ISSN:0149-0451    

DOI:10.1080/01490458909377866

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Sediment cores from the profundal region of relatively young (ca. 45 years), warm‐monomictic Lake Vechten were dated with Cs and210Pb and analyzed for major carotenoids, chlorophyll, and pheophytin. Vertical sediment accretion rates determined from a clay/sand horizon and from the radionuclide datings varied between 0.60 and 0.74 cm/year. Sedimentation rates based on paniculate matter collected in sediment traps agreed with results of the137Cs method with average values of respectively 2.9 and 2.3 kg dry weight m‐2year‐1. It was concluded that the profundal sediment is fairly undisturbed. Pigments showed a severalfold increase from the deepest to the superficial sediment layers. Their profiles were compared with limnological data obtained during previous studies of Lake Vechten. Evidence was provided that the distribution of pigments reflected grossly the trophic history of the lake, which became more eutrophic during the last two decades. Pigment analyses of sediment cores may be a useful tool to rapidly obtain rough basic information on the recent trophic development of stratified lakes liable to eutrophication.

ISSN:0149-0451    

DOI:10.1080/01490458909377867

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Surface microbiological investigations are critically dependent on the procedures used to collect samples for study. It can be difficult to distinguish between indigenous organisms and those encountered as contaminants during the drilling process. We found that coliform bacteria contaminated drilling mud slurries. These bacteria proved useful as tracer organisms in evaluating the degree of microbial contamination accidentally encountered while drilling for subterranean samples. While these organisms were found in high numbers in both the circulating muds and in the mud reservoir, few subsurface samples harbored conforms. Subsurface slurries did not inhibit the growth of a known coliform inoculum. These results indicate that the methods used to collect and field‐process cores from Atlantic coastal plain sediments were sufficient to prevent a large degree of bacterial contamination in most samples. The microflora in drilling fluids did not quantitatively or qualitatively account for the number and diversity of bacteria in subsurface samples. We conclude that a large and viable bacterial community is present in deep regions of the terrestrial subsurface.

ISSN:0149-0451    

DOI:10.1080/01490458909377868

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Shells of windowpane oyster[Placuna placenta(L)]in the intertidal zone of the Zuari estuary, Goa, were often found to be black in color. Microscopical observation of partially decalcified shells showed the presence of cyanobacterial filaments encrusted with black precipitate. Microchemical test (Prussian blue reaction) and wavelength dispersive x‐ray analysis confirmed this precipitate to be of iron. Mineralogical studies of this black precipitate, using x‐ray diffraction and scanning electron microscopy, suggested the presence of iron as iron oxides. The cyanobacteria from such black shells were cultured in enriched seawater medium. In this medium also they precipitated iron as confirmed by Prussian blue reaction. They were identified asPlectonema terebransBorn et Flah andPhormidiumsp.

ISSN:0149-0451    

DOI:10.1080/01490458909377869

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Stalagmites, which appear to be deposited by cyanobacterial action, have been identified in two caves in New South Wales (Australia). These have a characteristic morphology, which has given rise to local names likening them to crustaceans. We have studied these speleothems, and the cyanobacteria covering them, by microscopic and chemical techniques. Both calcite precipitation and aeolian sediment trapping are involved in their deposition, which is strongly controlled by environmental conditions. They can be regarded as stromatolites within currently accepted definitions of the term.

ISSN:0149-0451    

DOI:10.1080/01490458909377870

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Bioturbation is an important process for the transport and mixing of solutes and particles in sediments. Mixing of porewater caused by motile microorganisms has not previously been considered to be of significance in this context, although no conclusive evidence that it is negligible has been presented. We have developed a radiotracer method for the direct comparison of mixing of a soluble inert substance in microbially active and sterile sediments. We found clear evidence of porewater mixing caused by motile microorganisms. Estimated diffusion coefficients (expressed as “mixing”; coefficients) were found to be about 20% larger in microbially active sediments than in sterile ones.

ISSN:0149-0451    

DOI:10.1080/01490458909377871

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490458909377872

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0149-0451    

DOI:10.1080/01490458909377865

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor