Impact of global change on the biogeochemistry and ecology of an Arctic freshwater system   总被引：2，自引：0，他引：2  

John E. Hobbie  Bruce J. Peterson  Neil Bettez  Linda Deegan  W. John O'Brien  George W. Kling  George W. Kipphut  William B. Bowden  Anne E. Hershey 《Polar research》1999,18(2):207-214

Lakes and streams in the foothills near Tookik Lake, Alaska, at 68°N have been studied since 1975 to predict physical, chemical and biological impacts of future global change. Experimental manipulations include whole lake and continuous stream fertilization as well as removal and addition of predators (copepods, lake trout, grayling, sculpin). Based on our evidence the following scenario is likely. Warming thaws the upper layers of permafrost and streams and lakes become enriched with phosphorus. Streams respond quickly with higher production of diatoms but animal grazers keep biomass changes to a minimum. Fish productivity also increases. If phosphorus levels are too high, mosses become the dominant primary producer and sequester all of the nutrients. Growth of Arctic grayling under the present conditions only occurs in summers with higher than average stream flow. The present population would be stressed by warmer temperatures. When higher phosphorus levels reach lakes and cause slight europhication, the number of trophic levels will increase, especially within the microbial food web. Warmer lake temperatures increase stratification and, combined with eutrophication, could decrease oxygen in the hypolimnion. Oxygen levels will also decrease in winter under the ice cover. Eventually this habitat change will eliminate the lake trout, a top predator. Removal of lake trout results in a striking increase in abundance and productivity of smaller fish, including small lake trout, and the emergence of burbot as an alternate top predator. Large species of zooplankton will become virtually extinct.  相似文献   

Hydrodynamic characteristics of a lunate shape oscillating propulsor     

Pengfei Liu  Neil Bose   《Ocean Engineering》1999,26(6):325

Research was conducted to study the hydrodynamic efficiency of a foil with aft-swept wing tips. A potential flow based time domain panel method was formulated to predict the performance of a lunate and rectangular foil in large amplitude, unsteady motion. Skin drag was approximated and boundary layer growth and separation were also estimated. Hydrodynamic efficiency was evaluated in terms of propulsive efficiency and thrust coefficient of the foil. Results are presented for a lunate shaped planform and for a rectangular foil. Predictions show that the lunate shaped planform has a substantially higher propulsive efficiency (13% higher) than the rectangular foil under heavy load conditions when the feathering parameter is zero, throughout a range of reduced frequencies (0.2 to 1.8). Under a medium load condition, however, the rectangular foil gave a higher propulsive efficiency at reduced frequencies less than 0.5 and the same efficiency value at a reduced frequency of 1.8. For a practical range of reduced frequencies between 0.5 and 1.0, the lunate tail gave higher propulsive efficiency. The lunate planform gave a lower thrust coefficient at a heavy load and higher thrust at a medium load condition than the rectangular planform for all reduced frequencies.  相似文献   

Lower carboniferous (Dinantian) stratigraphy and structure in the Kingscourt Outlier,Ireland     

Peter Strogen  Ian D. Somerville  Neil A. H. Pickard  Gareth li. Jones 《Geological Journal》1995,30(1):1-23

Logging of 55 recent boreholes, together with remapping, has resulted in a fundamental reassessment of the stratigraphy and sedimentology of the Dinantian Kingscourt Outlier. Despite the present isolated position of the outlier within the Longford-Down Massif, the Kingscourt rocks are an integral part of the Dublin Basin succession. The newly defined Ardagh Platform marks the most northerly limit to basinal sedimentation in the Dinantian Dublin Basin. The Courceyan is a typical but thinner, north Dublin Basin succession with two new formal units: the Rockfield Sandstone Member and the Kilbride Formation. The latter, a coarse-grained, well washed limestone of latest Courceyan to early Chadian (late Tournaisian) age is the shallow water equivalent of the Feltrim Formation (Waulsortian facies), which is absent in the outlier. The Courceyan interval in the north of the outlier is markedly attenuated. In the succeeding Chadian-Brigantian interval basinal facies predominate in the south, but on the Ardagh Platform an almost complete coeval Viséan shallow water sequence is found. A new platform unit (Deer Park Formation) of latest Asbian to Brigantian age is defined in the Ardagh area. The Dee Member (Chadian) is newly defined for the lower part of the basinal Tober Colleen Formation and the Altmush Shale Member is formally defined for the upper part of the Loughshinny Formation. Two major structures dominate the Kingscourt Outlier: the NE-SW trending Moynalty Syncline in the south and the N-S trending Kingscourt Fault. Both are Hercynian structures, but probably represent reactivated Caledonide basement-controlled structures. Dinantian syn-depositional faulting is indicated in both the Courceyan (‘Kingscourt Sag’) and Chadian-Asbian. The latter period of faulting in the Ardagh area separates platform facies in the north from basinal facies to the south. In the late Asbian, platform facies with carbonate build-ups prograded south into the basin as far south as Nobber, but in the latest Asbian to Brigantian, basinal facies extended northwards over the collapsed platform margin.  相似文献   

