排序方式： 共有13条查询结果，搜索用时 15 毫秒
1.
Ian Shennan Sarah Hamilton Caroline Hillier Amanda Hunter Ruth Woodall Sarah Bradley Glenn Milne Anthony Brooks Sophie Bassett 《第四纪科学杂志》2006,21(6):601-613
Observations of relative sea‐level change and local deglaciation in western Scotland provide critical constraints for modelling glacio‐isostatic rebound in northern Britain over the last 18 000 years. The longest records come from Skye, Arisaig and Knapdale with a shorter, Holocene, record from Kintail. Biostratigraphic (diatom, pollen, dinoflagellate, foraminifera and thecamoebian), lithological and radiocarbon analyses provide age and elevation parameters for each sea‐level index point. All four sites reveal relative sea‐level change that is highly non‐monotonic in time as the local vertical component of glacio‐isostatic rebound and eustasy (or global meltwater influx) dominate at different periods. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
Developing a method to track oil and gas produced water discharges in estuarine systems using salinity as a conservative tracer. 总被引：1，自引：0，他引：1
Produced water is a high salinity by-product resulting from oil and gas production. Disposal methods include surface water discharge from a point source. The current field method used for fate and effect determinations in open water estuarine systems involves extending a compass oriented transect (COT) from the point source discharge--a method designed for a uniform offshore environment that might be inappropriate for the hydrologic and geomorphologic complexities found in estuarine systems. Research was conducted in a canal and a small, semi-enclosed bay to observe effluent behaviour and to determine if salinity could be used to track the effluent. A salinity/conductivity/temperature (SCT) probe measured water properties within 1 cm of the sediment surface and identified a thin, bottom salinity plume that would have gone undetected by conventional instruments. The plume flowed across the sediment surface and towards greater depths. Plume-affected sampling stations exhibited higher levels of sediment contaminant indicators (SCIs) and indicated that station location could affect impact conclusions. 相似文献
3.
Climatic regions as an indicator of forest coarse and fine woody debris carbon stocks in the United States 总被引：2，自引：0，他引：2
Background
Coarse and fine woody debris are substantial forest ecosystem carbon stocks; however, there is a lack of understanding how these detrital carbon stocks vary across forested landscapes. Because forest woody detritus production and decay rates may partially depend on climatic conditions, the accumulation of coarse and fine woody debris carbon stocks in forests may be correlated with climate. This study used a nationwide inventory of coarse and fine woody debris in the United States to examine how these carbon stocks vary by climatic regions and variables. 相似文献4.
R. Woodall 《Australian Journal of Earth Sciences》2013,60(3):231-237
Vision is concerned with making observations: quantitative observations such as measurements, and observations of form and pattern. Vision is perception: an awareness of the significance of observations and insight or intuition. We live and work with limited vision. 相似文献
5.
At a national scale, the carbon (C) balance of numerous forest ecosystem C pools can be monitored using a stock change approach based on national forest inventory data. Given the potential influence of disturbance events and/or climate change processes, the statistical detection of changes in forest C stocks is paramount to maintaining the net sequestration status of these stocks. To inform the monitoring of forest C balances across large areas, a power analysis of a forest inventory of live/dead standing trees and downed dead wood C stocks (and components thereof) was performed in states of the Great Lakes region, U.S. Using data from the Forest Inventory and Analysis (FIA) program of the U.S. Forest Service, it was found that a decrease in downed wood C stocks (?1.87 Mg/ha) was nearly offset by an increase in standing C stocks (1.77 Mg/ha) across the study region over a 5-year period. Carbon stock change estimates for downed dead wood and standing pools were statistically different from zero (α?=?0.10), while the net change in total woody C (?0.10 Mg/ha) was not statistically different from zero. To obtain a statistical power to detect change of 0.80 (α?=?0.10), standing live C stocks must change by at least 0.7 %. Similarly, standing dead C stocks would need to change by 3.8 %; while downed dead C stocks require a change of 6.9 %. While the U.S.’s current forest inventory design and sample intensity may not be able to statistically detect slight changes (<1 %) in forest woody C stocks at sub-national scales, large disturbance events (>3 % stock change) would almost surely be detected. Understanding these relationships among change detection thresholds, sampling effort, and Type I (α) error rates allows analysts to evaluate the efficacy of forest inventory data for C pool change detection at various spatial scales and levels of risk for drawing erroneous conclusions. 相似文献
6.
Background
Standing dead trees are one component of forest ecosystem dead wood carbon (C) pools, whose national stock is estimated by the U.S. as required by the United Nations Framework Convention on Climate Change. Historically, standing dead tree C has been estimated as a function of live tree growing stock volume in the U.S.'s National Greenhouse Gas Inventory. Initiated in 1998, the USDA Forest Service's Forest Inventory and Analysis program (responsible for compiling the Nation's forest C estimates) began consistent nationwide sampling of standing dead trees, which may now supplant previous purely model-based approaches to standing dead biomass and C stock estimation. A substantial hurdle to estimating standing dead tree biomass and C attributes is that traditional estimation procedures are based on merchantability paradigms that may not reflect density reductions or structural loss due to decomposition common in standing dead trees. The goal of this study was to incorporate standing dead tree adjustments into the current estimation procedures and assess how biomass and C stocks change at multiple spatial scales. 相似文献7.
