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1.
The frequency of nuisance algal blooms has been increasing during the last two decades in the shallow, headwater East Pond (Smithfield, Maine, USA). Meanwhile, the hydrologically linked North Pond has not experienced an increase in algal blooms, despite similar morphometry and higher external nutrient loads. Possible explanations for this difference include stronger trophic cascade effects from planktivorous white perch (Morone americana) in East Pond as well as differences in phosphorus (P) release from the sediments of these two lakes. We conducted a paleolimnological investigation of these two lakes to assess whether sedimentary evidence supported trophic cascade effects based on cladoceran ephippia size, diatom fossils, and fossil pigments or biogeochemical controls based on potential sedimentary P release as the primary driver of these increased algal blooms in East Pond. At the time of white perch introduction (~1930–1950), ephippia size increases in East Pond, although no changes are observed in either diatom abundance or trends in the algal pigments. Instead, algal pigments increase in recent decades (~1980 to present) along with an increase in diatom taxa with higher TP optima These results suggest that predation by white perch is not resulting in top-down effects on algal abundance in East Pond, as predicted by the trophic cascade hypothesis. While the P content of sediments from both lakes is relatively equal, the releasable P in the top 10 cm of sediment in East Pond constitutes a greater percentage of the P extracted. Also, North Pond sediments exhibit a greater capacity to permanently bury P via the mechanisms of sorption to Al(OH)3(s) and a slower mineralization of organic P compounds. The results of this investigation suggest that the ultimate driver of the recent algal blooms in East Pond is internal P release from the sediments instead of trophic cascade effects.  相似文献   

2.
In the 1960s and 1970s, acidification was identified as a major environmental problem in Scandinavia, Great Britain and North America. In Sweden, a liming program was launched in order to counteract the effects of acidification on surface waters. More than 30 years after large-scale liming began, there is still debate about whether liming actually achieves its goals, i.e., to prevent acidification in acid-sensitive surface waters and to restore natural conditions in acidified waters. We used Detrended Correspondence Analysis (DCA) and analogue matching of diatom assemblages in surface sediment samples (recent conditions) from 31 limed lakes and pre-industrial samples from 291 reference lakes to help answer the question as to whether the Swedish liming program achieves its goals. Diatoms are important primary producers in lakes and established indicator organisms for lake-water quality. First we compared pre-industrial with post-limed diatom communities to address the question whether liming causes unnatural conditions, i.e., diatom communities that have not previously occurred in Swedish lakes. Second, we addressed the issue of what is a realistic condition to use as a reference (natural condition) or a target in management programs. We found that the diatom communities in limed lakes were not different from the communities in the reference lakes. Most of the limed lakes had one or more analogues within the reference data set and many of them had at least one within-lake analogue. Hence, liming does not create unique diatom communities in lakes. Based on this and previous paleolimnological studies in Swedish lakes we suggest a conceptual model integrating the natural lake condition, the historical human impact, and the recent and contemporary human impact, when defining realistic targets in management programs.  相似文献   

3.
为了解南极淡水生态系统的水化学特征，完成了拉斯曼丘陵地区１３个湖泊和菲尔德斯半岛１０个湖泊以及雪样的调查分析。西南极乔治王岛菲尔德斯半岛和东南极拉斯曼丘陵的气候条件不同，前者属于极地海洋性气候、气温不很低、湿润、风小、夏季较长；后者属于极地大陆性气候、气温低，冬天严寒、干燥、风大，夏季较短。因此，两地区的湖泊地貌、成因、发育、水生生物种群结构以及水化学状态存在较明显的差异，虽然水化学类型均比较单一，但矿化度却相差甚大。本文还对两区饮水水源进行了评价。  相似文献   

4.
We have surveyed 7 inland salt lakes and 14 coastal saltworks in the People's Republic of China (P. R. China) which are natural habitats for the brine shrimpArtemia. We report here on the location of the lakes, the mode of reproduction of theArtemia and the opportunities for achieving self sufficiency in cyst production for use in the local aquaculture industry. Because of frequent misunderstandings regarding the identification of a specific habitat, a new identification system for each population is proposed, using a numerical code which identifies the province, the habitat and the date of collection. Information of newArtemia populations is included as well as data on their reproduction mode.International interdisciplinary study onArtemia populations coordinated by the Laboratory of Aquaculture &Artemia Reference Center, University of Ghent, Belgium.  相似文献   

