Isotopic study of sulfate sources and residence times in a subalpine watershed   总被引：3，自引：0，他引：3  

Cynthia L. Kester  Jill S. Baron  John T. Turk 《Environmental Geology》2003,43(5):606-613

Stable sulfur and oxygen isotope ratios and naturally occurring ³⁵S_SO4 activities were used to examine sulfate sources, address the role of sulfur dynamics, and estimate residence times of atmospherically derived sulfate in Loch Vale Watershed, Colorado. In 1996, surface water samples from small streams flowing through talus, forest, and wetland areas had '³⁴S_SO4 values ranging from 1.8 to 3.7‰. Values of '¹⁸O_SO4 at the three sites ranged from -1.3 to 3.7‰. Average '³⁴S_SO4 and '¹⁸O_SO4 values in Loch Vale precipitation (1991-1999) are higher (5.2 and 13.6, respectively) than surface water values, indicating that some of the deposited sulfate is transformed and/or mixed with other sulfur sources in the watershed (e.g. mineral and organic sulfur). Sulfate ages determined by ³⁵S_SO4 activities support this and show that deposited sulfate may be stored on a timescale of 1 year or more prior to being released to surface waters.  相似文献   

CLIMATE CHANGE, AGRICULTURE AND WETLANDS IN EASTERN EUROPE: VULNERABILITY, ADAPTATION AND POLICY   总被引：6，自引：1，他引：6  

Ellen KRACAUER Hartig  Ognyan Grozev  Cynthia Rosenzweig 《Climatic change》1997,36(1-2):107-121

Naturally-occurring wetlands perform such functions as flood control, pollution filtration, nutrient recycling, sediment accretion, groundwater recharge and water supply, erosion control, and plant and wildlife preservation. A large concentration of wetlands is located in Eastern Europe. A significant amount of Eastern European wetlands has been converted to agricultural use in the past, and remaining wetlands are subject to agricultural drainage. Drained wetlands are used as prime agriculture lands for a variety of food crops. Other agricultural uses of wetlands range from growing Phragmites australis (common reed) for thatch and livestock feed, to collecting peat for heating and cooking fuel. Altered hydrologic regimes due to global climate change could further exacerbate encroachment of agricultural land use into wetlands. The vulnerability and adaptation studies of the U.S. Country Studies Program are used to analyze where climate change impacts to agriculture may likewise impact wetland areas. Scenarios indicate higher temperatures and greater evapotranspiration altering the hydrologic regime such that freshwater wetlands are potentially vulnerable in Bulgaria, Czech Republic, and Russia, and that coastal wetlands are at risk in Estonia. Runoff is identified as a key hydrological parameter affecting wetland function. Since wetland losses may increase as a result of climate-change-induced impacts to agriculture, precautionary management options are reviewed, such as establishing buffer areas, promoting sustainable uses of wetlands, and restoration of farmed or mined wetland areas. These options may reduce the extent of negative agricultural impacts on wetlands due to global climate change.  相似文献   

Impact of Turbidity on TCE and Degradation Products in Ground Water     

Cynthia J. Paul  Robert W. Puls 《Ground Water Monitoring & Remediation》1997,17(1):128-133

Elevated particulate concentrations in ground water samples can bias contaminant concentration data. This has been particularly problematic for metal analyses where artificially increased turbidity levels can affect metals concentrations and confound interpretation of the data. However, few studies have been conducted to determine the impact of particulates on trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and vinyl chloride concentrations.
Laboratory batch studies and field investigations were conducted to evaluate the effects of suspended solids on VOC concentrations in ground water samples analyzed by purge-and-trap gas chromatography. Three different solids were used to assess the effects of suspended particulates. The solids were aquifer material from a field site in North Carolina and two reference clay minerals (kaolinite and Namontimorillonite). During the laboratory portion of this study, the solids were used to determine effects on TCE concentrations under controlled laboratory conditions.
The same solids were used in a field study to compare the laboratory results with field results. Solids were added to the sample vials prior it) sample collection to intentionally increase turbidity levels in the water samples. Results of the study indicate essentially no decrease in TCE, c-DCH, or vinyl chloride concentrations due to increased turbidity levels.  相似文献   

The Local Articulation of Policy Conflict: Land Use,Environment, and Amerindian Rights in Eastern Amazonia     

Cynthia S. Simmons 《The Professional geographer》2002,54(2):241-258

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The effect of changes in daily and interannual climatic variability on CERES-Wheat: A sensitivity study   总被引：4，自引：1，他引：4  

