Controls on carbon cycling in two contrasting temperate zone estuaries: The Tyne and Tweed, UK     

Jason M.E. Ahad  Johannes A.C. Barth  Raja S. Ganeshram  Robert G.M. Spencer  Günther Uher 《Estuarine, Coastal and Shelf Science》2008,78(4):685-693

In order to evaluate the respiration–photosynthesis dynamics in two contrasting North Sea estuaries, pH, temperature, alkalinity, chlorophyll-a (chl-a), and isotopic ratios of dissolved inorganic carbon (δ¹³C_DIC) and dissolved oxygen (δ¹⁸O_DO) were measured in the Tyne (July 2003) and Tweed (July 2003 and December 2003) estuaries. Using a concentration-dependent isotope mixing line, δ¹³C_DIC values in the Tweed (July 2003) demonstrated mostly conservative behaviour across the estuary, reflecting mixing between riverine and marine sources, although some samples were slightly more ¹³C-enriched than predicted δ¹³C_DIC values. Low pCO₂ (less than 2 times atmospheric pressure) and ¹⁸O-depleted δ¹⁸O_DO signatures below equilibrium with the atmosphere provided further evidence for net autotrophy in the Tweed estuary in summer 2003. Conversely, in the Tyne during the summer and in the Tweed during the winter higher pCO₂ (up to 6.5 and 14.4 times atmospheric partial pressure in the Tweed and Tyne, respectively), slightly ¹³C-depleted δ¹³C_DIC and ¹⁸O-enriched δ¹⁸O_DO values indicated heterotrophy as the dominant process. The relatively large releases of CO₂ observed during these two estuarine surveys can be attributed to significant oxidation of terrigenous organic matter (OM). This study therefore demonstrates the usefulness of combined δ¹⁸O_DO and δ¹³C_DIC isotopes in examining the relationship between respiration–photosynthesis dynamics and the fate of terrestrially derived OM during estuarine mixing.  相似文献   

哈萨克斯坦东部斋桑盆地恐龙蛋壳化石与白垩系-古近系界线     

Spencer G.LUCAS  Emily S.BRAY  Robert J.EMRY  Karl F.HIRSCH 《地层学杂志》2012,(2):417-435

在晚白垩世期间,哈萨克斯坦东部的斋桑盆地形成了一个湖盆,一直延续到现在。古斋桑湖中最老的沉积是Tayzhuzgen组,由厚达136m的泥岩、粉砂岩、页岩、石英砂岩、砾岩和淡水石灰岩红层组成。按照当地的地层名称,Tayzhuzgen组包括Manrak、Tayzhuzgen、Aulisbulak、Aktobe、Dysum bay和Kiin Kerish层。在斋桑湖以南的Tayzhuzgen河附近一个地点的Tayzhuzgen组下部,发现了恐龙蛋壳碎片,蛋壳至少包括有两个主要类型:圆形蛋类和长形蛋类。恐龙蛋壳指示了Tayzhuzgen组下部的时代为晚白垩世(可能是马斯特里赫特期)。在本组的较高层位,发现了晚?古新世的植物化石,因此斋桑盆地的白垩系-古近系界线在Tayzhuzgen组内部。在Tayzhuzgen组中,白垩纪与古新世化石层之间的地层间隔只有约50m,由此推测在Tayzhuzgen组内部可能存在一个或多个不整合,或是本组的中部为凝缩沉积,即在白垩系-古近系界线处的沉积速率非常缓慢。Tayzhuzgen组顶部有一个显著的不整合,那里中或晚始新世(Arshantan,Irdinmanhan或Egilian陆生哺乳动物"期")的地层存在于含哺乳动物化石剖面的底部。斋桑盆地的白垩系-古近系界线位于古斋桑湖沉积剖面的下部。这不是一个完整的界线剖面,可能是一个包含有一个或多个不整合和/或一个由慢速沉积造成的凝缩剖面。  相似文献   

Paleoenvironmental context of archaeological sites,implications for subsistence strategies under Holocene climate change,northern Kenya     

Gail M. Ashley  Emmanuel K. Ndiema  Joel Q.G. Spencer  John W.K. Harris  Purity W. Kiura 《Geoarchaeology》2011,26(6):809-837