5.
近35 a来新疆干旱区湖泊变化及原因分析   总被引：3，自引：1，他引：2  
朱刚  高会军  曾光 《干旱区地理》2015,38(1):103-110
应用“3S”技术,以流域为单元,对新疆干旱区1975-2010年近35 a来湖泊的变化进行了研究。研究结果表明：湖泊总体呈数量多、规模小的特点,以天然湖泊为主,湖泊分布面积最大的流域为准噶尔内流区、分布数量最多的流域为塔里木内流区;35 a来湖泊的变化呈1975-2000年数量与面积增大、2000-2010年数量与面积减少的特征;天然湖泊与人工湖泊变化差异显著,天然湖泊数量与面积均呈先增加后减少的变化特征,而人工湖泊数量及面积均呈持续增加的变化特征;1975-2000年各流域湖泊面积均增大,2000-2010年除伊犁河内流区外,各流域湖泊面积均大幅度减小;影响新疆干旱区湖泊变化的主要气候因素是降水与气温,人类活动是流域间湖泊变化幅度与变化趋势差异的主要影响因素,也是影响天然湖泊与人工湖泊变化趋势差异的主要原因。  相似文献   

6.
The numerous and widespread lakes of the Tibetan Plateau (TP) constitute the largest group of alpine lakes on Earth. Some of the lakes are fed mainly by glacier meltwater and others by precipitation and groundwater. Past changes in the environments of these lakes differed because of differences in lake hydrological regimes and the complex pattern of climate change on the TP. Here we present records of scanning XRF, inorganic carbon (IC) concentration n-alkanoic acid average chain length (ACL) and percent aquatic inputs (Paq) in sediment cores from two non-glaciated lakes on the central TP (Dagze Co and Jiang Co), which span the past 19,000 years. We used these measures to investigate past changes in catchment hydrology, climate and environment. Variations in the concentration of Ti and other lithogenic elements at the two sites were influenced mainly by surface runoff, which is supported by the variation of IC, Ca/(Al, Ti, Fe) (reflecting authigenic carbonate precipitation), Rb/Sr (a chemical weathering proxy), and ACL and Paq. We attribute variations in surface runoff to changes in the precipitation/evaporation ratio, caused by the pattern of climate change on the central TP since the late Pleistocene. During the late Pleistocene, stronger runoff (indicated by higher Ti, higher Rb/Sr and Paq, lower IC, Ca/(Al, Ti, Fe) and ACL) likely resulted from lower temperatures. Lower runoff during the Holocene may reflect intensified evaporation caused by higher temperatures. Comparison with records from glaciated lakes in the region reveals opposite trends in catchment hydrology. Overall, our results suggest that since the late Pleistocene the central TP was influenced mainly by the Indian Summer Monsoon.  相似文献   

7.
The paper presents a review of shallow lakes on two neighboring territories, Transbaikalia in Russia and Northeastern Mongolia. Five systems of shallow lakes are distinguished in the regions under study: Barguzin, Eravna-Gusinoozersk, Ingoda, Onon-Borzya, and Eastern-Mongolian systems. The shallow lakes are sub-grouped according to common chemical compositions and geochemical evolution types. Characteristics of ground- and surface waters feeding the lakes are considered. Based on results of trace element analyses of water samples from about 200 lakes and more than 100 springs, wells and boreholes, elements that manifest higher concentrations, resulting from evaporation of lacustrine waters, are determined. Prospects of assessment of ore-generating potential of the shallow lakes as ‘liquid ore’ sources in view of commercial extraction of Li, U, REE, and others metals are discussed.  相似文献   

8.
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.  相似文献   

9.
The mechanical denudation rates of 81 large lake basins (lake area > 500 km2) were determined from long-term river loads and erosion maps. Using the drainage area/lake area ratios the mean sedimentation rates of the lakes were calculated for a porosity of 0.3. The mean sedimentation rates of different lake types vary between 0.1 mm/a (glacial lakes, lowland) and 5.4 mm/a (mostly sag basin lakes). The calculated lifetimes of the lakes are based on the lake volumes and mean sedimentation rates, assuming steady-state conditions and solely clastic material. On average, glacial lakes in highlands and fault-related lakes show the shortest lifetimes (c. 70 ka), glacial lakes in lowlands and rift lakes have the longest lifetimes (c. 1 Ma). Some lakes remain unfilled for very long time spans due to rapid subsidence of their basin floors. The calculated lifetimes are compared with those derived from sediment core studies. Most core studies indicate lower mechanical sedimentation rates than the calculated ones because a major part of the incoming sediment is trapped in deltas. However, a number of lakes (e.g., the Great Lakes of North America) show the opposite tendency which is largely caused by extensive shoreline erosion and resuspension. The lifetimes of large glacial lakes often exceed the duration of interglacials. Hence, their lifetimes are restricted by glaciation and not by sediment infill. Rift lakes persist for long time periods which exceed the calculated lifetimes in some cases. Time-dependent subsidence, basin extension, as well as the impact of climate change are briefly described.  相似文献   