Linda O. Mearns  Cynthia Rosenzweig  Richard Goldberg 《Climatic change》1996,32(3):257-292

We investigate the effect of changes in daily and interannual variability of temperature and precipitation on yields simulated by the CERES-Wheat model at two locations in the central Great Plains. Changes in variability were effected by adjusting parameters of the Richardson daily weather generator. Two types of changes in precipitation were created: one with both intensity and frequency changed; and another with change only in persistence. In both types mean total monthly precipitation is held constant. Changes in daily (and interannual) variability of temperature result in substantial changes in the mean and variability of simulated wheat yields. With a doubling of temperature variability, large reductions in mean yield and increases in variability of yield result primarily from crop failures due to winter kill at both locations. Reduced temperature variability has little effect. Changes in daily precipitation variability also resulted in substantial changes in mean and variability of yield. Interesting interactions of the precipitation variability changes with the contrasting base climates are found at the two locations. At one site where soil moisture is not limiting, mean yield decreased and variability of yield increased with increasing precipitation variability, whereas mean yields increased at the other location, where soil moisture is limiting. Yield changes were similar for the two different types of precipitation variability change investigated. Compared to an earlier study for the same locations wherein variability changes were effected by altering observed time series, and the focus was on interannual variability, the present results for yield changes are much more substantial. This study demonstrates the importance of taking into account change in daily (and interannual) variability of climate when analyzing the effect of climate change on crop yields.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Estimating Stable Measured Values and Detecting Anomalies in Groundwater Geochemistry Time Series Data Across the Athabasca Oil Sands Area,Canada     

Manchuk  John G.  Birks  Jean S.  McClain  Cynthia N.  Bayegnak  Guy  Gibson  John J.  Deutsch  Clayton V. 《Natural Resources Research》2021,30(2):1755-1779

Regional groundwater monitoring in the Athabasca region of Alberta, Canada, provides information on groundwater quality and geochemical changes over time, including data useful for evaluating potential impacts of industrial activity such as oil sands mining and in situ operations. Data collected from over 5000 wells from the 1950s to 2014, including 161 wells from government’s monitoring network, were used to develop and apply bootstrap techniques for the detection of changes in groundwater geochemistry over time and at specific points in time. Increasing temporal anomalies were identified in Cl, TDS, B, and naphthenic acids in the McMurray formation across 2003 and 2008, while decreasing anomalies were found for SO₄. Temporal variance for 15 indicators was quantified for a smooth bootstrap approach to arrive at stable values representative of the most recent samples taken from wells in the study area. Stable values revealed sampling bias in the Devonian, Grand Rapids, Empress, Channel Beverly, and Muriel Lake formations suggesting expansion of sampling may be necessary. Although temporal anomalies were found in the McMurray formation, sampling bias was not identified. The entropy and relative magnitude of time series were evaluated to identify candidate wells for continued observations, which consist of wells with low measurements and low entropy that are near active industry lease boundaries. Temporal anomalies, stable values, and entropy were combined into type-well information to provide plots for visual inspection and interpretation. Stable values are useful for regional mapping, for detecting future changes and trends, and for identifying areas of interest warranting further investigation.

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Potential CO2-induced climate effects on North American wheat-producing regions   总被引：4，自引：0，他引：4  

Cynthia Rosenzweig 《Climatic change》1985,7(4):367-389

The environmental requirements for growth of winter, spring, and fallsown spring wheats in North America are specified and compared to temperature results from the control run of the Goddard Institute for Space Studies general circulation model (GISS GCM) and observed precipitation in order to generate a simulated map of current wheat production regions. The simulation agrees substantially with the actual map of wheat-growing regions in North America. Results from a doubled CO₂ run of the climate model are then used to generate wheat regions under the new climatic conditions. In the simulation, areas of production increase in North America, particularly in Canada, due to increased growing degree units (GDU). Although wheat classifications may change, major wheat regions in the United States remain the same under simulated doubled CO₂ conditions. The wheat-growing region of Mexico is identified as vulnerable due to high temperature stress. Higher mean temperatures during wheat growth, particularly during the reproductive stages, may increase the need for earlier-maturing, more heat-tolerant cultivars throughout North, America. The soil moisture diagnostic of the climate model is used to analyze potential water availability in the major wheat region of the Southern Great Plains.  相似文献   

Dewatering and extensional deformation of the Shikoku Basin hemipelagic sediments in the Nankai Trough     

