AN URBAN MANAGEMENT INFORMATION SERVICE USING LANDSAT IMAGERY     

P. Carter    W. E. Gardner    T. F. Smith  M. J. Jackson  † 《The Photogrammetric Record》1977,9(50):157-171

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The role of cryptogams in runoff and erosion control on bariland in the Nepal Middle Hills of the Southern Himalaya     

Steve Gaskin  Rita Gardner 《地球表面变化过程与地形》2001,26(12):1303-1315

Cryptogams are communities of non-vascular plants that live on the soil surface. Numerous functions have been attributed to these crusts, including changes in soil fertility and nutrient status, soil hydrology and soil erosion. Most significant for this paper is the reported benefit of cryptogams in reducing soil erosion by water in semi-arid areas. However, to date there have been few attempts to understand the soil conservation value of cryptogams in subsistence agricultural systems or in humid mountain environments. This paper investigates the potential of cryptogams in soil erosion by water on agricultural hillslope terraces (bariland) in the Nepal Middle Hills of the southern monsoonal Himalaya. The research is significant because the loss of fertile topsoil is considered by some to be the biggest threat to the livelihoods of subsistence farmers in the area in the medium and long term. The current study was conducted in the field between two of the weeding events that take place under maize cover, grown in the traditional manner. Three groundcover types which represented (i) maize only (types A), (ii) maize and weed cover (types B), and (iii) maize and cryptogam cover (types C) were monitored utilizing multiple microerosion plots. Measurements of runoff and soil loss data were collected sequentially on a storm-by-storm basis throughout the monitored period from 24 July 1997 to 29 August 1997. Measurements of infiltration rates were also taken on each of the groundcover types at selected times. Results collected from the erosion plots demonstrate that runoff and soil losses over distances of <2 m can be significantly reduced by up to 50 per cent with cryptogam cover, compared to maize-only canopies. Mean runoff for all storm events sampled from plot types A, B and C were 3·4 l m⁻², 1·6 l m⁻² and 1·5 l m⁻² respectively. For soil loss, the results were 21·7 g m⁻², 11·3 g m⁻² and 10·2 g m⁻² respectively. Therefore, cryptogams would appear to offer a similar degree of protection to the soil surface from runoff and raindrop erosion, to that afforded by weed cover. Weed and cryptogam covers protect the soil surface from rainfall kinetic energies and work to preserve surface microtopographies, depressional storage and surface water detention. Terminal infiltration rates taken at the end of the monitored period showed that well developed maize- and cryptogam-covered soil surfaces (types C) have a mean terminal infiltration rate of 35·0 mm h⁻¹ compared to 44·5 mm h⁻¹ for comparable maize- and weed-covered soil surfaces (types B), and 15·5 mm h⁻¹ for maize-only soil surfaces (types A). These results show that cryptogams and weeds also have relatively higher infiltration rates than comparable maize-only covered plots, devoid of groundcover. The findings in this study may have implications for traditional weed management practices used by local hill farmers, which often destroy cryptogam soil coatings two to three times during the maize growing period. However, further work needs to be done to ascertain farmers' understandings of cryptogams. It is hoped that conservationists will benefit from incorporating cryptogams into the design of future soil erosion studies relating to development programmes. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Net, actual, and potential sediment-water interface NH₄ fluxes in the northern Gulf of Mexico (NGOMEX): Evidence for NH₄ limitation of microbial dynamics     

Xiao Lin  Mark J. McCarthy  Stephen A. Carini  Wayne S. Gardner 《Continental Shelf Research》2011,31(2):120-128

A new approach, combining ¹⁵NH₄⁺ isotope dilution and continuous-flow techniques, provided estimates of “actual” and “net” NH₄⁺ flux and sediment NH₄⁺ demand (SAD) at the sediment-water interface (SWI) of sites in the northern Gulf of Mexico (NGOMEX). The sites included a hypoxic site (C6), two sites with intermediate oxygen levels (B7 and F5), and a normoxic site (CT). Control cores without isotope addition and other cores from the same site treated with ¹⁵NH₄⁺ labeled overflowing water differentiated between net and actual regeneration flux and actual vs. potential uptake flux of NH₄⁺. Experiments were conducted in 2008 before (July) and after (September) two successive hurricanes (Gustav and Ike) and in January and August, 2009. Actual regeneration was significantly higher than net flux at most sites. Net flux did not differ significantly in most sites/dates, but the actual regeneration, and the actual and potential uptake, showed temporal and spatial variation; the flux at the hypoxic site was more active than non-hypoxic sites. SAD, the difference between potential and actual NH₄⁺ uptake flux, was higher at the hypoxic site than at non-hypoxic sites before and after the hurricanes in 2008 and during the hypoxia season in 2009. SAD related negatively to bottom water DO values. Conclusions: (1) net flux often underestimated actual regeneration, (2) hurricane activity decreased N dynamics, and (3) microbial N limitation status at the hypoxic site related to NH₄⁺ removal processes that were independent of oxygen (e.g., anaerobic heterotrophic uptake or anammox). These results indicate a rather consistent NH₄⁺ demand at the SWI during the hypoxic season and suggest that reduced nitrogen may limit microbial dynamics in the region.  相似文献   