10.
Since the 1970s liming has been practised on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly. The Swedish monitoring program ISELAW (Integrated Studies of the Effects of Liming Acidified Waters) studies the long-term effects of liming. This paper summarizes the paleolimnological part of the program. Sediment cores from 12 lakes were analysed to study the development of the lakes from pre-industrial time until the present, and address questions about natural conditions and the effects of early human impact, acidification, and liming. Diatoms were used to reconstruct the pH history and to study shifts in species composition due to acidification and liming. Analyses of lead and spheroidal carbonaceous particles were applied for indirect dating and as indicators of the atmospheric deposition of pollutants associated with acid rain. Pollen analysis was performed in eight of the lakes to study the vegetation and agricultural history. The natural pH (prior to human disturbance) was between 5.3 and 6.5 in the eight lakes where the complete post-glacial sediment sequence was recovered. Pollen from anthropochores and apophytes indicated early agricultural land use in the vicinity of the lakes from 1000 to 2000 years ago, and pH increased with land use in six of these lakes. Five of the lakes have been acidified during recent decades, and in all 12 lakes some effects of liming were recorded in the diatom assemblage. The lakes show different responses to liming, including a return to a pre-acidification diatom composition or a shift to a state previously not recorded in the lake’s histories. This study accentuates the complexity of biological response to acidification and liming, and highlights the importance of historical perspectives to assess the current state of a lake’s ecosystem and to establish adequate restoration goals.  相似文献   

11.
Presented are the results from determining the principal ion composition of the waters and the composition of chemical elements, including rare and rare-earth elements) in the waters of three salt lakes: Shara-Nur, Dus-Khol and Bai-Khol, on the territory of the drainless Ubsunur depression. Common to these lakes are their small depth, and their location in the bottoms of basins without outflow, between small bald mountains in the zone of dry climate with abrupt temperature fluctuations. More likely these lakes have their origins in the remnants of ancient water basins. Accumulation of salts in the lakes is associated with continental salinization processes.  相似文献   

12.
Four Wisconsin, USA lakes were examined with paleolimnological techniques to determine the effects of shoreland development on water quality. Geochemical parameters such as aluminum, iron, manganese, phosphorus, nitrogen, and carbon were used to document watershed inputs while redox sensitive elements provided information on changes in hypolimnetic oxygen levels. Changes in the diatom community were used to assess the impacts of development upon the lakes' trophic status as well as changes in the littoral community. We assessed the relative sensitivity of high vs. low ANC lakes.The initial shoreland development, late in the 19th or early in the 20th century, involved seasonal cabins and minimal disturbance of the shoreland. This development phase had minimal impact upon the lakes compared to that during the mid- and late-twentieth century. Increased levels of iron and aluminum indicated the highest input of sediment occurred during the construction phase of converting shoreland homes from seasonal to year-round usage. Phosphorus deposition increased moderately in the high alkalinity lakes but more so in the low alkalinity lakes. In the low alkalinity stratified lake, increased levels of iron and manganese in the last decade indicated more anoxia in the hypolimnion. Phosphorus levels have also increased during this time period most likely as a result of elevated phosphorus release from the sediments.In the high alkalinity lakes, as the nutrient levels increased, diatom production initially shifted from benthic taxa of the family Fragilariaceae to metalimnetic taxa and as nutrients increased further, epilimnetic species. In the low alkalinity lakes, prior to settlement the major site of diatom prodution was the open water. Coincidental with the early shoreland development was an increase of macrophyte density as indicated by the epiphytic diatom Achnanthidium minutissimum ((Kützing) Czarnecki (= Achnanthes minutissima Kützing). The water quality in the high alkalinity lakes showed some improvement following completion of the home construction phase, especially in the lake with lower development density. The low alkalinity lakes did not show improved water quality and appear more sensitive to shoreland development.  相似文献   

