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491.
近150年来湖北太白湖摇蚊记录与湖泊营养演化 总被引:4,自引:3,他引:1
通过太白湖北部湖区沉积岩芯中摇蚊亚化石分析,结合210Pb和137Cs年代测定和降趋势对应分析(DCA),研究了太白湖近150年来摇蚊种属组合变化和湖泊营养演化过程.结果表明:20世纪中期(1950年左右),摇蚊种群中与大型水生植物关系密切的Paratanytarsus,Paratanytarsus penicillatus-type,Polypedilum nubeculosum-type和Dicrotendipes nervosus-type等属种迅速减少或消失,而耐营养的属种Chironomus plumosus-type,Microchironomus tabarui,Procladius,Propsilocerus akamusi和Tanypus增多,表明大型水生植物减少,湖泊富营养化开始.20世纪90年代以来,Chironomus plumosus-type和Microchironomus tabarui等富营养种的比例增加反映了营养水平的进一步提高,并呈现加重趋势.摇蚊组合变化反映的太白湖营养水平的增加与流域人类活动影响密切相关,早期湖泊富营养化响应流域土壤侵蚀及湖泊水产养殖,而1990年以来湖泊富营养化的加重则与化肥的大量使用、人类活动的进一步加强及流域内工业废水污染物的开始排放有关. 相似文献
492.
To investigate trace elements in wet precipitation over the Tibetan Plateau (TP), a total of 79 event-based precipitation samples were collected from September 2007 to September 2008 at Nam Co Station. Samples were analyzed for concentrations of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb using inductively coupled plasma-mass spectrometry (ICP-MS). The annual volume-weighted concentrations of elements were generally comparable to other background sites, and much lower than urban areas. The enrichment factors (EF) showed that, in comparison with the Tibetan soils, the wet precipitation had elevated concentrations of Cr, Co, Ni, Cu, Zn, Cd and Pb, probably indicating their anthropogenic origins. Other elements (Al, Fe, Mn and V) with enrichment factor value of <10 may derive mainly from crustal sources. The principal component analysis further confirmed the two different groups of elements in wet deposition samples. The backward trajectories were calculated for each precipitation event using the NOAA HYSPLIT model. The results indicated significant differences of EF for trace elements of anthropogenic origin between the summer monsoon and non-monsoon seasons. The data obtained in the present study indicated that pollutants can affect remote high altitude regions like the Tibetan Plateau through long-range transport, especially in the summer monsoon season. 相似文献
493.
494.
MA Jie WANG Wanyin DU Xiangdong LUO Xingang CAI Wenjie YANG Min WANG Dingding 《《地质学报》英文版》2021,95(1):305-318
In the Gulf of Mexico and adjacent landmasses,faults are very complex,and their distribution is closely related to plate tectonics,ocean-land boundary,and former structure.The plane position of the faults can be identified by the maximum characteristic of the vertical derivative of the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)of the Bouguer gravity anomaly.The apparent depth of the faults is inverted by the Bouguer gravity anomaly curvature property.Based on tectonic evolutionary processes and the plane distribution and apparent depth characteristics of the faults,a complete fault system for the Gulf of Mexico and adjacent areas has been established,including 102 faults.The apparent depths of 33 first-class faults are 16-20 km and for 69 second-class faults are 12-16 km.The F1-2and F1-3subduction fault zones are two caused by the subduction of the Cocos Plate into the old Yucatan and Chorti landmasses;F1-11and F1-12fault zones extend westward to the coast of Guatemala and do not extend into the continent;F1-17and F1-20faults,which control the boundary of the oceanic crust,do not extend southward into the continent.The fault system,which radiates in a"fan-shaped"structure as a whole,unfolds to the northeast.Faults of different nature and sizes are distributed in the Cocos Plate subduction zone,Continental,Gulf of Mexico,Yucatan old landmass and Caribbean Plate in NW,NNW,NS,NE and NEE directions.In the Gulf of Mexico region,the fault system is a comprehensive reflection of former tectonic movements,such as plate movement,drift of old landmasses and expansion of oceanic crusts.The first-class faults control the plate and ocean-continental boundaries.The second-class faults are subordinate to the first-class faults or related to the distribution of different sedimentary layers. 相似文献
495.