Local economic linkages to community‐based tourism in rural Costa Rica     

Bernardo Trejos  Lan‐Hung Nora Chiang 《Singapore journal of tropical geography》2009,30(3):373-387

This paper reports on the contribution of tourism to the wellbeing of rural residents through the development of economic linkages engaged by community‐based tourism (CBT) in rural Costa Rica. In a qualitative case study of local economic linkages surrounding one such project in Chira Island, economic linkages were assessed at two levels: discourse and practice. The findings indicate that CBT does not involve the collective property of the community, but rather, the collective property of a group of community members organized in a formal association. As a result, a discourse on local economic linkages has been promoted by CBT support organizations in which hopes of wider benefits are placed on small linkages to services and products provided by local community members. However, a field survey suggested that the economic linkages generated by CBT in the community were sporadic and polyvalent and, furthermore, that the linkages with agriculture are negatively affected by scale and seasonality, resulting in leakages out of the community. These findings caution practitioners that CBT may only have small‐scale positive impacts on the local economy.  相似文献   

Ciliate communities in a constructed mangrove wetland for wastewater treatment     

Qing-Hua Chen  Nora Fung-Yee Tam  Paul K.S. Shin  Siu-Giu Cheung  Run-Lin Xu 《Marine pollution bulletin》2009,58(5):711-719

In wetlands constructed for treating municipal and industrial wastewater, including mangroves, the effect of wastewater discharged on the substrate has often been neglected. Ciliates, an important group of protozoa, are sensitive to pollutants and any changes in ciliate diversity and community structure reflects the habitat quality. The ciliate communities at six sections along a constructed mangrove belt (33 m in length) planted with Aegicerascorniculatum were investigated in Shenzhen, South China. In all samples collected in both rainy and dry seasons, 183 ciliate species were observed. Most species (56%) were free-swimming forms, while only 10.8% were sessile ciliates. The abundance and species number of ciliates were both found to decrease from the anterior (the wastewater inlet) to the posterior (the outlet) parts of the wetland belt, indicating that organic matter and bacteria in wastewater, which served as food for most ciliates, were gradually removed by the constructed wetland. The r/K (number of r- and K-selected species) ratios at the six sections were relatively small, between 0.2 and 0.4, whereas the C/P (abundance of colpodids and polyhymenophorans) quotient at some sections was higher than 1. These results indicate that although most of the environments along the constructed wetland belt were not stressful for ciliate communities, there were habitats that favored colpodids in high abundances.  相似文献   

Use of ciliates (Protozoa: Ciliophora) as bioindicator to assess sediment quality of two constructed mangrove sewage treatment belts in Southern China     

Chen QH  Xu RL  Tam NF  Cheung SG  Shin PK 《Marine pollution bulletin》2008,57(6-12):689-694

To complement physical and chemical data, information of biological communities is important to assess the qualities of mangrove sediments receiving wastewater. Ciliate communities have cosmopolitan distribution, short life cycle and high sensitivity to pollutants, which make them useful as biological indicators of the sediment environment. In most literature, ciliates are widely used as bioindicators for the state of water quality. In this study, the physico-chemical parameters and ciliate community structure of surface sediment collected at different sampling points from two constructed mangrove (Aegiceras and Sonneratia) belts for treatment of municipal sewage in southern China were investigated. Results showed that most (> 80%) of the 216 species ciliates identified at the two constructed mangrove belts were either omnivorous or bacterivorous. Sediment redox potential (Eh) was considered an important factor to govern the distribution of ciliate species within the mangrove sediment. The saprobic system originally derived from freshwater ecosystem was used to evaluate the saprobic degrees of these constructed mangrove belts. Saprobic index (SI) values declined from the sewage inlet to the outlet points of the constructed belts, suggesting better sediment quality at the outlet point caused by treatment processes within the mangrove belt system. Sediment quality of the sewage outlet area of the constructed Aegiceras belt was determined as class II-III (SI = 2.48), while that of the Sonneratia belt was as class III (SI = 2.71) according to the saprobic classification, indicating that a better sewage treatment efficiency was apparent in the Aegiceras than Sonneratia belt. The present data suggested that ciliates could serve as a good bioindicator in assessing organically polluted sediment qualities.  相似文献   