13.
On the basis of analyzing long-term field data, we investigated the vertical thermal structure of 66 lakes of the North-West of Russia during the freeze-up period. The largest variability in thermal structure is characteristic for low-drainage shallow water bodies. Detailed data were obtained at self-contained buoy stations located in a small Lake Vendyurskoe (southern Karelia) were used to identify water temperature changes at the depths for a winter season as well as making assessments of het flows at the water–bottom and water–ice interfaces. The interannual water temperature variability at the depths reaches 2°C. The main geographical factors influencing the formation of thermal stratifications in the 66 lakes used in the study during the winter period are their mean depth, area, water residence time and geographical latitude. The largest vertical water temperature gradients are characteristic for the group of the smallest and shallow lakes, in the bottom layers of which the water temperature exceeds the temperature of maximum density, whereas in the deep lakes (more than 15 m) the water temperature is below 4°C. The lowest values of water temperature are observed in large lakes. The water temperature in the upper layer (up to 10 m) of drainage water bodies also decreases to 0–1°C as the result of the removal of heat with the river discharge. According to the thermal stratifications, the lakes are categorized as small (shallow, deep and drainage lakes), medium-sized and large shallow and large deep lakes. The suggested regression model permits a typical water temperature to be assessed at standard depths at the end of a winter season for any water body in the study region using available geographical information. The verification of the model is done from independent data for eight lakes of Finland.  相似文献   

14.
青藏高原盐湖赋存着丰富的钾资源元素。近年来,在全球变暖和大规模人工开发背景下,青藏高原盐湖卤水钾含量和矿化度发生显著变化。系统对比了青藏高原31个盐湖近年来和1990s之前卤水的钾离子含量和矿化度变化情况,分析其主要影响因素。结果显示,近年来青藏高原盐湖钾离子含量和矿化度总体呈现下降趋势,但不同盐湖变化程度不同;藏北高原、可可西里高原、西昆仑等地区盐湖主要受气候-构造-水文等自然因素影响,钾离子和矿化度下降明显;柴达木盆地盐湖受资源开发和人为干预等因素影响,卤水钾离子含量下降,而矿化度略有增加。  相似文献   

15.
Macrophytes are a critical component of lake ecosystems affecting nutrient and contaminant cycling, food web structure, and lake biodiversity. The long-term (decades to centuries) dynamics of macrophyte cover are, however, poorly understood and no quantitative estimates exist for pre-industrial (pre-1850) macrophyte cover in northeastern North America. Using a 215 lake dataset, we tested if surface sediment diatom assemblages significantly differed among lakes that have sparse (<10% cover; group 1), moderate (10–40% cover; group 2) or extensive (>40% cover; group 3) macrophyte cover. Analysis of similarity indicated that the diatom assemblages of these a priori groups of macrophyte cover were significantly different from one another (i.e., difference between: groups 1 and 3, R statistic = 0.31, P < 0.001; groups 1 and 2, R statistic = 0.049, P < 0.01; groups 3 and 2, R statistic = 0.112, P < 0.001). We then developed an inference model for macrophyte cover from lakes classified as sparse or extensive cover (145 lakes) based on the surface sediment diatom assemblages, and applied this model using the top-bottom paleolimnological approach (i.e., comparison of recent sediments to pre-disturbance sediments). We used the second axis of our correspondence analysis, which significantly divided sparse and extensive macrophyte cover sites, as the independent variable in a logistic regression to predict macrophyte cover as either sparse or extensive. Cross validation, using 48 randomly chosen sites that were excluded from model development, indicated that our model accurately predicts macrophyte cover 79% of the time (r 2 = 0.32, P < 0.001). When applied to the top and bottom sediment samples, our model predicted that 12.5% of natural lakes and 22.4% of reservoirs in the dataset have undergone a ≥30% change in macrophyte cover. For the sites with an inferred change in macrophyte cover, the majority of natural lakes (64.3%) increased in cover, while the majority of reservoirs (87.5%) decreased in macrophyte cover. This study demonstrates that surface sediment diatom assemblages from profundal zones differ in lakes based on their macrophyte cover and that diatoms are useful indicators for quantitatively reconstructing changes in macrophyte cover.  相似文献   

