The Impact of Herder Sedentarization on Natural Resource Access in Northeastern Ghana     

Rita Yembilah  Miriam Grant 《社会与自然资源》2014,27(6):621-635

The Fulani of West Africa have increasingly migrated to humid West Africa since the Sahelian droughts of the 1970s, drawing opposition from indigenous groups that are concerned about the deprivation of their livelihood and monopolization of resources for herders’ livestock. This research, which involved farmers, shepherds, and Fulani herders, addressed three issues: the nature of indigenous grazing and watering regimes, shepherd–herder relations, and herders’ impact on resource access for indigenes’ livestock. The research indicates that in-community and off-community platforms for resource access exist. The former has not been impacted by the herders; the latter has experienced changes insufficient to constitute an overhaul of resource access at the expense of indigenes’ livestock. Instead, a “shepherd–herder” category of resource access has emerged that is characterized by negotiation for resource space, opening avenues for addressing broader resource access issues, and typically tense indigene–herder relationships.  相似文献   

Demography and biomass of the seagrass Zostera marina in a Mexican Coastal Lagoon     

Miriam Poumian-Tapia  Silvia E. Ibarra-Obando 《Estuaries and Coasts》1999,22(4):837-847

From January 1987 to February 1988 the annual biomass cycle and demography of the seagrass Zostera marina were assessed in San Quintin Bay, a shallow coastal lagoon on the Pacific coast of Baja California, Mexico. Shoot density and aboveground biomass were sampled monthly along two intertidal transects parallel to the shore. Belowground biomass was sampled every 2 mo. Shoot density differed between transects, ranging from 929±71 (SE) in July to 279 ±80 shoots m⁻² in December, at the deeper transect (I). At the shallow transect (II) there was not a significant difference through time, and a mean of 737 shoots m⁻² was calculated. Lateral shoots were present year round and represented between 1% and 30% of total density at transect I and between 3% and 25% at transect II. Reproductive shoots were present from March to September at both transects, with a density range of 77±28 shoots m⁻² (March) to 9±3 shoots m⁻² (September), and represented 5% of total shoot density. Neither aboveground biomass nor LAI (Leaf Area Index) differed between transects, with values ranging between 77±14.5 g dry wt m⁻² (October 1987) and 13±2.4 g dry wt m⁻² (February 1988) for aboveground biomass, and between 0.6±0.2 m² leves m⁻² substrate (January) and 2.7±0.3 m² leaves m⁻² substrate (September) for LAI. Neither root biomass nor rhizome biomass differed between transects, or as a function of time; the mean value for roots was 17 g dry wt m⁻² and for rhizomes 29 g dry wt m⁻². Belowground biomass represented 54% of total biomass. We found a significant correlation between aboveground biomass and LAI (r=0.949 for transect I, and 0.926 for transect II) as well as between total biomass (aboveground and belowground) and LAI (r=0.814), which allows us to consider using LAI as a predictor of these variables. Biomass changes were related to changes in shoot weight (r=0.676 at transect I; 0.582 at transect II), more than to changes in shoot number. Water temperature was found to be the driver of biomass changes in the aboveground compartment.  相似文献   

Diatoms on Earth, Comets, Europa and in Interstellar Space     

Richard B. Hoover  Fred Hoyle  N.C. Wickramasinghe  Miriam J. Hoover  S. Al-Mufti 《Astrophysics and Space Science》1999,268(1-3):197-224

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of acosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.  相似文献   

Microstructures documenting Cenozoic extension processes in the northern continental margin of the South China Sea     

Liheng Sun  Xiaolong Huang  Yingde Jiang  Joann Miriam Stock 《International Geology Review》2020,62(7-8):1094-1107

ABSTRACT

In order to investigate the thinning process of the northern continental margin of the South China Sea, petrographic and microstructural analysis were carried out on 20 greenschistfacies mylonite samples, which were obtained from Site U1504 of IODP Expedition 367/368 in the Outer Margin High of the region. The mineral assemblage of the greenschist-facies mylonite is chlorite + epidotite + albite (Ab = 94.7–99.9) + quartz, which contains 10-30% gravel components. Microstructural analysis indicates that the greenschist-facies mylonite experienced two episodes of deformation：early ductile deformation followed by a later stage of brittle deformatio. Both episodes of deformation suggest an extensional environment. The extensive development of bulging recrystallization (BLG) of quartz, microscopic fractures and fine granulation of albite suggest that the temperature of ductile deformation is about 300-400°C, compatiable with a ductile shearing at shallow crust levels (~5-10 km). Petrographic features suggest that the greenschist-facies mylonite might originate from volcanic sedimentary rocks or sedimentary rocks affected by the intrusion of mafic magma. Combined with seismic interpretation, we propose that the greenschist-facies mylonite might be formed by crustal exhumation after thick Mesozoic sediments were denuded by a major extension.  相似文献   

Key structural parameters affecting earthquake ground motion in 2D and 3D sedimentary structures     

Peter Moczo  Jozef Kristek  Pierre-Yves Bard  Svetlana Stripajová  Fabrice Hollender  Zuzana Chovanová  Miriam Kristeková  Deborah Sicilia 《Bulletin of Earthquake Engineering》2018,16(6):2421-2450

