Maori Geography or Geography of Maoris   总被引：1，自引：0，他引：1  

Evelyn Stokes 《New Zealand geographer》1987,43(3):118-123

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Subglacial bedform evidence for a major palaeo‐ice stream and its retreat phases in Amundsen Gulf,Canadian Arctic Archipelago     

C. R. Stokes  C. D. Clark  M. C. M. Winsborrow 《第四纪科学杂志》2006,21(4):399-412

Ascertaining the location of palaeo‐ice streams is crucial in order to produce accurate reconstructions of palaeo‐ice sheets and examine interactions with the ocean–climate system. This paper reports evidence for a major ice stream in Amundsen Gulf, Canadian Arctic Archipelago. Mapping from satellite imagery (Landsat ETM+) and digital elevation models, including bathymetric data, is used to reconstruct flow‐patterns on southwestern Victoria Island and the adjacent mainland (Nunavut and Northwest Territories). Several flow‐sets indicative of ice streaming are found feeding into the marine trough and cross‐cutting relationships between these flow‐sets (and utilising previously published radiocarbon dates) reveal several phases of ice stream activity centred in Amundsen Gulf and Dolphin and Union Strait. A large erosional footprint on the continental shelf indicates that the ice stream (ca. 1000 km long and ca. 150 km wide) filled Amundsen Gulf, probably at the Last Glacial Maximum. Subsequent to this, the ice stream reorganised as the margin retreated back along the marine trough, eventually splitting into two separate low‐gradient lobes in Prince Albert Sound and Dolphin and Union Strait. The location of this major ice stream holds important implications for ice sheet–ocean interactions and specifically, the development of Arctic Ocean ice shelves and the delivery of icebergs into the western Arctic Ocean during the late Pleistocene. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Toxicological Study of Fluorescent Hydrologic Tracer Dye Effects on Cave Bacteria     

Thomas L. Kieft  Evelyn Byrd  George Veni 《Ground water》2022,60(3):404-409

Fluorescent dyes are commonly used as hydrologic tracers in a variety of surface and subsurface environments, including karst aquifers and caves, but the fragile nature of karstic groundwater ecosystems suggests a cautious approach to selecting dyes. This study tested the effects of four fluorescent dye tracers (uranine, eosin, pyranine, sulforhodamine B) on microorganisms from Fort Stanton Cave, New Mexico, United States. Toxicity of the dyes was tested on bacteria isolated from the cave and on a sediment sample collected adjacent to Snowy River in Fort Stanton Cave. The isolates showed minimal inhibition by the four dyes in an agar diffusions assay. Minimum inhibitory concentrations calculated from liquid culture assays of one isolate were 35 g/L for uranine, 3.5 g/L for eosin, 0.1 g/L for pyranine, and 10 mg/L for sulforhodamine B. A ¹⁴C-glucose radiotracer experiment showed zero inhibition of overall microbial activity in a sediment sample at all dye concentrations, except at 350 g/L eosin. Thus, there are no cave-specific findings to indicate that Fort Stanton's microbes are especially sensitive to these commonly used dyes. Moreover, a literature survey of mutagenicity tests on these dyes indicates they are safe for environmental use. These results corroborate previous dye toxicity tests and suggest that these four dyes are suitable for use at Fort Stanton Cave in the concentration ranges commonly used for groundwater tracing. While broader testing of dyes with microbes from other caves is advised, the results suggest the dyes may be safe for all karst aquifers.  相似文献   

Functional and Compositional Responses of Periphyton Mats to Simulated Saltwater Intrusion in the Southern Everglades     

Viviana Mazzei  Evelyn E. Gaiser  John S. Kominoski  Benjamin J. Wilson  Shelby Servais  Laura Bauman  Stephen E. Davis  Steve Kelly  Fred H. Sklar  David T. Rudnick  Joseph Stachelek  Tiffany G. Troxler 《Estuaries and Coasts》2018,41(7):2105-2119

Periphyton plays key ecological roles in karstic, freshwater wetlands and is extremely sensitive to environmental change making it a powerful tool to detect saltwater intrusion into these vulnerable and valuable ecosystems. We conducted field mesocosm experiments in the Florida Everglades, USA to test the effects of saltwater intrusion on periphyton metabolism, nutrient content, and diatom species composition, and how these responses differ between mats from a freshwater versus a brackish marsh. Pulsed saltwater intrusion was simulated by dosing treatment chambers monthly with a brine solution for 15 months; control chambers were simultaneously dosed with site water. Periphyton from the freshwater marsh responded to a 1-ppt increase in surface water salinity with reduced productivity and decreased concentrations of total carbon, nitrogen, and phosphorus. These functional responses were accompanied by significant shifts in periphytic diatom assemblages. Periphyton mats at the brackish marsh were more functionally resilient to the saltwater treatment (~?2 ppt above ambient), but nonetheless experienced significant shifts in diatom composition. These findings suggest that freshwater periphyton is negatively affected by small, short-term increases in salinity and that periphytic diatom assemblages, particularly at the brackish marsh, are a better metric of salinity increases compared with periphyton functional metrics due to functional redundancy. This research provides new and valuable information regarding periphyton dynamics in response to changing water sources in the southern Everglades that will allow us to extend the use of periphyton, and their diatom assemblages, as tools for environmental assessments related to saltwater intrusion.  相似文献   