The Holocene was time of dramatic climate change in East Africa, shifting from wetter climate in the Early–Mid Holocene (∼10–5ka) to drier climates in the Late Holocene, followed by a slight reversal at <1ka. The Holocene was a time of cultural change from hunter‐gatherer and fishing to pastoralism. Recent excavations along the eastern shores of Lake Turkana, Kenya (4°N) provide new archaeological materials, a high‐resolution stratigraphic and paleoenvironmental data set, OSL dates, and cultural records in the context of documented environmental change (falling lake levels). Archaeological site FwJj25 (4.20 ± 0.28ka), on the northeastern margin of Lake Turkana, provides one of the earliest records of pastoralism in the region. The palimpsest record of FwJj5 (0.90 ± 0.06ka) was in a small valley containing a groundwater seep located 5km from the lake. FwJj5 reflects occupation by people who may have covered great distances in accessing resources, but were likely drawn to an environmental refugia of freshwater springs during times of regional aridity. © 2011 Wiley Periodicals, Inc.  相似文献   

Roles of forest disturbance and climate variability on streamflow components in snow-dominated paired watersheds at multiple temporal scales     

Qiang Li  Mingfang Zhang  Xiaohua Wei  Rita Winkler  Sheena Spencer  Yiping Hou  David F. Scott 《水文研究》2021,35(12):e14414

The paired watershed experimental (PWE) approach has long been used as an effective means to assess the impacts of forest change on hydrology in small watersheds (<100 km²). Yet, the effects of climate variability on streamflow are not often assessed in PWE design. In this study, two sets of paired watersheds, (1) Camp and Greata Creeks and (2) 240 and 241 Creeks located in the Southern Interior of British Columbia, Canada, were selected to explore relative roles of forest disturbance and climate variability on streamflow components (i.e., baseflow and surface runoff) at different time scales. Our analyses showed that forest disturbance is positively related to annual streamflow components. However, this relationship is statistically insignificant since forest disturbance can either increase or decrease seasonal streamflow components, which eventually limited the positive effect on streamflow at the annual scale. Interestingly, we found that forest disturbance consistently decreased summer streamflow components in the two PWEs as forest disturbance can augment earlier and quicker snow-melt processes and hence reduce soil moisture to maintain summer streamflow components. More importantly, this study revealed that climate variability played a more significant role than forest disturbance in both annual and seasonal streamflow components, for instance, climate variability can account for as much as 90% of summer streamflow components variation in Camp, suggesting the role of climate variability on streamflow should be highlighted in the traditional PWE approach to truly advance our understanding of the interactions of forest change, climate variability and water for sustainable water resource management.  相似文献   

Modified sediments and subsurface hydrology in natural and recreated salt marshes and implications for delivery of ecosystem services          下载免费PDF全文

James A. Tempest  Gemma L. Harvey  Kate L. Spencer 《水文研究》2015,29(10):2346-2357

Recreation or restoration of salt marsh through the deliberate removal of flood defences (managed realignment or de‐embankment) is a common practice across Europe and the USA, with potential to enhance delivery of ecosystem services. However, recent research suggests that physical, chemical and ecological processes may be impaired in recreated sites as a result of the modified morphology, sediment structure and hydrology associated with both the restoration process and historic land use. This paper compares physical sediment properties and subsurface water levels recorded in paired natural and de‐embanked (recreated) salt marshes in SE England. Using a combination of statistical and time‐series modelling, significant differences between the natural and recreated marshes are identified. Sediment properties (bulk density, moisture content and organic content) within each marsh were statistically different and imply that de‐embanked sediments are compacted, which may affect subsurface water movement. Analysis of hydrological time series reveals that the de‐embanked salt marsh is characterized by a damped response to tidal flooding with elevated and less variable water levels. This, combined with analysis of hydrographs and hysteresis patterns over individual tidal cycles, suggests that fast, horizontal near‐surface flows enhanced by the relict land surface may play a greater role in drainage of the de‐embanked salt marsh. The importance of hydrological functioning in governing many important physical and biogeochemical processes in salt marshes suggests any modifications would have significant implications for the delivery of ecosystem services. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Norovirus Outbreak Caused by a New Septic System in a Dolomite Aquifer   总被引：3，自引：0，他引：3  

