Hypolimnetic density currents traced by sulphur hexafluoride (SF6)     

Jürg W. Schlatter  Alfred Wüest  Dieter M. Imboden 《Aquatic Sciences - Research Across Boundaries》1997,59(3):225-242

The artificial tracer sulphur hexafluoride (SF₆) has been used to study the density-driven deep water exchange between two sill-separated basins of Lake Lucerne, Gersauersee and Urnersee. The sources of the density gradients between the two basins are (1) salinity differences between the major inlets due to the different geology of their drainage areas, and (2) temperature differences due to spatial variation of wind forcing. Wind speeds are generally larger in Urnersee, especially in spring during the so-called Föhn events, when winds blow from the south. In contrast, Gersauersee is protected form these winds. In spring 1989, a total of 630 g of SF₆ was released at 80 to 120 m depth in the small Treib Basin located between Urnersee and Gersauersee. During about 100 days the distribution of SF₆ in the lake was determined by gaschromatography. Two models are used to quantify the exchange flow, (1) a one-box mass balance model for SF₆ in the deep part of Treib Basin, and (2) a one-dimensional diffusion/advection model describing the temporal and vertical temperature variation in Urnersee. According to the first model, the flow into the deep hypolimnion of Urnersee, decreases from 21·10⁶ m³·d^?1 at the end of March to about 8·10⁶ m³·d^?1 in late April. The second model yields similar flow rates. The decrease of the flow rate during spring, confirmed by both approaches, is consistent (1) with the decreasing strength of the density gradient above the sill during spring and early summer, and (2) with hydrographic information collected in Lake Lucerne during other years.  相似文献   

Paleoclimatological and paleoenvironmental records since 4 000 a B. P. in sediments of alpine lakes in Taiwan     

Jiann-Yuh Lou  Chen-Tung Arthur Chen 《中国科学D辑(英文版)》1997,40(4):424-431

The 3 310-m-high Chia-min Lake records the climatic history since 4 ka B. P. in Taiwan. The warm/wet period before 2.2 ka B.P. seemed to correspond to the later part of the Holocene Megathermal, and the cold/dry period during 0–2.2 ka B. P. corresponded to the Katathermal. Before the termination of the Megathermal, an especially warm and humid segment (2.2–2.4 ka B. P.) emerged. The paleoclimatic records from Yuen-yang and Chi-tsai Lakes support the notion that the Megathermal in Taiwan terminated during 2—2.3 ka B. P. A warm segment (820–1 320 AD) in the Katathermal could be considered the Medieval Warm Period. The climate turned cold and dry after 1 320 AD and this indicated the onset of the Little Ice Age. These paleoclimatic variations are also in good agreement with those recorded in Great Ghost Lake.  相似文献   

Comparison of Cu and Zn cycling in eutrophic lakes with oxic and anoxic hypolimnion     

HanBin Xue  René Gächter  Laura Sigg 《Aquatic Sciences - Research Across Boundaries》1997,59(2):176-189

Data on the cycling of Cu and Zn in two eutrophic lakes are presented: Lake Greifen that becomes seasonally anoxic in its hypolimnion and Lake Sempach that is aerated during winter and oxygenated during summer. They suggest that hypolimnetic oxygenation 1) enhances the release of copper from the sediment but 2) also accelerates the entrapment and deposition of Cu and Zn by freshly formed Mn- and Fe-oxides.  相似文献   

紫色土丘陵区典型小流域水体N、P含量及其环境特征   总被引：8，自引：0，他引：8  

高美荣  朱波  陈克亮  李庆召 《地球科学进展》2004,(Z1)

N、P各形态浓度在川中丘陵区小流域的水体中显示出明显的时空特征,在地表水中,以旱地为主的小流域上部的硝态氮、氨态氮、全氮要低于小流域下部水田的,而以流域人口密度较大的群英池和小流域下部的沟道水中氨态氮浓度较高,说明人为活动对其影响较大。在地下水中以小流域上部为最高,明显高于该流域的中下部;它们的季节变化与流域降水的季节变化基本是一致的。紫色土丘陵区水体富N,地下水NO_3~--N超标率达60％,;地表水和地下水均尚未出现P的富营养,但潜在的污染不可忽视。  相似文献   

Revising macroseismic data in Switzerland: The December 20, 1720 earthquake in the region of Lake Constance     

