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961.
Since 1999, Ohio EPA hydrogeologists have used two analytic element models (AEMs), the proprietary software GFLOW and U.S. EPA's WhAEM, to delineate protection areas for 535 public water systems. Both models now use the GFLOW2001 solution engine, integrate well with Geographic Information System (GIS) technology, have a user-friendly graphical interface, are capable of simulating a variety of complex hydrogeologic settings, and do not rely upon a model grid. These features simplify the modeling process and enable AEMs to bridge the gap between existing simplistic delineation methods and more complex numerical models. Ohio EPA hydrogeologists demonstrated that WhAEM2000 and GFLOW2000 were capable of producing capture zones similar to more widely accepted models by applying the AEMs to eight sites that had been previously delineated using other methods. After the Ohio EPA delineated protection areas using AEMs, more simplistic delineation methods used by other states (volumetric equation and arbitrary fixed radii) were applied to the same water systems to compare the differences between various methods. GIS software and two-tailed paired t-tests were used to quantify the differences in protection areas and analyze the data. The results of this analysis demonstrate that AEMs typically produce significantly different protection areas than the most simplistic delineation methods, in terms of total area and shape. If the volumetric equation had been used instead of AEMs, Ohio would not have protected 265 km2 of critical upgradient area and would have overprotected 269 km2 of primarily downgradient land. Since an increasing number of land-use restrictions are being tied to drinking water protection areas, this analysis has broad policy implications. 相似文献
962.
We investigate the performance of vertical hydraulic barriers in combination with extraction wells for the partial hydraulic isolation of contaminated aquifer areas. The potential advantage of such combinations compared to a conventional pump-and-treat system has already been demonstrated in a previous study. Here we extend the scope of the performance analysis to the impact of uncertainty in the regional flow direction as well as to highly heterogeneous aquifer transmissivity distributions. In addition, two new well-barrier scenarios are proposed and analyzed. The hydraulic efficiency of the scenarios is rated based on the expected (mean) reduction of the pumping rate that is required to achieve downgradient contaminant capture. The uncertain spatial distribution of aquifer transmissivity is considered by means of unconditioned Monte Carlo simulations. The significance of uncertain background flow conditions is incorporated by computing minimized pumping rates for deviations of the regional flow direction up to 30 degrees from a normative base case. The results give an answer on how pumping rates have to be changed for each barrier-well combination in order to achieve robust systems. It is exposed that in comparison to installing exclusively wells, the barrier-supported approach generally yields savings in the (average) pumping rate. The particular efficiency is shown to be highly dependent on the interaction of variance and integral scale of transmissivity distribution, well and barrier position, as well as direction of background flow. 相似文献
963.
964.
Bothner MH Reynolds RL Casso MA Storlazzi CD Field ME 《Marine pollution bulletin》2006,52(9):1034-1047
Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mobility/resuspension along the fringing coral reef off southern Molokai (February 2000-May 2002). Two storms with high rainfall, floods, and exceptionally high waves resulted in sediment collection rates>1000 times higher than during non-storm periods, primarily because of sediment resuspension by waves. Based on quantity and composition of trapped sediment, floods recharged the reef flat with land-derived sediment, but had a low potential for burying coral on the fore reef when accompanied by high waves. The trapped sediments have low concentrations of anthropogenic metals. The magnetic properties of trapped sediment may provide information about the sources of land-derived sediment reaching the fore reef. The high trapping rate and low sediment cover indicate that coral surfaces on the fore reef are exposed to transient resuspended sediment, and that the traps do not measure net sediment accumulation on the reef surface. 相似文献
965.
