Lake Stage Research Articles

A 15.4-ka paleoclimate record inferred from δ13C and δ15N of organic matter in sediments from the sub-alpine Daping Swamp, western Nanling Mountains, South China

We inferred past climate conditions from the δ13C and δ15N of organic matter (OM) in a sediment core (DP-2011-02) from the sub-alpine Daping Swamp, in the western Nanling Mountains, South China. In the study region, a 1000-m increase in altitude results in a ~0.75‰ decrease in δ13C and a ~2.2‰ increase in δ15N. Organic carbon stable isotope (δ13C) values of the dominant modern vegetation species, surface soils, and the core samples taken in the swamp exhibit a strong terrestrial C3 plant signature. Comprehensive analysis of the core indicates both terrestrial and aquatic sources contribute to the OM in sediment. Temperature and precipitation are most likely the critical factors that influence δ13C: warm and wet conditions favor lower δ13C, whereas a dry and cool climate leads to higher δ13C values. Higher δ15N values may result from greater water depth and increased primary productivity, promoted by large inputs of dissolved inorganic nitrogen, induced by high surface runoff. Lower δ15N values are associated with lower lake stage and reduced productivity, under drier conditions. Therefore, stratigraphic shifts in these stable isotopes were used to infer past regional climate. Measures of δ13C and δ15N in deglacial deposits, in combination with total organic carbon (TOC) and nitrogen (TN) concentrations, the TOC/TN ratio, coarse silt and sand fractions, dry bulk density and low-frequency mass magnetic susceptibility, reveal two dry and cold events at 15,400–14,500 and 13,000–11,000 cal a BP, which correspond to Heinrich event 1 and the Younger Dryas, respectively. A pronounced warm and wet period that occurred between those dry episodes, from 14,500 to 13,000 cal a BP, corresponds to the Bolling–Allerod. The δ13C and δ15N data, however, do not reflect a warm and wet early Holocene. The Holocene optimum occurred between ~8000 and 6000 cal a BP, which is different from inferences from the nearby Dongge cave stalagmite δ18O record, but consistent with our previous results. This study contributes to our understanding of climate-related influences on δ13C and δ15N in OM of lake sediments in South China.

Combining sediment Cladocera remains and geochemistry to reveal the role of a large catchment in driving changes in a small subalpine lake (Lake Ledro, N-Italy)

<p>Sediment Cladocera remains and geochemistry were analyzed at Lake Ledro, a small subalpine lake with a large catchment area located in northern Italy. The aim of the study was to investigate human, climate and hydrological impacts on the Cladocera community and on the geochemical components during the last few centuries. A sediment core was collected from the deepest point of Lake Ledro and radiometrically dated. Cladocera remains were analyzed to track the trophic lake evolution. The core bottom section revealed the dominance of Bosminidae in concomitance with nutrient pulses entering into the lake during major flood events. The abundance of species preferring cold water temperatures confirmed the deposition of this core section during the Little Ice Age. The flood event occurred in the first half of the 19<sup>th</sup> century produced a drastic increase in littoral species, due to the development of new habitats. The decrease in Cladocera densities during the following lake stage was followed by a rapid increase in planktonic species during the nutrient enrichment after the 1960s. Statistical analyses revealed a clear response of Cladocera community to climate variability during oligotrophic periods, while no relation to temperature changes was recorded during high nutrient levels. A preliminary study on Bosminidae and Daphnidae body size and appendages length was carried out to reconstruct major changes in the lake food web. Only <em>Bosminia</em> spp. revealed clear body size changes: minor shifts were recorded before the 1930s in relation to the low nutrient concentrations, while the major changes occurred during the 1980s were interpreted as related to the appearance of Cladocera invertebrate predators. Geochemical components were studied using X-ray fluorescence spectroscopy (XRF) analysis in order to recognize the impact of the large catchment area and from the lake-level regulations on the lake hydrology. Moreover the Si:Al ratios profile confirmed the increase in lake productivity after the 1960s. Although both Cladocera and geochemical analysis indicate major changes since the 1960s, they also revealed diverse responses to common external and local forcing, thus confirming the value of a multi-proxy approach for disentangling the lake responses to different environmental stressors. Moreover, it outlined the importance of larger catchment areas on small lakes as they are to a larger extent influenced by the modifications occurring in the drainage basin.</p>

