共查询到20条相似文献,搜索用时 15 毫秒
1.
Bent Vad Odgaard 《Journal of Paleolimnology》1993,8(3):171-187
Spheroidal carbonaceous particles (SCP) from combustion of oil and coal have been quantified in cores from top sediments of Danish shallow lakes. Chronologies were provided by 210Pb-dating supplemented by measurements of other radionuclides (137Cs, 134Cs, 241Am). All cores show indications of sediment mixing but most still retain a characteristic SCP record. Deposition rates of SCP were low until the 1920s, increased strongly after World War II, reached maximum levels around 1970 and decreased thereafter. These results were used to infer a new chronology for a sediment core from a shallow lake, from which a 210Pb chronology had previously been published.SCP inventories are positively correlated with 210Pb inventories and dry matter accumulated since 1900, suggesting that absolute SCP accumulation rates may be more influenced by sedimentary processes than by atmospheric fluxes. The concentrations of SCP in surface sediments of the six lakes do, however, correlate with regional SO2 emissions. 相似文献
2.
《The Professional geographer》2012,64(1):1-8
The Great Plains is the grasslands of the central United States, but precise delineation of this region has evaded agreement due to the transition between Great Plains grasslands and forests of the eastern United States. After comparing Great Plains delineations in readily available geographic information system layers, I established a northeastern boundary using evidence from historical tree surveys during the 1800s. Additionally, I described tree presence within the Great Plains over time and potential drivers of change. The definition documented here diverges from others by including most of Iowa and part of Illinois, and even small sections in Indiana and Wisconsin, but excluding Missouri due to regular tree presence overall at landscape scales of ecological subsections. In this definition, the Great Plains had an extent of 2.29 million km2 in fifteen states, including Indiana and Wisconsin, and 2.19 million km2 after removal of open forests in Oklahoma and Texas. Tree presence occurs within the Great Plains and tree encroachment is not a new process; however, tree encroachment is increasing in the Great Plains, which causes a decrease in the grasslands region. Nevertheless, clarifying the historical eastern boundary provides a solution to the problem of competing versions of the Great Plains region. Key Words: ecotone, prairie, savanna, tree encroachment. 相似文献
3.
Within-basin profile variability and cross-correlation of lake sediment cores using the spheroidal carbonaceous particle record 总被引:2,自引:0,他引:2
Spheroidal carbonaceous particles (SCPs) from the high temperature combustion of fossil-fuels are stored in lake sediments and provide an unambiguous record of industrially derived atmospheric contamination. It has been assumed that a single sediment core provides an accurate representation of SCP accumulation but to date there have been no studies to determine within-lake variability of the SCP sediment record. This paper describes the SCP profiles of ten sediment cores taken from the deep water area of Loch Coire nan Arr, a remote lake in north-west Scotland, UK. Although each core shows the basic SCP profile used for sediment dating in the UK there is considerable variation between cores. The conversion of SCP concentrations to cumulative percentages resolves a great deal of this variation with the result that more accurate cross-correlation and hence date allocation is possible, especially in the post-1945 section of the cores. However, significant departures from the usual SCP profile still reduce the effectiveness of this approach. It is concluded that: (i) SCP profiles from single cores from the deepest areas of the lake usually provide an accurate representation of the historical record of atmospherically deposited pollutants and that inter-core variability or noise does not affect the temporal interpretation of that profile, and (ii) comparisons of total SCP inventories are a better way of comparing historical deposition between sites as the impact of temporary variability is considerably reduced. 相似文献
4.
Changing Properties of Snowpack in the Great Salt Lake Basin,Western United States,from a 26-Year SNOTEL Record 总被引:1,自引:1,他引:0
Daily observations from automated snowpack telemetry (SNOTEL) stations from within the drainage basin of the Great Salt Lake over the period from 1982 to 2007 are analyzed. The major finding is a shift toward an earlier date of peak snow water equivalent (SWE) by around fifteen days. Less robust findings are reductions in the amounts of peak SWE and 1 April SWE. This suggests increased chances of late-summer water shortages, especially when combined with rapid recent population growth. Less freshwater is likely to be available to flow into the Great Salt Lake, increasing its salinity and potentially affecting its ecology. 相似文献
5.