How important is groundwater availability and stream perenniality to riparian and floodplain tree growth?   总被引：1，自引：0，他引：1       下载免费PDF全文

Neil E. Pettit  Ray H. Froend 《水文研究》2018,32(10):1502-1514

Riparian vegetation is important for stream functioning and as a major landscape feature. For many riparian plants, shallow groundwater is an important source of water, particularly in areas where rainfall is low, either annually or seasonally, and when extended dry conditions prevail for all or part of the year. The nature of tree water relationships is highly complex. Therefore, we used multiple lines of evidence to determine the water sources used by the dominant tree species Eucalyptus camaldulensis (river red gum), growing in riparian and floodplain areas with varying depth to groundwater and stream perenniality. Dendrometer bands were used to measure diel, seasonal, and annual patterns of tree water use and growth. Water stable isotopes (δ²H and δ¹⁸O) in plant xylem, soil water, and groundwater were measured to determine spatial and temporal patterns in plant water source use. Our results indicated riparian trees located on relatively shallow groundwater had greater growth rates, larger diel responses in stem diameter, and were less reactive to extended dry periods, than trees in areas of deep groundwater. These results were supported by isotope analysis that suggested all trees used groundwater when soil water stores were depleted at the end of the dry season, and this was most pronounced for trees with shallow groundwater. Trees may experience more frequent periods of water deficit stress and undergo reduced productivity in scenarios where water table accessibility is reduced, such as drawdown from groundwater pumping activities or periods of reduced rainfall recharge. The ability of trees to adapt to changing groundwater conditions may depend on the speed of change, the local hydrologic and soil conditions as well as the species involved. Our results suggest that E. camaldulesis growing at our study site is capable of utilizing groundwater even to depths >10 m, and stream perenniality is likely to be a useful indicator of riparian tree use of groundwater.  相似文献   

Simple Resistivity Probe System for Real-Time Monitoring of Injected Reagents     

David Stevenson  Felipe Solano  Yunxiao Wei  Neil R. Thomson  James F. Barker  J. F. Devlin 《Ground Water Monitoring & Remediation》2020,40(4):54-66

In situ treatment usually requires contact between an injected reagent and target contaminant to realize mass removal from source zones and plumes. Despite significant site characterization efforts, unknown heterogeneities that exist at all spatial scales often hinder prediction of the distribution of injected reagents. To provide remediation practitioners with additional information on the distribution of injected reagents, a prototype real-time monitoring probe was designed and tested. This new probe comprises a two-wire resistivity circuit, hence the designation dipole resistivity probe (DRP). The low-cost DRPs were built to be attached as arrays to a central stalk, and installed by direct-push techniques. An installed network of multilevel DRPs can be used to detect the arrival, persistence, and relative concentration of a high-conductivity reagent solution in real-time across a zone of interest. Static cell and sandbox experiments were conducted to test and refine the DRP design before field testing. Static cell experimental results indicated that the DRP was sensitive to solution electrical conductivity (EC), and that the probe response and EC relationship is nonlinear and dependent on the fixed resistor used. The choice of fixed resistor can be adjusted to optimize the DRP response over a critical EC range of interest. Under dynamic conditions in the sandbox, the DRP was able to reproduce breakthrough profiles collected by a commercial EC sensor. The results from two field studies demonstrated the utility of the DRPs to generate information regarding the arrival and persistence of reagents in an efficient and cost-effective manner. The first field study used a network of DRPs to monitor the land application of a sodium sulfate solution, and the second field study employed DRPs to monitor the distribution and longevity of a persulfate solution. While additional field testing is warranted, the results presented are encouraging and suggest that this low-cost system can be used to improve our understanding of the detailed migration of injected reagents in treatment zones.  相似文献   

Reflections from the Editor-in-Chief of Groundwater Monitoring & Remediation     

Neil R. Thomson 《Ground Water Monitoring & Remediation》2020,40(4):15-18

  相似文献   

Recent remote sensing applications for hydro and morphodynamic monitoring and modelling          下载免费PDF全文

