Changes in submerged macrophyte abundance altered diatom and chironomid assemblages in a shallow lake     

Jesse C. Vermaire  Marie-Hélène Greffard  Émilie Saulnier-Talbot  Irene Gregory-Eaves 《Journal of Paleolimnology》2013,50(4):447-456

Submerged macrophyte abundance strongly influences aquatic ecosystems. Because of a lack of monitoring data, however, the long-term dynamics of such aquatic plants are poorly understood. Increasingly, paleolimnologists use changes in subfossil algae and invertebrates to infer past submerged macrophyte dynamics and assess how human activities have altered this important primary producer component of aquatic ecosystems. We evaluated the sensitivity of subfossil diatom and chironomid assemblages to historically documented changes in macrophyte abundance in Chenango Lake, New York, USA, where macrophyte cover has been monitored since 1978. We also tested the ability of a semi-quantitative diatom-based macrophyte-abundance inference model to detect the pronounced macrophyte decline that was observed between 1993 and 2001. Diatoms responded to the recent loss of macrophytes, with a decline in the relative abundance of macrophyte-associated taxa. Estimates of macrophyte abundance fluctuated according to the diatom-based inference model. Chironomid changes were coherent with the diatom-inferred macrophyte zones. The largest shifts in subfossil assemblages occurred before the start of the monitoring record and coincided with construction of a ~4.3-m-high dam on the lake, which substantially expanded the littoral habitat. Even in heavily managed systems, large reductions in macrophyte abundance can be detected with paleolimnological approaches.  相似文献   

Active Citizenship in Later Life: Older Volunteers in a Deprived Community in England     

Irene Hardill  Susan Baines 《The Professional geographer》2013,65(1):36-45

Older people are typically characterized as recipients of care who make ever increasing demands on overstretched and underfunded social care services. This article is about older people as givers of care to nonhousehold members. It draws on an in-depth study of volunteering in an English community beset by concentrated poverty and worklessness. Older adults, especially women, make up a significant component of those who give time through volunteering for organizations that provide social welfare services for people in need in that community. Although older adults had diverse ways of thinking about volunteering, they often undertook the effort as an expression of care and support to others.  相似文献   

Evaluating the seismic hazard to the National Capital (Delhi) Region,India, from moderate earthquakes using simulated accelerograms     

Dinesh Kumar  Irene Sarkar  V. Sriram  S. S. Teotia 《Natural Hazards》2012,61(2):481-500

The National Capital Region (NCR) of India is exposed to high seismic hazard and risk due to a great earthquake in the central seismic gap of Himalaya and/or due to moderate-size earthquake within NCR. The high population density, rapid growth of infrastructure, and old engineering structures in the region make it more vulnerable to the human as well as economic loss due to moderate-size earthquakes also. The evaluation of seismic hazard is the first step to prepare a proper mitigation plan for the region. The aim of this paper is to evaluate the seismic hazard and risk due to moderate-size earthquakes in the vicinity of NCR. For this purpose, a suit of accelerograms have been generated from hypothetical moderate-size earthquakes (M 5.5 and 6.0) in the region. A basic fault-plane solution is assumed for this purpose. The ranges of the different parameters like depth of focus and stress drop values have been used in order to examine the effect of these parameters on hazard. The accelerograms have been synthesized using two basic velocity models, one representing a hard site and the other a site with a significant low-velocity cover. These two velocity models represent the ridge area and trans-Yamuna river area in the NCR. The decay of peak ground acceleration (pga) values with distance is fast in trans-Yamuna region (with low-velocity surface layer of 100 m) as compared to that of ridge area (with low-velocity surface layer of 1 m). Also, the decay of pga becomes slower if we increase the depth of focus from 10 to 20 km. The response spectra (5% damping) of the synthetic accelerograms for the three periods T = 0.4s, 0.75s, and 1.25s have been estimated and presented in the form of decay curves. The amplifications as a function of epicentral distance and stress drop have also been estimated. We note that the amplifications in 100-m layer case do not occur uniformly at all the distances, rather it is dependent on the angle of incidence of energy into the layers. The pga values are generally amplified by more than twice with increase in stress drop from 100 to 400 bars. The seismic exposure of the population in Delhi city has been presented. The results presented in this study may serve as an important input in the planning of mitigation and disaster management programs in the National Capital Region.  相似文献   