Estimates of energetic demands for carnivore species can be valuable for estimating their annual prey requirements and thus, their potential impact on prey populations. This is the case for the coyote (Canis latrans) which has a ubiquitous distribution and preys on a wide variety of wild and domestic prey species. We took data on daily activity of coyotes and with standard energy models, estimated the daily field metabolic rate (FMR) of adult male and female coyotes in the Great Basin desert of the western United States. We then calculated the total annual energy demand and from this, extrapolated annual prey needs for lagomorph and rodent-sized prey. Daily FMR of male coyotes in the Great Basin desert averaged 1170.1 kcal±29.1, S.E. (n=11) and was significantly higher than 988.6 kcal±44.3 (n=8) for females (p=0.002). The highest reproductive cost for females was lactation (1441.1 kcal/day above FMR). Males and females need to consume 192 and 162 lagomorphs, or 3681 and 3110 rodents/year, respectively. For reproduction, females should consume 37 more lagomorphs or 700 more rodents per year. We concluded that preference for lagomorphs by coyotes reflects the most reasonable energy return on their hunting investment. 相似文献
6.
7.
Evaluation of Weights of Evidence to Predict Epithermal-Gold Deposits in the Great Basin of the Western United States 总被引:7,自引:0,他引:7
The weights-of-evidence method provides a simple approach to the integration of diverse geologic information. The application addressed is to construct a model that predicts the locations of epithermal-gold mineral deposits in the Great Basin of the western United States. Weights of evidence is a data-driven method requiring known deposits and occurrences that are used as training sites in the evaluated area. Four hundred and fifteen known hot spring gold–silver, Comstock vein, hot spring mercury, epithermal manganese, and volcanogenic uranium deposits and occurrences in Nevada were used to define an area of 327.4 km2 as training sites to develop the model. The model consists of nine weighted-map patterns that are combined to produce a favorability map predicting the distribution of epithermal-gold deposits. Using a measure of the association of training sites with predictor features (or patterns), the patterns can be ranked from best to worst predictors. Based on proximity analysis, the strongest predictor is the area within 8 km of volcanic rocks younger than 43 Ma. Being close to volcanic rocks is not highly weighted, but being far from volcanic rocks causes a strong negative weight. These weights suggest that proximity to volcanic rocks define where deposits do not occur. The second best pattern is the area within 1 km of hydrothermally altered areas. The next best pattern is the area within 1 km of known placer-gold sites. The proximity analysis for gold placers weights this pattern as useful when close to known placer sites, but unimportant where placers do not exist. The remaining patterns are significantly weaker predictors. In order of decreasing correlation, they are: proximity to volcanic vents, proximity to east-west to northwest faults, elevated airborne radiometric uranium, proximity to northwest to west and north-northwest linear features, elevated aeromagnetics, and anomalous geochemistry. This ordering of the patterns is a function of the quality, applicability, and use of the data. The nine-pattern favorability map can be evaluated by comparison with the USGS National Assessment for hot spring gold–silver deposits. The Spearman's ranked correlation coefficient between the favorability and the National Assessment permissive tracts is 0.5. Tabulations of the areas of agreement and disagreement between the two maps show 74% agreement for the Great Basin. The posterior probabilities for 51 significant deposits in the Great Basin, both used and not used in the model, show the following: 26 classified as favorable; 25 classified as permissive; and 1, Florida Canyon, classified as nonpermissive.The Florida Canyon deposit has a low favorability because there are no volcanic rocks near the deposit on the Nevada geologic map used. The largest areas of disagreement are caused by the USGS National Assessment team concluding that volcanic rocks older than 27 Ma in Nevada are not permissive, which was not assumed in this model. The weights-of-evidence model is evaluated as reasonable and delineates permissive areas for epithermal deposits comparable to expert's delineation. The weights-of-evidence model has the additional characteristics that it is well defined, reproducible, objective, and provides a quantitative measure of confidence. 相似文献
8.
