属性识别模型在艾比湖水质评价中的应用

根据新疆博尔塔拉蒙古自治州环境监测站对艾比湖5个代表性的监测断面最近5年的水质实测资料,结合熵权法和国家地表水环境质量标准系统地建立了属性识别模型,运用属性计算和属性得分详细评价了艾比湖的水质.模型评价结果表明:艾比湖的水质污染主要为氨氮、磷、砷的污染.就空间而言,湖心2水质较好,没有出现V类水质,其次为喇叭口,博乐河口与精河河口水质较差;就时间而言,2003年各监测断面水质均属I类,之后逐渐恶化,到2008年半数以上的监测断面属于V类水质,且与改进密切值法的评价结果比较,结果较吻合.采用属性识别模型评价湖泊水质,概念清晰,计算简单,评价结果客观、合理,可以反映出艾比湖水质的现状,是湖泊水质评价中简便实用的评价方法之一.     

Late Quaternary lake response to climate change and anthropogenic impact: biomarker evidence from Lake Constance sediments

This study used organic matter in oligotrophic Lake Constance (southern Germany) to reconstruct lake environment and to disentangle the multiple factors, such as climate change and human impacts, which influence sedimentation in large lakes. A sediment core from Upper Lake Constance, which represents 16,000 years of Late Glacial and Holocene lake history, was analysed for organic biomarkers, hydrogen index and elements calcium, strontium, and magnesium. Magnetic susceptibility was measured to establish a high-resolution stratigraphic framework for the core and to obtain further information about changes with respect to relative allochthonous versus autochthonous sedimentation. Dinosterol—a biomarker for dinoflagellates—and calcium have low concentrations in Younger Dryas sediments and consistently high concentrations between 10,500 and 7,000 cal. years BP. These variations are attributed to changes in lake productivity, but are not reflected in the proportion of total organic carbon within the sediment. During the Younger Dryas and between 6,000 and 2,800 cal. years BP, concentrations and accumulation rates of land-plant-derived C₂₉-steroids (β-sitosterol, stigmastanol and stigmasterol), in combination with a relatively low HI, indicate periods of enhanced terrigenous input to the lake. For the Younger Dryas, higher runoff can be attributed to a cold climate, leading to decreased vegetation cover and increased erosion. After 6,000 cal. years BP, high terrestrial input may be explained by enhanced precipitation. Biomarker and HI results, in combination with archaeological studies, raise the question as to whether lakeshore settlements affected sedimentation in Upper Lake Constance between 6,000 and 2,800 cal. years BP.     

Sediment accumulation of Dianchi Lake determined by 137Cs dating

The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentation rates of Dianchi Lake are determined by 137Cs dating. However, 137Cs vertical distribution in sediment cores of Dianchi Lake has special characteristics because Dianchi Lake is located on the southeast of the Qinghai-Tibet Plateau, the Kunming quasi-stationary front is over the borders of Yunnan and Guizhou where the specific precipitation is distributed. Besides 1954, 1963 and 1986 137Cs marks can be determined in sediment cores, a 137Cs mark of 1976 representing the major period of 137Cs released from China unclear test can be determined and used for an auxiliary dating mark. Meanwhile Dianchi Lake is divided into seven sections based on the water depth, basin topography, hydrological features and supplies of silt and the lakebed area of each section is calculated. The mean annual sedimentation rates for seven sections are 0.0810, 0.1352, 0.1457, 0.1333, 0.0904, 0.1267 and 0.1023 g/cm2a in 1963–2003, respectively. The gross sediment accumulation of the lake is 26.18×104 t/a in recent 17 years and 39.86×104 t/a in recent 50 years.     

Recent water quality trends and a comparison to sediment-core records for two riverine lakes of the Upper Mississippi River basin: Lake St. Croix and Lake Pepin

Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix. Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003 period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue.     

Walking through volcanic mud: the 2,100-year-old Acahualinca footprints (Nicaragua)

We present the stratigraphy, lithology, volcanology, and age of the Acahualinca section in Managua, including a famous footprint layer exposed in two museum pits. The ca. 4-m-high walls of the main northern pit (Pit I) expose excellent cross sections of Late Holocene volcaniclastic deposits in northern Managua. We have subdivided the section into six lithostratigraphic units, some of which we correlate to Late Holocene eruptions. Unit I (1.2 m thick), chiefly of hydroclastic origin, begins with the footprint layer. The bulk is dominated by mostly massive basaltic-andesitic tephra layers, interpreted to represent separate pulses of a basically phreatomagmatic eruptive episode. We correlate these deposits based on compositional and stratigraphic evidence to the Masaya Triple Layer erupted at Masaya volcano ca. 2,120 ± 120 a B.P.. The eruption occurred during the dry season. A major erosional channel unconformity up to 1 m deep in the western half of Pit I separates Units II and I. Unit II begins with basal dacitic pumice lapilli up to 10 cm thick overlain by a massive to bedded fine-grained dacitic tuff including a layer of accretionary lapilli and pockets of well-rounded pumice lapilli. Angular nonvesicular glass shards are interpreted to represent hydroclastic fragmentation. The dacitic tephra is correlated unequivocally with the ca. 1.9-ka-Plinian dacitic Chiltepe eruption. Unit III, a lithified basaltic-andesitic deposit up to 50 cm thick and extremely rich in branch molds and excellent leaf impressions, is correlated with the Masaya Tuff erupted ca. 1.8 ka ago. Unit IV, a reworked massive basaltic-andesitic deposit, rich in brown tuff clasts and well bedded and cross bedded in the northwestern corner of Pit I, cuts erosionally down as far as Unit I. A poorly defined, pale brown mass flow deposit up to 1 m thick (Unit V) is overlain by 1–1.5 m of dominantly reworked, chiefly basaltic tephra topped by soil (Unit VI). A major erosional channel carved chiefly between deposition of Units II and I may have existed as a shallow drainage channel even prior to deposition of the footprint layer. The swath of the footprints is oriented NNW, roughly parallel to, and just east of, the axis of the channel. The interpretation of the footprint layer as the initial product of a powerful eruption at Masaya volcano followed without erosional breaks by additional layers of the same eruptive phase is strong evidence that the group of 15 or 16 people tried to escape from an eruption.     