Heavy metals deposited from the atmosphere on upland Scottish soils: Chemical and lead isotope studies of the association of metals with soil components   总被引：2，自引：0，他引：2  

Jeffrey R. Bacon  Irene J. Hewitt 《Geochimica et cosmochimica acta》2005,69(1):19-33

Three soil profiles taken from the Hartwood Research Station in Central Scotland have been analyzed using chemical digestion and extraction techniques to investigate the chemical association of heavy metals deposited from the atmosphere. Total digestion, EDTA extraction and the BCR (Bureau Communitaire de Reference) sequential extraction procedure were used. In addition, lead isotope ratios in the whole soils and in the fractions from the sequential extraction procedure were measured using thermal ionisation mass spectrometry. All the digestion and extraction procedures gave clear indication of enhanced concentrations of heavy metals in surface soils, in particular for lead and zinc. Whereas total digestion gave a good indication of the heavy metal status of the soils, the extraction procedures were necessary to provide information on chemical association of the metals with soil components, information needed to understand the soil processes involved in mobilization of metals. Lead isotope analysis of the whole soils revealed a consistent picture of lower ²⁰⁶Pb/²⁰⁷Pb ratios in surface soils (1.140-1.147) than in soils at 20-30 cm depth (1.182-1.190). The steady progression from the lower to higher ratios down the profile was clear indication that anthropogenic lead had penetrated to some degree into the deeper soils. The combination of sequential extraction and lead isotope analysis proved to be a powerful approach to studying this effect in more detail and showed that the fractions extractable from 20 to 30 cm soils contained lead with much lower ²⁰⁶Pb/²⁰⁷Pb ratios (1.174-1.178) than the residual fraction (1.196-1.200). As the extractable fractions contained ≥85% of the lead in the soil, a substantial portion of lead at 20-30 cm depth was of anthropogenic origin. The ²⁰⁶Pb/²⁰⁷Pb ratios of 1.174-1.178 found in the extractable fractions suggested that the mobile component of the anthropogenic lead was that deposited before the introduction of leaded petrol.  相似文献   

Evaluating the importance of accessibility to congestion response using a GIS-based travel simulator     

Irene Casas 《Journal of Geographical Systems》2003,5(1):109-127

 This paper examines the effect of accessibility on individual response to unexpected traffic delays and congestion. The dataset used was collected by means of a travel simulator developed within a geographic information system (GIS) environment. The simulator models a commute trip where congestion takes place, and subjects are asked to respond by making a choice among alternative courses of action. Available alternatives for dealing with the unexpected traffic delay include changing the location of the planned activities or changing the activities to be performed. Accessibility to the new locations and to the different activities is computed using a cumulative measure. Analysis using CHAID tree technique found that accessibility is a good predictor of subjects' choice when responding to unexpected traffic delays. Received: September 2002 / Accepted: January 2003 Support for this research by a grant from the Center of Intelligent Transportation Research of the Ohio State University is gratefully acknowledged. The author would also like to thank Joe Weber, Mei-Po Kwan and two anonymous reviewers for their valuable comments.  相似文献   

A simulation of earthquake induced undrained pore pressure changes with bearing on some soil liquefaction observations following the 2001 Bhuj earthquake     

Sarkar  Irene  Chander  Ramesh 《Journal of Earth System Science》2003,112(3):471-477

The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction within the Kachch peninsula. It has been pointed out that inundation due to soil liquefaction was short lived in some parts than in others in the affected region. Several geological, seismological and hydrological factors would have cumulatively contributed to these observed changes. We simulate in this article, undrained or short-term change in pore pressure in a poroelastic half space, in response to a simplified model of the Bhuj earthquake source. We find that the regions of relatively shorter lived inundation due to soil liquefaction may fall in the region where pore pressure responsible for soil liquefaction attributable to strong ground shaking was counteracted by pore pressure changes due to undrained poroelastic effect and vice versa.  相似文献   

Global acceleration of lake sediment accumulation rates associated with recent human population growth and land-use changes     

