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991.
It is well known that snow plays an important role in land surface energy balance; however, modelling the subgrid variability of snow is still a challenge in large‐scale hydrological and land surface models. High‐resolution snow depth data and statistical methods can reveal some characteristics of the subgrid variability of snow depth, which can be useful in developing models for representing such subgrid variability. In this study, snow depth was measured by airborne Lidar at 0.5‐m resolution over two mountainous areas in south‐western Wyoming, Snowy Range and Laramie Range. To characterize subgrid snow depth spatial distribution, measured snow depth data of these two areas were meshed into 284 grids of 1‐km × 1‐km. Also, nine representative grids of 1‐km × 1‐km were selected for detailed analyses on the geostatistical structure and probability density function of snow depth. It was verified that land cover is one of the important factors controlling spatial variability of snow depth at the 1‐km scale. Probability density functions of snow depth tend to be Gaussian distributions in the forest areas. However, they are eventually skewed as non‐Gaussian distribution, largely due to the no‐snow areas effect, mainly caused by snow redistribution and snow melt. Our findings show the characteristics of subgrid variability of snow depth and clarify the potential factors that need to be considered in modelling subgrid variability of snow depth. 相似文献
992.
Daniel D.P. McCarthy Graham S. Whitelaw Scott Anderson Donald Cowan Fred McGarry Anthony Robins Holly L. Gardner Christine D. Barbeau Nadia A. Charania Zachariah General Jeff Liedtke Celine Sutherland Paulo Alencar Leonard J.S. Tsuji 《Geoforum》2012,43(2):305-314
The remote First Nation (FN) communities of the Mushkegowuk Territory on the west coast of James Bay, Ontario, Canada are currently facing increased development pressures and the imposition of a government land use planning process. The land use planning process is mandated in the Far North Act (received Royal Assent on September 23, 2010). There is a need for capacity enhancement for community-based natural resource planning and management in the Territory. A number of frameworks are emerging for addressing change brought on by resource development and building resilience to such change at the community level. Among these include the concept of adaptive capacity. In collaboration with FN community leaders, we explored the use of “collaborative geomatics” tools to foster adaptive capacity. Our action research suggests that collaborative geomatics technologies should enhance the Mushkegowuk First Nations’ adaptive capacity to address environmental and policy change by allowing them to collect and manage data collaboratively (e.g., traditional environmental knowledge, western science) to create opportunities for innovative community development, including natural resource development and management. 相似文献
993.
High-resolution pollen and magnetic susceptibility (MS) analyses have been carried out on a sediment core taken from a high-elevation alpine bog area located in Sierra Nevada, southern Spain. The earliest part of the record, from 8200 to about 7000 cal yr BP, is characterized by the highest abundance of arboreal pollen and Pediastrum, indicating the warmest and wettest conditions in the area at that time. The pollen record shows a progressive aridification since 7000 cal yr BP that occurred in two steps, first shown by a decrease in Pinus, replaced by Poaceae from 7000 to 4600 cal yr BP and then by Cyperaceae, Artemisia and Amaranthaceae from 4600 to 1200 cal yr BP. Pediastrum also decreased progressively and totally disappeared at ca. 3000 yr ago. The progressive aridification is punctuated by periodically enhanced drought at ca. 6500, 5200 and 4000 cal yr BP that coincide in timing and duration with well-known dry events in the Mediterranean and other areas. Since 1200 cal yr BP, several changes are observed in the vegetation that probably indicate the high-impact of humans in the Sierra Nevada, with pasturing leading to nutrient enrichment and eutrophication of the bog, Pinus reforestation and Olea cultivation at lower elevations. 相似文献
994.
Behzad Mortazavi Ashley A. Riggs Jane M. Caffrey Hélène Genet Scott W. Phipps 《Estuaries and Coasts》2012,35(3):862-877
Benthic oxygen, dinitrogen, and nutrient fluxes (NH4+, NO3−, and PO43−) were measured monthly during a 1-year period at two locations in Weeks Bay, a shallow (1.4 m) and eutrophic estuary in Alabama.
Gross primary productivity (GPP), ecosystem respiration (R), and net ecosystem metabolism were determined from high-frequency
dissolved oxygen measurements. Peak water column NO3− (55 μM) and chlorophyll a (138 μg/l) concentrations were measured during spring and fall, respectively. Sediments were a net source of NH4+ (102 μmol m−2 h−1) and PO43− (0.9 μmol m−2 h−1) but a sink for NO3− (−30 μmol m−2 h−1). Benthic N2 fluxes indicated net N fixation (12 μmol N m−2 h−1). Sediment oxygen demand (0.55 g O2 m−2 day−1) accounted for <10% of R (7.3 g O2 m−2 day−1). Despite high GPP rates (4.7 g O2 m−2 day−1), the estuary was net heterotrophic. Benthic regeneration supplied, on average, 7.5% and 4% of primary productivity N and
P demands, respectively. These results contrast with the conventional view that benthic regeneration accounts for a large
fraction of phytoplankton nutrient demand in shallow estuaries. 相似文献
995.
Characterizing dietary resources and species interactions in estuaries is challenging, particularly when considering the dynamic
nature of these ecosystems, the ranges in body sizes of species, and the potential for trophic roles to vary with ontogeny.
