Nitrogen cycling in the German Bight (SE North Sea) — Clues from modelling stable nitrogen isotopes     

Johannes Pätsch  Alexandra Serna  Kirstin Dähnke  Tim Schlarbaum  Astrid Johannsen  Kay-Christian Emeis 《Continental Shelf Research》2010

Nitrogen isotope values (δ¹⁵N) of surface sediments in the German Bight of the North Sea exhibit a significant gradient from values of 5–6‰ of the open shelf sea to values above 11‰ in the German Bight. This signal has been attributed to high reactive N (N_r) loading enriched in ¹⁵N from rivers and the atmosphere. To better understand the processes that determine the intensity and spatial distribution of δ¹⁵N anomalies in surface sediments, and to explore their usefulness for reconstructions of pristine N-input from rivers, we modeled the cycling of the stable isotopes ¹⁴N and ¹⁵N in reactive nitrogen through the ecosystem of the central and southern North Sea (50.9–57.3°N, 3.4°W−9.2°E) for the year 1995. The 3D-ecosystem model ECOHAM amended with an isotope-tracking module was validated by δ¹⁵N data of surface sediments within the model domain. A typical marine value (δ¹⁵N_nitrate=5‰) was prescribed for nitrate advected into the model domain at the seaside boundaries, whereas δ¹⁵N_nitrate of river inputs were those measured bi-monthly over 1 year; δ¹⁵N values of atmospheric deposition were set to 6‰ and 7‰ for NO_x and NH_y, respectively. The simulated δ¹⁵N values of different nitrogen compounds in the German Bight strongly depend on the mass transfers in the ecosystem. These fluxes, summarized in a nitrogen budget for 1995, give an estimate of the impacts of hydrodynamical and hydrological boundary conditions, and internal biogeochemical transformations on the nitrogen budget of the bight.  相似文献   

Runout of the Socompa volcanic debris avalanche, Chile: a mechanical explanation for low basal shear resistance   总被引：1，自引：0，他引：1  

Tim Davies  Mauri McSaveney  Karim Kelfoun 《Bulletin of Volcanology》2010,72(8):933-944

We propose a mechanical explanation for the low basal shear resistance (about 50 kPa) previously used to simulate successfully the complex, well-documented deposit morphology and lithological distribution produced by emplacement of the 25 km³ Socompa volcanic debris avalanche deposit, Chile. Stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow, and we show that such fragmentation generates a basal shear stress, retarding motion of the avalanche, that is a function of the flow thickness and intact rock strength. The topography of the Socompa deposit is realistically simulated using this fragmentation-derived resistance function. Basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow.  相似文献   

Shifts in discharge‐concentration relationships as a small catchment recover from severe drought          下载免费PDF全文

Tim P. Burt  Fred Worrall  Nicholas J. K. Howden  Malcolm G. Anderson 《水文研究》2015,29(4):498-507

This paper provides evidence of the recovery of a small, moorland catchment to a severe drought, the most extreme on record in the UK. We present a detailed water quality time series for the post‐drought recovery period, from the first significant storm event at the end of the drought through three very wet months during which time the catchment fully wetted up. High‐frequency observations were obtained using pump water samplers, at 15‐min intervals for storm events and 2 hourly at other times. There are significant shifts in discharge‐concentration response as the catchment wets up; initial behaviour is very different to later storms. Extreme drought may become more common in a warmer world, so it is increasingly important to understand water quality response during and after such episodes, if their impact on water resources and in‐stream ecology is to be better anticipated. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Managing Ontong Java: Social institutions for production and governance of atoll resources in Solomon Islands   总被引：2，自引：2，他引：0  

Tim Bayliss-Smith  Katherine V. Gough  reas Egelund Christensen  Søren Pilgaard Kristensen 《Singapore journal of tropical geography》2010,31(1):55-69

This paper explores the changing nature of social institutions and organizations for resource management on Ontong Java and their central role in maintaining livelihoods. Using detailed field data for three time periods, 1970–72, 1986 and 2006–07, and drawing on earlier secondary data, a longitudinal analysis of changes in governance and livelihoods is undertaken. Increased exploitation of marine resources has widened the resource base and increased people's access to goods and services. Following the ban in 2005 on the bêche-de-mer trade, however, livelihoods have reverted to being more subsistence oriented. For almost two decades after 1978, a communal organization, the Area Council, succeeded in regulating exploitation of the atoll's marine resources to ensure sustainable use, but in the 1990s it collapsed. In addition there was a paralysis of institutions that had once settled land disputes. This failure of atoll governance is a greater threat to future 'sustainability' than the usual processes that are invoked for atolls and small islands generally. As the Solomon Islands state is also failing, we argue that local institutions and organizations have a vital role to play in managing access to resources and the future of livelihoods on Ontong Java atoll.  相似文献   

Small island sustainability in the Pacific: Introduction to the special issue     

Katherine V. Gough  Tim Bayliss-Smith  John Connell  Ole Mertz 《Singapore journal of tropical geography》2010,31(1):1-9

