排序方式： 共有33条查询结果，搜索用时 31 毫秒
1.
2.
Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 meter depth in Lake Tanganyika (East Africa) yielded 77 morphotypes, among which 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Chironominae (Chironomini and Tanytarsini) in this collection. As the living chironomid fauna of Lake Tanganyika has never been comprehensively studied, we also briefly discuss faunistic aspects, and the ecology of the recovered species and genera in relation to benthic habitat diversity in Lake Tanganyika. 相似文献
3.
4.
Hilde Maritz H. C. C. Cloete Jacobus H. Elsenbroek 《Geostandards and Geoanalytical Research》2010,34(3):265-273
The Council for Geoscience (CGS, South Africa) has a statutory mandate to carry out regional geochemical mapping in South Africa that needs to be rapidly and accurately analysed. Both simultaneous X-ray fluorescence spectrometry (S-XRF) and a newly developed method using inductively coupled plasma-mass spectrometry (ICP-MS) were employed. Various trace elements that could not previously be analysed by S-XRF can now be analysed by ICP-MS for the regional geochemical mapping programme, e.g., Cd, Mo, Te and Li. Using both techniques, the CGS aims to report element distributions for some fifty elements. To ensure that element concentration levels correlate over map boundaries, quality control measures in the sampling, sample preparation and analyses were of critical importance. This paper aims to discuss the sample preparation and quality control measures as applied to the ∼5500 samples of the Giyani and Tzaneen 1:100000 scale map sheets sampled at a density of one soil sample per km2. ICP-MS batch- and instrumental drift-correction procedures will be discussed. As a final step, geochemical data were overlain over simplified geological maps using geographical information system software. These maps complement existing geological information of South Africa, help in the identification of exploration targets, test exploration models and initiate further geological research. 相似文献
5.
Jessica R. Rodysill James M. Russell Satria Bijaksana Erik T. Brown La Ode Safiuddin Hilde Eggermont 《Journal of Paleolimnology》2012,47(1):125-139
Variations in the location and strength of convection in the Western Pacific Warm Pool (WPWP) have a profound impact on the
distribution and amount of global rainfall. Much of the variability in WPWP convection is attributed to variations in the
El Ni?o-Southern Oscillation, for which the long-term trends and forcing mechanisms remain poorly understood. Despite the
importance of WPWP convection to global climate change, we have very few paleohydrological reconstructions from the region.
Here we present a new paleolimnologic and paleohydrologic record spanning the past 1,400 years using a multi-proxy dataset
from Lake Logung, located in East Java, Indonesia that provides insights into centennial-scale trends in warm pool hydrology.
Organic matter δ13C data indicate that East Java became wetter over the last millennium until ca. 1800 Common Era (CE), consistent with evidence
for the southward migration of the Intertropical Convergence Zone (ITCZ) during this time. Superimposed on this long-term
trend are four decade- to century-scale droughts, inferred from organic matter δ13C and calcite abundance data. They are centered at 1030, 1550, 1830, and 1996 CE. The three more recent droughts correlate
with hydrologic anomalies documented in other proxy records from the WPWP region on both sides of the equator, and the two
most recent droughts correlate in time with historically documented periods of multiple, intense El Ni?o events. Thus, our
record provides strong evidence that century-scale hydrologic variability in this region relates to changes in the Walker
Circulation. Human activity within the lake catchment is apparent since 1860 CE. 相似文献
6.
Yan-Chun Zhang Caroline P. Slomp Hilde F. Passier 《Geochimica et cosmochimica acta》2009,73(22):6716-6726
This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating (3H/3He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe2+ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. Significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50% lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO3, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1996 and 2006 show systematic decreases most likely due to declining fertilizer use. 相似文献
7.
A field experiment was conducted to investigate how water-based drill cuttings and sediment type influence colonization of soft bottom communities. Bottom frames with trays containing defaunated sediments were placed at the seabed for 6 months to study colonization of macrofauna. Two different sediments (coarse and fine) were used, and 6 or 24 mm layer of water-based drill cuttings were added on top of these sediments. Some of the sediments were controls with no additions. In the end of the experiment, the oxygen availability in sediment porewater and macrofaunal abundance were reduced in treatments with 24 mm drill cuttings compared to controls. Tube-building annelids were particularly sensitive to drill cuttings. However, these responses were only minor, and notably, the drill cuttings initiated a weaker faunal response than sediment type and site of the bottom frame. Sediments capped with water-based drill cuttings thus showed a rapid colonization of macrofaunal communities. 相似文献
8.
Kirsten Linnow Michael Steiger Christine Lemster Hilde De Clercq Maja Jovanović 《Environmental Earth Sciences》2013,69(5):1609-1620
Several double salts have been detected in building materials and most of these salts are incongruently soluble compounds. In contrast to single salts, however, no systematic investigations of the crystallization behavior and deleterious effects of incongruently soluble double salts exist. To assess the damage potential of these salts, a systematic investigation of their highly complex behavior is desirable. This paper deals with the crystallization behavior of various solids in the ternary mixed NaNO3–Na2SO4 system including the formation of the double salt darapskite, Na3NO3SO4·H2O. The crystallization sequence during droplet evaporation experiments at room conditions was determined using Raman and polarization microscopy. The basic idea of this research is to use deviations of the crystallization sequence of a salt or a mixed salt solution from the equilibrium pathway as an indicator to detect the degree of supersaturation. The observed crystallization pathway includes the formation of the metastable phases Na2SO4(III), Na2SO4(V) and darapskite. The experimental observations are discussed on the basis of the NaNO3–Na2SO4–H2O phase diagram and the results provide evidence for crystal growth from highly supersaturated solutions in both systems. If the crystals growing under these conditions are confined, these supersaturations result in substantial crystallization pressures. 相似文献
9.
The present paper discusses the implementation of the SGHR method (Sakurai, Goossens, and Hollweg, 1991; Goossens, Ruderman, and Hollweg, 1995) in a numerical scheme for determining resonantly driven Alfvén waves in nonuniform magnetic flux tubes. This method is based on jump conditions over the dissipative layer which are obtained from an asymptotic analysis of analytical solutions to simplified versions of the linear non-ideal MHD equations in this dissipative layer. The emphasis is on the computational simplicity and the accuracy of the method. The method derives its computational simplicity from the fact that it circumvents the numerical integration of the non-ideal MHD equations. The implementation only requires the numerical integration of the ideal MHD equations away from the resonant position. There is no need for a special integration scheme and a PC suffices as a hardware tool.The accuracy of the method is verified by means of test computations. These test computations deal with the loss of power of acoustic waves in sunspots by resonant absorption of Alfvén waves. Results for the absorption coefficients obtained with the SGHR method are compared with known results in the literature obtained by integration of the full set of the linearized non-ideal MHD equations. The agreement is excellent and identifies the SGHR method as a powerful and extremely easy to use tool for studying resonant Alfvén waves. 相似文献
10.