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Shellfish production areas are often located in shallow estuarine and coastal systems impacted by fluxes of faecal indicator organisms (FIOs) that exhibit extreme spatial and temporal variability. FIO abundance and distribution in the marine environment are determined by the combined effects of light intensity, water mixing, sewage content and suspended particulate matter. Favourable conditions for FIO survival are low solar radiation, low temperature, low salinity, low densities of micro-predators and high levels of organic matter. Rainfall is the parameter most commonly associated with peak levels of FIOs. Resuspension of contaminated sediments in the water column dominates FIO distribution in shallow and depositional estuaries during storm conditions. Water/flesh FIO ratios may differ between shellfish growing waters because salinities and water temperatures also influence filter-feeding activity. Data are lacking on the role of biological processes on FIOs uptake and clearance in shellfish, particularly during periods of good water quality. FIO accumulation is usually of higher magnitude in mussels and cockles than in oysters and surf clams. It is proposed that differences in FIO accumulation rates are associated with the biological activity and the position of shellfish in the water column in relation to the location of impacting pollution sources. Accurate information on catchment hydrology, land uses, FIO loads from sewerage-related sources and livestock production areas are required to adequately characterise the microbiological status of shellfisheries. 相似文献
83.
Ron Johnston 《Urban geography》2013,34(7):1064-1066
In this paper, we explore a “grassroots” neighborhood revitalization effort engendered at the national scale without regard to local geographies of race and class. Specifically, we examine the Harambee Great Neighborhood Initiative, convened by the well-known nonprofit Habitat for Humanity together with Milwaukee’s Local Initiatives Support Corporation, in Milwaukee, Wisconsin. Drawing from participant observation, analysis of print and digital media, volunteer surveys, and interviews with area residents and local nonprofit representatives, we demonstrate the ways in which the six-year program of planning and neighborhood development was conceived and driven by an extra-local nonprofit with significant blind spots to local and organizational politics of race and without sufficient collaboration with the Harambee community. Our analysis points to the importance of race in nonprofit governance and community revitalization efforts. Moreover, we contribute to urban geographic scholarship on nonprofit governance by examining the dynamics of privilege, inclusion, and exclusion as they relate to practices of engagement and volunteerism in nonlocal “grassroots” projects. 相似文献
84.
A very large literature has explored the intensity of urban residential segregation using the index of dissimilarity. Several recent studies have undertaken such analyses at multiple spatial scales, invariably reaching the conclusion that the finer grained the spatial scale, the greater the segregation. Such findings, however, overstate the intensity of segregation at finer spatial scales because they fail to take into account an argument made by Duncan et al. some sixty years ago that indexes derived from fine-scale analyses must necessarily incorporate those from coarser scales, with the consequence that finer scale segregation is invariably overestimated. Moreover, most studies ignore stochastic variation that results in upward bias in the estimates of segregation. This article demonstrates the importance of a recently developed multilevel modeling procedure that identifies the “true” intensity of segregation at every level in a spatial hierarchy net of its intensity at other levels and also net of stochastic variation This is illustrated by both a simulated data set and an empirical study of an English city, with the latter raising important substantive issues regarding the interpretation of segregation patterns and the processes underlying them. Key Words: dissimilarity, multilevel modeling, scale, segregation. 相似文献
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Ron Johnston 《GeoJournal》2009,74(4):347-362
English-language geographical magazines present very different geographical imaginations to their readers than those portrayed
by academic geographers, with whom the editors and publishers of those magazines have very little contact. There is a mutual
lack of appreciation—which could have substantial consequences for the academic discipline. To increase academic geographers’
appreciation of the popular geographies being portrayed, the contents of recent volumes of three magazines—National Geographic, Geographical, and New Zealand Geographic—are distilled, with their major themes identified. One clear conclusion is that there is virtually no contact between the
two imaginations: popular geographical magazines almost entirely ignore the work of academic geographers. 相似文献
87.
The prospects of an adjustment policy based on collective learning in old industrial regions 总被引:1,自引:0,他引:1
This paper aims to discuss the possibilities of adopting a policy based on collective learning in old industrial regions. This is particularly interesting because old industrial regions are believed to have lost their learning capabilities, as indicated by notions of `technological' and `institutional' lock-in. Moreover, the success stories where positive effects of interactive learning have been observed (Silicon Valley, Baden-Württemberg) all share the lack of an industrial past.First, we specify how a theoretical framework based on interactive learning, which tries to explain the industrial decline of old agglomerations, may look like, and how such an approach differs from other approaches. Then, we set out a policy framework that aims to deal with the process of structural adjustment and which incorporates the ideas of interactive learning based on socio-cultural factors. In this respect, we distinguish between two possible routes of adjustment, which reveal a complex interplay between different types of agglomeration economies, innovations and restructuring processes. Finally, we devote attention to the problems such a policy based on the notion of the learning region may face, such as the problem of how to overcome a negative lock-in situation caused by localized path dependency. 相似文献
88.
Martin G. Shepley Nick Schmidt Matt J. Senior Stephen R. H. Worthington Ron B. Scheckenberger 《Ground water》2020,58(2):269-277
Storm sewer systems and their associated utility trenches may strongly influence the effects of urbanization on a groundwater system. This study was undertaken to identify the causes of district-wide basement infiltration in an aquitard system. It comprised widespread continuous monitoring of utility trench wells and dye tracing from storm sewer system exfiltration tests. The results indicate that a major effect of urbanization on shallow groundwater is related to storm sewer system exfiltration, which is marked by a characteristic pattern of head variations in the aquitard unrelated to distributed surface infiltration. The aquitard constrains flow from storm sewer system exfiltration to the utility trench, creating an urban flow path for groundwater discharge. Temporary buildup of water levels in the utility trench drives relatively high-velocity flow through the permeable sewer bedding material of the utility trench to a separate foundation drainage collector system, ultimately causing a severe “urban karst” effect that produces system surcharging and widespread basement water infiltration. The main conditions causing the “urban karst” are the large hydraulic conductivity ratio between the utility trench material and the aquitard, and the shallow depth and low gradient of the storm sewer system imposed by a very flat drainage basin. 相似文献
89.
The hydrogeochemistry of shallow groundwater has been characterized in the Allt a'Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the influence of groundwater on the quality and quantity of stream flow. Shallow groundwater in superficial drift deposits is circumneutral (pH∽7·1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (>900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of baseflow in the catchment and also buffers the chemistry of stream water at high flows: groundwater may account for as much as 50–60% of annual runoff in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. © 1998 John Wiley & Sons, Ltd. 相似文献
90.