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Constraining the uncertainty in fracture geometry using tracer tests     

Peter B. Johnston  Tim Atkinson  John Barker  Noelle Odling 《Hydrogeology Journal》2009,17(3):527-539

In fractured-rock aquifers, the geometric and hydraulic properties of the fractures commonly have a dominant influence on transport. Tracer tests are often used to estimate directly the gross transport properties of a fractured rock mass. The prospects for understanding characteristics of the heterogeneities in a fractured porous medium were explored from evidence provided by tracer experiments. The approach was to simulate flow and transport on a large set of prescribed fracture networks in a two-dimensional homogeneous permeable medium, thus generating synthetic tracer test data. The fracture orientation, aperture, spacing and network geometry were systematically altered from one case to the next. A classification scheme was devised for the tracer breakthrough curves using principal component analysis and this classification was linked to the fracture pattern properties. Even under highly simplified and controlled conditions, quite different fracture patterns can produce very similar breakthrough curves. The classification scheme thus demonstrates that a single breakthrough curve cannot reveal the fracture geometry with any precision. However, the scheme provided a methodology for rejecting geometric properties that do not belong to the fracture pattern under investigation, thus reducing the uncertainty in fracture geometry.  相似文献   

Modelling the impact of afforestation on average annual streamflow in the Loess Plateau,China   总被引：1，自引：0，他引：1  

Xiao Ping Zhang  Lu Zhang  Tim R. McVicar  Tom G. Van Niel  Ling Tao Li  Rui Li  QinKe Yang  Liang Wei 《水文研究》2008,22(12):1996-2004

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Simplification of a Sequential Extraction Scheme To Determine the Mobilisable Heavy Metal Pool in Soils     

Tim Koeckritz  Jorg Thming  Christine Gleyzes  Knut E. degrd 《洁净——土壤、空气、水》2001,29(4):197-205

This investigation had the purpose of evaluating the reliability of a sequential extraction procedure according to Zeien and Brümmer (1989) which is performed routinely to analyse the distribution of heavy metals to different soil phases. Reliability was tested by two hypotheses. According to the first hypothesis an error propagation increased during a morefold extraction of heavy metals from a single soil sample to such an extend that it does not allow a statistical comparison of different analyses. This assumption was confirmed in an interlaboratory study of five participants applying the sequential extraction scheme on two different soils. The heavy metal amounts extracted by the different partners were of the same magnitude, but from the results no statistical correspondence at the 95% confidence level could be observed. The second hypothesis stated that also weak extraction agents were able to release metals from the more immobile soil fractions, especially if the amount of easily soluble metals was comparatively small. To answer this question the sequential extraction was modified by carrying out selected weak extraction steps several times. As expected the intensified extraction conditions caused a decrease of the element content within the more resistant phases. However, the additional release in the first four extraction steps of Pb, Mn, Fe, and Zn was only in the range of 5 to 10%. Furthermore, it was observed that a single EDTA extraction (step four within the sequential extraction scheme) was capable to extract the same amount of metals as the first four extraction steps of the original scheme at a variation of about 15%. From these results it was concluded that the EDTA step alone already represents a reliable pool of mobilisable metals. Thus it can be maintained that such a simple single EDTA extraction can be used to assess the environmental risk from heavy metal contaminated soils or to predict the potential heavy metal release of soil remediation processes.  相似文献   

南亚高压季节内变化与热带季节内振荡之间的关系     

林爱兰  LI Tim  王璐  李春晖 《大气科学》2021,45(3):633-650

采用观测分析和数值试验等方法,分析夏季南亚高压与热带季节内振荡(ISO)之间的关系,并对两者之间的相互作用进行量化诊断,探讨其物理过程.主要结果表明:南亚高压ISO与热带ISO活动关系密切,当热带ISO处于印度洋位相(第1、2、3位相),则南亚高压东脊点位置偏西,当ISO处于太平洋位相(第5、6、7位相),则南亚高压东...  相似文献   

热力和动力环境因子对与台风“海燕”路径相似的两类台风强度的相对贡献          下载免费PDF全文

徐昝敏  李天明 《大气科学学报》2024,47(2):224-234

本文分析了热力、动力环境因子对与百年一遇超强台风“海燕”有相似路径的热带气旋的强度的影响。为了定量分析环境因子的相对重要性,将相似路径下的台风分为超强台风和一般台风两类。结果表明,相较于动力因子,热力因子对生成超强台风更为重要。根据BDI(Box Difference Index)指数的排序,选择925 hPa湿静力能MSE(Moist Static Energy)、950 hPa比湿、900 hPa温度作为重要预测因子来判断是否生成超强台风。此外,海洋热容量和台风移动速度在两类台风中有着明显差异,也可以作为辅助预测因子。最后,用WRF模式(Weather Research and Forecasting)设计理想数值试验,揭示环境温度和水汽垂直剖面对台风强度影响的相对重要性。敏感性试验结果表明,环境水汽和温度的相对贡献比约为1∶4,它们的共同作用使得相似路径下的一般台风可以发展成为超强台风。  相似文献