Sonication of bacteria, phytoplankton and zooplankton: Application to treatment of ballast water   总被引：2，自引：0，他引：2  

Holm ER  Stamper DM  Brizzolara RA  Barnes L  Deamer N  Burkholder JM 《Marine pollution bulletin》2008,56(6):1201-1208

We investigated the effect of high power ultrasound, at a frequency of 19 kHz, on the survival of bacteria, phytoplankton and zooplankton, in order to obtain estimates of effective exposure times and energy densities that could be applied to design of ultrasonic treatment systems for ballast water. Efficacy of ultrasonic treatment varied with the size of the test organism. Zooplankton required only 3-9s of exposure time and 6-19 J/mL of ultrasonic energy to realize a 90% reduction in survival. In contrast, decimal reduction times for bacteria and phytoplankton ranged from 1 to 22 min, and decimal reduction energy densities from 31 to 1240 J/mL. Our results suggest that stand-alone ultrasonic treatment systems for ballast water, operating at 19-20 kHz, may be effective for planktonic organisms >100 microm in size, but smaller planktonic organisms such as phytoplankton and bacteria will require treatment by an additional or alternative system.  相似文献   

Development of a new connection for precast concrete walls subjected to cyclic loading     

Ramin Vaghei  Farzad Hejazi  Hafez Taheri  Mohd Saleh Jaafar  Farah Nora Aznieta Abdul Aziz 《地震工程与工程振动(英文版)》2017,16(1):97-117

The Industrialized Building System (IBS) was recently introduced to minimize the time and cost of project construction. Accordingly, ensuring the integration of the connection of precast components in IBS structures is an important factor that ensures stability of buildings subjected to dynamic loads from earthquakes, vehicles, and machineries. However, structural engineers still lack knowledge on the proper connection and detailed joints of IBS structure construction. Therefore, this study proposes a special precast concrete wall-to-wall connection system for dynamic loads that resists multidirectional imposed loads and reduces vibration effects (PI2014701723). This system is designed to connect two adjacent precast wall panels by using two steel U-shaped channels (i.e., male and female joints). During casting, each joint is adapted for incorporation into a respective wall panel after considering the following conditions: one side of the steel channel opens into the thickness face of the panel; a U-shaped rubber is implemented between the two channels to dissipate the vibration effect; and bolts and nuts are used to create an extension between the two U-shaped male and female steel channels. The developed finite element model of the precast wall is subjected to cyclic loads to evaluate the performance of the proposed connection during an imposed dynamic load. Connection performance is then compared with conventional connections based on the energy dissipation, stress, deformation, and concrete damage in the plastic range. The proposed precast connection is capable of exceeding the energy absorption of precast walls subjected to dynamic load, thereby improving its resistance behavior in all principal directions.  相似文献   

A quantitative approach to sedimentary surface structures contoured by the interplay of microbial colonization and physical dynamics   总被引：4，自引：0，他引：4  

Nora Noffke  & Wolfgang E. Krumbein 《Sedimentology》1999,46(3):417-426

In the tidal flats of Mellum Island (southern North Sea), biofilms and microbial mats, generated largely by cyanobacteria, colonize the sedimentary surfaces. Biostabilization effects and biomass enrichment influence erosional and depositional dynamics resulting from tidal flushing and storm surges. The overlapping of both biological and physical forces causes the development of characteristic sedimentary structures. To obtain a quantitative expression of the degree of effectiveness of microbial colonization in the formation of structures in an extended tidal area, a modification index (MOD-I) was developed based on the following values: (i) the proportion of mat-covered area related to a defined investigation area (I_A); (ii) the degree of steepness of slope angles of raised erosional remnants (I_S); and (iii) the degree of microbial levelling of a rippled sedimentary surface (I_N). The MOD-I was calculated for several defined regions within the study area, and both winter and summer situations were considered. The MOD-I values show, first, that the lower intertidal zone is characterized by index values approaching zero. This implies that microbially induced effects in this zone are negligible, even in summer. Second, the upper intertidal zone is characterized by lower index values in winter and relatively high values in summer. This implies a predominantly seasonal control on the biofilm development in this zone. Third, in the lower supratidal zone, the index values are almost identical during both winter and summer. This implies non-seasonal biological effects in this zone. Concomitant empirical studies on the composition of microbial mats and films suggest that the dominant microbial type influences the MOD-I value.  相似文献   

