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In an experimental study on the effect of parrotfish (probably Scarus taeniurus) grazing on the structure of benthic reef communities, fishes in densities of 0.6 to 1.5 parrotfish per m2 or 9 to 17 g wet weight of fish per m2 of feeding surface were found to have an optimum effect, resulting in the greatest benthic species richness and biomass on 2-dimensional surfaces. The presence of refuges (3-dimensional habitats), however, has a greater impact on bemthic community structure (number of species and biomass) than does just the density of parrotfish in such an experimental system. Coral recruitment is enhanced by the presence of refuges and, like coralline algae, is more successful under increased grazing pressure. These optimum densities of parrotfishes relate well to observed field densities where, in a collection from a Hawaiian patch reef, there were 1.1 fish or 10.8 g wet weight of parrotfish per square meter of collection area. The success of coralline algae and corals under high grazing pressure may have important consequences for the stability and structure of modern coral reefs. 相似文献
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西安作为汾渭平原地区最大的城市,大气颗粒物污染形势严峻.2017年夏季期间,在西安市浐灞生态园区运用气溶胶化学组分监测仪,对大气亚微米颗粒物中的非难挥发性组分(NR-PM1)进行了在线监测.观测期间NR-PM1的平均质量浓度为(30.1?±?15.4)μg???m?3.其中有机物含量最高,占NR-PM1总质量浓度的63... 相似文献
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David Medvigy Paul R. Moorcroft Roni Avissar Robert L. Walko 《Environmental Fluid Mechanics》2005,5(1-2):109-134
This paper examines the spatio-temporal patterns of atmospheric carbon dioxide transport predicted by the Regional Atmospheric Modeling System (RAMS). Forty-eight hour simulations over northern New England incorporating a simple representation of the diurnal summertime surface carbon dioxide forcing arising from biological activity indicate that, in its native formulation, RAMS exhibits a significant degree of mass non-conservation. Domain-wide rates of non-physical mass gain and mass loss are as large as three percent per day which translates into approximately eleven parts per million per day for carbon dioxide — enough to rapidly dilute the signature of carbon dioxide fluxes arising from biological activity. Analysis shows that this is due to the approximation used by RAMS to compute the Exner function. Substitution of the exact, physically complete equation improves mass conservation by two orders of magnitude. In addition to greatly improving mass conservation, use of the complete Exner function equation has a substantial impact on the spatial pattern of carbon dioxide predicted by the model, yielding predictions differing from a conventional RAMS simulation by as much as forty parts per million. Such differences have important implications both for comparisons of modeled atmospheric carbon dioxide concentrations to observations and for carbon dioxide inversion studies, which use estimates of atmospheric transport of carbon dioxide in conjunction with measurements of atmospheric carbon dioxide concentrations to infer the spatio-temporal distribution of surface carbon dioxide fluxes. Furthermore, use of the complete Exner function equation affects the vertical velocity and water mixing ratio fields, causing significant changes in accumulated precipitation over the region. 相似文献
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Heather Moorcroft 《Local Environment》2016,21(5):591-614
In Australia, redressing past injustices and recognising Indigenous peoples' spiritual and cultural connections to land have resulted in the return of significant amounts of land to Indigenous people. Parallel to this, in attempts to address declining biodiversity, innovative and neo-liberal approaches to conservation under a new paradigm have been promoted. The role and influence of the non-state sector are increasing, and Indigenous peoples’ involvement in conservation is also growing. This paper reviews the history of conservation and Indigenous social justice policy in Australia. It describes how the social justice agenda has been the primary motivator of returning land to Indigenous Australians, and historically has been the driver and catalyst for Indigenous peoples' involvement in conservation, whilst the conservation agenda has increased conservation on private lands and the role and influence of the non-state conservation sector. The paper reveals how the trajectories of conservation and Indigenous social justice have become intrinsically linked with the emergence of new paradigms, providing opportunities for a propitious niche. Yet it also shows how the two trajectories have manifested themselves with a paradox of disparity; achievements secured under an Indigenous social justice agenda are being enjoyed by conservation under the new paradigm, whilst Indigenous social justice is increasingly becoming dependent on a conservation agenda. 相似文献
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Myller S. Tonhá Daniel F. Araújo Rafael Araújo Bruno C.A. Cunh Wilson Machado Joelma F. Portel João PR Souz Hikari K. Carvalho Elton L. Dantas Henrique L. Roig Patrick Seyler Jeremie Garnier 《环境科学学报(英文版)》2021,33(3):313-325
The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ66/64ZnJMC ≈ + 0.30‰) and anthropogenic (δ66/64ZnJMC ≈ + 0.15‰) end members. The lighter δ66/64ZnJMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds. 相似文献
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Lee Eunjee Livino Angela Han Shin-Chan Zhang Ke Briscoe John Kelman Jerson Moorcroft Paul 《Regional Environmental Change》2018,18(6):1871-1881
Regional Environmental Change - Over the past 40 years, the discharge in South America’s Paraná River basin has increased despite no evidence of significant rainfall increases... 相似文献
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