Alison J. Smith 《Journal of Paleolimnology》1993,8(2):121-134
The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 S cm-1) to saline water (17 000 S cm-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.This publication is the second of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr Evans is serving as Guest Editor for this series. 相似文献
9.
Vertical trends within the prograding Salt Wash distributive fluvial system,SW United States
下载免费PDF全文
![点击此处可从《Basin Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Progradation is an important mechanism through which sedimentary systems fill sedimentary basins. Although a general progradational pattern is recognized in many basins, few studies have quantified system scale spatial changes in vertical trends that record fluvial system progradation. Here, we provide an assessment of the spatial distribution of vertical trends across the Salt Wash distributive fluvial system (DFS), in the Morrison Formation SW, USA. The vertical distribution of proximal, medial and distal facies, and channel belt proportion and thickness, are analysed at 25 sections across approximately 80 000 km2 of a DFS that spanned approximately 100 000 km2. The stratigraphic signature of facies stacking patterns that record progradation varies depending on location within the basin. An abrupt and incomplete progradation succession dominates the proximal region, whereby proximal deposits directly overlie distal deposits. A more complete succession is preserved in the medial region of the DFS. The medial to distal region of the DFS are either simple aggradational successions, or display progradation of medial over distal facies. Spatial variations in facies successions patterns reflects preservation changes down the DFS. A spatial change in vertical trends of channel belt thickness and proportion is not observed. Vertical trends in channel belt proportion and thickness are locally highly variable, such that systematic up‐section increases in these properties are observed only at a few select sites. Progradation can only be inferred once local trends are averaged out across the entire succession. Possible key controls on trends are discussed at both allocyclic and autocyclic scales including climate, tectonics, eustasy and avulsion. Eustatic controls are discounted, and it is suggested that progradation of the Salt Wash DFS is driven by upstream controls within the catchment. 相似文献
10.
11.
Bryan Shuman 《Journal of Paleolimnology》2003,30(4):371-385
Loss-on-ignition analysis of Quaternary lake sediments provides an inexpensive and easy way to investigate past environmental changes. The mass loss on ignition at 550 °C (LOI) from lake sediment cores may vary because of temporal changes in: (1) sediment composition controlled by factors such as productivity, inorganic inputs, and decomposition; and (2) the patterns of sediment accumulation controlled by factors such as basin morphology and water level. Climatic changes can alter both. Here, modern surface samples and transects of sediment cores, collected across small (<10 ha), shallow (<4 m) lakes in the northeastern United States, show that LOI varies little (2–5%) across the deep portions of these small lakes at a given time. Large changes in LOI occur only at the transition into the littoral (shallow) zone. LOI variations in sediment cores that exceed 2–5%, therefore, appear to represent meaningful environmental changes. However, because of the many possible controls, changes in the LOI of a single core are often hard to interpret. Multiple cores increase the interpretability. At lakes studied here, similar LOI trends among several cores confirm that some LOI changes resulted from basin-wide shifts in sediment composition. Differences among cores, however, developed during the early- and mid-Holocene and indicate that the edge of the littoral zone moved towards the centers of the lakes during two periods of low lake levels, at ca. 11 000–8000 and ca. 5400–3000 cal yr B.P. The basin-wide balance of sediment sources controlled the LOI from deep-water sediments, but sedimentation patterns, which changed as lake levels changed, were also important. LOI differences among cores may therefore help identify past lake-level changes in other lakes. 相似文献
12.