Baud  Alexandre  Jenny  Jean-Philippe  Francus  Pierre  Gregory-Eaves  Irene 《Journal of Paleolimnology》2021,66(4):453-467

Journal of Paleolimnology - Sediment Accumulation Rate (SAR; measured as mm yr?1) and Mass Accumulation Rate (MAR; measured as g cm?2 yr?1) data were collected from...  相似文献   

Identifying Environmental and Human Factors Associated With Tick Bites using Volunteered Reports and Frequent Pattern Mining   总被引：1，自引：0，他引：1       下载免费PDF全文

Irene Garcia‐Martí  Raul Zurita‐Milla  Arno Swart  Kees C. van den Wijngaard  Arnold J.H. van Vliet  Sita Bennema  Margriet Harms 《Transactions in GIS》2017,21(2):277-299

Tick populations and tick‐borne diseases like Lyme borreliosis have been steadily increasing since the mid‐1990s. Realizing the threat that ticks pose to public health, two Dutch citizen science projects have collected tick bite reports since 2006. This unique volunteered geographical dataset, which currently has nearly 35,000 reports, was used to identify environmental and other circumstantial factors associated with tick bites. For this, we first enriched the tick bite reports with temperature, precipitation, vegetation and volunteered data associated with the location of the tick bite. Using this enriched dataset, we then derived a series of features to characterize the environmental and volunteer‐related conditions in which each tick bite occurred. Next, we discretized these features using the Jenks Natural Breaks algorithm and, after that, we mined frequent environmental patterns associated with tick bites using the AprioriClose algorithm. Finally, we checked that these patterns are specifically associated with the tick bites by comparing them with the frequent patterns mined from pseudo‐random locations. The frequent patterns were visualized using heat maps and ring maps and two representative patterns associated with tick bites were projected into geographic space to study their spatio‐temporal distribution. Our results show that factors linked to human activity are more relevant to model tick bites than seasonal accumulations of temperature, vegetation or precipitation. In particular, the number of warm and dry days per season are present in a significant number of patterns and the majority of tick bites are produced within a distance of half a kilometer of a forest, recreational or built‐up area. The study of patterns in the time‐series revealed that there are several persistent patterns consistently occurring each year and the validation process showed that the volunteer tick bites collection is capturing environmental conditions associated with tick bites, suggesting that these reports have a high scientific value. These results support the creation of a Dutch tick bite risk map that, in turn, will open the door to the design of public health interventions to reduce the incidence of Lyme disease.  相似文献   

Plankton: Its chemical composition and its significance as a source of pelagic sediments     

Kurt Bostrom  Oliva Joensuu  Irene Brohm 《Chemical Geology》1974,14(4):255-271

The absolute concentrations of minor and trace elements vary considerably in plankton. However, normalization of elemental abundances versus the minor elements Fe, Al and Zn (instead of the commonly used normalization versus seawater concentrations) demonstrates that these elements show remarkably constant proportions vis à vis each other. Thus, Ti, Fe, Al, Mn, V, and Zr occur in marine lower organisms in the same proportions as in the average shale, whereas Ba, Cr, Cu, Ni, Cd, Pb, Zn and B are enriched relative to the shale abundances, as are also Ca, Mg, Na, K, and Sr. These patterns appear to suggest that marine plankton are rich in lithogenic matter, but this is probably not the normal case.Contrary to the uniformity of plankton, sediments from the Pacific vary considerably in composition. Under the Equatorial high-productivity region the sediments show striking similarities with a mixture of average shale and average plankton mass, as could be expected, whereas sediments from the East Pacific Rise differ considerably from such mixtures. An iron—manganese phase (of deep-seated origin?), mixed with biological matter, on the other hand, yields model sediments with remarkable similarities to the East Pacific Rise deposits. It is therefore likely that biological processes account for a considerable fraction of some elements such as Cu, Ni, Zn and Ba also in the East Pacific Rise metalliferous sediments.  相似文献   

Cytogenetic evidence of inducible processes linked with xenobiotic metabolism in larval and adult Mytilus edulis     

D.R. Dixon  Irene M. Jones  Florence H. Harrison 《Marine environmental research》1984,14(1-4)

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