Earth observations during space shuttle flight STS‐35: Columbia's mission to planet earth,December 2–10, 1990     

Kamlesh P. Lulla  Cynthia A. Evans  Michael R. Helfert  Vance D. Brand  Guy S. Gardner  John M. Lounge 《国际地球制图》2013,28(4):71-80

The article describes methodology of space monitoring of the existing landscapes as it is practised in the CIS (former USSR). Different points of mew are presented concerning environmental monitoring as well as the aspects of its practical organization. The objectives of automation of the ecological data acquisition, storage and processing are also dealt with; necessity of geographic information systems creation is substantiated. Experience gained in the operation of geoinformation systems is considered with plans on geo‐information base development for the needs of geographical and ecological studies of the CIS landscapes. Practical experience with case studies on identifying and mapping the ecological disaster zones is described in the Aral Sea basin and the Kyzyl Kum desert.  相似文献   

Coupled three-dimensional discrete element-lattice Boltzmann methods for fluid-solid interaction with polyhedral particles     

Michael Gardner  Nicholas Sitar 《国际地质力学数值与分析法杂志》2019,43(14):2270-2287

Interaction between solid particles and fluid is of fundamental interest to scientists and engineers in many different applications—cardiopulmonary flows, aircraft and automobile aerodynamics, and wind loading on buildings to name a few. In geomechanics, particle shape significantly affects both particle-particle and particle-fluid interaction. Herein, we present a generalized method for modeling the interaction of arbitrarily shaped polyhedral particles and particle assemblages with fluid using a coupled discrete element method (DEM) and lattice Boltzmann method (LBM) formulation. The coupling between DEM and LBM is achieved through a new algorithm based on a volume-fraction approach to consider three-dimensional convex polyhedral particles moving through fluid. The algorithm establishes the interaction using linear programming and simplex integration and is validated against experimental data. This approach to modeling the interaction between complex polyhedral particles and fluid is shown to be accurate for directly simulating hydrodynamic forces on the particles.  相似文献   

Benthic community structure and water column characteristics at two sites in the Kermadec Islands Marine Reserve,New Zealand     

Jonathan P. A. Gardner  Martin J. Curwen  Joanne Long  Robert J. Williamson  Ann R. Wood 《新西兰海洋与淡水研究杂志》2013,47(1):179-194

The Kermadec Islands Marine Reserve (KIMR), which is located at 30°S, is New Zealand's largest marine reserve at 748 000 ha, and its biota is composed of a mix of warm temperate, subtropical, and tropical species. A depth‐stratified ecological survey was conducted of the abundance and percentage cover of macrobenthic species and of the water column at two sites (Meyer Island and West Chanter Island), 2km apart. Significant differences in benthic community structure and in water column turbidity and chlorophyll concentrations were observed between the two sites despite their proximity and physical similarity. Compared with other “snapshot” surveys of benthic community structure at sites within the KIMR there was a high degree of similarity among the species observed, but often a low degree of similarity in species abundance or percentage cover as a function of depth. We suggest that despite its isolation and the degree of difficulty of working at this location, a full‐scale ecological survey of the coastal marine biota of the KIMR is warranted to better understand New Zealand's subtropical marine biota and its affinities with other marine biotas of the South Pacific.  相似文献   

Tracking Groundwater Discharge to a Large River using Tracers and Geophysics   总被引：1，自引：0，他引：1  

Glenn A. Harrington  W. Payton Gardner  Tim J. Munday 《Ground water》2014,52(6):837-852

Few studies have investigated large reaches of rivers in which multiple sources of groundwater are responsible for maintaining baseflow. This paper builds upon previous work undertaken along the Fitzroy River, one of the largest perennial river systems in north‐western Australia. Synoptic regional‐scale sampling of both river water and groundwater for a suite of environmental tracers (⁴He, ⁸⁷Sr/⁸⁶Sr, ²²²Rn and major ions), and subsequent modeling of tracer behavior in the river, has enabled definition and quantification of groundwater input from at least three different sources. We show unambiguous evidence of both shallow “local” groundwater, possibly recharged to alluvial aquifers beneath the adjacent floodplain during recent high‐flow events, and old “regional” groundwater introduced via artesian flow from deep confined aquifers. We also invoke hyporheic exchange and either bank return flow or parafluvial flow to account for background ²²²Rn activities and anomalous chloride trends along river reaches where there is no evidence of the local or regional groundwater inputs. Vertical conductivity sections acquired through an airborne electromagnetic (AEM) survey provide insights to the architecture of the aquifers associated with these sources and general groundwater quality characteristics. These data indicate fresh groundwater from about 300 m below ground preferentially discharging to the river, at locations consistent with those inferred from tracer data. The results demonstrate how sampling rivers for multiple environmental tracers of different types—including stable and radioactive isotopes, dissolved gases and major ions—can significantly improve conceptualization of groundwater—surface water interaction processes, particularly when coupled with geophysical techniques in complex hydrogeological settings.  相似文献   

