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941.
A precise understanding of the aboveground biomass of desert steppe and its spatio-temporal variation is important to understand how arid ecosystems respond to climate change and to ensure that scarce grassland resources are used rationally. On the basis of 756 ground survey quadrats sampled in western Inner Mongolia steppe in 2005–2011 and remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS)—the normalized difference vegetation index (NDVI) dataset for the period of 2001–2011—we developed a statistical model to estimate the aboveground biomass of the desert steppe and further explored the relationships between aboveground biomass and climate factors. The conclusions are as follows: (1) the aboveground biomass of the steppe in the research area was 5.27 Tg (1 Tg=1012 g) on average over 11 years; between 2001 and 2011, the aboveground biomass of the western Inner Mongolia steppe exhibited fluctuations, with no significant trend over time; (2) the aboveground biomass of the steppe in the research area exhibits distinct spatial variation and generally decreases gradually from southeast to northwest; and (3) the important factor causing interannual variations in aboveground biomass is precipitation during the period from January to July, but we did not find a significant relationship between the aboveground biomass and the corresponding temperature changes. The precipitation in this period is also an important factor influencing the spatial distribution of aboveground biomass (R2=0.39, P<0.001), while the temperature might be a minor factor (R2=0.12, P<0.01). The uncertainties in our estimate are primarily due to uncertainty in converting the fresh grass yield estimates to dry weight, underestimates of the biomass of shrubs, and error in remote sensing dataset. 相似文献
942.
Hg bioaccumulation in marine copepods around hydrothermal vents and the adjacent marine environment in northeastern Taiwan 总被引:1,自引:0,他引:1
The Hg concentration in seawater and copepod samples collected from the area around hydrothermal vents at Kueishan Island and the adjacent marine environment in northeastern Taiwan were analyzed to study Hg bioaccumulation in copepods living in polluted and clean marine environments. The seawater collected from the hydrothermal vent area had an extremely high concentration of dissolved Hg, 50.6–256 ng l−1. There was slightly higher Hg content in the copepods, 0.08–0.88 μg g−1. The dissolved Hg concentration in the hydrothermal vent seawater was two to three orders of magnitude higher than that in the adjacent environment. The bioconcentration factor of the studied copepods ranged within 103–106, and showed higher dissolved concentration as the bioconcentration factor was lower. A substantial abundance, but with less copepod diversity was recorded in the seawater around the hydrothermal vent area. Temora turbinata was the species of opportunity under the hydrothermal vent influence. 相似文献
943.
AbstractFloods, as extreme hydrological phenomena, can be described by more than one correlated characteristic, such as peak, volume and duration. These characteristics should be jointly considered since they are generally not independent. For an ungauged site, univariate regional flood frequency analysis (FA) provides a limited assessment of flood events. A recent study proposed a procedure for regional FA in a multivariate framework. This procedure represents a multivariate version of the index-flood model and is based on copulas and multivariate quantiles. The performance of the proposed procedure was evaluated by simulation. However, the model was not tested on a real-world case study data. In the present paper, practical aspects are investigated jointly for flood peak (Q) and volume (V) of a dataset from the Côte-Nord region in the province of Quebec, Canada. The application of the proposed procedure requires the identification of the appropriate marginal distribution, the estimation of the index flood and the selection of an appropriate copula. The results of the case study show that the regional bivariate FA procedure performed well. This performance depends strongly on the performance of the two univariate models and, more specifically, the univariate model of Q. The results show also the impact of the homogeneity of the region on the performance of the univariate and bivariate models.
Editor D. Koutsoyiannis 相似文献
944.
945.
Spatial distribution of cadmium and lead in the sediments of the western Anzali wetlands on the coast of the Caspian Sea (Iran) 总被引:1,自引:0,他引:1
Rasool Zamani-Ahmadmahmoodi Abbas Esmaili-Sari Jahangard Mohammadi Alireza Riyahi Bakhtiari Mozhgan Savabieasfahani 《Marine pollution bulletin》2013
Spatial distribution patterns of total cadmium (Cd) and lead (Pb), their bioavailable fractions and total organic matter in sediment from Anzali wetlands are provided. Total sediment Pb was higher than Cd (34.95 versus 0.024 μg/g dry weight). The geoaccumulation index indicated that the sediment was “uncontaminated”, but some stations were categorized as “unpolluted” to “moderately polluted”. Less than 0.01 of Pb existed in exchangeable and carbonate fractions. The sum of exchangeable and carbonate-bound fractions of Cd was 42%, suggesting that Cd poses high risk to the aquatic ecosystems. Total Cd and Pb exhibited positive relationships with total organic matter. Considering spatial distribution maps of total and bioavailable fractions of metals suggested that high concentrations of metals does not necessarily indicate high bioavailable fraction. The methodologies we used in this study can be in more effective management of aquatic ecosystems, as well as ecological risk assessment of metals, and remediation programs. 相似文献
946.