Galloway TS Brown RJ Browne MA Dissanayake A Lowe D Depledge MH Jones MB 《Marine pollution bulletin》2006,53(1-4):186-194
The ECOMAN was initiated in 2001 by the University of Plymouth, UK, Plymouth Marine Laboratory and the Department of the Environment, Fisheries and Rural Affairs (DEFRA) to address the need for more pragmatic assessment techniques linking environmental degradation with its causes. The primary aim of the project was to develop an evidence-based approach in which suites of easy-to-use, cost-effective and environmentally valid biological responses (biomarkers) could be used together to assess the health of coastal systems through the general condition of individuals. A range of sub-lethal endpoints, chosen to reflect successive levels of biological organisation (molecular, cellular, physiological), was evaluated in common coastal organisms showing different feeding types (filter feeding, grazing, predation) and habitat requirements (estuary, rocky shore). Initially, the suite of biomarkers was used in laboratory studies to determine the relative sensitivities of key species within different functional groups to common contaminants. These results were then validated in field studies performed in a range of ecosystems exhibiting different degrees/signatures of contamination. Here, an example is provided of a field study in the Humber Estuary, UK, which illustrates how multivariate statistical analysis can be used to identify patterns of response to discriminate between contaminated and clean sites. The use of a holistic, integrated approach of this kind is advocated as a practical means of assessing the impact of chemical contamination on organismal health and of ranking the status of marine ecosystems. 相似文献
966.
A representative economic model is used to analyze local policies to reestablish full employment. It addresses three types of barriers: 1. Rigid wages, 2. Occupational (or industrial) immobility, and 3. Geographic immobility. These factors are considered in the framework of three types of policies: 1. Laissez-faire, 2. Narrowly targeted employment incentives, and 3. Broadly targeted incentives. The paper concludes that the usefulness of the abstract model will depends upon the ability of local development officials to combine the implications of the model with information about the local economic development narrative. In turn, the narrative depends upon an in-depth local knowledge of history, institutions, practices and personalities. 相似文献
967.
Richard B. Brugam Michael Ketterer Laylonda Maines Zhi Qing Lin William A. Retzlaff 《Journal of Paleolimnology》2012,47(1):101-112
A simple binary mixing model is used to determine the isotopic ratios of lead (Pb) pollution sources to a lake located near
a smelter closed because of excessive Pb aerosols (Horseshoe Lake Madison County, Illinois, USA). As a control, we also examine
a relatively unpolluted lake in a rural area of Southern Illinois (Horseshoe Lake Alexander County). Sediment cores were taken
from both lakes and analyzed for Pb and Pb isotopes by ICP-MS. The mixing model shows that Madison County Horseshoe Lake had
3 different sources of Pb in its history. The first source is sediment from the Mississippi River with an intermediate 206Pb/207Pb ratio (1.223 ± 0.009) which dominates inputs in pre-settlement times. From 1750 to 1933, the source of pollution Pb has
the high 206Pb/207Pb ratio (1.256 ± 0.005) characteristic of ore from the southeast Missouri Pb mines. The most recently deposited pollution
Pb comes from a source with a low 206Pb/207Pb ratio (1.202 ± 0.005). This source is similar in isotopic composition to pollution Pb found by several other investigators
in the Eastern US and probably represents the mixture of ores used in modern industrial processes. It is unclear from the
isotopic composition whether this source at Horseshoe Lake is the local Pb smelter or vehicle exhaust. The sediment core from
Horseshoe Lake, Alexander County, shows a less variable isotopic composition. The binary mixing model showed a source composition
of 1.225 ± 0.003 before 1850 and 1.231 ± 0.003 after this date. The change does not indicate a pollution source, but may be
a shift in the sources of natural sediment with slightly different isotopic ratios to the lake. Our results show the value
of simple binary mixing models to reconstruct the isotopic composition of Pb sources to lakes. 相似文献
968.