Alluvial valleys generate strong effects on earthquake ground motion (EGM). These effects are rarely accounted for even in site-specific studies because of (a) the cost of the required geophysical surveys to constrain the site model, (b) lack of data for empirical prediction, and (c) poor knowledge of the key controlling parameters. We performed 3D, 2D and 1D simulations for six typical sedimentary valleys of various width and depth, and for a variety of modifications of these 6 “nominal models” to investigate sensitivity of EGM characteristics to impedance contrast, attenuation, velocity gradient and geometry. We calculated amplification factors, and 2D/1D and 3D/2D aggravation factors for 10 EGM characteristics, using a representative set of recorded accelerograms to account for input motion variability. The largest values of the amplification and aggravation factors are found for the Arias intensity and cumulative absolute velocity, the lowest for the root-mean-square acceleration. The aggravation factors are largest for the vertical component. For each model, at least one EGM characteristic exhibits a significant 2D/1D aggravation factor, while all EGM characteristics exhibit significant 2D/1D aggravation factor on the vertical component. For all investigated sites, there is always an area in the valley for which 1D estimates are not sufficient. 2D estimates are insufficient at several sites. The key structural parameters are the shape ratio and overall geometry of the sediment-bedrock interface, impedance contrast at the sediment-bedrock interface, and attenuation in sediments. The amplification factors may largely exceed the values that are usually considered in GMPEs between soft soils and rock sites.  相似文献   

Probabilistic long-term reservoir operation employing copulas and implicit stochastic optimization     

&#;vila  Leandro  Mine  Miriam R. M  Kaviski  Eloy 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(7):931-947

Stochastic Environmental Research and Risk Assessment - This paper explores and combines implicit stochastic optimization (ISO) with copula functions to simulate long-term operating policies for a...  相似文献   

Evidence of field-scale shifts in transpiration dynamics following bark beetle infestation: Stomatal conductance responses     

Meijun Li  Wei Shao  Ye Su  Miriam Coenders-Gerrits  Jerker Jarsjö 《水文研究》2024,38(5):e15162

Amplified eruptive outbreaks of bark beetles as a consequence of climate change can cause tree mortality that significantly affects terrestrial water and carbon fluxes. However, the lack of field-scale observations of underlying physiological mechanisms currently hampers the expression of such ecosystem disturbances in predictive modelling. Based on a unique flux tower dataset from a subalpine forest located in the Rocky Mountains, mechanisms of stomatal response to an extensive bark beetle outbreak were investigated using various models and parametrizations. The datasets cover a decade, including the periods of pre-infestation, infestation, and post-infestation. Field measurements showed considerable decreases in evapotranspiration (ET), transpiration (T), and leaf area index (LAI) during the two-year infestation period compared to the pre-infestation period. Model interpretations of observed water and carbon fluxes indicated that the overall reductions in T were not solely due to decreased LAI, but also to changes in physiological behaviours. The summer season's canopy-scale stomatal conductance was significantly reduced during the infestation period, from 0.0018 to 0.0011 m s⁻¹. One primary reason for the observed variations is likely that the bark beetle infestation hampers the water transport in the xylem. The damage of xylem has important implications for water use efficiency (WUE), which also significantly influences the parameterization of stomatal conductance. When using stomatal conductance models to forecast ecosystem dynamics, it is crucial to recalibrate the model's parameters to ensure the accurate depiction of stomatal dynamics during various infestation periods. The neglect of the temporal variability of canopy-scale stomatal conductance under ecosystem disturbances (e.g., bark beetle infestations) in current earth system models, therefore, requires specific attention in assessments of large-scale water and carbon balances.  相似文献   

A 3.5 ka record of paleoenvironments and human occupation at Angkor Borei,Mekong Delta,southern Cambodia     

Paul Bishop  Dan Penny  Miriam Stark  Marian Scott 《Geoarchaeology》2003,18(3):359-393

Microfossil and sedimentological data from a 3.1 m core extracted from a reservoir (baray) at the ancient Cambodian settlement of Angkor Borei in the Mekong Delta have provided a continuous record of sedimentation and paleoenvironments dating from about 2000 cal yr B.C. Palynological data indicate that for much of the cal. 1st and 2nd millennia B.C. mangroves dominated the regional vegetation, while extensively and regularly burnt grasslands dominated the local vegetation. Turbid, nutrient‐rich standing water characterized the core locality, perhaps suggesting a connection with rivers in the area. An abrupt change during the cal. 5th to 6th centuries A.D. involved a dramatic reduction in grasslands and the expansion of secondary forest or re‐growth taxa. These changes are synchronous with an abrupt decline in the concentration of microscopic charcoal particles in the sediments, and the colonization of the core locality by swamp forest plants. These changes are taken to indicate a shift in land‐use strategies or, possibly, a period of land abandonment. The age for the construction of the baray is interpreted to be in the 17th–19th centuries, but this dating remains speculative. Construction of the Angkor Borei baray exploited a preexisting body of standing water, so its construction was fundamentally different from the methods used at the Angkorian capital in northern Cambodia. © 2003 Wiley Periodicals, Inc.  相似文献