Mark Woodall Robert G. Cromley R. Keith Semple Milford B. Green 《The Professional geographer》1980,32(4):412-420
Recent federal court decisions have emphasized the need to eliminate schools whose racial composition varies from that of the whole district by more than a fixed percent. A linear programming model is presented to assist school administrators in developing desegregation plans that comply with these guidelines. An efficient solutional technique that exploits the special structure of this model increases problem-size capabilities. A study of the Columbus City School District examines the tradeoffs involved at different levels of desegregation. 相似文献
8.
Brown trout (Salmo trutta) are known to have effects on multiple trophic levels in New Zealand streams, but their impacts on lower trophic levels are less well understood within lentic systems. We examined the effects of brown trout removal using rotenone on zooplankton and phytoplankton community composition in the Upper Karori Reservoir, New Zealand. Significant shifts were observed in zooplankton and phytoplankton composition following removal of brown trout from the reservoir. Shifts in zooplankton community composition did not occur immediately following trout removal (February), but instead followed the likely timing of galaxiid spawning (July). The removal of brown trout likely resulted in reduced predation pressure on galaxiids. A major change occurred in the zooplankton community with the dominance shifting from larger crustaceans to smaller rotifers, indicating an increased predation pressure from the larval native galaxiid. A delayed response in zooplankton community composition change indicates rotenone was not the direct cause of this. A major shift in phytoplankton community composition occurred immediately following trout removal. This was not consistent with the trophic cascade hypothesis of reduced grazing pressure from larger zooplankton due to increased galaxiid predation as a result of brown trout removal. 相似文献
9.
Produced water is a high salinity by-product resulting from oil and gas production. Disposal methods include surface water discharge. The current field method used to determine its fate in estuarine systems involves extending a compass oriented transect (COT) from the point source discharge--a method designed for a uniformly dispersing effluent discharged into a uniform offshore environment that may be inappropriate for the hydrologic and geomorphologic complexities found in estuarine systems. Prior research established the viability of the salinity stratification transect (SST) method. Both COT and SST methods were used in a small open bay to determine which more accurately detected effluent dispersion. Determination was based on sediment contaminant indicators (SCIs), including interstitial salinity, hydrocarbons, metals, and radium concentrations. Additionally, SCIs were evaluated for their ability to serve as indicators of effluent dispersion. The data revealed that SST stations exhibited higher contaminant concentrations and that this approach was more accurate in tracking the produced water plume. The data also suggested that SCIs varied in their ability to serve as indicators. Good indicators included interstitial salinity, total targeted aromatic hydrocarbons substantiated with a modified fossil fuel pollution index value, certain metals, and radium-228. 相似文献
10.
Barry Tyler Wilson Christopher W Woodall Douglas M Griffith 《Carbon balance and management》2013,8(1):1-15
The U.S. has been providing national-scale estimates of forest carbon (C) stocks and stock change to meet United Nations Framework Convention on Climate Change (UNFCCC) reporting requirements for years. Although these currently are provided as national estimates by pool and year to meet greenhouse gas monitoring requirements, there is growing need to disaggregate these estimates to finer scales to enable strategic forest management and monitoring activities focused on various ecosystem services such as C storage enhancement. Through application of a nearest-neighbor imputation approach, spatially extant estimates of forest C density were developed for the conterminous U.S. using the U.S.’s annual forest inventory. Results suggest that an existing forest inventory plot imputation approach can be readily modified to provide raster maps of C density across a range of pools (e.g., live tree to soil organic carbon) and spatial scales (e.g., sub-county to biome). Comparisons among imputed maps indicate strong regional differences across C pools. The C density of pools closely related to detrital input (e.g., dead wood) is often highest in forests suffering from recent mortality events such as those in the northern Rocky Mountains (e.g., beetle infestations). In contrast, live tree carbon density is often highest on the highest quality forest sites such as those found in the Pacific Northwest. Validation results suggest strong agreement between the estimates produced from the forest inventory plots and those from the imputed maps, particularly when the C pool is closely associated with the imputation model (e.g., aboveground live biomass and live tree basal area), with weaker agreement for detrital pools (e.g., standing dead trees). Forest inventory imputed plot maps provide an efficient and flexible approach to monitoring diverse C pools at national (e.g., UNFCCC) and regional scales (e.g., Reducing Emissions from Deforestation and Forest Degradation projects) while allowing timely incorporation of empirical data (e.g., annual forest inventory). 相似文献