushing on post-hurricane mangrove recovery were measured across a gradient of hurricane disturbance (in order of decreasing wind intensity: Captiva, North Sanibel, Central Sanibel, and East Sanibel). Each region consisted of replicate study plots with either reduced tidal exchange (tidally restricted location) or an open tidal connection (tidally unrestricted location). Locations with reduced tidal exchange displayed significantly lower (two-way ANOVA, p ≤ 0.0001) tidal amplitude, decreased seedling densities, and decreased productivity (recruitment, growth, and litter fall) when compared to the tidally unrestricted locations. Results also indicated significant regional variations in measures of mangrove stand structure (seedlings and canopy) and productivity (recruitment, growth, and litter fall) up to 4-years post-hurricane disturbance. These findings suggest that the legacy effects from hurricane disturbance vary with degree of wind intensity, acting both independently and synergistically with the effects of tidal restriction to influence post-hurricane mangrove structure and function.  相似文献   

The Green Bay ecosystem and assessment of climate change impacts     

R. B. Wenger  H. J. Harris 《Frontiers of Earth Science》2010,4(3):326-332

Climate change will have major impacts in the Great Lakes region of North America. Particularly vulnerable are shallow freshwater estuaries, such as Lake Michigan’s Green Bay, located in the north-eastern part of the State of Wisconsin. Green Bay and the Lower Fox River, its major tributary, were considered to be severely polluted as early as 1925. As a result of large expenditures of money and a major research effort that has been conducted over the past 40 years or more, some progress has been made toward the restoration of ecosystem integrity. However, work remains, and within this context, potential climate change impacts pose additional challenges. We discuss in this paper a methodology that can be used to assess climate change impacts on ecosystems, and describe an application to the Green Bay ecosystem. The methodology employs numerical methods to evaluate the inputs from scientific, policy, and management experts who are knowledgeable about the ecosystem under study. The Green Bay ecosystem application reveals that runoff from agriculture and urban sources, already a major ecosystem stressor, will be exacerbated in the future as a result of climate change impacts.  相似文献   

Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland     

Esther Ruth Gudmundsdóttir  Jón Eiríksson  Gudrún Larsen 《第四纪科学杂志》2011,26(6):589-602

Nine tephra layers in marine sediment cores (MD99‐2271 and MD99‐2275) from the North Icelandic shelf, spanning the Late Glacial and the Holocene, have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments, to pinpoint the stratigraphic level of the time signal the tephra layers provide, and to discriminate between primary and reworked tephra layers in a marine environment. These nine tephra layers are the Borrobol‐like tephra, Vedde Ash, Askja S tephra, Saksunarvatn ash, and Hekla 5, Hekla 4, Hekla 3, Hekla 1104 and V1477 tephras. The methods used were visual inspection, magnetic susceptibility, X‐ray photography, mineralogical counts, grain size and morphological measurements, and microprobe analysis. The results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment, revealing all nine tephra layers in question. Definition of the tephra layers revealed a 2–3 cm diffuse upper boundary in eight of the nine tephra layers and 2–3 cm diffuse lower boundary in two tephra layers. Using a multi‐parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra. The first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked. Morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely. The study shows that there is a need to apply a combination of methods to detect, define (the time signal) and discriminate between primary and reworked tephra in marine environments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Deep Hubble space telescope ultraviolet imaging of the M87 jet     

Juan P. Madrid  William B. Sparks  D. E. Harris  Eric S. Perlman  Duccio Macchetto  John Biretta 《Astrophysics and Space Science》2007,311(1-3):329-333

Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength. The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure, knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope.  相似文献   

High seas marine protected areas: Benthic environmental conservation priorities from a GIS analysis of global ocean biophysical data     