Macrophytes are a critical component of lake ecosystems affecting nutrient and contaminant cycling, food web structure, and
lake biodiversity. The long-term (decades to centuries) dynamics of macrophyte cover are, however, poorly understood and no
quantitative estimates exist for pre-industrial (pre-1850) macrophyte cover in northeastern North America. Using a 215 lake
dataset, we tested if surface sediment diatom assemblages significantly differed among lakes that have sparse (<10% cover;
group 1), moderate (10–40% cover; group 2) or extensive (>40% cover; group 3) macrophyte cover. Analysis of similarity indicated
that the diatom assemblages of these a priori groups of macrophyte cover were significantly different from one another (i.e., difference between: groups 1 and 3, R statistic = 0.31, P < 0.001; groups 1 and 2, R statistic = 0.049, P < 0.01; groups 3 and 2, R statistic = 0.112, P < 0.001). We then developed an inference model for macrophyte cover from lakes classified as sparse or extensive cover (145
lakes) based on the surface sediment diatom assemblages, and applied this model using the top-bottom paleolimnological approach
(i.e., comparison of recent sediments to pre-disturbance sediments). We used the second axis of our correspondence analysis,
which significantly divided sparse and extensive macrophyte cover sites, as the independent variable in a logistic regression
to predict macrophyte cover as either sparse or extensive. Cross validation, using 48 randomly chosen sites that were excluded
from model development, indicated that our model accurately predicts macrophyte cover 79% of the time (r
2 = 0.32, P < 0.001). When applied to the top and bottom sediment samples, our model predicted that 12.5% of natural lakes and 22.4%
of reservoirs in the dataset have undergone a ≥30% change in macrophyte cover. For the sites with an inferred change in macrophyte
cover, the majority of natural lakes (64.3%) increased in cover, while the majority of reservoirs (87.5%) decreased in macrophyte
cover. This study demonstrates that surface sediment diatom assemblages from profundal zones differ in lakes based on their
macrophyte cover and that diatoms are useful indicators for quantitatively reconstructing changes in macrophyte cover. 相似文献
13.
《The Professional geographer》2013,65(3):349-366
Cloud-to-ground (CG) lightning observations for the warm seasons (May-September) of 1989 and 1990 were analyzed for the Great Lakes region in order to assess the diurnal variations in the lightning characteristics. Several parameters, including flash rate, the spatial extent of lightning activity, first stroke peak current, and the percentage of positive flashes, varied markedly over the course of the day. In contrast, other parameters, such as the frequency of lightning periods and the multiplicity of both negative and positive CG flashes, displayed little diurnal variation. A large degree of intraseasonal (i.e., month-to-month) variation was observed in the diurnal patterns for several of the lightning parameters. 相似文献
14.
Cloud-to-ground (CG) lightning observations for the warm seasons (May-September) of 1989 and 1990 were analyzed for the Great Lakes region in order to assess the diurnal variations in the lightning characteristics. Several parameters, including flash rate, the spatial extent of lightning activity, first stroke peak current, and the percentage of positive flashes, varied markedly over the course of the day. In contrast, other parameters, such as the frequency of lightning periods and the multiplicity of both negative and positive CG flashes, displayed little diurnal variation. A large degree of intraseasonal (i.e., month-to-month) variation was observed in the diurnal patterns for several of the lightning parameters. 相似文献
15.
The Past,Present, and Future of Geodemographic Research in the United States and United Kingdom 总被引:2,自引:0,他引:2
This article presents an extensive comparative review of the emergence and application of geodemographics in both the United States and United Kingdom, situating them as an extension of earlier empirically driven models of urban socio-spatial structure. The empirical and theoretical basis for this generalization technique is also considered. Findings demonstrate critical differences in both the application and development of geodemographics between the United States and United Kingdom resulting from their diverging histories, variable data economies, and availability of academic or free classifications. Finally, current methodological research is reviewed, linking this discussion prospectively to the changing spatial data economy in both the United States and United Kingdom. 相似文献
16.