A resurgence in urban living? Trends in residential location patterns of young and older adults since 2000     

Evelyn Blumenberg  Anne Brown  Kelcie Ralph  Brian D. Taylor  Carole Turley Voulgaris 《Urban geography》2013,34(9):1375-1397

ABSTRACT

Some have heralded a resurgence of urban living in the U.S., particularly among young adults. Are Americans abandoning suburbs in favor of more urban lifestyles? What is the scope and scale of this urban resurgence? We develop a typology of neighborhoods to analyze the residential location of young and older U.S. adults from 2000 to 2011–15. Census and national travel survey data reveal that suburban population growth continues to outpace that in urban neighborhoods. Although young adults are more likely than older adults to live in urban neighborhoods, recent urban population growth is neither associated with suburban decline, nor being led by young adults. Significant recent population growth in the newest, suburban neighborhoods suggests that greenfield development remains the primary means to increase American housing supply. Shifting metropolitan growth from the suburban fringe would likely require expanding housing supply in urban neighborhoods, and bringing urban amenities to established inner-ring suburbs.  相似文献   

Challenges in using siliceous subfossils as a tool for inferring past water level and hydroperiod in Everglades marshes     

Christopher Sanchez  Evelyn E. Gaiser  Colin J. Saunders  Anna H. Wachnicka  Nicholas Oehm  Christopher Craft 《Journal of Paleolimnology》2013,49(1):45-66

Successfully rehabilitating drained wetlands through hydrologic restoration is dependent on defining restoration targets, a process that is informed by pre-drainage conditions, as well as understanding linkages between hydrology and ecosystem structure. Paleoecological records can inform restoration goals by revealing long-term patterns of change, but are dependent on preservation of biomarkers that provide meaningful interpretations of environmental change. In the Florida Everglades, paleohydrological hind-casting could improve restoration forecasting, but frequent drying of marsh soils leads to poor preservation of many biomarkers. To determine the effectiveness of employing siliceous subfossils in paleohydrological reconstructions, we examined diatoms, plant and sponge silico-sclerids from three soil cores in the central Everglades marshes. Subfossil quality varied among cores, but the abundance of recognizable specimens was sufficient to infer 1,000–3,000 years of hydrologic change at decadal to centennial resolution. Phytolith morphotypes were linked to key marsh plant species to indirectly measure fluctuations in water depth. A modern dataset was used to derive diatom-based inferences of water depth and hydroperiod (R² = 0.63, 0.47; RMSE = 14 cm, 120 days, respectively). Changes in subfossil quality and abundances at centennial time-scales were associated with mid-Holocene climate events including the Little Ice Age and Medieval Warm Period, while decadal-scale fluctuations in assemblage structure during the twentieth century suggested co-regulation of hydrology by cyclical climate drivers (particularly the Atlantic Multidecadal Oscillation) and water management changes. The successful reconstructions based on siliceous subfossils shown here at a coarse temporal scale (i.e., decadal to centennial) advocate for their application in more highly resolved (i.e., subdecadal) records, which should improve the ability of water managers to target the quantity and variability of water flows appropriate for hydrologic restoration.  相似文献   

Diatom-based paleolimnological reconstruction of regional climate and local land-use change from a protected sinkhole lake in southern Florida, USA     

Amanda K. Quillen  Evelyn E. Gaiser  Eric C. Grimm 《Journal of Paleolimnology》2013,49(1):15-30

Despite their sensitivity to climate variability, few of the abundant sinkhole lakes of Florida have been the subject of paleolimnological studies to discern patterns of change in aquatic communities and link them to climate drivers. However, deep sinkhole lakes can contain highly resolved paleolimnological records that can be used to track long-term climate variability and its interaction with effects of land-use change. In order to understand how limnological changes were regulated by regional climate variability and further modified by local land-use change in south Florida, we explored diatom assemblage variability over centennial and semi-decadal time scales in an ~11,000-yr and a ~150-yr sediment core extracted from a 21-m deep sinkhole lake, Lake Annie, on the protected property of Archbold Biological Station. We linked variance in diatom assemblage structure to changes in water total phosphorus, color, and pH using diatom-based transfer functions. Reconstructions suggest the sinkhole depression contained a small, acidic, oligotrophic pond ~11000–7000 cal yr BP that gradually deepened to form a humic lake by ~4000 cal yr BP, coinciding with the onset of modern precipitation regimes and the stabilization of sea-level indicated by corresponding palynological records. The lake then contained stable, acidophilous planktonic and benthic algal communities for several thousand years. In the early AD 1900s, that community shifted to one diagnostic of an even lower pH (~5.6), likely resulting from acid precipitation. Further transitions over the past 25 yr reflect recovery from acidification and intensified sensitivity to climate variability caused by enhanced watershed runoff from small drainage ditches dug during the mid-twentieth Century on the surrounding property.  相似文献   

Response of diatom assemblages to 130 years of environmental change in Florida Bay (USA)     

Anna Wachnicka  Laurel S. Collins  Evelyn E. Gaiser 《Journal of Paleolimnology》2013,49(1):83-101

Coastal ecosystems around the world are constantly changing in response to interacting shifts in climate and land and water use by expanding human populations. The development of agricultural and urban areas in South Florida significantly modified its hydrologic regime and influenced rates of environmental change in wetlands and adjacent estuaries. This study describes changes in diatom species composition through time from four sediment cores collected across Florida Bay, for the purposes of detecting periods of major shifts in assemblage structure and identifying major drivers of those changes. We examined the magnitude of diatom assemblage change in consecutive 2-cm samples of the ²¹⁰Pb-dated cores, producing a record of the past ~130 years. Average assemblage dissimilarity among successive core samples was ~30%, while larger inter-sample and persistent differences suggest perturbations or directional shifts. The earliest significant compositional changes occurred in the late 1800s at Russell Bank, Bob Allen Bank and Ninemile Bank in the central and southwestern Bay, and in the early 1900s at Trout Cove in the northeast. These changes coincided with the initial westward redirection of water from Lake Okeechobee between 1881 and 1894, construction of several canals between 1910 and 1915, and building the Florida Overseas Railroad between 1906 and 1916. Later significant assemblage restructurings occurred in the northeastern and central Bay in the late 1950s, early 1960s and early 1970s, and in the southwestern Bay in the 1980s. These changes coincide with climate cycles driving increased hurricane frequency in the 1960s, followed by a prolonged dry period in the 1970s to late 1980s that exacerbated the effects of drainage operations in the Everglades interior. Changes in the diatom assemblage structure at Trout Cove and Ninemile Bank in the 1980s correspond to documented eutrophication and a large seagrass die-off. A gradual decrease in the abundance of freshwater to brackish water taxa in the cores over ~130 years implies that freshwater deliveries to Florida Bay were much greater prior to major developments on the mainland. Salinity, which was quantitatively reconstructed at these sites, had the greatest effect on diatom communities in Florida Bay, but other factors—often short-lived, natural and anthropogenic in nature—also played important roles in that process. Studying the changes in subfossil diatom communities over time revealed important environmental information that would have been undetected if reconstructing only one water quality variable.  相似文献   

Correspondence of historic salinity fluctuations in Florida Bay, USA, to atmospheric variability and anthropogenic changes     

Anna Wachnicka  Evelyn Gaiser  Laurel S. Collins 《Journal of Paleolimnology》2013,49(1):103-115

Florida Bay is a highly dynamic estuary that exhibits wide natural fluctuations in salinity due to changes in the balance of precipitation, evaporation and freshwater runoff from the mainland. Rapid and large-scale modification of freshwater flow and construction of transportation conduits throughout the Florida Keys during the late nineteenth and twentieth centuries reshaped water circulation and salinity patterns across the ecosystem. In order to determine long-term patterns in salinity variation across the Florida Bay estuary, we used a diatom-based salinity transfer function to infer salinity within 3.27 ppt root mean square error of prediction from diatom assemblages from four ~130 year old sediment records. Sites were distributed along a gradient of exposure to anthropogenic shifts in the watershed and salinity. Precipitation was found to be the primary driver influencing salinity fluctuations over the entire record, but watershed modifications on the mainland and in the Florida Keys during the late-1800s and 1900s were the most likely cause of significant shifts in baseline salinity. The timing of these shifts in the salinity baseline varies across the Bay: that of the northeastern coring location coincides with the construction of the Florida Overseas Railway (AD 1906–1916), while that of the east-central coring location coincides with the drainage of Lake Okeechobee (AD 1881–1894). Subsequent decreases occurring after the 1960s (east-central region) and early 1980s (southwestern region) correspond to increases in freshwater delivered through water control structures in the 1950s–1970s and again in the 1980s. Concomitant increases in salinity in the northeastern and south-central regions of the Bay in the mid-1960s correspond to an extensive drought period and the occurrence of three major hurricanes, while the drop in the early 1970s could not be related to any natural event. This paper provides information about major factors influencing salinity conditions in Florida Bay in the past and quantitative estimates of the pre- and post-South Florida watershed modification salinity levels in different regions of the Bay. This information should be useful for environmental managers in setting restoration goals for the marine ecosystems in South Florida, especially for Florida Bay.  相似文献   

Extracting palaeoflood data from coarse‐grained Pleistocene river terrace archives: an example from SE Spain          下载免费PDF全文

Anne Mather  Martin Stokes 《地球表面变化过程与地形》2016,41(13):1991-2004

Field‐based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long‐term landscape evolution. However, the reconstruction of past flow event histories (magnitude and frequency) over long‐term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach, which is applied to coarse‐grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross‐section and in longitudinal section and calibrated against the sedimentology for palaeo‐flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream ‘boulder starvation’. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献