湖泊生态恢复的关键因子分析

中国是一个多湖泊的国家。由于经济快速发展及湖泊资源不合理的开发利用,中国湖泊的污染问题和生态系统退化相当普遍。特别是由于氮、磷等营养元素的富集造成的水体富营养化,导致蓝藻水华频繁发生,甚至出现了饮用水危机事件。由于缺乏基础理论的指导,中国湖泊富营养化治理曾经走过弯路。在没有实现控源截污的条件下,片面强调生态恢复来净化湖泊水环境,一度成为富营养化湖泊治理的主流思想。实际上,湖泊生态恢复是有条件的,而对这些条件的诊断和分析是开展湖泊生态恢复的前提和基础。通过对太湖水生植物分布及其影响因子分析,确定沉水植物恢复的核心条件是水下光照条件。水下光照条件受富营养水平、悬浮物浓度与水深等因子的影响。只有当一个水域的真光层深度接近水深的情况(比值>0.8),恢复水生植物才有可能。改善水下光照条件,包括降低水深,提高透明度,消除风浪等措施,实际上,都是增加真光层深度与水深的比值。在上述生态恢复条件不具备的情况下,湖泊治理与恢复的工作更多地应该聚焦在控源截污方面。这对中国湖泊污染治理与生态恢复具有普遍的意义。     

Quantitative models for reconstructing catchment ice-extent using physical-chemical characteristics of lake sediments

The physical characteristics of surface sediments from a suite of pristine lakes on Signy Island, maritime Antarctic, were used to develop a quantitative link between catchment ice-extent and lake-sediment response. Percentage dry weight, median particle size, percentage loss-on-ignition and wet density of the lakes' surface sediments were the most significant variables explaining contemporary catchment ice-extent. Two independent reconstruction models – Partial Least Squares (PLS) and a Modern Analog Technique (MAT) – were applied to dated sediment cores at two sites on Signy Island. The validity of the reconstructions was tested against historical information on catchment ice-extent. With sufficiently high sedimentation rates and sampling resolution, the models can predict sub-decadal changes in ice-extent. The model results are best regarded as indicators of erosion resulting from meltwater activity in the catchment. Comparison of results with Twentieth Century climate records affirms the hypothesis that climatic warming is the most likely cause for the ice retreat observed on Signy Island during the last 40 yrs. Similar reconstruction models using these simple sedimentary measures could be developed for analogous locations in the Antarctic and in Arctic and Alpine regions.     

微量元素在湖积物、土壤的垂向分布与稻谷中的分配

报道了“江苏省国土生态地球化学调查”项目有关湖积物、土壤柱微量元素垂向分布及稻谷样元素分配研究的初步成果。通过对有关样品元素含量的分析对比,指出洪泽湖沉积柱元素垂向分布与其动荡的沉积环境关系密切、太湖局部沉积物在其目前20cm以上深度存在人为重金属污染,这二湖沉积物中其氮与总有机碳含量呈显著正相关;认为城市化可使当地土壤环境受重金属等污染的深度显著加大、城市土壤环境受人为活动的影响要显著高于农村;发现Mo易富集于稻米、重金属与营养元素易富集于稻皮、各元素在米-谷间的分配关系不确定。     

盐湖丰产元素与Zintl化合物(续完)

Zintl化合物是以Edward Zintl命名的化合物,是一类由电正性的碱金属或碱土金属与电负性的13族或14族元素形成的特殊金属间化合物。其价键模式可以是离子键、金属键和共价键共存,其中的准金属可以共价键的形式形成各种形式的离子簇,因而其结构复杂多样。这类化合物的部分阴离子簇不仅具有稳定的笼状、层状和链状结构,并且具有特殊的光、电、磁等性能,使得在半导体、催化、电极材料等方面都有应用的前景和发展潜力。介绍了几个特殊Zintl化合物体系,盐湖丰产元素在Zintl化合物中的作用,指出了含有盐湖丰产元素的Zintl化合物的应用前景和方向。     

The Stanley unconformity in Lake Huron basin: evidence for a climate-driven closed lowstand about 7900 <Superscript>14</Superscript>C BP,with similar implications for the Chippewa lowstand in Lake Michigan basin

J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 ¹⁴C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the Lake Stanley phase. A re-examination of sediment stratigraphy in northwestern Lake Huron using seismic reflection and new core data corroborates the sedimentological evidence of Hough’s Stanley unconformity, but not its inferred chronology or the level of the associated lowstand. Erosion of previously deposited sediment, causing the gap in the sediment sequence down to 70 m present depth, is attributed to wave erosion in the shoreface of the Lake Stanley lowstand. Allowing for non-deposition of muddy sediment in the upper 20 m approximately of water depth as occurs in the present Great Lakes, the inferred water level of the Stanley lowstand is repositioned at 50 m below present in northwestern Lake Huron. The age of this lowstand is about 7.9 ± 0.3¹⁴C ka, determined from the inferred ¹⁴C age of the unconformity by radiocarbon-dated geomagnetic secular variation in six new cores. This relatively young age shows that the lowstand defined by Hough’s Stanley unconformity is the late Lake Stanley phase of the northern Huron basin, youngest of three lowstands following the Algonquin lake phases. Reconstruction of uplift histories for lake level and outlets shows that late Lake Stanley was about 25–30 m below the North Bay outlet, and about 10 m below the sill of the Huron basin. The late Stanley lowstand was hydrologically closed, consistent with independent evidence for dry regional climate at this time. A similar analysis of the Chippewa unconformity shows that the Lake Michigan basin also hosted a hydrologically closed lowstand, late Lake Chippewa. This phase of closed lowstands is new to the geological history of the Great Lakes. This is the ninth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M Lewis were guest editors of this special issue.     