Mark A. Borchardt  Kenneth R. Bradbury  E. Calvin Alexander Jr.  Rhonda J. Kolberg  Scott C. Alexander  John R. Archer  Laurel A. Braatz  Brian M. Forest  Jeffrey A. Green  Susan K. Spencer 《Ground water》2011,49(1):85-97

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Avalanche fatalities in the western United States: a comparison of three databases     

Jeremy M. Spencer  Walker S. Ashley 《Natural Hazards》2011,58(1):31-44

Reported avalanche fatalities in the United States increased markedly through the latter half of the twentieth century, a result of the increasing popularity of winter sports. Despite this increase, the literature concerning US avalanche fatalities is sparse. This paper presents a comparison of three US databases containing avalanche fatality information: Storm Data, the West Wide Avalanche Network (WWAN) dataset, and the National Avalanche Database (NAD). The frequency of avalanche fatalities, their temporal trends, spatial distributions, and the demographic characteristics of the victims were analyzed in each database for the years 1998–2009 for the US mountainous west. The data were then pooled to arrive at an estimate of avalanche fatality frequency in the United States for the study period. While the results indicate a considerable amount of overlap between the datasets, Storm Data reports fewer avalanche fatalities than both the WWAN and NAD datasets. All three datasets report a maximum of fatalities in January and display three spatial maxima: the Rocky Mountains of west-central Colorado, the intermountain region from central Utah through Idaho to west-central Montana, and the northern Cascade Ranges of Washington; however, a large void appears in the Storm Data records in the vicinity of the Montana maximum. These maxima result from a juxtaposition of avalanche hazard in these mountainous environments with a high concentration of winter sports activities.  相似文献   

Distributional choices in EU climate policy: 20 years of policy practice     

Thomas Spencer 《Climate Policy》2013,13(2):240-258

The distributional choices of the EU in three policy phases, spanning 20 years, are examined: the negotiations on emissions reduction targets for the EU15 under the first commitment period of the Kyoto Protocol, the negotiation of National Allocation Plans for Phase II of the EU Emissions Trading Scheme (ETS) between 2008 and 2012, and the formulation of the 2008 Climate and Energy Package for the period 2013–2020. A flexible and pragmatic framework, consisting of the normative principles of capacity, responsibility, equality, and need, is used to elucidate the indicators and policies used in deciding how the EU Member States are to share the cost of meeting climate policy objectives. The analysis extends the literature by applying a common analytical framework across the three different policy phases and provides a structured basis for the assessment of what the EU and other jurisdictions can learn from them.

Policy relevance

Distributing the cost of climate policy is a key policy concern, both at the domestic and international level. The EU has more than 20 years of policy experience with such distributional choices and is also preparing the next steps of its policy, where distributional choices will again be central. A framework is developed to assess the modalities and rationale for EU distributional choices in order to inform the future climate policy of the EU and other jurisdictions.  相似文献   

Ionospheric imaging of the northern crest of the Equatorial Anomaly     

M. Materassi  C. N. Mitchell  P. S. J. Spencer 《Journal of Atmospheric and Solar》2003,65(16-18):1393-1400

The dominant structure in free electron concentration in the tropical ionosphere is the Equatorial Anomaly, where the largest values of TEC are found. This structure follows the geomagnetic equator and extends some 40° in latitude. The edges of the structure (crests) are characterised by steep, latitudinal gradients in TEC, which are temporally as well as spatially variable.This phenomenology is traditionally explained in terms of the theory of “fountain effect”, which is shortly reviewed in this work before presenting our results.Here we study the northern crest of the Equatorial Anomaly using a program that can perform multi-instrument two- or three-dimensional time-evolving mathematical inversions. This program is designed to unify a number of different measurement techniques, thus allowing the spatial and temporal study of the ionospheric features at hand. The paper reports on experimental results from winter 2000/2001. This is a highly significant period to study the ionospheric anomalies because it is around the maximum of the 11-year solar cycle and TEC is at a maximum.  相似文献   

The symbiotic star CH Cygni – III. A precessing radio jet     

M. M. Crocker  R. J. Davis  R. E. Spencer  S. P. S. Eyres  M. F. Bode  A. Skopal 《Monthly notices of the Royal Astronomical Society》2002,335(4):1100-1108

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