Peter T. Harris  Tanya Whiteway 《Ocean & Coastal Management》2009,52(1):22-38

Designing a representative network of high seas marine protected areas (MPAs) requires an acceptable scheme to classify the benthic (as well as the pelagic) bioregions of the oceans. Given the lack of sufficient biological information to accomplish this task, we used a multivariate statistical method with 6 biophysical variables (depth, seabed slope, sediment thickness, primary production, bottom water dissolved oxygen and bottom temperature) to objectively classify the ocean floor into 53,713 separate polygons comprising 11 different categories, that we have termed “seascapes”. A cross-check of the seascape classification was carried out by comparing the seascapes with existing maps of seafloor geomorphology and seabed sediment type and by GIS analysis of the number of separate polygons, polygon area and perimeter/area ratio. We conclude that seascapes, derived using a multivariate statistical approach, are biophysically meaningful subdivisions of the ocean floor and can be expected to contain different biological associations, in as much as different geomorphological units do the same. Less than 20% of some seascapes occur in the high seas while other seascapes are largely confined to the high seas, indicating specific types of environment whose protection and conservation will require international cooperation. Our study illustrates how the identification of potential sites for high seas marine protected areas can be accomplished by a simple GIS analysis of seafloor geomorphic and seascape classification maps. Using this approach, maps of seascape and geomorphic heterogeneity were generated in which heterogeneity hotspots identify themselves as MPA candidates. The use of computer-aided mapping tools removes subjectivity in the MPA design process and provides greater confidence to stakeholders that an unbiased result has been achieved.  相似文献   

Mesoscale physical variability affects zooplankton production in the Labrador Sea     

L. Yebra  R.P. Harris  E.J.H. Head  I. Yashayaev  L.R. Harris  A.G. Hirst 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(5):703-715

Surface distribution (0–100 m) of zooplankton biomass and specific aminoacyl-tRNA synthetases (AARS) activity, as a proxy of structural growth, were assessed during winter 2002 and spring 2004 in the Labrador Sea. Two fronts formed by strong boundary currents, several anticyclonic eddies and a cyclonic eddy were studied. The spatial contrasts observed in seawater temperature, salinity and fluorescence, associated with those mesoscale structures, affected the distributions of both zooplankton biomass and specific AARS activity, particularly those of the smaller individuals. Production rates of large organisms (200–1000 μm) were significantly related to microzooplankton biomass (63–200 μm), suggesting a cascade effect from hydrography through microzooplankton to large zooplankton. Water masses defined the biomass distribution of the three dominant species: Calanus glacialis was restricted to cold waters on the shelves while Calanus hyperboreus and Calanus finmarchicus were widespread from Canada to Greenland. Zooplankton production was up to ten-fold higher inside anticyclonic eddies than in the surrounding waters. The recent warming tendency observed in the Labrador Sea will likely generate weaker convection and less energetic mesoscale eddies. This may lead to a decrease in zooplankton growth and production in the Labrador basin.  相似文献   

An assessment of miniaturised electrical imaging equipment to monitor pollution plume evolution in scaled centrifuge modelling     

N. Depountis  C. Harris  M. C. R. Davies 《Engineering Geology》2001,60(1-4):83-94

This paper demonstrates the capabilities and limitations of a miniaturised electrical imaging technique (resistivity tomography) developed at Cardiff University to image contaminant plumes in scaled centrifuge models of the vadose zone. For this purpose a generic model of contaminant infiltration into unsaturated sand was designed. The imaging technique produces two-dimensional contoured plots of the resistivity distribution before and during contaminant infiltration experiments. During the experiments, dyed NaCl solution was released into the model and the change in resistivity associated with the contaminant plume evolution was imaged as a function of time and g-level. Capillary pressure was monitored constantly by matrix potential probes (tensiometers) in order to investigate the effect of capillary forces on plume evolution. Tests at 1g (static conditions) and 10g are described in this paper. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the 1g test showed this imaging technique to be highly effective.

Contaminant plume evolution in the unsaturated sand model was observed to be mainly gravity-driven, with plume migration and geometry being strongly affected by a tenfold increase in gravity in the centrifuge experiment. It is concluded that miniaturised electrical imaging can be a useful tool for monitoring pollution plume evolution during centrifuge tests, but when plume evolution is rapid, the time taken to interrogate each array restricts the effectiveness of the technique in monitoring changes in plume geometry. However, in such cases, resistivity tomography does provide valuable information on residual levels of contaminant fluid retained within the soil after passage of the plume.  相似文献   

Bioremediation of acid mine drainage using decomposable plant material in a constant flow bioreactor   总被引：1，自引：0，他引：1  

