排序方式： 共有18条查询结果，搜索用时 203 毫秒
11.
12.
13.
Szilvia Simon Judit M��dl-Sz?nyi Imre M��ller Gy?rgy Pog��cs��s 《Hydrogeology Journal》2011,19(3):701-717
The Duna-Tisza Interfluve, Hungary, is characterized by patchy surface salinization. However, in the Duna Valley, salinized wetlands appear in a N?CS trending continuous zone (Lake Kelemenszék area). The source of the salts is reported to be the overpressured NaCl-type water of the Pre-Neogene basement and the NaHCO3-type water of the Neogene sediments. This ??basement and basin origin of salts?? concept is based on the strong correlation between the regional distribution of surface salinization and the basinal flow pattern. This study, applying integrated methods, presents hydrogeological evidence for this theory and creates a conceptual model for the salinization. The model reflects that the basement water rises near to the surface through conductive faults crosscutting an extensive aquitard and aquifer. These faults ensure ??shortcut??-type water exchange between the basement and the uppermost aquifer. This hydraulic setting generates chemical anomalies in this aquifer up to the surface, producing Na?CHCO3?CCl-type water. This water causes extensive surface salinization in those discharge areas where the infiltrating freshwater does not superimpose the upwelling saline water. Where a freshwater lens is located above the ascending saline water, this fresh gravity-driven flow controls the surface distribution of salts, which results in saline patches. 相似文献
14.
Smith TB Nemeth RS Blondeau J Calnan JM Kadison E Herzlieb S 《Marine pollution bulletin》2008,56(12):1983-1991
Managing the effects of anthropogenic disturbance on coral reefs is highly dependant on effective strategies to assess degradation and recovery. We used five years of field data in the US Virgin Islands to investigate coral reef response to a potential gradient of stress. We found that the prevalence of old partial mortality, bleaching, and all forms of coral health impairment (a novel category) increased with nearshore anthropogenic processes, such as a five-fold higher rate of clay and silt sedimentation. Other patterns of coral health, such as recent partial mortality, other diseases, and benthic cover, did not respond to this potential gradient of stress or their response could not be resolved at the frequency or scale of monitoring. We suggest that persistent signs of disturbance are more useful to short-term, non-intensive (annual) coral reef assessments, but more intensive (semi-annual) assessments are necessary to resolve patterns of transient signs of coral health impairment. 相似文献
15.
Gábor Szilágyi Pál Sümegi Dávid Molnár Szilvia Sávai 《Central European Journal of Geosciences》2013,5(4):465-479
The malacological material of the mound bodies (kurgans) of the Great Hungarian Plain indicates a mixed vegetation of dry and humid environments, developed on a mosaic of alkaline and chernozem soils in the period of the construction of the kurgan. The malacofauna that evolved in the upper soil horizon of the mound indicates the extremely dry environmental conditions of steppes, charaterized by the dominance of thermoxerophilous species. Dominant species of this kurgan are Chondrula tridens, Helicopsis striata, Granaria frumentum and Cepaea vindobonensis. The species composition shows that there are differences in the malacofauna of the Danube-Tisa Interfluves region compared to that of the lowlands east of River Tisza, indicated by the higher dominance of Granaria frumentum and Helicopsis striata in the former region. Following the construction of the kurgans an island-like, dry habitat developed on their surface, covered by black soil and populated by a steppe fauna, the composition of which is comparable mostly with the mollusc fauna of loess steppes and forest steppe, irrespectively of the floodplain or wind-blown sand character of the original surface. 相似文献
16.
17.
We explain a new method of quantifying seagrass cover and describing seagrass species composition during fisheries-independent monitoring. This new method is similar to a point-intercept method developed to estimate arboreal crown cover, but it uses an aquascope designed for shallow water. The method does not require a diver. Seagrass cover (cover ratio) distinguished different percentage cover categories in 0.25-m2 seagrass plots. Estimates of species composition determined by using the new method were most similar to those obtained by using estimates of aboveground biomass. Within each 141-m2 area sampled with a 21.3-m fish seine, we accurately estimated seagrass cover ratio and species composition with six observations that typically required less than 6 total minutes. Within such areas, 42 trials were conducted to evaluate the precision with which different observers estimated seagrass cover ratio and species composition. In 98% of the trials, observers attained statistically similar estimates of cover ratio, and in 100% of the trials in areas with multiple seagrass species, observers attained statistically similar estimates of species composition. We conclude that the new method provided efficient and reasonably accurate means to quantify seagrass cover and species composition. 相似文献
18.
The research applies a geographic perspective to the interface of biotic, atmospheric and socio-economic factors. Wind as a factor in biotic distributions helps explain the existence and quality of life on many isolated islands. In the late summer of 1988, there were reports of African desert Locust (Schistocerca gregaria) invasion of the Windward Islands. The event was historically unprecedented, and agricultural experts in the eastern Caribbean were alarmed. A tentative hypothesis was that Hurricane Joan provided the transport mechanism. An alternative hypothesis is suggested here. The discussion helps explain why transatlantic African Desert Locust migrations are so unusual. Analysis is based on primary and secondary data sources that include synoptic weather maps, formal and informal scientific reports, written correspondence with agricultural experts in the impact area, and newspaper coverage of the invasion. 相似文献