We examined the influence of season and location on relationships between body size and δ15N, δ13C, and δ34S values across a range of fishes from two subtropical estuaries. The results suggest that isotopic values of estuarine fishes
are independent of body size. However, seasonal variation propagated throughout the assemblage as the majority of fishes integrated
different δ15N, δ13C, or δ34S values. The absence of δ15N–, δ13C–, and δ34S–body size relationships suggests that either (1) dietary preference of these fishes do not shift within the range of body
sizes sampled, (2) these fishes shift to an alternate diet that is not isotopically distinct, or (3) that spatial and temporal
variation in isotopic signatures of prey negate any size-based relationships. Seasonal variability in the isotopic values
of these fishes suggests either movement to an alternative habitat or a shift in organic matter source associated with the
transition of dry to wet seasons. Moreover, variance distributions of the best-fit models indicate that seasonal dietary preferences
of conspecifics do not vary over moderate spatial scales. Seasonal variability among fishes in these estuaries suggests plasticity
in feeding strategies that may afford greater adaptive flexibility to these species in response to changes in food availability
resulting from variable environmental conditions. 相似文献
996.
In the tails of dromaeosaurid dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally. The fully articulated and three-dimensionally preserved caudal series of some dromaeosaurid specimens show that individually these caudal rods were flexible, not rigid as previously thought. However, examination of the arrangement of the caudal rods in cross-section indicates that the combined effect of multiple caudal rods did provide substantial rigidity in the dorsoventral, but not in the lateral, plane. The results of digital muscle reconstructions confirm that dromaeosaurids and rhamphorhynchids also shared greatly reduced caudofemoral muscles in the anterior tail region. The striking similarities between the tails of dromaeosaurids and rhamphorhynchids suggest that both evolved under similar behavioral and biomechanical pressures. Combined with recent discoveries of primitive deinonychosaurs that phylogenetically bracket the evolution of dromaeosaurid caudal rods between two arboreal gliding/flying forms, these results are evidence that the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle. 相似文献
997.
998.
Lance Wollwage Scott Fedick Sergey Sedov Elizabeth Solleiro‐Rebolledo 《Geoarchaeology》2012,27(5):441-456
Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatán Peninsula, México. Detailed study of dated soil‐sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices. 相似文献
999.
Peng Cui Chao Dang Jian-qi Zhuang Yong You Xiao-qing Chen Kevin M. Scott 《Environmental Earth Sciences》2012,65(4):1055-1065
Landslides and rock avalanches triggered by the 2008 Wenchuan Earthquake produced 257 landslide dams, mainly situated along
the eastern boundary of the Qinghai-Tibet Plateau where rivers descend approximately 3,000 m into the Sichuan Basin. The largest
of these dams blocked the Tongkou River (a tributary of the Fujiang River) at Tangjiashan. The blockage, consisting of 2.04 × 107 m3 of landslide debris, impounded a lake with a projected maximum volume of 3.15 × 108 m3, potentially inundating 8.92 km2 of terrain. Its creation during the rainy season and the possibility of an uncontrolled release posed a serious, impending
threat to at least 1.3 million people downstream that could add substantially to the total of 69,200 individuals directly
killed by the earthquake. Risk assessment of the blockage indicated that it was unlikely to collapse suddenly, and that eventual
overtopping could be mitigated by notching the structure in order to create an engineered breach and achieve safe drainage
of the lake. In addition to the installation of monitoring and warning instrumentation, for emergency planning we estimated
several outburst scenarios equivalent to 20, 25, 33, and 50% of the dam failing suddenly, creating, respectively, 3.35, 3.84,
4.22, and 4.65 km2 of flooded area, and overbank water depths of 4.6, 5.1, 5.7, and 6.2 m, respectively, in Mianyang, the second largest city
in Sichuan Province, 48 km downstream from the blockage. Based on these scenarios, recommendations and plans for excavating
a sluiceway, draining the lake, and downstream evacuation were proposed and later were implemented successfully, with the
blockage breached by overtopping on June 10, less than a month after dam emplacement. The peak discharge of the release only
slightly exceeded the flood of record at Mianyang City. No lives were lost, and significant property damage was avoided. Post-breaching
evaluation reveals how future similar mitigation can be improved. Although initial breach erosion was slow, later erosion
was judged uncontrollably rapid; increased slope of the engineered channel and adoption of a compound, trapezoid–triangular
cross-section can be considered, as can other measures to control the rate of breach incision. Evacuees from Mianyang City
spent an unnecessarily long time (12 days) in temporary settlements; more precise risk management planning can reduce this
time in the future. 相似文献
1000.
Effects of precipitation pulses on water and carbon dioxide fluxes in two semiarid ecosystems: measurement and modeling 总被引:2,自引:2,他引:0
Jun Fan Scott B. Jones Li Bing Qi Quan Jiu Wang Ming Bin Huang 《Environmental Earth Sciences》2012,67(8):2315-2324
Modeling of soil?Cwater, ?Cheat and ?Ccarbon (C) fluxes provides an important tool for predicting mass and energy transfers based on a hydraulic-, thermal- and C-mass balance approach. Model predictions were evaluated using measured data from two water-limited study sites, one pasture and one supporting an alfalfa crop, to indentify differences between these ecosystems. Soil water content, temperature, and evapotranspiration (ET) data were used to validate soil water dynamics components of a process-based numerical model. Soil surface CO2 efflux estimates (i.e., fluxes from soil respiration) were also made to estimate soil CO2 emissions. The results show that the Hydrus-1D numerical model can be parameterized to simulate the soil hydrodynamics and CO2 fluxes measured at both locations. Rainfall and irrigation events triggering increases in plant root and microbial respiration rates were simulated to recreate observed pulsed CO2 fluxes. There were distinct differences in ET and soil CO2 effluxes between the ecosystems and watering events significantly modified the fluxes. Differences in potential evapotranspiration and soil texture could help explain these discrepancies. The results demonstrate that numerical modeling can be a useful tool for estimating soil surface fluxes in calibrated ecosystems when micrometeorological methods may not be suitable. 相似文献