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1.
Multi-proxy evidence of long-term changes in ecosystem structure in a Danish marine estuary, linked to increased nutrient loading 总被引:3,自引:0,他引:3
Marianne Ellegaard Annemarie L. Clarke Nina Reuss Simon Drew Kaarina Weckstrm Stephen Juggins N. John Anderson Daniel J. Conley 《Estuarine, Coastal and Shelf Science》2006,68(3-4):567
This paper presents a study of changes in eutrophication over the past 100 years in a fertile estuary. The Danish estuary Mariager Fjord is a long, narrow sill-fjord with a permanently anoxic basin. In 1997 anoxia spread from the basin to the entire inner estuary, killing almost all eukaryotes and prompting debate on the causes. This paper reports a multi-proxy survey of 210Pb-dated sediment cores from the anoxic basin. Analyses of diatoms, dinoflagellates, pigments and geochemical proxies were used to determine changes in ecosystem structure over the past 100 years. The aim was to establish ‘base-line conditions’, for management purposes, of the biological structure prior to 1900, and to examine possible causes of changes observed. Geochemical proxies total nitrogen (TN), total carbon (TC) and biogenic silica (BSi) were consistently high throughout the sediment record. Increased concentrations of pigments and natural isotopes (δ13C, δ15N) suggested increasing production and nutrient loading. The main changes in the biological proxies occurred between 1915 and the 1940s, and indicated that the estuary has been somewhat eutrophic since 1900, but that the eutrophication process increased over the past 100 years. A reconstruction of TN concentration by a diatom-based transfer function supports this interpretation, with inferred TN ca. 1900 around 60 μmol l−1, and an increase in TN concentration over the past century to ca. 130 μmol l−1 by 1995. Inferred TN decreased to ca. 100 μmol l−1 by 2001, similar to present day monitoring data. 相似文献
2.
Adrian Lawrence Marianne Stuart Colin Cheney Neil Jones Richard Moss 《Hydrogeology Journal》2006,14(8):1470-1482
Contaminant migration behaviour in the unsaturated zone of a fractured porous aquifer is discussed in the context of a study site in Cheshire, UK. The site is situated on gently dipping sandstones, adjacent to a linear lagoon historically used to dispose of industrial wastes containing chlorinated solvents. Two cores of more than 100 m length were recovered and measurements of chlorinated hydrocarbons (CHCs), inorganic chemistry, lithology, fracturing and aquifer properties were made. The results show that selecting an appropriate vertical sampling density is crucial both to providing an understanding of contaminant pathways and distinguishing whether CHCs are present in the aqueous or non-aqueous phase. The spacing of such sampling should be on a similar scale to the heterogeneity that controls water and contaminant movement. For some sections of the Permo-Triassic aquifer, significant changes in lithology and permeability occur over vertical distances of less than 1 m and samples need to be collected at this interval, otherwise considerable resolution is lost, potentially leading to erroneous interpretation of data. At this site, although CHC concentrations were high, the consistent ratio of the two main components of the plume (tetrachloroethene and trichloroethene) provided evidence of movement in the aqueous phase rather than in dense non-aqueous phase liquid (DNAPL). 相似文献
3.
A. Ankilov A. Baklanov M. Colhoun K. -H. Enderle J. Gras Yu. Julanov D. Kaller A. Lindner A. A. Lushnikov R. Mavliev F. McGovern T. C. O'Connor J. Podzimek O. Preining G. P. Reischl R. Rudolf G. J. Sem W. W. Szymanski A. E. Vrtala P. E. Wagner W. Winklmayr V. Zagaynov 《Atmospheric Research》2002,62(3-4)
During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles. 相似文献
4.
Marianne Font Jean-Louis Lagarde Daniel Amorese Jean-Pierre Coutard Jean-Claude Ozouf 《Comptes Rendus Geoscience》2002,334(3):171-178
The degradation of the Jobourg fault-scarp occurred by cryoclastic processes in a periglacial environment during a part of Quaternary time. An attempt of quantification indicates a bulk scarp erosion of about 39 m3 m?2, while the head accumulated at the bottom of the fault scarp only represents 4.6 m3 m?2. To cite this article: M. Font et al., C. R. Geoscience 334 (2002) 171–178. 相似文献
5.
Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a high arctic lake that received raw sewage for almost 50 years from the Canadian Department of Transport Base. The lake was sampled from 1968–72 during the International Biological Programme, as part of the Char Lake Project. As the number of users at the Transport Base declined throughout the 1990s, so too did the lake's nutrient levels, and Meretta Lake is now classified as oligotrophic. A previous diatom-based paleolimnological study revealed marked species assemblage shifts coincident with sewage inputs beginning in the late 1940s; however, because the core was taken at a time when nutrient levels were still relatively high (i.e., 1993), the diatom record did not yet track any signs of recovery. In this present study, we examined fossil diatom assemblages from a sediment core taken in 2001. Our results indicate a shift to the pre-impact diatom assemblages in the most recent sediments, indicating that the paleolimnological record is tracking the decreased nutrient inputs to this high arctic lake, and confirms that no significant lags exist in these largely ice-covered lakes. 相似文献
6.
7.
Patricia O'Connor 《The Australian geographer》2004,35(2):169-176
When a researcher undertakes research into his/her own ethnic group, issues of positionality abound. These issues relate not only to the impact of inherent insider positionality when interacting with study participants but also in the interpretation and presentation of study findings. My research with contemporary Irish immigrants not only reinforced the advantages of being an insider but also highlighted the incomplete and unstable nature of insiderness. Heterogeneity within the study group, in terms of their geo-political, regional and religious origins, meant that presumptions of insiderness and outsiderness were frequently challenged. A new awareness of the conditionality of each positionality was forged from these experiences. 相似文献
8.
Upwelling plumes, superswells and true polar wander 总被引:1,自引:0,他引:1
Marianne Greff-Lefftz 《Geophysical Journal International》2004,159(3):1125-1137
9.
Summary Techniques presented herein show how reflected voltage pulses from coaxial antenna cable grouted in rock masses can be employed to quantify the type and magnitude of rock mass deformation. This measurement is similar to that obtained from a combined full profile extensometer (to measure local extension) and inclinometer (to measure local shearing). Rock mass movements deform the grouted cable, which locally changes cable capacitance and thereby the reflected wave form of the voltage pulse. Thus, by monitoring changes in these reflection signatures, it is possible to monitor rock mass deformation.This paper presents laboratory measurements necessary to quantitatively interpret the reflected voltage signatures. Cables were sheared and extended to correlate measured cable deformation with reflected voltage signals. Laboratory testing included development of grout mixtures with optimum properties for field installation and performance of a TDR (Time Domain Reflectometry) monitoring system. Finally, the interpretive techniques developed through laboratory measurements were applied to previously collected field data to extract hitherto unrealized information. 相似文献
10.
P. McArdle M. Fitzell M. G. Oosterom P. J. O'Connor P. S. Kennan 《Mineralium Deposita》1989,24(2):154-159
Initial investigations designed to test the potential for gold in a series of lithologies associated with tourmalinites and coticules in the neighbourhood of the Caledonian Leinster Granite of southeast Ireland are reported. The results of geological mapping, geochemical analyses and panning of stream sediments indicate that significant levels of gold are associated with some tourmalinite zones. The possible exploration implication of this work is that tourmalinites have potential as target indicators, although secondary controls on mineralization are also important. 相似文献