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High-resolution spectroscopic study of pore-water dissolved organic matter in Holocene sediments of Lake Peipsi (Estonia/Russia) 总被引:1,自引:0,他引:1
Ultraviolet–visible absorption and fluorescence spectroscopies allow simultaneous detection of several organic substances. These spectra also contain information on whether the organic matter is produced in the water body or in its catchment. In this work various spectral indices, which are widely used in aquatic studies to determine humic substances, proteinaceous matter, chlorophyllous pigments and the origin (autochthonous versus allochthonous) of organic matter, were applied to track changes in a Holocene record from the large and shallow northern temperate Lake Peipsi (Estonia/Russia) at a high-resolution scale. Absorption and three-dimensional fluorescence spectra of the organic matter fraction dissolved in sediment pore water (pDOM) were analysed. In addition to the spectral measurements of pDOM, the sediment samples were analysed for main constituents (water and organic and mineral matter) and magnetic properties. The core chronology was established by nine radiocarbon datings. Temporal changes in pDOM in the record were quite variable; however, three periods in the development of the lake can be distinguished: a 2500 yr period in the early Holocene and a 2500 yr period in the late Holocene, when drastic changes in the accumulated matter occurred, and a rather stable 5000 yr period in between. We postulate that the changes over the period in the early Holocene reflect a rise of water level in the lake; the oscillations over the relatively steady period were probably caused by climatic factors, and alterations over the period in the late Holocene were due to the expansion of agricultural activity in the lake catchment. Our findings indicate that the use of spectral indices in palaeoinvestigations offers valuable information for reconstructing natural and human-induced developments of lakes. 相似文献
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Mehis Viru Eva Jansson Atko Viru Carl Johan Sundberg 《European journal of applied physiology and occupational physiology》1998,77(6):517-522
To test the influence of the accumulation of metabolites on exercise-induced hormone responses, plasma concentrations of
cortisol, growth hormone (GH), insulin, testosterone, thyrotropin (TSH), free thyroxine (fT4) and triiodothyronine (T3) were compared during exercise performed under normal conditions (control) and under conditions of restricted blood flow
of exercising leg muscles (ischaemia) in nine healthy young men. Blood supply was reduced by 15%–20% by the application of
50 mmHg external pressure over the exercising leg. During 45-min cycling exercise during ischaemia the increase in GH concentration
was twice as large as under normal conditions. Despite the below-threshold exercise intensity for activation of the pituitary-adrenocortical
system under normal exercise conditions ischaemic exercise elicited cortisol and T3 responses (concentration increases of 83% and 9.5%, respectively). Ischaemic exercise attenuated the decrease of plasma insulin
concentration found under normal conditions. The concentrations of testosterone, TSH and fT4 were not changed significantly during exercise performed in either condition. The results support the suggested essential
role of muscle metaboreceptors in the control of hormone responses during muscle activity.
Accepted: 6 November 1997 相似文献