Catastrophic events reveal the dynamic nature of salt-marsh vegetation in Southern California   总被引：1，自引：0，他引：1  

Joy B. Zedler  Jordan Covin  Chris Nordby  Phil Williams  John Boland 《Estuaries and Coasts》1986,9(1):75-80

Recent hydrological disturbances, including flooding, dry-season streamflow, and drought, greatly altered coastal wetland habitats in sourthern California. At Tijuana Estuary, a six-year study of salt-marsh vegetation patterns during these rare conditions documented substantial temporal variability in plant growth and distribution. Important to cordgrass (Spartina foliosa Trin.) dynamics were the amount and timing of streamflows, which reduced soil salinity and alleviated stresses on plant growth. Poorest growing conditions occurred in 1984 when both river and tidal flows were lacking; soils had low moisture and extreme salinities (avg.=104‰ in September). Plant stress was documented in 1984 as high mortality (62% fewer stems than in 1983) and reduced height (19% less than in 1983). Cordgrass height was greatest in 1980 following winter flooding (20% increase over 1979); densities were greatest in 1983 with summer freshwater influxes (60% increase over 1982). A carbon allocation model is proposed to explain the varied responses.  相似文献   

Modelling for forest growing stock assessment using satellite data — A case study     

SS Benchalli  RC Prajapati 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):15-21

The satellite digital vegetation index data has been correlated with the forest growing stock by fitting linear regression models. The goodness of fit was tested. The analysis showed that the vegetation index which is the ratio of reflectance of vegetation in near infrared band to red wave band of electromagnetic spectrum is highly correlated to forest growing stock and the same can be used to predict the volume in remote forest areas for quick assessment purpose. Implications for future forest inventory are discussed.  相似文献   

Lamellar structures in low-calcium orthopyroxenes   总被引：1，自引：0，他引：1  

James N. Boland 《Contributions to Mineralogy and Petrology》1974,47(3):215-222

Clinoenstatite lamellae are found to be distributed in three distinct patterns that define three microstructural types. There are regions of the crystal devoid of lamellae and these correspond to ordered or O-orthopyroxene. When the lamellae are present but not in any periodic arrangement, disordered or D-orthopyroxene is identified. In some areas, the lamellae are spaced periodically and these are regions of “superlattice” orthopyroxene. These microstructural types explain all previous X-ray results on orthopyroxenes. Microstructural differences between low and high calcium orthopyroxenes are discussed.  相似文献   

海拉尔盆地基底晚古生代adakite的发现及其地质意义   总被引：5，自引：1，他引：4  

章凤奇  陈汉林  曹瑞成  蒙启安  朱德丰  王志国 《岩石学报》2010,26(2):633-641

海拉尔盆地的前中生代基底隶属中亚造山带东段的兴蒙造山带。 在盆地基底地层中发现了具有adakite成分特征的粗面安山岩、英安岩和闪长玢岩。 这些火成岩与晚古生代沉积地层交互或伴生, 共同构成晚中生代裂陷盆地的基底。 地球化学研究表明, 这些火成岩基本上属于高钾钙碱性和准铝质岩石系列, 具有高SiO₂和Al₂O₃含量, 高Sr、Sr/Y和La/Yb值, 富集轻稀土(LREE), 亏损重稀土(HREE)、Y和高场强元素(HFSE),Eu表现弱的负异常或轻微的正异常, 相容元素Mg、Cr和Ni含量低, 这些特征与增厚下地壳部分熔融成因的adakite非常相似, 而明显不同于典型的由俯冲洋壳熔融形成的adakite。 样品的(⁸⁷Sr/⁸⁶Sr)_i值基本一致,为0.7041, (¹⁴³Nd/¹⁴⁴Nd)_i值为0.51243~0.51247, ε_Nd (t)为正值(+3.7~+4.5), 显示其岩浆源区可能源于弱亏损地幔, 或亏损地幔受到地壳物质混染。 本文认为海拉尔地区晚古生代adakite型岩浆很可能是由当时新底侵的玄武质下地壳在角闪岩相向榴辉岩相过度或榴辉岩相条件下部分熔融形成。 这些adakite岩石的出现反映了兴蒙造山带晚古生代受到了古亚洲洋的俯冲消减引起的强烈的地幔玄武质岩浆底侵作用, 并由此导致地壳垂向上显著的增生加厚过程。  相似文献   

An echelle spectrograph for high resolution studies of the solar vacuum ultraviolet spectrum     

B. C. Boland  B. B. Jones  S. F. T. Engstrom 《Solar physics》1971,17(2):333-354

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Public participation in China’s green communities: Mobilizing memories and structuring incentives     

Alana Boland  Jiangang Zhu 《Geoforum》2012,43(1):147-157

In recent years, there has been heightened interest in creating more environmentally sustainable forms of urban development in China. Central in these greening initiatives has been increased attention on promoting public participation in community-based environmental activities. Focusing on China’s green community initiatives, we examine the production and effects of participation in a state-led development program. Our analysis considers how incentives for program organizers and participants are structured by broader political and economic imperatives facing Chinese cities. We also consider what influence China’s history of neighborhood-based mobilization campaigns had on the meanings and methods of participation in green communities. To understand how urban development processes and memories of mobilization influence participation at the local level, we present two examples of the community greening process from the city of Guangzhou, comparing policy outcomes between a new and older neighborhood. This article seeks to demonstrate that the participatory processes associated with such an urban environmental initiative cannot be adequately understood without reference to earlier participatory practices and broader policy priorities guiding development in Chinese cities.  相似文献   

A system-level modelling perspective of the KwaZulu-Natal Bight ecosystem,eastern South Africa     

UM Scharler  RC van Ballegooyen  MJ Ayers 《African Journal of Marine Science》2016,38(1):S205-S216

The KwaZulu-Natal Bight comprises the only sizeable shelf region on the eastern coast of South Africa, and is influenced by both the Agulhas Current on its seaward side and rivers and estuaries on its landward side. Established knowledge of the effect of the Agulhas Current includes the influence on nutrient concentrations in the bight of a semi-permanent upwelling cell at its northern border (St Lucia) and, to a much lesser extent, of a semi-permanent eddy feature at its southern extremity. Current modelling efforts, however, point to a very important role of land-derived nutrients, which supplement the productivity of food webs of the bight. This connectivity of the bight to its adjacent ecosystems has various implications. First, its productivity has traditionally been viewed via phytoplankton growth, whereas ecosystem modelling efforts point to a very high reliance on imported detritus (mainly land-derived) in order to sustain especially the rich benthic food web. The benthos in the bight dominates the food web, and is in marked contrast to the upwelling system of the west coast of South Africa (Atlantic Ocean) where water-column productivity dominates. Second, the importance of the connectivity of the Thukela Bank prawn-trawling ground to estuarine nursery areas, which has been modelled quantitatively, highlights the significance of this particular ecosystem connectivity for fisheries and also for the Thukela Bank food web. Heterogeneity across the bight is apparent for nutrient turnover rates (carbon, nitrogen, phosphorus), CNP content and stoichiometry, whereas nitrogen is a limiting nutrient across the entire bight. The food web near the Thukela River is richer in nutrient content and more active (higher turnover rates) compared to the northern and southern parts of the bight. This environmental heterogeneity was also apparent from the CNP content and stoichiometry of the various species and species groups in the bight. Requirements to take the hydrodynamic, biogeochemical and first ecosystem modelling efforts towards a meaningful predictive capability are discussed. The importance of adopting a system-level view of the bight and its connected systems for realistic exploration of global change scenarios is highlighted.  相似文献   

Sediment oxygen consumption and benthic nutrient fluxes on the Louisiana continental shelf: A methodological comparison     

Tina Miller-Way  Gregory S. Boland  Gilbert T. Rowe  Robert R. Twilley 《Estuaries and Coasts》1994,17(4):809-815