西藏羊卓雍湖流域近45 年气温和降水的变化趋势

利用西藏羊卓雍湖流域气象、水文观测站1961-2005 年逐月的平均气温、降水量等资 料, 分析了近45 年流域气温、降水的年际和年代际变化特征和异常年份, 以及羊湖水位变化趋势及影响因子, 结果表明： 近45 年流域年平均气温以0.25 ^oC/10a 的速率显著升高, 增温主要表现在秋、冬季。近25 年, 流域平均降水量除冬季呈减少趋势外, 其他各季节表现为显 著的增加趋势, 增幅为11.4~30.0 mm/10a, 夏季增幅最大; 年降水量以54.2 mm/10a 的速率明显增加。20 世纪60 年代至90 年代, 除夏季外, 其他3 季表现为逐年代增温趋势。在夏季, 降水量除80 年代偏少外, 其他3 个年代偏多; 而冬季相反, 80 年代降水偏多, 其他3 个年代偏少。流域年平均气温异常偏高年出现过3 次, 且发生在20 世纪90 年代末至21 世纪初; 60 年代后期和70 年代初降水多异常年份。自1997 年发电以来, 降水量呈增加趋势, 流域平均降水量达409.7 mm, 明显高于平衡降水量, 水位呈较明显的上升趋势。降水增多、日照减少, 以及气温明显升高、冰雪融水增加是造成水位上升的主要原因。     

Middle Pleistocene lacustrine deposits in eastern Essex,England and their palaeogeographical implications

Investigations in quarry exposures in the Asheldham Gravel and related deposits of southeast Essex are described. Section logging, mapping and borehole investigations are supported by clast lithological, heavy and clay mineralogical determinations. The sediments are derived from reworking of local Thames basin materials, fine sediment being predominantly from the London Clay. The sequence is shown to represent an aggradation that began as the fluvial infilling of the River Medway valley. The River Thames, diverted into this valley by glaciation further west, overwhelmed the Medway, reworking the deposits. The valley was subsequently drowned and fine laminated lake sediment was initially deposited. This was during a period when the valley was drowned by the glacial lake ponded in the southern North Sea basin by the Anglian/Elsterian ice sheet. Progradation by a braid-delta complex advanced along the valley and subsequently fluvial deposition returned. Valley widening and straightening accompanied the delta progradation. The deposits were dissected by deep fluvial valleys infilled by Hoxnian interglacial sediments. The Asheldham Gravel is therefore placed in the Anglian/Elsterian Stage.     

岱海14 C测年的现代碳库效应研究*

碳库效应的复杂性是影响建立湖泊沉积物高精度年代序列的一大障碍。本项研究通过我国内蒙古半干旱区封闭湖泊表层沉积物、湖水、现生沉水植物狐尾藻、现生鲤鱼鱼骨和湖岸表层土壤等一系列样品的¹⁴ C年代测定,表明现代岱海确实存在碳库效应。碳库效应年龄因湖水盐度在湖区的不均而有所变化,岱海西部湖区弓坝河径流补给量大,湖水盐度较东部稍低,碳库效应年龄也略小于东部湖区。表层沉积物中有机质包含浮游生物和沉水植物的混合信息,因而其碳库效应年龄较沉水植物年龄轻,岱海湖心表层沉积物碳库效应年龄在2000a左右。这一碳库效应年龄较通过沉积钻孔¹⁴ C年龄线性回归获得的年龄偏大,可能的原因是在时间序列上碳库效应并非恒定。     

熵值理论和改进BP网络在湖泊富营养化评价中的应用研究

针对湖泊型饮用水源地水体污染、富营养化加剧的问题,引入熵值理论,建立单指标营养状态指数(TSI)和熵权藕合的湖泊综合营养状态指数模型(STSI),计算得到湖泊综合富营养状态指数判断湖泊富营养综合状态;基于神经网络仿真理论和Matlab软件系统,采用附加动量法和自适应学习速率改进BP算法,建立5-3-1结构型式的BP网络模型对湖泊富营养状态进行仿真预测。综合富营养化指数模型及改进BP模型应用于评价及预测固城湖富营养状态,并对模型评价结果进行验证。结果表明,改进BP网络模型可以有效地综合判断水体状态,为富营养评价及预测提供新的方法。