Cynthia J. Bray  Daniel E. Karig 《Pure and Applied Geophysics》1988,128(3-4):725-747

The Shikoku Basin hemipelagic sequence, which underlies the Nankai Trough wedge, S.W. Japan, thins by 50% between the outer edge of the trench wedge and DSDP Site 582, 14 km arcward. A sedimentation model, which incorporates changes in sedimentation rates with time and with distance from the trench wedge toe, indicates that 57% of the total thinning occurs as a result of temporally varying sedimentation rates and a time transgressive facies boundary between the trench wedge turbidites and the underlying hemipelagites. Burial-induced consolidation beneath the wedgeshaped turbiditic overburden, accounts for the remaining 43% of arcward thinning within the hemipelagic unit. Rapid dewatering, modeled as one-dimensional consolidation suggests that the excess pore water pressures are quite low during this progressive dewatering. Thus, high pore water pressures should not be assumed to occur universally in convergent margin settings. Normal faults and vein structures in the hemipelagites suggest near-horizontal extension in addition to vertical consolidation. The estimates of excess pore water pressures together with fault geometries and horizontal extensional strains, determined from the geometry of the subducting oceanic plate, can be used to constrain the stress conditions at failure. The expulsion of hot water from the rapidly dewatering sediments in the Nankai Trough may help to explain anomalously high heat flow in the central part of the trough.  相似文献   

Siliceous microfossil succession in the recent history of two basins in Lake Baikal, Siberia     

Mark B. Edlund  E. F. Stoermer  Cynthia H. Pilskaln 《Journal of Paleolimnology》1995,14(2):165-184

As part of the international cooperative Baikal Drilling Project, siliceous microfossil assemblage succession was analyzed in two short ( 30-cm) sediment cores from Lake Baikal. One core was recovered from the north basin (Core 324, 55°15N, 109°30E), a second from between the central and southern basins (Core 316, 52°28N, 106°5E). The northern core had higher amounts of biogenic silica (40 g SiO₂ per 100 g dry weight sediment) compared to the southern core, and increased deposition in the more recent sediments. Weight percent biogenic silica was lower in the southern core, ranging from approximately 20–30 g SiO₂ per 100 g dry weight sediment throughout the entire core. Trends in absolute microfossil abundance mirror those of biogenic silica, with generally greater abundance in the northern core (86–275×10⁶ microfossils g^–1 dry sediment) compared to the southern core (94–163×10⁶ microfossils g^–1 dry sediment).Cluster analyses using relative abundance of the dominant diatom and chrysophyte taxa revealed four zones of microfossil succession in each core. Microfossil assemblage succession in the north basin may be reflecting shifts in nutrient supply and cycling driven by climatic changes. The most recent sediments in the northern basin (Zone 1,c. 1890's–1991 A.D.) were characterized by an increased abundance ofAulacoseira baicalensis andAulacoseira spore. Zone 3 (c. 1630's–1830's A.D.) was dominated by the endemicCyclotella spp. and reduced abundance of theAulacoseira spp. Zone 3 corresponds approximately to the Little Ice Age, a cooler climatic period. The microfossil assemblages between Zones 1 and 3 (Zone 2,c. 1830's–1890's A.D.) and below Zone 3 (Zone 4,c. 830's–1430's A.D.) are similar to one another suggesting they represent transitional intervals between warm and cold periods. Southern basin sediments record similar changes in the endemic taxa. However, the increased abundance of non-endemic planktonic taxa (e.g.Stephanodiscus binderanus, Synedra acus, Cyclostephanos dubius) during two periods in recent history (post World War II and late 1700's) suggests evidence for anthropogenic induced changes in southern Lake Baikal.  相似文献   

Hotelling Revisited: Oil Prices and Endogenous Technological Progress     

C.-Y. Cynthia Lin  Haoying Meng  Tsz Yan Ngai  Valeria Oscherov  Yan Hong Zhu 《Natural Resources Research》2009,18(1):29-38

This article examines the Hotelling model of optimal nonrenewable resource extraction in light of empirical evidence that petroleum and minerals prices have been trendless despite resource scarcity. In particular, we examine how endogenous technology-induced shifts in the cost function would have evolved over time if they were to maintain a constant market price for nonrenewable resources. We calibrate our model using empirical data on world oil, and find that, depending on the estimate of the initial stock of reserve, oil reserves will likely be depleted some time between the years 2040 and 2075.  相似文献