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Effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake 总被引：1，自引：0，他引：1
Resuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m−2 dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m−2. The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind-exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m−2 and 4971 g m−2, respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short. 相似文献
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R.J. LYTLE D.L. LAGER E.F. LAINE J.D. SALISBURY J.T. OKADA 《Geophysical Prospecting》1981,29(4):627-638
High-frequency electromagnetic probing is used to monitor the rate and direction of flow of fluids injected into the ground. This method shows the potential for providing more detailed information than procedures presently used. The experimental technique and the test-of-concept experimental results are discussed. This technique has applications in oil-reservoir engineering and in hydrology studies concerning storage of chemical wastes. 相似文献
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JUKKA KÄYHKÖ 《Geografiska Annaler: Series A, Physical Geography》2007,89(1):65-81
Aeolian processes in the subarctic ecocline were investigated by measuring present‐day erosion and deposition rates over a decade in blowouts scoured into stabilized Early to Mid‐Holocene dunes. Four localities from different vegetation zones in Finnish Lapland were surveyed using precision levelling (infrared tachymeter) along eight transects at 1‐m intervals. During an 11‐year observation period, a total of 1439 observation points were monitored in three measurement campaigns, in 1993, 1994 and 2004. Together with dating results reported elsewhere, the results demonstrate the relative quiescence of these subarctic blowouts compared to many coastal dunes. On average, the deflation rate of the studied basins was 8.8 mm a‐1, which corresponds well with the age and depth of the blowouts. Net deposition had taken place at 30% of the observation points, and one of the eight studied transects showed net deposition as the transect average. Symmetrical, smooth basins showed more consistent changes than basins with a complex form, indicating that internal factors are important in blowout formation under the Lapland climatic range. The deepest part of a blowout was generally found in the upwind end. The erosion/deposition patterns of the transects over a one‐year monitoring period were interpreted with Fourier analysis revealing along‐transect cyclicity, possibly reflecting the movement of small migrating bedforms in the blowouts. Generally, deflation rates at the latitudinal pine forest line were smaller than at those well outside the pine forest suggesting that the coniferous forest at the subarctic ecocline affects the intensity of present‐day aeolian activity in Fennoscandia. 相似文献
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The temporal and spatial variations in the rate of sedimentation and sediment resuspension in Lake Rehtijärvi (southern Finland) were studied by sediment traps deployed in the stratifying and non‐stratifying regions of the lake. Both the gross sedimentation rate and the resuspension rate recorded by near‐bottom traps were significantly higher in the stratifying region (>20 m depth) than in the shallow part of the lake (2 m depth). These rate changes were caused by temporarily elevated hypolimnetic resuspension rates exceeding 40 g dry weight m?2 day?1 in July 2005, whereas in the shallow station no such peak was observed and the resuspension rate remained below 30 g dry weight m?2 day?1 throughout the study. The elevated resuspension rate in the hypolimnion could not be attributed to surface wave action or sediment disturbance by fish, but was due to the occurrence of internal seiches. The seiche amplitude was on average the highest in July, although the wind velocities were low; this was because winds temporarily were blowing along the longitudinal axis of the lake. Due to the steep slopes, the sediments of Lake Rehtijärvi are prone to redistribution and sediment focusing towards the accumulation areas also affected trap catches in the deep stations. 相似文献
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Remote sensing of the impact of reindeer grazing on vegetation in northern Fennoscandia using SPOT XS data 总被引：1，自引：0，他引：1
Digital image analysis and SPOT XS satellite data recorded on 1 August 1991 were used to monitor vegetation in the border region between Enontekio municipality, Finland, and Kautokeino municipality, Norway. A supervised classification on the red wave length channel was undertaken using training areas for maximum likelihood classifier to produce seven spectral land cover classes. The classification revealed great differences in vegetation between Finland and Norway. The largest difference was the lack of Cladinalichens on the Finnish side of the border. The area on the Finnish side is used for grazing all year round, while the area on the Norwegian side is a winter range only. According to official data for the local reindeer population, the average annual grazing pressure (head/area/time) is higher on the Norwegian side of the reindeer fence. The Finnish grazing practice is believed to have a detrimental impact on the vegetation, and has lead to pasture land degradation. 相似文献