Adam S. Parris Paul R. Bierman Anders J. Noren Maarten A. Prins Andrea Lini 《Journal of Paleolimnology》2010,43(1):29-49
The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine are identified using 14C and high-resolution (cm-by-cm) particle size analysis of sediment cores taken from six post-glacial lakes (~0.1–1.4 km2). A total of nine sediment cores (4.5–6 m long) were taken near the base of stream delta foreslopes. End-member modeling
of the particle-size frequency distributions from each core produces 3–5 representative end member distributions, or end members
(EMs). Concurrent increases in mean and median particle size, and in the relative abundance of the coarsest EM(s), indicate
increased transport capacity of inflowing tributaries, resulting from rainstorms. In all 9 cores, particle size data show
clear signs of episodic, high-energy sediment transport events where proxy measurements such as loss-on-ignition and magnetic
susceptibility do not, demonstrating the sensitivity of particle size analysis in paleostorm investigations made using lake
sediment cores. Floods caused by storms in this region peaked around 1.4, 2.1, 3.0, 3.9, 6.8, 8.2, and 11.5 ka cal BP, and
presently appear to be increasing in frequency. Periods of storminess in New Hampshire and Maine correlate well with other
records of precipitation and climate in the northeastern United States during the Holocene, further supporting modern records
which show tropical air masses as a primary driver of extreme precipitation events in New England (Ludlum 1996; Konrad 2001; Sisson and Gyakum 2004). 相似文献
17.
William M. Last 《Geomorphology》1993,8(4)
Large-scale salt dissolution is an important process affecting the sediments of many of the saline lakes in the northern Great Plains region of western Canada. The most easily recognized features of this salt karst are water-filled chimneys, vertical shafts, and collapse structures. The largest individual chimneys can be up to 20 m deep and 50 m in diameter, with volumes exceeding 25,000 m3. Large, mud-filled chimneys and cavities, and salt-filled chimneys have also been identified in both the modern lakes and in the Quaternary sediments of the basins, which can adversely affect the salt mining potential of the basins. Because these salt karst features can affect large vertical sections of the sediment fill in the lakes, their recognition is of fundamental importance in attempting to use the stratigraphic records of the basins for paleoenvironmental research. 相似文献
18.
Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain their age.We obtained lake-bottom samples of 50 cm length from lake BLH-A and 25 cm length from lake BLH-B.Environmental 137 Cs and 210 Pb and radiocarbon age dating techniques were applied to the 50 cm and 25 cm samples,respectively.The results indicate that the initiation of BLH-A is about 800-900 a B.P.,and approximately 1,450±30 a B.P.to 2,230±30 a B.P.for BLH-B.These results will provide scientific bases for sedimentological study and thermokarst activity in Beiluhe Basin. 相似文献
19.
Jorunn Larsen 《Journal of Paleolimnology》2000,23(4):343-363
Sediments from two naturally acid lakes have been used to investigate whether there is any local impact of atmospheric pollution from an oil refinery at Mongstad in Western Norway. The refinery started production in 1975 and expanded in 1987. One lake was selected as a reference site as it only receives long-range transported air pollution, whereas a second lake was selected as it was expected to receive both long-range transported and local air pollution from the refinery. Heavy metal (Pb, Ni and Zn) and spheroidal carbonaceous particle (SCP) (> 5 µm in diameter) concentrations and accumulation rates have been estimated and lake-water pH has been reconstructed by weighted averaging and weighted averaging partial least squares regression and calibration from the fossil diatom assemblages.Heavy metals that are in the size range for which atmospheric residence time is greatest do not show any enhanced levels in the sediments after 1975 that could be associated with local impacts from the refinery. SCPs in the sediments that are in the size range thought to be effectively removed by dry deposition, and thus have a more local deposition pattern, show an increase after 1975 and an additional large increase after 1987 that can be explained by impacts from the local oil refinery. After 1975 the SCP diameter distribution changed from being dominated by SCPs with a small diameter in the range 5-10 µm to SCPs with larger diameters. The SO2 emission from the oil refinery seems to have had no significant effect on lake pH. The reconstructed lake pH history is complex, possibly related to land-use changes and long-range transported air pollution. 相似文献
20.