M. Harris  S. Ragusa 《Environmental Geology》2001,40(10):1192-1204

Under stagnant conditions, the ability of 15 earth materials (non-lime) including various inorganic 2:1 and 1:1 layer silicates, an amorphous oxide, and two 'whole' soils were tested for their pH-buffering efficiency in an acid mine drainage (AMD) water. The purpose was to decrease AMD acidity to a level where sulfate-reducing bacteria (SRB) placed in it may be activated. Of all materials, a whole soil (a high cation-exchange capacity clayey mollisol containing 40% clay, and 4% soil organic matter) caused the greatest pH increases from 2.5 up to 5.5 units after 10 days in the AMD water. Influent AMD was then ameliorated at various speeds through an SRB driven bioreactor using a 50/50 weight over weight (w/w) combination of the mollisol and ryegrass (MR) as the pH buffer substrate. This substrate combination decreased the SRB acclimatisation period (from 50 days in a previous experiment utilising sludge + ryegrass) to <10 days in the present experiment. After causing pH increases from 2.8 to >6 units in 5 days, the buffer reduced the hydraulic retention time (HRT) of the constant-flow reactor from 12 days at flow speeds of 100 ml/day to 2 days at 25 ml/day, respectively. After 10 days, soluble Fe, Al and sulfate were all decreased >1,800-, >40- and 3-fold, respectively. This was a more efficient performance than the no-flow bioreactor of a previous experiment using sludge + ryegrass. This method of AMD rehabilitation is an alternative for localities that lack cheap sources of calcium compounds for chemical treatment, but have a similar soil type and copious quantities of fresh decomposable plant wastes.  相似文献   

Oxygen isotope geochemistry of the Mesozoic anorogenic complexes of Damaraland,northwest Namibia: evidence for crustal contamination and its effect on silica saturation     

Chris Harris 《Contributions to Mineralogy and Petrology》1995,122(3):308-321

 Fifty-six new oxygen isotope analyses of minerals separated from nine Mesozoic anorogenic complexes of Damaraland in northwest Namibia have been used to estimate the δ¹⁸O values of the original magmas (δ_magma). These complexes range in composition from nepheline syenite to alkaline and peraluminous granites, often with a variety of rock types present at a single centre. The silica-undersaturated rock types show a relatively small spread of values of δ_magma from 6.0 to 7.0‰ (mean 6.6‰), which is consistent with their derivation from the mantle with little or no subsequent crustal contamination. The silica-oversaturated rocks show a wide range of δ_magma values from 4.9 to 12.0‰, with a mean value of 8.3‰. The high values of δ_magma in the silica-oversaturated rocks can only be explained with considerable involvement of the continental crust in their petrogenesis, and those rocks with δ_magma>10‰ are interpreted as essentially crustal melts. It is generally accepted that the Damaraland complexes were generated as a result of rifting across the Tristan plume, with the plume providing both mantle-derived magma and with it the heat required for crustal melting. In addition to their mantle-like oxygen isotope ratios, the undersaturated rocks of the Damaraland complexes possess the trace element characteristics (e.g. low Zr/Nb ratios) of ocean island basalt, suggesting that their parental magmas were produced from the plume itself. In contrast, the oversaturated complexes generally have higher Zr/Nb ratios that are consistent with a larger crustal input. The highest values of δ_magma in the Damaraland complexes are found in granitic rocks that intrude the central zone of the Pan-African Damara Orogen where presumably there is a substantial component of sedimentary origin in the lower to middle crust. Received: 3 April 1995/Accepted: 24 July 1995  相似文献   

The volcanic eruption on Tristan da Cunha in 1961     

P. G. Harris 《Bulletin of Volcanology》1964,27(1):113-114

On 10th October 1961, after two months of localized earth tremors, a dome of lava was extruded, about 300 yards east of the island settlement, on the northern coast of Tristan da Cunha. The dome grew rapidly to about 300 feet above its surroundings, and its seaward margin slowly moved outwards. Between 20th and 27th October the seaward side of the dome collapsed or was carried away, and mobile lava was emitted. This formed two series of lobes, extending into the sea along a front of about 1300 yards. This activity had ceased by the end of January 1962. In February, a dome up to 130 yards wide and 320 yards long, was pushed up 100 feet above the lava field, extending along the line of the lava stream from the central vent. By mid-March, this activity had ceased, and the only subsequent activity has been the continuation of fumarolic vents in the lava field. The trachyandesitic lava was of almost identical composition at each stage of the eruption, and closely resembled that from a previous eruption about 300 years ago at the other end of the island. The island has many well-preserved volcanic cones and scoria mounds. Such features as explosion craters, lava levees and lava channels also occur. The rocks of the Tristan da Cunha group range from ankaramites through basalts and trachybasalts to trachyandesites and trachytes. Leucite-bearing rocks are frequent and all the rocks have relatively-high contents ofK, Ba, Sr andNb. The origin of such a group of potassic rocks in a mid-oceanic environment is of considerable petrological interest. The 1961 eruption and the general geology of the Tristan da Cunha group was studied by members of the Royal Society Expedition to Tristan da Cunha. Their findings will be published in the Philosophical Transactions of the Royal Society (P. E. Baker, I. G. Gass, P. G. Harris andR. W. Le Maitre).  相似文献