Composition of Coronal Streamers from the SOHO Ultraviolet Coronagraph Spectrometer   总被引：1，自引：0，他引：1  

J. C. Raymond  J. L. Kohl  G. Noci  E. Antonucci  G. Tondello  M. C. E. Huber  L. D. Gardner  P. Nicolosi  S. Fineschi  M. Romoli  D. Spadaro  O. H. W. Siegmund  C. Benna  A. Ciaravella  S. Cranmer  S. Giordano  M. Karovska  R. Martin  J. Michels  A. Modigliani  G. Naletto  A. Panasyuk  C. Pernechele  G. Poletto  Peter L. Smith  R. M. Suleiman  L. Strachan 《Solar physics》1997,175(2):645-665

The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers the 940–1350 Å range as well as the 470–630 Å range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance scattering of emission lines from the solar disk dominates the intensities of a few lines, but electron collisional excitation produces most of the lines observed. Resonance, intercombination and forbidden lines are seen, and their relative line intensities are diagnostics for the ionization state and elemental abundances of the coronal gas. The elemental composition of the solar corona and solar wind vary, with the abundance of each element related to the ionization potential of its neutral atom (First Ionization Potential–FIP). It is often difficult to obtain absolute abundances, rather than abundances relative to O or Si. In this paper, we study the ionization state of the gas in two coronal streamers, and we determine the absolute abundances of oxygen and other elements in the streamers. The ionization state is close to that of a log T = 6.2 plasma. The abundances vary among, and even within, streamers. The helium abundance is lower than photospheric, and the FIP effect is present. In the core of a quiescent equatorial streamer, oxygen and other high-FIP elements are depleted by an order of magnitude compared with photospheric abundances, while they are depleted by only a factor of 3 along the edges of the streamer. The abundances along the edges of the streamer (‘legs’) resemble elemental abundances measured in the slow solar wind, supporting the identification of streamers as the source of that wind component.  相似文献   

Sensitive fluorometric procedure to determine individual amino acids in marine waters     

Wayne S. Gardner 《Marine Chemistry》1978,6(1):15-26

Improved methodology for amino acid analysis coupled with semi-micro isolation techniques make feasible the measurement of individual amino acids from marine waters where sample volumes are limited (e.g., sediment pore water or culture filtrates). If a water sample contains more than 20 nmole 1^?1 of the respective compounds, dissolved free amino acids (DFAA) can be isolated from 5 ml of filtrate by cation exchange and measured on a sensitive amino-acid analyzer equipped with a fluorometric detector. Two ml generally provides sufficient sample to determine total dissolved amino acids. Lower concentrations of amino acids can be measured after concentration from larger samples (250 ml) by ligand exchange.  相似文献   

Seasonal Dynamics in Dissolved Organic Carbon Concentrations in a Coastal Water-Table Aquifer at the Forest-Marsh Interface     

Miguel A. Goñi  I. Robert Gardner 《Aquatic Geochemistry》2003,9(3):209-232

The seasonal dynamics of dissolved organic carbon (DOC) in a subterranean estuary were examined in a coastal water-table aquifer extending across a forest-marsh interface into an adjacent tidal creek that leads to North Inlet (SC). The aquifer is characterized by groundwater flow from the forest recharge area towards the creek. DOC concentrations range from 50 to 140 mg L^-1 in the shallow portions of the aquifer below the forest and undergo seasonal changes that are inversely related to temperature and precipitation conditions. Markedly lower DOC concentrations (<10 mg L^-1) in the deep portion of the aquifer are consistent with the loss of a large fraction of the original DOC along the groundwater flow paths. Mass balance estimates indicate that over 60% of the DOC losses are due to sorption reactions whereas the rest appear to be caused by heterotrophic decay. Groundwater DOC discharge from the forest, which occurs in a restricted zone of the high marsh, is 5.5 mg carbon m^-2 d^-1 and accounts for a minor component of the annual carbon export from North Inlet. In contrast, moderately saline (2–12 ppt) ground waters below the marsh display elevated DOC concentrations (20 mg L^-1) that appear to be the result of mixing of fresh ground waters and surface seawater during tidal seepage and concentration during evapotranspiration. The flux of DOC associated with the discharge of these saline ground waters is 600 mg carbon m^-2 d^-1, which represents a significant fraction of the annual DOC budget for North Inlet.  相似文献