Microbial signatures in peritidal siliciclastic sediments: a catalogue   总被引：12，自引：0，他引：12  

Gisela Gerdes  Thomas Klenke  & Nora Noffke 《Sedimentology》2000,47(2):279-308

A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic determinants. It summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones (temperate humid: Mellum Island, southern North Sea; subtropical arid: coast of southern Tunisia). Textural geometries reveal a high structural diversity, but their determinants are primarily based upon six major parameters: (1) intrinsic biofactors: structural diversification of sedimentary microbial films and mats inherent in the organisms, i.e. their construction morphology, growth, taxis and behaviour, and local abundance of specific morphotypes. Most prominent are the ensheathed filamentous cyanobacteria Microcoleus chthonoplastes and Lyngbya aestuarii, and the sheathless filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to physical disturbances: sediment supply, erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats. (3) Trapping/binding effects: physicobiological processes give rise to grain orientations and wavy to lenticular lamina, lamina‐specific grain arrangements and ‘sucrose’ calcium carbonate accumulations. (4) Secondary physical deformation of biogenic build‐ups: mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from mechanical effects of gas formation from decaying mats, and features related to the formation of authigenic minerals (calcium carbonates, calcium sulphates, pyrite). (6) Bioturbation and grazing: post‐depositional structures, such as Skolithos‐type dwellings, traces of burrowing insects, gastropod grazing traces and faecal pellets. In synopsis, the catalogue firstly comprises a sound set of ubiquitous signatures. This uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings. The catalogue secondly documents signatures that are extremely sensitive to tidal position, hydrodynamic regime and overall climatic conditions. These kinds of signature indicate narrow facies zones, which often coincide with the activity or dominance zones of certain organisms. An overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings.  相似文献   

Hydrological and catchment controls on event-scale dissolved organic carbon dynamics in boreal headwater streams     

Adrienne A. Ducharme  Nora J. Casson  Scott N. Higgins  Karl Friesen-Hughes 《水文研究》2021,35(7):e14279

Hydrological events transport large proportions of annual or seasonal dissolved organic carbon (DOC) loads from catchments to streams. The timing, magnitude and intensity of these events are very sensitive to changes in temperature and precipitation patterns, particularly across the boreal region where snowpacks are declining and summer droughts are increasing. It is important to understand how landscape characteristics modulate event-scale DOC dynamics in order to scale up predictions from sites across regions, and to understand how climatic changes will influence DOC dynamics across the boreal forest. The goal of this study was to assess variability in DOC concentrations in boreal headwater streams across catchments with varying physiographic characteristics (e.g., size, proportion of wetland) during a range of hydrological events (e.g., spring snowmelt, summer/fall storm events). From 2016 to 2017, continuous discharge and sub-daily chemistry grab samples were collected from three adjacent study catchments located at the International Institute for Sustainable Development-Experimental Lakes Area in northwestern Ontario, Canada. Catchment differences were more apparent in summer and fall events and less apparent during early spring melt events. Hysteresis analysis suggested that DOC sources were proximal to the stream for all events at a catchment dominated by a large wetland near the outlet, but distal from the stream at the catchments that lacked significant wetland coverage during the summer and fall. Wetland coverage also influenced responses of DOC export to antecedent moisture; at the wetland-dominated catchment, there were consistent negative relationships between DOC concentrations and antecedent moisture, while at the catchments without large wetlands, the relationships were positive or not significant. These results emphasize the utility of sub-daily sampling for inferring catchment DOC transport processes, and the importance of considering catchment-specific factors when predicting event-scale DOC behaviour.  相似文献   

