A Comparison of Water Quality Between Low- and High-Flow River Conditions in a Tropical Estuary, Hilo Bay, Hawaii   总被引：1，自引：0，他引：1  

Tracy N. Wiegner  Lucas H. Mead  Stephanie L. Molloy 《Estuaries and Coasts》2013,36(2):319-333

Effects of storms on the water quality of Hilo Bay, Hawaii, were examined by sampling surface waters at 6 stations 10 times during low-flow and 18 times during high-flow (storms) river conditions. The direction of a storm’s impact on water quality parameters was consistent among storms and most stations; however, direction of the impact varied with the parameter. High river flow conditions increased concentrations of nitrate and decreased those of dissolved organic nitrogen (N); effects on ammonium and particulate N were station specific. Storms also increased dissolved organic and particulate carbon (C) concentrations. Dissolved phosphorus (P) concentrations were not affected by high river flow events. Dissolved organic forms dominated the N, C, and P pools under both low- and high-flow river conditions. Soil-derived particles and fecal indicator bacteria increased during storms, while chlorophyll a concentrations and bacterial cell abundances decreased. Our results suggest that an increase in storms with global warming could impact water quality of tropical estuaries.  相似文献   

Rapid mapping in support of emergency response after earthquake events   总被引：1，自引：1，他引：0  

Stephanie Wegscheider  Tobias Schneiderhan  Alexander Mager  Hendrik Zwenzner  Joachim Post  Günter Strunz 《Natural Hazards》2013,68(1):181-195

Earthquakes and other sudden onset natural disasters require quick and efficient emergency response. Earth observation (EO) data can make a valuable contribution to emergency response efforts if provided within hours and at the most days after the event. Mechanisms like the International Charter Space and Major Disasters and the European GMES Emergency Response Service provide the necessary basis for an efficient and rapid provision of EO data and damage mapping. This paper provides an overview of earthquake damage assessment methodologies, their potential and their limitations in a rapid mapping context and outlines a methodology for casualty estimation. Two case studies—the 2010 Haiti earthquake and the 2011 Van (Turkey) earthquake—are presented, where DLR’s Center for satellite-based crisis information (ZKI) provided rapid damage maps using a team-based visual interpretation approach. Additionally, the application of a casualty estimation method in the immediate aftermath of an earthquake is outlined.  相似文献   

An inter-hemispheric comparison of the tropical storm response to global warming     

Stephanie Gleixner  Noel Keenlyside  Kevin I. Hodges  Wan-Ling Tseng  Lennart Bengtsson 《Climate Dynamics》2014,42(7-8):2147-2157

Model studies do not agree on future changes in tropical cyclone (TC) activity on regional scales. We aim to shed further light on the distribution, frequency, intensity, and seasonality of TCs that society can expect at the end of the twenty-first century in the Southern hemisphere (SH). Therefore, we investigate TC changes simulated by the atmospheric model ECHAM5 with T213 (~60 km) horizontal resolution. We identify TCs in present-day (20C; 1969–1990) and future (21C; 2069–2100) time slice simulations, using a tracking algorithm based on vorticity at 850 hPa. In contrast to the Northern hemisphere (NH), where tropical storm numbers reduce by 6 %, there is a more dramatic 22 % reduction in the SH, mainly in the South Indian Ocean. While an increase of static stability in 21C may partly explain the reduction in tropical storm numbers, stabilization cannot alone explain the larger SH drop. Large-scale circulation changes associated with a weakening of the Tropical Walker Circulation are hypothesized to cause the strong decrease of cyclones in the South Indian Ocean. In contrast the decrease found over the South Pacific appears to be partly related to increased vertical wind shear, which is possibly associated with an enhanced meridional sea surface temperature gradient. We find the main difference between the hemispheres in changes of the tropical cyclones of intermediate strength with an increase in the NH and a decrease in the SH. In both hemispheres the frequency of the strongest storms increases and the frequency of the weakest storms decreases, although the increase in SH intense storms is marginal.  相似文献   

Spatiotemporal index for analyzing controls on snow climatology: application in the Colorado Front Range     

Eric E. Richer  Stephanie K. Kampf  Steven R. Fassnacht  Cara C. Moore 《自然地理学》2013,34(2):85-107

