Isotopic Tracing of Trophication Processes over the Last Millennia on Lake Chenghai

Multi-parameter studies (stable isotopes in carbonate and organic matter, pigment,organic carbon and nitrogen contents) from a 660-yr continuous sediment core from Lake Cheng-hai, a closed, eutropic lake in southern China, provide information on lake historical eutrophi-cation. During the last 660 years, great changes have taken place in productivity and eutrophi-cation of Lake Chenghai in response to human activities. In 1690, the productivity of the lakebegan to increase as Lake Chenghai became closed from agriculture in the lake‘‘ s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an increase in organic carbon, ni-trogen, CaC03, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-scale population immigration during the period. In 1984, in-tensive human activities induced modern lacustrine productivity and eutrophic level. Human-in-duced trophic changes during the past few decades have affected the Lake Chenghai ecosystem tosuch an extent that it has never experienced before in the last 660 years.     

莱州湾南岸平原古湖泊消亡原因初探

莱州湾南岸平原是指西起小清河口，东至胶莱河口的广大沿岸地区，这一地区近年来是我国工农业发展较快的地区，也是我国地下咸水入侵较为严重的地区。历史上，莱州湾南岸平原地区曾有一些湖泊存在，如巨淀湖、黑冢泊、别画湖，但现在早已荡然无存了。研究这些古湖泊的消亡原因对于恢复该区古地理环境以及确立湖迹区今后的发展方向具有十分重要的意义。本文运用查阅历史文献、地层剖面分析、地名考证、遥感解译等多种方法，对莱州湾南岸古湖泊的消亡原因进行了研究与分析，并指出该区古湖泊消亡的原因是气候变干、河流变迁、人类活动影响等，其中气候变化是古湖泊消亡的根本原因，河流变迁是古湖泊消亡的直接原因，而人类活动则加速了古湖泊消亡的进程。     

Atmospheric nitrogen inputs into the North Sea: effect on productivity

The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANICE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m⁻² day⁻¹, which has the potential to promote primary productivity of 5.3 mmol C m⁻² day⁻¹. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km⁻¹, i.e. 0.19 mmol N m⁻² day⁻¹ which has the potential to promote primary productivity of 1.2 mmol C m⁻² day⁻¹. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NO_x and NH₃ are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m⁻² day⁻¹, i.e. 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m² is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem.     

A review of the physics and ecological implications of the thermal bar circulation

Following recent applications of numerical modelling and remote sensing to the thermal bar phenomenon, this paper seeks to review the current state of knowledge on the effect of its circulation on lacustrine plankton ecosystems. After summarising the literature on thermal bar hydrodynamics, a thorough review is made of all plankton observations taken in the presence of a thermal bar. Two distinct plankton growth regimes are found, one with production favoured throughout the inshore region and another with a maximum in plankton biomass near the position of the thermal bar. Possible explanations for the observed distributions are then discussed, with reference to numerical modelling studies, and the scope for future study of this interdisciplinary topic is outlined.     

西藏纳木错晚更新世以来湖面变化和藏北高原古大湖的演化

根据西藏纳木错及邻区发现的多处湖岸阶地和高位湖相沉积,确定了藏北高原古大湖的存在。水准测量表明,在纳木错沿岸发育了6级湖岸阶地,以及拔湖48～139.2m的高位湖相沉积;在拔湖26m以下,发育有8～30条湖岸堤;一条明显的湖蚀凹槽则集中出现在拔湖17.5～19.8m的高度上,与纳木错和仁错的分水垭口的高度相当。纳木错沿岸和邻区湖相或湖滨相沉积物的铀系年龄测定表明,高位湖相沉积形成于115.9～71.8kaB.P.的晚更新世早期;第6至第2级阶地形成于53.7～28.2kaB.P.的晚更新世中晚期;与湖蚀凹槽相当的湖滨相沉积则稍早于29.3kaB.P.;第2至第1级阶地,14C测定结果为2350～10390aB.P.。     

鄱阳湖地区土壤,植被光谱混合模型的研究

本文针对鄱阳湖地区的土壤、植被的特点设计了一套非线性混合光谱模型、较好了地预测了实际的混合光谱，从预测精度上看，要优于传统的线性混合光谱模型。     

末次盛冰期以来全球湿润状况的地质证据──全球古湖泊数据库及其湖水位变化的大尺度时空分析

介绍了正在建设中的全球湖泊数据库的情况，以及该数据库的水位资料所反映的晚更新世末期以来全球湿润状况的变化。通过大尺度湖水位变化的时空分析，结果显示当今湖泊水位状态较历史时期而言，位于低纬干旱或半干旱地区的湖泊水位较低，而中纬及高纬湿润地区的湖泊水位较高。自末次冰盛期以来，北美大陆中南部地区湖泊水位自高至低，反映出该地区气候条件由湿变干，至早、中全新世达最干旱。而在非洲及南亚季风地区，冷期偏干，暖期偏湿。特别是在早、中全新世的温暖时期，为历史上最湿润时期。北半球中纬度地带的气候干湿变化与北半球冰盖的存在及其消融导致的西风带的南北摆动有关；而北半球季风区在早、中全新世出现的高潮面与北半球夏季辐射的增加有密切联系。     

ON BIO-EFFECTS ON KARST LANDSCAPE IN JIUZHAIGOU CONSERVATION, SICHUAN PROVINCE, CHINA—WITH SPECIAL REFERENCE TO A MICROMORPHOLOFICAL APPROACH

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The phytoplankton of some saline lakes in Central Asia

The Aral Sea, Lake Balkhash, and Lake Kamyslybas are closed lakes in Central Asia. They range from oligosaline to metasaline. The salinity of the Aral Sea has increased by more than 30 g L⁻¹ since widespread irrigation began in its catchment area. Few studies of the phytoplankton have been conducted on these lakes since extensive irrigation started. The investigation reported here compares the flora of phytoplankton in these saline lakes. In the Small Aral Sea, phytoplankton density gradually decreased with increasing electrical conductivity (EC) (∼ salinity), but there was no such relation in Lake Balkhash and Lake Kamyslybas. In the Aral Sea, Dinophyceae and Bacillariophyceae were frequently observed in most areas of high EC value, and Cyanophyceae were most conspicuous in the area of medium and lower EC values. In Lake Balkhash, Cyanophyceae were most conspicuous, but Chlorophyceae were also noticeable. Most Cyanophyceae in Aral Sea formed filaments with heterocysts. The distinct characteristic of the phytoplankton of the Lake Balkhash was that all dominant species form colonies covered with a gelatinous film. Siliceousplankton diversity gradually decreased with increasing EC values in the Aral Sea and Lake Balkhash.