Monika Gisler  Donat Fäh  Reto Schibler 《Journal of Seismology》2004,8(2):179-192

Upgrading the Earthquake Catalog of Switzerland (ECOS) included revising the earthquake of 1720. This change has major importance for history and seismology.Although that quake has been the subject of several publications, none was based on critical methods. This re-evaluation of the event is built upon a new and more reliable database established after investigating archives and libraries. Using data from such historical sources, we assigned new site intensities, adopting the criteria established by the European macroseismic scale EMS 98 (Grünthal, 1998).We discovered that the event had been assigned an overestimated intensity, due to interpretation errors in former earthquake catalogs and compilations. We recommend reducing the intensity from I₀= VIII to I₀= VI (EMS 98). The moment magnitude is given as M_W= 4.6. Since the event had been considered the largest for its respective area, downgrading it now will influence the seismic hazard assessment for this region.  相似文献   

Distribution, abundance and life history of Mysis relicta (Lovén) in the Feldberg Lake District, Germany     

Julia Scharf  Rainer Koschel 《Limnologica》2004,34(3):199-212

Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m⁻², respectively. Highest abundance of adults was 110.4 ± 76.5 m⁻² in summer, lowest abundances of 2.0 ± 4.0 m⁻² occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m⁻² was detected in summer and lowest of 0.8 ± 1.8 m⁻² in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m⁻² in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m⁻² in Lake Zansen. There were great spatial differences in abundance in both lakes.  相似文献   

On the Limnology of Deep and Saline Lake Burdur in Turkey     

Snmez Girgin  Nilgün Kazanc&#x;  Muzaffer Dügel 《洁净——土壤、空气、水》2004,32(3):189-200

Limnological characteristics of Lake Burdur in Lake District in south‐western Turkey are presented. It is a deep, tectonic (estimated max. depth 100 m), athalassic, highly alkaline, and saline lake. A set of physical and chemical variables was monitored, phyto‐ and zooplankton was sampled from surface layer of the lake during 1997. Physico‐chemical variables indicated that the lake is hyposaline and composed of some hydrochemically different water layers formed by groundwater sources located on the bottom of the lake. The phytoplankton composition of Lake Burdur consisted of Cyanophyta, Chlorophyta, Bacillariophyta, Dinophyta, and Chrysophyta. The abundance and number of species of Chlorophyta and Cyanophyta were higher than the other taxa. The zooplankton composition of the Lake consisted of Rhizopoda, Rotifera, and Crustacea. Number of species of Rotifera was higher than the other taxa. The diversities of the phyto‐ and zooplankton were calculated according to the Shannon‐Weaver diversity index. The diversity of each group was found to be low in the lake.  相似文献   

天目湖热力学状况的监测与分析   总被引：16，自引：0，他引：16       下载免费PDF全文

张运林  陈伟民  杨顶田  黄文钰  江晶 《水科学进展》2004,15(1):61-67

根据2001年6月～2002年5月在天目湖进行的每月一次的全湖水温观测以及2002年5月25～26日在1号点的定点24h连续水温观测资料,分析研究了天目湖水温时空分布、垂直分布、温跃层的形成与变化以及湖泊热力学对溶解氧、营养盐的影响,揭示了各自的基本变化规律。结果表明:天目湖水温的日变化、年变化及垂直分布明显,而其水平差异不大;温跃层随着季节的变化而呈现增强-稳定-减弱-消失的周期变化;水温的变化以及温跃层的存在引起了水中溶解氧以及营养盐的变化。  相似文献   

洞庭湖河湖疏浚对洪水位影响分析   总被引：2，自引：0，他引：2  

周北达  李正最 《水文》2004,24(2):35-39,54

洞庭湖是长江中游的重要调蓄湖泊，但由于接纳湘江、资水、沅江、澧水四水和长江三口洪水、泥沙，造成河道湖泊泥沙淤积，洪水位抬高，加重湖区的防洪负担，造成严重的洪涝灾害。根据洞庭湖河湖疏浚规划和典型河段疏挖竣工资料，运用水力学和水文学方法对疏浚前后洪水位的变化进行了分析。  相似文献   

鄱阳湖区平垸行洪、退田还湖后的防洪减灾形势分析   总被引：4，自引：0，他引：4  

吴敦银李荣昉  王永文 《水文》2004,24(6):26-31

根据鄱阳湖区“退田还湖”的实际资料，采用洪水模拟的方法分析计算出“退田还湖”降低湖口站洪水位和减少1954年洪水超额分洪量，分析了“退田还湖”后鄱阳湖区的防洪减灾形势，提出应继续加强对鄱阳湖区防洪工程的建设，探讨了“退田还湖”后江湖洪水关系的变化趋势。  相似文献