Geochemical signatures of two different coastal depositional environments within the same catchment

The geochemistry of lake (Renstradträsket) and estuarine (Pieni Pernajanlahti Bay) sediment was investigated in a medium sized watershed draining to the Gulf of Finland, Baltic Sea. Catchment land-use types were compared and found similar. Sediment cores were dated using ²¹⁰Pb- and ¹³⁷Cs-chronologies and analyzed for Al, K, Cu, Zn, Fe, Mn, phosphorus fractions, TN, TC and biogenic silica (BSi). Differences between the sediment cores were studied by using linear regression analysis and principal components analysis (PCA). Despite similarities in catchment land-use and history, the sediment geochemical profiles of the sites varied significantly. Some of the differences could be related to differences in chemical sedimentation environment (lacustrine versus estuarine). TP concentration was found to be positively correlated with sediment iron content in estuarine sediment but negatively correlated with Fe in lake sediment. In the estuarine core sedimentary iron was not correlated to lithogenic potassium and aluminum but in the lake core the iron seemed to be lithogenic in origin, as suggested by the strong positive correlations (r ² = 0.95–0.96) between these three variables. Most similarities among the cores were found in Al concentrations. Estuarine nutrient profiles appeared relatively monotonous compared to the lake core. This is probably due to more vigorous mixing of the sediments that may ensure more rapid and complete consumption of the organic matter deposited on the bottom of the estuary. Therefore the lake sediment appeared to preserve the historical record of eutrophication better. Biologically less active and more particle-bound materials like the trace metals Cu and Zn seemed to retain good records of anthropogenic impact also in the estuarine core. The study highlights the need to take the sedimentation environment into account when interpreting geochemical record.     

粒度和元素证据指示的居延海1.5kaBP来环境演化

居延海是黑河的终端湖, 在最近3 000 a来已由原来面积 800 km2逐渐萎缩而最终干涸, 同时其周边环境也发生了巨大的变化.东居延海(索果诺尔)湖相沉积的粒度和元素资料研究结果表明: 明清以前湖泊的变化主要受气候变化的影响, 温暖时期, 气候偏湿, 入湖水量增多, 湖泊面积扩大, 流域化学风化作用增强; 寒冷时期, 气候偏干, 入湖水量减小, 湖泊萎缩, 流域化学风化作用减弱.明清之后特别是近40 a来, 由于黑河上中游地区大规模的土地开发及水资源利用, 入湖水量不断减小, 甚至河流断流, 最终导致了目前居延海的干涸.     

青土湖地区9500a BP以来的环境变化研究

通过对青土湖地区ZY剖面的代用指标分析,研究了该区9500aBP以来的气候环境变化.在9500～6700aBP期间,剖面为风成砂沉积,平均粒径、磁化率、碳酸盐含量和C/N代用指标值均出现了的最低值,代表了湖泊干涸状态下强烈的风力搬运堆积,反映为一种暖干的古气候环境;6700～5800aBP期间,为碳酸盐粉砂质粘土沉积,代用指标的值均为高值,指示高水位、暖湿的古气候环境;5800～2700aBP为碳酸盐粉砂沉积,代用指标的值均表现为中等,代表了低水位状态下的碳酸盐沉积,反映夏季风减弱,区域降水量减少;2700～1100aBP期间为沼泽沉积,此时湖泊水量变化是以人为因素为主还是自然因素为主,需要进一步研究.     

基于IMOP的流域环境-经济系统规划

流域是涵盖众多因素的复杂巨系统,其健康持续的发展需要科学的综合规划。作者采用不确定性多目标规划 (IMOP) 模型来研究这一复杂系统。该模型是传统多目标规划法的一种拓展,它将多种系统组分纳入一个框架综合考虑,较好地协调多个目标,尤其能有效处理系统中的不确定性信息。基于此模型,针对流域环境-经济系统特点,建立了流域环境-经济系统不确定性多目标规划模型 (IMOPWEES)。同时,将模型运用于四川省邛海流域规划,得到2种情景不同阶段下的优化方案,以种植结构、旅游服务业结构、水资源配置、污染物排放、森林扩展及水土流失为例予以结果说明和情景比较。研究表明,IMOPWEES用于流域环境-经济系统规划,具有科学性,实用性和可操作性,其为流域相关研究工作提供了一种有效工具。     

近50年来人类活动对博斯腾湖水位影响的量化研究

博斯腾湖是新疆最大的湖泊,也是中国最大的内陆淡水湖,其巨大的环境、生态和经济价值一向为人们所关注。近50年来,博斯腾湖水位发生了很大变化,1958~1987年水位持续下降,1988~2002年水位又转为持续上升,目前处于50年来的最高水位。针对其水位变化,利用近50年来的实测数据分析了人类活动对水位变化的影响,定量还原了天然状况下博斯腾湖的水位。研究结果表明,自1958年以来人类活动对博斯腾湖水位变化的影响经历了弱→强→弱的变化过程,其中20世纪70~80年代人类活动对水位变化影响最为显著,90年代以后影响强度有所减弱。