Effects of land use intensity on stormwater runoff and its temporal occurrence in cold climates          下载免费PDF全文

Marjo Valtanen  Nora Sillanpää  Heikki Setälä 《水文研究》2014,28(4):2639-2650

The impacts of land use intensity, here defined as the degree of imperviousness, on stormwater volumes, runoff rates and their temporal occurrence were studied at three urban catchments in a cold region in southern Finland. The catchments with ‘High’ and ‘Intermediate’ land use intensity, located around the city centre, were characterized by 89% and 62% impervious surfaces, respectively. The ‘Low’ catchment was situated in a residential area of 19% imperviousness. During a 2‐year study period with divergent weather conditions, the generation of stormwater correlated positively with catchment imperviousness: The largest annual stormwater volumes and the highest runoff coefficients and number of stormwater runoff events occurred in the High catchment. Land use intensity also altered the seasonality of stormwater runoff: Most stormwater in the High catchment was generated during the warm period of the year, whereas the largest contribution to annual stormwater generation in the Low catchment took place during the cold period. In the two most urbanized catchments, spring snow melt occurred a few weeks earlier than in the Low catchment. The rate of stormwater runoff in the High and Intermediate catchments was higher in summer than during spring snow melt, and summer runoff rates in these more urbanized catchments were several times higher than in the Low catchment. Our study suggests that the effects of land use intensity on stormwater runoff are season dependent in cold climates and that cold seasons diminish the differences between land use intensities. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Spatio‐temporal patterns of major ions in urban stormwater under cold climate          下载免费PDF全文

Maija Taka  Teemu Kokkonen  Kirsi Kuoppamäki  Tero Niemi  Nora Sillanpää  Marjo Valtanen  Lassi Warsta  Heikki Setälä 《水文研究》2017,31(8):1564-1577

Multiple natural and anthropogenic factors affect urban water chemistry. However, little is known about the abundance or temporal variation of major ions in urban runoff. This study explores the spatio‐temporal variation of major dissolved ions (Na, K, Ca, Mg, Cl, NO₃, and SO₄) and total dissolved solids (TDS) in cold climate urban stormwater. Three watersheds with varying degrees of urban land use intensity and imperviousness (from 36% to 66%) in Helsinki, Finland, were continuously monitored for 5 years using an automated sampling procedure to obtain stormwater discharge and ion concentrations and, thus, loadings. High‐resolution datasets, including long‐term continuous discharge, both measured and simulated (using Storm Water Management Model), and automatic water quality sampling enabled the accurate calculation of loads of ions and TDS. Water quality was related to explanatory watershed characteristics (e.g., watershed physiography and sampling time) using hierarchical clustering, nonmetric multidimensional scaling, and hierarchical partitioning methods. Urban land use contributed to increased ion concentrations and loads year‐round. This study highlights how stormwater ion concentrations are elevated across seasons, indicating chronic pollution phenomena. The greatest loads occurred during summer (except for Na and Cl), while the highest variation in loads was observed in autumn. Significant clusters among ions were found in the hierarchical cluster analysis, suggesting similar temporal patterns and sources for the ions in each cluster. The importance of land use was evident, though in the most urbanized watershed, concentrations were not linked to any of the investigated watershed characteristics. Based on our results, only Na and Cl are manageable by alternative winter road antiskid practices, whereas other ions resulted from diffuse pollution sources, being therefore more difficult to control. Finally, this study contributes to an increased understanding of the temporal and spatial patterns of ions in stormwater and highlights the need for consistent time series data for ion monitoring under cold climatic conditions in order to enable reliable estimates of their loads to adjacent water bodies. Finally, year‐round stormwater treatment is highly recommended.  相似文献