Erosion characteristics and floc strenght of Athabasca river cohesive sediments: towards managing sediment-related issues

Purpose: Most of Canada’s tar sands exploitations are located in the Athabasca river basin. Deposited cohesive sediments in Athabasca river and tributaries are a potential source of PAHs in the basin. Erosional behavior of cohesive sediments depends not only of fluid turbulence but on sediments structure and particularly the influence of organic content. This research tries to describe this behavior in Athabasca river sediments. Methods: An experimental study of cohesive sediments dynamics in one of the tributaries, the Muskeg river, was developed in a rotating annular flume. Variation of the shear stress allowed the determination of erosional strength for beds with different consolidation periods. Particle size measurements were made with a laser diffraction device operated in a continuous flow through mode. Optical analyses of flocs (ESEM and TEM) were performed with samples taken at the end of the experiments. Results: An inverse relationship between suspended sediment concentration (SS) and the consolidation period was found. The differences are related in this research to the increasing organic content of the sediments with consolidation period. The particle size measurements during the experiments showed differences on floc strength that are also related to changing organic content during different consolidation periods. ESEM and TEM observations confirm the structural differences for beds with different consolidation periods. The effects of SFGL on floc structure and in biostabilization of the bed are discussed. Conclusions: It is recommended in this paper that consolidation period should be taken into account for the modeling of erosion of cohesive sediments in the Athabasca river. Relating to transport models of pollutants (PAHs) it is highly recommended to consider flocs organic content, particularly algae, in the resuspension module.Environment Canada, CONACY

A comparative study of the gas exchange potential between three wetland species using sulfur hexafluoride as a tracer

The gas-exchange potential of three wetland species (helophytes) was examined in an aquatic model vegetation facility (AMOVA) using sulfur hexafluoride (SF6) as a tracer. Three beds containing gravel and vegetated with Phragmites australis, Typha latifolia and Schoenoplectus lacustris were compared to an unvegetated gravel bed as a reference. A mass balance of SF6 emissions revealed a different seasonal emission pattern for the three species investigated. Helophytes capable of pressurized ventilation, e.g. Phragmites and Typha, showed the highest gas-exchange values. On an annual basis net SF6 emission values of Phragmites were the highest in the autumn month of October (65.8%) and the lowest in the winter month of January (37.1%). P. australis represents a helophyte species with highly developed gas-exchange tissues facilitating diffusion and transport of the tracer gas SF6 to the atmosphere via the intercellular lacunar system. (C) 2001 Elsevier Science B.V. All rights reserved

Phytoremediation of selenium by two helophyte species in subsurface flow constructed wetland

The phytoremediation of selenium by two different wetland species was investigated. Selenium (20.4 mug/l) was supplied continuously to subsurface flow constructed wetlands, one vegetated with Typha latifolia L. and the other with Phragmites australis (Cav.) Trin. ex Steud. The beds of both species had same hydraulic loading rate (0.079 m(3)/m(2)/d) and water retention time (24 h). However, the mass loading rate was 1.27 mg Se/m(2)/d for Phragmites and 1.35 mg Se/m(2)/d for Typha. In the Typha bed Se migrated faster than in the Phragmites bed. After 25 d of Se supplementation in the Typha bed about 54% of the Se inlet concentration remained in the outlet water. In the Phragmites bed Se was removed completely from the water after passing through 3/4 of the bed length. After 65 d of Se supplementation the highest amount of Se (2.8 mug/g dry matter) was determined in the organic material of the Typha bed. Roots and rhizomes accumulated 2,2 and 1.8 mug/g dry matter respectively. Phragmites accumulated Se in the leaves and stems, but not in the rhizomes. The accumulation in the leaves (1.8 mug Se/g dry matter) was three times higher than in the sterns (0.6 mug Se/g dry matter). (C) 2002 Elsevier Science Ltd. All rights reserved

Phytoremediation of selenium using subsurface-flow constructed wetland

The potential of two plant species, Phragmites australis (common reed) and Typha latifolia (cattail), in the phytoremediation process of selenium (Se) was studied in subsurface-flow constructed wetland (SSF). Se was supplemented continuously at a concentration of 100 microg Se L(-1) in the inlet of the cultivation beds of the SSF. Water samples collected from the outlet of the Phragmites bed after 1, 3, 6, 9, and 12 wk of treatments showed that Se content was under detectable limits. Water samples collected from the Typha bed at the same five periods showed that Se concentrations in the outlet were 55, 47, 65, 76, and 25 microg/L, respectively. The results of bioaccumulation in the biomass of both species after 12 wk of treatment indicated that Typha plants accumulated Se mainly in fine roots. Phragmites accumulated Se mainly in leaves and rhizomes, and moderate levels were found in stems and fine organic materials. The results indicate that common reed is a very good species for Se phytoextraction and phytostabilization (immobilization) and that cattail is only a phytostabilization species. The use of common reed and cattail for Se phytoremediation in a SSF system and in constructed wetland models are discussed

Integralidade da atenção e integração de serviços de saúde: desafios para avaliar a implantação de um "sistema sem muros" Comprehensive health care and integrated health services: challenges for evaluating the implementation of a "system without walls"

Neste texto, partimos do pressuposto de que a integralidade da atenção é um eixo prioritário da investigação e avaliação dos serviços e sistemas de saúde, estruturados como redes assistenciais interorganizacionais que articulam dimensões clínicas, funcionais, normativas e sistêmicas em sua operacionalização, reconhecendo que nenhuma organização reúne a totalidade dos recursos e competências necessárias para a solução dos problemas de saúde de uma população, em seus diversos ciclos de vida. Em virtude da complexidade desse "sistema sem muros", que elimina as barreiras de acesso entre os diversos níveis de atenção, em resposta às necessidades de saúde nos âmbitos local e regional, julgamos oportuno compartilhar algumas "lições preliminares" aprendidas em experiências pessoais e na literatura sobre a integração de serviços, que nos parecem de interesse comum aos pesquisadores e gestores comprometidos com a sua implantação.<br>The premise of this paper is that comprehensive health care is a major component in the investigation and evaluation of health services and systems, structured as inter-organizational health care networks articulating clinical, functional, normative, and systemic dimensions in their operationalization and based on the understanding that no organization combines all the necessary resources and capabilities to solve the health problems of a population with its various life cycles. Given the complex nature of this "system without walls", eliminating barriers to access in the various health care levels in response to local and regional health, we take this opportunity to share a few "preliminary lessons" from our experience and from the literature on integrated health services which may interest researchers and managers concerned with the implementation of such services