Résumé Le modèle proposé est un générateur stochastique d'averses couplé à un modèle empirique de calcul de leurs érosivités, calé à une série pluviographique de 15 ans d'observations. Notre objectif est de développer une démarche probabiliste, qui permettrait d'étudier les conséquences érosives des pluies dans le temps, en cumulant l'érosivité consécutive des pluies simulées durant plusieurs années, supposée proportionnelle à la dégradation des sols, ou au transport solide en suspension sur la même période. Cette génération peut en effet se faire sur plusieurs années calendaires, et nous permettrait de ce fait d'éviter d'être limité par la taille des échantillons. L'ensemble pouvant être utilisé en mode opérationnel, pour reconstituer de très longus séries d'épisodes pluvieux dans l'objectif d'étudier le cumul de leur érosivité dans le temps. Cette démarche ne contredit pas les approches expérimentales, qui ont une réalité concrète de terrain, bien au contraire elle les conforte et permet d'avancer davantage dans la réflexion posée par la problématique de l'érosion hydrique. 相似文献
947.
ABSTRACTIn this surface water modelling study, a new spatial evaluation for assessing the impact of urbanization was applied for the semi-arid watersheds intersecting with the Gaza coastal aquifer. The SWAT model was calibrated and validated in a semi-automated approach for streamflow in the main watersheds. The results show that the model could simulate water budget components adequately within the complex semi-arid watersheds. Linear relationships between the change in urban area and the corresponding change in surface runoff or percolation were concluded for the urbanized sub-basins. The urban-surface runoff index (USI) and the urban-percolation index (UPI) were developed to represent a micro-level evaluation of different urban change scenarios in the sub-basins. The global urban-surface runoff index (GUSI) and the global urban-percolation index (GUPI) were derived as macro-level factors reflecting the influence on the overall Gaza coastal aquifer due to urban area expansion.
Editor D. Koutsoyiannis Associate editor E. Rozos 相似文献
948.
Evaluation of Composts from Agricultural Wastes with Fish Pond Sediment as Bulking Agent to Improve Compost Quality 总被引:1,自引:0,他引:1
Tanmoy Karak Pradip Bhattacharyya Ranjit Kumar Paul Tapati Das Subhrajit K. Saha 《洁净——土壤、空气、水》2013,41(7):711-723
Composts with five different ratios of agricultural wastes, viz. rice straw (RS), wheat straw (WS), potato plant (PP), and mustard stover (MS) were prepared with or without fish pond bottom sediment to investigate the compost maturity and their suitability for field application. The composting process was monitored through the changes in physico‐chemical parameters and germination index (GI) at every 7 days interval of the composting process. All the composts were dark brown and smelled like forest soil within 56 days of composting, which reflected its matured status. On the basis of the physico‐chemical parameters (bulk density: 0.84 g/cm3; pH 7.05; electrical conductivity: 3.52 mS/cm; cation exchange capacity:82.4 cmol/kg; total carbon:321.4 g/kg; total nitrogen: 16.9 g/kg; As: 6.8 mg/kg; Cd: 2.96 mg/kg; Cr: 29.6 mg/kg, Cu: 243.6 mg/kg; Hg: 0.019 mg/kg; Ni: 24.3 mg/kg; Pb: 62.1 mg/kg and Zn: 812 mg/kg) and GI (89–96%), it could be concluded that RS/WS/PP/MS, 1:1:2:1 v/v/v/v with fish pond sediment produced better compost in accordance with the Indian compost standard. Application of a combined randomized block design analysis revealed that there is a significant difference in the responses of the five composts, in relation to the time of composting. Hierarchical clustering algorithm was applied with a view to form homogeneous groups of five different composts on the basis of different physico‐chemical parameters. Therefore, the ratio of waste incorporation is an important decision for composting and addition of pond sediment can improve the quality of compost. 相似文献
949.
《Urban geography》2013,34(1):66-82
Measuring the level of segregation often encounters two methodological issues: measures are sensitive to changes in the geographical scale of the data and the effectiveness of the measure in reflecting spatial segregation. Several spatial measures have been suggested to measure spatial segregation, but whether they are more or less sensitive to changes in spatial scale has not been investigated, while some spatial measures are relatively scale-insensitive. Using the 1990 Census data of 30 selected U.S. metropolitan areas, this paper demonstrates that these spatial measures, similar to the aspatial measure, report higher levels of segregation when smaller areal units are used in the analysis. Some spatial measures are even more sensitive to scale changes than aspatial measures. Certain patterns of the scale sensitivity were identified, but no general rules can be formulated. A preliminary explanation of the scale effect on spatial segregation measures is offered. 相似文献
950.
《自然地理学》2013,34(5):473-490
This paper presents a novel method for detecting and mapping movements of ecotone boundaries, over both time and space, using existing fossil pollen data. The method combines existing statistical techniques, including discriminant analysis and spatial interpolation, to generate statistically robust maps of ecotone boundaries over time. This method was applied to provide a comprehensive vegetative history of the forest tension zone in the Lower Peninsula of Michigan during the last 10,000 years. Pollen data for nine lakes in the Lower Peninsula were analyzed with discriminant analysis and spatially interpolated with inverse distance weighted to track ecotone movements of the forest tension zone. The forest tension zone has been in existence over the last 10,000 years and has been highly variable over space and time, with at least three major latitudinal shifts, spanning 320 km and 6° of latitude, as well as several less pronounced shifts. These shifts occurred primarily in response to millennial-scale oscillations in climate such as the warmer and dryer conditions associated with the mid-Holocene. A slighter shift was evident in association with the cooler and drier conditions of the Little Ice Age (600-100 cal yr BP). This research demonstrates the sensitivity of Great Lakes forest communities to Holocene climate change and suggests a similar sensitivity of future ecotone dynamics in response to modern global warming. 相似文献