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Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan 总被引：2，自引：0，他引：2
Landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10‐fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 103 m3 km?2 compared with 1·3 × 103 m3 km?2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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During surveillance on the toxicity of invertebrates such as bivalves inhabiting the coasts of Hiroshima Bay in 2001 and 2002, the carnivorous gastropod rapa whelk Rapana venosa collected in the estuary of Nikoh River, was found to contain toxins which showed paralytic actions in mice; the maximum toxicities (as paralytic shellfish poison, PSP) were 4.2 MU/g (May 2001) and 11.4 MU/g (April 2002). Their total toxicities were 224 and 206 MU/viscera of one specimen throughout the monitoring period. Attempts were made to identify the toxic principle in the gastropod. The viscera were extracted with 80% ethanol acidified with acetic acid, followed by defatting with dichloromethane. The aqueous layer obtained was treated with activated charcoal and then applied to a Sep-Pak C18 cartridge. The unbound toxic fraction was analyzed by high-performance liquid chromatography techniques. The gastropod toxin was rather unexpectedly identified as PSP. It was comprised of high toxic component (gonyautoxin-3; GTX3, GTX2, saxitoxin; STX) as the major components, which accounted for approximately 91 mol% of all components along with C1 and C2, which are N-sulfocarbamoyl derivatives. Judging from their toxin patterns, it is suggested that the PSP toxification mechanism of the gastropod that PSP toxins produced by phytoplankton such as Alexandrium tamarense, are transferred to and accumulated in plankton feeders such as the short-necked clam, and then transferred to this carnivorous rapa whelk R. venosa through predation. 相似文献
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Beppu R Nojima K Tsuruda S Gomez-Delan G Barte-Quilantang M Taniyama S Sagara T Nishio S Takayama H Miyazawa K Asakawa M 《Marine pollution bulletin》2008,56(4):758-763
During surveillance of the distribution of the paralytic shellfish poison (PSP)-producing dinoflagellate in 2003, 2004 and 2005 along the coastlines of the Seto Inland Sea, Hiroshima Prefecture, Japan, some species of toxic phytoplankton were isolated from the eastern coasts, Bingo-Nada, the central regions of the Seto Inland Sea. It was rather unexpectedly revealed from the basis of the morphological characteristics that they were unambiguously identified as Alexandrium tamiyavanichii and Alexandrium catenella. Two strains (ATY041106, ATY051018) of A. tamiyavanichii showed a specific toxicity of 38.7 x 10(-6) and 111.5 x 10(-6)MU/cell, respectively. These values seemed to be several times or much higher than that of A. catenella (AC030816, AC040614), having a specific toxicity of 4.5 x 10(-6) and 4.1 x 10(-6)MU/cell, respectively, isolated in the same area. From the results of HPLC-furuorometric analysis, it revealed that the toxins in ATY041106 exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 72.7 mol%. The toxin profiles of this strain are featured by the presence of a large amount of GTX3 (59.1 mol%) and a small amount (20.6%) of C1 and 2 in comparison with the PSP compositions of A. tamarense, which is isolated as the main responsible species in Hiroshima Bay, a western part of coastal sea in Hiroshima Prefecture. On the other hand, it revealed that the toxin profiles of two strains (AC030816, AC040614) of A. catenella exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 81.8 and 56.5 mol%, as the same manner. The toxin profiles of these two strains are featured by the presence of a large amount of C2 (80.5 and 46.3 mol%) in comparison with the PSP compositions of A. tamiyavanichii. To our knowledge, this is the first record to show the distribution and harmful influence of A. tamiyavanichii and A. catenella in Bingo-Nada in Hiroshima Prefecture. Though contamination of bivalves with these PSP-producing planktons in this area has not occurred yet so far, attention should be paid to this species as well as the other causative dinoflagellate from the stand point of public health and food hygiene. 相似文献
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