Mountain snowpacks are important water supplies that are susceptible to climate change, yet snow measurements are sparse relative to snowpack heterogeneity. We used remote sensing to derive a spatiotemporal index of snow climatology that reveals patterns in snow accumulation, persistence, and ablation. Then we examined how this index relates to climate, terrain, and vegetation. Analyses were based on Moderate Resolution Imaging Spectroradiometer eight-day snow cover from 2000 to 2010 for a mountain watershed in the Colorado Front Range, USA. The Snow Cover Index (SCI) was calculated as the fraction of years that were snow covered for each pixel. The proportion of SCI variability explained by independent variables was evaluated using regression analysis. Independent variables included elevation, northing, easting, slope, aspect, northness, solar radiation, precipitation, temperature, and vegetation cover. Elevation was the dominant control on SCI patterns, due to its influence on both temperature and precipitation. Grouping SCI values by elevation, we identified three distinct snow zones in the basin: persistent, transitional, and intermittent. The transitional snow zone represents an area that is sensitive to losing winter snowpack. The SCI can be applied to other basins or regions to identify dominant controls on snow cover patterns and areas sensitive to snow loss.  相似文献   

Cryptic microtextures and geological histories of K-rich alkali feldspars revealed by charge contrast imaging     

Stephanie?FludeEmail author  Martin?R.?Lee  Sarah?C.?Sherlock  Simon?P.?Kelley 《Contributions to Mineralogy and Petrology》2012,163(6):983-994

Charge contrast imaging in the scanning electron microscope can provide new insights into the scale and composition of alkali feldspar microtextures, and such information helps considerably with the interpretation of their geological histories and results of argon isotope thermochronological analyses. The effectiveness of this technique has been illustrated using potassium-rich alkali feldspars from the Dartmoor granite (UK). These feldspars contain strain-controlled lamellar crypto- and microperthites that are cross-cut by strain-free deuteric microperthites. The constituent albite- and orthoclase-rich phases of both microperthite generations can be readily distinguished by atomic number contrast imaging. The charge contrast results additionally show that sub-micrometre-sized albite ‘platelets’ are commonplace between coarser exsolution lamellae and occur together to make cryptoperthites. Furthermore, charge contrast imaging reveals that the orthoclase-rich feldspar is an intergrowth of two phases, one that is featureless with uniform contrast and another that occurs as cross-cutting veins and grains with the {110} adularia habit. Transmission electron microscopy shows that the featureless feldspar is tweed orthoclase, whereas the veins and euhedral grains are composed of irregular microcline that has formed from orthoclase by ‘unzipping’ during deuteric or hydrothermal alteration. The charge contrast imaging results are especially important in demonstrating that deuteric perthites are far more abundant in alkali feldspars than would be concluded from investigations using conventional microscopy techniques. The unexpected presence of such a high volume of replacement products has significant implications for understanding the origins and geological histories of crustal rocks and the use of alkali feldspars in geo- and thermochronology. Whilst the precise properties of feldspars that generate contrast remain unclear, the similarity between charge contrast images and corresponding cathodoluminescence images of deuteric microperthites indicates that trace element chemistry and possibly also elastic strain within the crystal play a major role.  相似文献   

Spatial characterization of land surface energy fluxes and uncertainty estimation at the Salar de Atacama,Northern Chile     

Stephanie K. Kampf  Scott W. Tyler 《Advances in water resources》2006

We use Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) data to estimate spatial energy flux and evaporation distributions at the Salar de Atacama, a playa in Northern Chile. Our approach incorporates ASTER surface kinetic temperature, emissivity, and reflectance data, ground-based meteorological measurements, and empirical parameters. Energy flux distributions are estimated using either spatially constant or spatially distributed values of model parameters, with spatially distributed parameters assigned separately to each land cover category in an image classification. We test the sensitivity of energy budget calculations to state variable and parameter values by conducting Monte Carlo simulations for regions with ground energy budget measurements. Results show that assigning spatially distributed model parameters via land cover classifications yields significant improvements to ground and sensible heat flux predictions. Latent heat fluxes cannot, however, be predicted with sufficient accuracy to allow estimation of area-integrated evaporative moisture loss at this low-evaporation playa.  相似文献   

A threshold in soil formation at Earth’s arid-hyperarid transition     

Stephanie A. Ewing  Brad Sutter  Kunihiko Nishiizumi  Steven S. Cliff  William Dietrich  Ronald Amundson 《Geochimica et cosmochimica acta》2006,70(21):5293-5322

The soils of the Atacama Desert in northern Chile have long been known to contain large quantities of unusual salts, yet the processes that form these soils are not yet fully understood. We examined the morphology and geochemistry of soils on post-Miocene fans and stream terraces along a south-to-north (27° to 24° S) rainfall transect that spans the arid to hyperarid transition (21 to ∼2 mm rain y⁻¹). Landform ages are ? 2 My based on cosmogenic radionuclide concentrations in surface boulders, and Ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2.1 My. A chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall. In the arid (21 mm rain y⁻¹) soil, total mass loss to weathering of silicate alluvium and dust (−1030 kg m⁻²) is offset by net addition of salts (+170 kg m⁻²). The most hyperarid soil has accumulated 830 kg m⁻² of atmospheric salts (including 260 kg sulfate m⁻² and 90 kg chloride m⁻²), resulting in unusually high volumetric expansion (120%) for a soil of this age. The composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in-soil chemical transformation and loss. Long-term rates of atmospheric solute addition were derived from the ion inventories in the driest soil, divided by the landform age, and compared to measured contemporary rates. With decreasing rainfall, the soil salt inventories increase, and the retained salts are both more soluble and present at shallower depths. All soils generally exhibit vertical variation in their chemistry, suggesting slow and stochastic downward water movement, and greater climate variability over the past 2 My than is reflected in recent (∼100 y) rainfall averages. The geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold: in wetter soils, the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 10⁵ to 10⁶ years, while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion. The specific geochemistry of hyperarid soils is a function of atmospheric sources, and is expected to vary accordingly at other hyperarid sites. This work identifies key processes in hyperarid soil formation that are likely to be independent of location, and suggests that analogous processes may occur on Mars.  相似文献   

Controls on nutrient and phytoplankton dynamics during normal flow and storm runoff conditions, southern Kaneohe Bay, Hawaii     

Stephanie Ringuet  Fred T. Mackenzie 《Estuaries and Coasts》2005,28(3):327-337

Fluvial effects on nutrient and phytoplankton dynamics were evaluated in southern Kaneohe Bay, Oahu, Hawaii. Fluvial inputs occurred as small, steady baseflows interrupted by intense pulses of storm runoff. Baseflow river inputs only affected restricted areas around stream mouths, but the five storm events sampled during this study produced transient runoff plumes of much greater spatial extent. Nutrient loading via runoff generally led to an increase of the phytoplankton biomass and gross primary productivity in southern Kaneohe Bay, but the rapid depletion of nutrients resulted in a decline of the algal populations in the relatively short time of days. Under baseline conditions, water column primary productivity in southern Kaneohe Bay is normally nitrogen limited. Following storm events, the high ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIN:DIP, 25–29) fluxes of runoff nutrients drove bay waters towards phosphorus limitation. A depletion of phosphate relative to DIN in surface waters was observed following all storm events. Due to high flushing rates, recovery times of bay waters from storm perturbations ranged from 3 to 8 d and appeared to be correlated with tidal range. Storm inputs have a significant effect on the water column ecosystem and biogeochemistry in southern Kaneohe Bay. The perturbations were only transient events and the system rapidly recovered to prestorm conditions.  相似文献   

Evaporation and land surface energy budget at the Salar de Atacama, Northern Chile   总被引：3，自引：0，他引：3  

Stephanie K. Kampf  Scott W. Tyler  Cristin A. Ortiz  Jos F. Muoz  Paula L. Adkins 《Journal of Hydrology》2005,310(1-4):236-252

Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km² playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d⁻¹, and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d⁻¹ in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d⁻¹ in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation.  相似文献   

A numerical study on the influence of geometry on the formation of sandbanks     

Noel Carbajal  Stephanie Piney  Jorge Gómez Rivera 《Ocean Dynamics》2005,55(5-6):559-568

Applying a two-dimensional, non-linear hydrodynamic numerical model in combination with a semiempirical equation for bedload sediment transport, the influence of geometry on the formation of sandbanks is investigated. In the first experiment, the formation of sandbanks in an ideal rectangular basin, resembling the Taylor’s problem, was calculated. Sandbanks occur in a small area at the closed boundary. Similar experiments were carried out for a range of wavelengths of the incident Kelvin wave. The results reveal that large wavelengths favor the generation of sandbanks. In subsequent calculations, the basin was modified by introducing new geographical features like bays and peninsulas. The numerical experiments show that geometry is a fundamental factor to determine the position where groups of sandbanks appear. The results suggest that in regions where the Kelvin wave is diffracted, the formation of sandbanks occurs. An experiment, in which we applied an ideal geometric configuration representing that of the Southern Bight of the North Sea, generated sandbank patterns resembling those observed in the region.  相似文献