Neil Entwistle  George Heritage  David Milan 《地球表面变化过程与地形》2018,43(10):2283-2291

It is not new to recognize that data from remote sensing platforms is transforming the way we characterize and analyse our environment. The ability to collect continuous data spanning spatial scales now allows geomorphological research in a data rich environment and this special issue [coming just eight years after the 2010 special issue of Earth Surface Processes and Landforms (ESPL) associated with the remote sensing of rivers] highlights the considerable research effort being made to exploit this information, for studies of geomorphic form and process. The 2010 special issue on the remote sensing of rivers noted that fluvial remote sensing articles made up some 14% of the total river related articles in ESPL. A similar review of articles up to 2017 reveals that this figure has increased to around 25% with a recent proliferation of articles utilizing satellite‐based data and structure from motion photogrammetry derived data. It is interesting to note, however that many studies published to date are proof of concept, concentrating on confirming the accuracy of the remotely sensed data at the expense of generating new insights and ideas on fluvial form and function. Data is becoming ever more precise and researchers should now be concentrating on analysing these early data sets to develop increased geomorphic insight, to challenge existing paradigms and to advance geomorphic science. The prospect of this occurring is increased by the fact that many of the new remote sensed platforms allow accurate spatial data to be collected cheaply and efficiently, reducing the need for substantial research funding to advance river science. Fluvial geomorphologists have never before been in such a liberated position. As techniques and analytical skills continue to improve it is inevitable that the prediction that remotely sensed data will revolutionize our understanding of geomorphological form and process will prove true, altering our ideas on the very nature of system functioning in the process. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Through the impact glass: Insight into the evolution of melt at the Mistastin Lake impact structure     

Patrick J. A. Hill  Gordon R. Osinski  Neil R. Banerjee 《Meteoritics & planetary science》2020,55(3):591-621

By analyzing impact glass, the evolution of the impact melt at the Mistastin Lake impact structure was investigated. Impact glass clasts are present in a range of impactites, including polymict breccias and clast‐rich impact melt rock, and from a variety of settings within the crater. From the glass clasts analyzed, three petrographic subtypes of impact glass were identified based on their clast content, prevalence of schlieren, color, texture, and habit. Several alteration phases were also observed replacing glass and infilling vesicles; however, textural observations and quantified compositional data allowed for the identification of pristine impact glass. Although the various types of glasses show significant overlap in their major oxide composition, several subtle variations in the major oxide chemistry of the glass were observed. To investigate this variation, a least‐squares mixing model was implemented utilizing the composition of the glass and the known target rock chemistry to model the initial melt composition. Additionally, image analysis of the glass clasts was used to investigate whether the compositional variations correlated to textural difference in the lithologies. We propose that the textural and compositional dichotomy observed is a product of the evolution, assimilation, and emplacement of the glass. The dichotomy is reflective of the melt either being ballistically emplaced (group 2 glasses: occurring in melt‐poor polymict breccias at lowermost stratigraphic position outside the transient crater) or the result of late‐stage melt flows (group 1 glasses, occurring in melt‐bearing polymict breccias and impact melt rocks at higher stratigraphic positions outside the transient crater).  相似文献   

Petrography and geochemistry of lunar meteorites Dhofar 1673, 1983, and 1984     

Patrick J. A. Hill  Gordon R. Osinski  Neil R. Banerjee  Randy L. Korotev  Sobhi J. Nasir  Christopher D. K. Herd 《Meteoritics & planetary science》2019,54(2):300-320

The Dhofar 1673, Dhofar 1983, and Dhofar 1984 meteorites are three lunar regolith breccias classified based on their petrography, mineralogy, oxygen isotopes, and bulk chemistry. All three meteorites are dominated by feldspathic lithic clasts; however, impact melt rock clasts and spherules are also found in each meteorite. The bulk chemistry of these samples is similar to other feldspathic highland meteorites with the Al₂O₃ content only slightly lower than average. Within the lithic clasts, the Mg # of mafic phases versus the anorthite content of feldspars is similar to other highland meteorites and is found to plot intermediate of the ferroan‐anorthositic suite and magnesian suite. The samples lack any KREEPy signature and have only minor indications of a mare basalt component, suggesting that the source region of all three meteorites would have been distal from the Procellarum KREEP Terrane and could have possibly been the Feldspathic Highland Terrane. All three meteorites were found within 500 m of each other in the Dhofar region of Oman. This, together with their similar petrography, stable isotope chemistry, and geochemistry indicates the possibility of a pairing.  相似文献   

Ice sheets and Late Quaternary environmental change by M. J. Siegert,John Wiley and Sons Ltd,Chichester, 2001. No of pages: 231. ISBN 0 471 98569 4 (paperback); 0 471 98570 8 (hardback).     

Neil Glasser 《Geological Journal》2003,38(2):188-189

  相似文献