There has been considerable discussion but little experimental evidence regarding the comparability of in-situ and remote (shipboard or laboratory) incubations for the determination of sediment oxygen consumption and benthic nutrient flux rates. This paper presents the results of such a comparison, using in situ chamber and shipboard chemostatic systems, for a shallow station on the Louisiana, continental shelf during April 1992. Results indicated no methodological differences between rates of sediment oxygen consumption and nutrient flux (NH₄ ⁺, NO₅ ^?, NO₂ ^?, PO₄ ^3?, and SiO₂/Si(OH)₂) that could be attributed to the removal of cores from shelf sediments. This conclusion implies that subcoring from box cores is no more destructive of sediment structure and salient environmental characteristics than chamber emplacement. Differences between the methods occurred when ambient oxygen concentrations were low (<2 ml l^?1). These differences were caused by initial reaeration of bottom water in the shipboard system and reflect the sensitivity of heterotrophic metabolism, dissolution kinetics, and diffusive fluxes to low oxygen concentrations. The differences in exchange rates observed in this study reiterate the importance in maintaining ambient conditions in the experimental apparatus. The results of this study corroborate the small body of, data that addresses this issue and extends methodological similarities to include nutrient exchanges. Given the comparability of rates, use of remote chemostatic systems is more advantageous for work in shelf environments than in-situ batch methods due to increased statistical rigor, logistical convenience, and the ability to minimize changes in experimental conditions during incubations.  相似文献   

Dislocation deformation mechanisms in peridotite xenoliths in kimberlites     

J. N. Boland  J. M. A. Buiskool Toxopeus 《Contributions to Mineralogy and Petrology》1977,60(1):17-30

The dislocation substructures in olivine from coarse-grained peridotite xenoliths in kimberlites from the Lesotho region have been determined. The [100] dislocations may be located in simple (100) tilt boundaries while the density of free or individual [100] dislocations is 10⁶/cm² or less. The [001] dislocations form (010) twist arrays or more complex (100) subboundaries with the [100] dislocations; the density of free [001] dislocations increases to 8 × 10⁸/cm² in those grains in which tangles are observed. The simple (100) subboundaries are considered to result from a high temperature, slow strain-rate deformation (creep-like process) while the more complex subboundaries composed of [100] and [001] dislocations, as well as the high density of [001] dislocations, indicate faster strain rates and/or lower deformation temperatures than the creep deformation. These two broad phases of deformation have been interpreted as an early stage of mantle-type flow followed by deformation during or subsequent to the emplacement of the kimberlite.  相似文献   

Marine debris accumulation in the nearshore marine habitat of the endangered Hawaiian monk seal, Monachus schauinslandi 1999-2001     

Boland RC  Donohue MJ 《Marine pollution bulletin》2003,46(11):1385-1394

Large amounts of marine debris are present in shallow reefs adjacent to beach haulouts of the critically endangered Hawaiian monk seal, Monachus schauinslandi. These areas serve as seal pup nurseries, and injury and death caused by entanglement in marine debris are undermining population recovery efforts. We investigated the extent of this threat by measuring the accumulation of potentially entangling derelict fishing gear in nursery zones, 1999-2001. Plots of reef 1.0-1.3 km2 at three Northwestern Hawaiian Islands were initially cleaned of derelict fishing gear in 1999 then resurveyed in 2000 and 2001. Submerged debris densities across sites ranged from 16 to 165 debris items/km2. Resurveyed sites yielded annual marine debris accumulation rates from 0 to 141 debris items/km2. This large range was attributed to the physiography of reef areas surveyed. Trawl net webbing was significantly more common than other types of debris recovered and represented 84% of all debris encountered, suggesting that much of the debris originated from distant North Pacific Ocean fisheries. The likely source of most debris is the multinational trawl fisheries of the North Pacific Ocean. An international solution to this problem is needed. Targeted marine debris removal is a short-term, successful, entanglement mitigation strategy.  相似文献