16.
为了研究碱湖N2O释放速率及其对盐度与pH的响应,选取内蒙古大克泊碱湖的五个沉积物样点,采用15N同位素标记模拟实验,研究反硝化和厌氧氨氧化的速率、相对比例和气体产生情况,揭示高盐和高pH对碱湖氮移除的影响。发现大克泊湖潜在氮移除速率为0~16.06 n mol N mL-1 h-1,潜在反硝化速率为0~12.62 n mol N mL-1 h-1,潜在厌氧氨氧化速率为0~9.81 n mol N mL-1 h-1;当盐度34.00 g·L-1与pH 10.22时,厌氧氨氧化对氮移除贡献较大,达到43.18%~71.79%。反硝化过程气体产物以N2为主,几乎无N2O气体释出。另外,该区域潜在氮移除速率与pH呈正相关关系,与TOC、NO-3、HCO-3呈负相关关系;未发现氮移除速率与盐度之间的相关关系。因此,在研究的碱湖中,氮移除过程中主要为N2排放,而N2O低于检测水平;氮移除过程的影响因素复杂且不限于最主要的环境变量(盐度与pH)。这些结果为研究湖泊N2O排放提供了数据基础。  相似文献   

17.
The construction of a comprehensive observation platform for natural-resource elements would provide data support for studies of dynamic changes in various natural resources, and could serve the needs of natural-resource management and the construction of ecological civilization during a period of global change. As the second-largest inland river basin in NW China, the Heihe River Basin (HRB) lies in the central part of the Silk Road Economic Belt, consequently, pilot studies of resource management in the basin are urgently needed. This paper describes the construction of a comprehensive natural-resource elements observation network in the HRB to meet requirements for natural-resource management, based on natural-resource and Earth-system science. Based on current observations and research, thirteen observation stations were established in different river basins through integration with existing stations, reconstruction and upgrading, and new construction. The main types of land-surface resources in the HRB (grassland, forests, rivers, lakes, deserts, wetlands, and farmland) were included in the observation network constructed for the monitoring of natural-resource elements. Long-term, continuous, and stable observation can yield key data concerning coupling processes, trends of change, and rates of change in natural resources. This is of great significance in improving cognitive ability, scientific management, and strategic decision-making regarding natural resources in the HRB, and can provide a reference paradigm for the observation of and research into natural resources in other basins.  相似文献   

18.
Mega-urban agglomerations are strategic core areas for national economic development and the main regions of new urbanization. They also have important roles in shifting the global economic center of gravity to China. However, the development of mega-urban agglomerations has triggered the interactive coercion between resources and the eco-environment. The interactive coupled effects between urbanization and the eco-environment in mega-urban agglomerations represent frontier and high-priority research topics in the field of Earth system science over the next decade. In this paper, we carried out systematic theoretical analysis of the interactive coupling mechanisms and coercing effects between urbanization and the eco-environment in mega-urban agglomerations. In detail, we analyzed the nonlinear-coupled relationships and the coupling characteristics between natural and human elements in mega-urban agglomerations. We also investigated the interactive coercion intensities between internal and external elements, and the mechanisms and patterns of local couplings and telecouplings in mega-urban agglomeration systems, which are affected by key internal and external control elements. In addition, we proposed the interactive coupling theory on urbanization and the eco-environment in mega-urban agglomerations. Furthermore, we established a spatiotemporal dynamic coupling model with multi-element, multi-scale, multi-scenario, multi-module and multi-agent integrations, which can be used to develop an intelligent decision support system for sustainable development of mega-urban agglomerations. In general, our research may provide theoretical guidance and method support to solve problems related to mega-urban agglomerations and maintain their sustainable development.  相似文献   

19.
我国350多个盐湖湖表卤水水化学成分综合研究表明,成矿元素K、Li、B主要分布在青藏高原地区,但新疆一些富K、B盐湖也具有较好的开发潜力。我国盐湖卤水中的Br、I、Rb、Cs呈现明显的区域分异,富Br和I盐湖主要分布在内蒙古的中东部,而Rb和Cs则主要分布在青藏高原地区。我国盐湖区按主要成矿元素禀赋情况可以分为3种类型,K+B+Li资源综合利用型;K+B(Li)资源综合利用型以及单一的K(B或Li)资源利用型。青藏高原地区的盐湖卤水矿床以前两者为主,新疆和内蒙的盐湖则以后两者为主。  相似文献   

20.
韩凤清 《盐湖研究》1995,3(1):21-27
应用数学地质中常用的点群（聚类）分析方法研究了柴达木盆地盐湖的地球化学分类，并与其它学者盐湖水化学分类法进行了对比研究，探讨了二者之间的共同点与差异，并且对新的分类中各类元素的地球化学特征进行了总结  相似文献   

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