Gunnar Luderer Valentina Bosetti Michael Jakob Marian Leimbach Jan C. Steckel Henri Waisman Ottmar Edenhofer 《Climatic change》2012,114(1):9-37
This paper synthesizes the results from the model intercomparison exercise among regionalized global energy-economy models conducted in the context of the RECIPE project. The economic adjustment effects of long-term climate policy are investigated based on the cross-comparison of the intertemporal optimization models ReMIND-R and WITCH as well as the recursive dynamic computable general equilibrium model IMACLIM-R. A number of robust findings emerge. If the international community takes immediate action to mitigate climate change, the costs of stabilizing atmospheric CO2 concentrations at 450?ppm (roughly 530?C550?ppm-e) discounted at 3% are estimated to be 1.4% or lower of global consumption over the twenty-first century. Second best settings with either a delay in climate policy or restrictions to the deployment of low-carbon technologies can result in substantial increases of mitigation costs. A delay of global climate policy until 2030 would render the 450?ppm target unachievable. Renewables and CCS are found to be the most critical mitigation technologies, and all models project a rapid switch of investments away from freely emitting energy conversion technologies towards renewables, CCS and nuclear. Concerning end use sectors, the models consistently show an almost full scale decarbonization of the electricity sector by the middle of the twenty-first century, while the decarbonization of non-electric energy demand, in particular in the transport sector remains incomplete in all mitigation scenarios. The results suggest that assumptions about low-carbon alternatives for non-electric energy demand are of key importance for the costs and achievability of very low stabilization scenarios. 相似文献
969.
The influence of negative emission technologies and technology policies on the optimal climate mitigation portfolio 总被引:1,自引:1,他引:0
Derek M. Lemoine Sabine Fuss Jana Szolgayova Michael Obersteiner Daniel M. Kammen 《Climatic change》2012,113(2):141-162
Combining policies to remove carbon dioxide (CO2) from the atmosphere with policies to reduce emissions could decrease CO2 concentrations faster than possible via natural processes. We model the optimal selection of a dynamic portfolio of abatement, research and development (R&D), and negative emission policies under an exogenous CO2 constraint and with stochastic technological change. We find that near-term abatement is not sensitive to the availability of R&D policies, but the anticipated availability of negative emission strategies can reduce the near-term abatement optimally undertaken to meet 2°C temperature limits. Further, planning to deploy negative emission technologies shifts optimal R&D funding from ??carbon-free?? technologies into ??emission intensity?? technologies. Making negative emission strategies available enables an 80% reduction in the cost of keeping year 2100 CO2 concentrations near their current level. However, negative emission strategies are less important if the possibility of tipping points rules out using late-century net negative emissions to temporarily overshoot the CO2 constraint earlier in the century. 相似文献
970.
Cesar Villanoy Laura David Olivia Cabrera Michael Atrigenio Fernando Siringan Porfirio Aliño Maya Villaluz 《Climatic change》2012,112(2):493-505
Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely recognized to provide protection against
the devastating effects of strong waves associated with tsunamis and storms. The predicted warming climate brings to fore
the role of these ecosystems in providing protection against stronger typhoons that can result in more devastating waves of
greater amplitude. We performed a model simulation of storm generated waves on a Philippine reef, which is located along the
path of tropical storms, i.e., at least 10 typhoons on the average pass through the study site yearly. A model to simulate
wave propagation was developed using Simulating Waves Nearshore (SWAN) and DELFT3D-WAVE computer simulation software. Scenarios
involving local monsoonal wind forcing and storm conditions were simulated. In addition, as climate change may also result
to increased relative sea level, a 0.3 m and 1 m rise in sea level scenarios were also used in the wave model simulations.
Results showed that the extensive reef system in the site helped dissipate wave energy that in turn reduced wave run-up on
land. A significant reduction in wave energy was observed in both climate change, i.e., stronger wind and higher sea level,
and non-climate change scenarios. This present study was conducted in a reef whose coral cover is in excellent condition (i.e.,
50 to 80% coral cover). Estimates of coral reef growth are in the same order of magnitude as estimates of relative sea level
rise based on tide gauge and satellite altimeter data, thus it is possible that the role of reefs in attenuating wave energy
may be maintained if coral reef growth can keep up with the change in sea level. Nonetheless, to maintain reef growth, it
is imperative to manage coral reef ecosystems sustainably and to eliminate the stressors that are within human control. Minimizing
activities such as illegal and destructive blast and poison fishing methods, pollution and siltation, is crucial to minimize
the impacts of high-energy waves that may increase with climate change. 相似文献