Paleolimnology and diatom flora of the Miocene Quincy Diatomite, Washington, USA

The Quincy Diatomite, central Washington, USA, is a middle Miocene (∼15 Ma) lacustrine deposit located between flows of the Columbia River Basalt Group. Two primary localities along the western margin of the deposit are examined for stratigraphic and geographic variation. Three lithologic units are recognized in the deposit and are distinguished by distinct diatom floras and subtle lithologic differences. Diatom assemblages vary geographically along the western margin of the basin. Distinctions between these assemblages are confirmed through analysis of point count data using nonMetric Multidimensional Scaling and cluster analyses. Three stages of lake development, directly influenced by the regional geology and geography, are recognized. The earliest stage was likely deposited in a series of small-interconnected pocket lakes that were eutrophic and slightly alkaline. This lake stage was succeeded by a period of shallower water depth, and dominated by benthic species. The latest stage of the lake is interpreted as representing a deepening and expansion of the lake, based on the dominance of planktonic diatom species. Tectonic uplift of the western Frenchman Hills Anticline combined with overall subsidence of the Quincy Basin during intermediate and late stages of lake development is interpreted to be the driver for relative changes in lake bathymetry.

The Turning Point: Preliminary Results of Underwater Research of the Former Herrn-see at the Village of Lubanowo (Western Pomerania, Poland)

In October 2014 and June 2015, a team of scholars and students from the Institute of Archaeology, University of Warsaw featuring the Institute of Archaeology and Ethnology, Polish Academy of Sciences, made an underwater survey in the unnamed lake (formerly Herrn-See) in the village of Lubanowo (formerly Liebenow) in Western Pomerania. During the underwater research, weapons, tools and horse harness parts (including chain reins) were found. They are dated mainly to the Roman Period, but also to the Middle Ages. Some items bear traces of ritual destruction. Parallels may be pointed out with weapons in Przeworsk culture, and to some extent also in Scandinavia. The site should be attributed to sacrificial military deposits. Its extraordinary character lies in the fact that so far it is the only site of its type which is still in its ‘lake stage’, i.e. not a marsh or bog. Most probably it was used by local inhabitants, the people of the Lubusz group. Key words: Herrn-See, Lubanowo village, underwater research, weapon deposit, Roman Period. DOI: http://dx.doi.org/10.15181/ab.v23i0.1296

Dam-Breach hydrology of the Johnstown flood of 1889-challenging the findings of the 1891 investigation report.

In 1891 a report was published by an ASCE committee to investigate the cause of the Johnstown flood of 1889. They concluded that changes made to the dam by the South Fork Fishing and Hunting Club did not cause the disaster because the embankment would have been overflowed and breached if the changes were not made. We dispute that conclusion based on hydraulic analyses of the dam as originally built, estimates of the time of concentration and time to peak for the South Fork drainage basin, and reported conditions at the dam and in the watershed.We present a LiDAR-based volume of Lake Conemaugh at the time of dam failure (1.455 × 107 m3) and hydrographs of flood discharge and lake stage decline. Our analytical approach incorporates the complex shape of this dam breach. More than 65 min would have been needed to drain most of the lake, not the 45 min cited by most sources. Peak flood discharges were likely in the range 7200 to 8970 m3 s−1. The original dam design, with a crest ∼0.9 m higher and the added capacity of an auxiliary spillway and five discharge pipes, had a discharge capacity at overtopping more than twice that of the reconstructed dam. A properly rebuilt dam would not have overtopped and would likely have survived the runoff event, thereby saving thousands of lives.We believe the ASCE report represented state-of-the-art for 1891. However, the report contains discrepancies and lapses in key observations, and relied on excessive reservoir inflow estimates. The confidence they expressed that dam failure was inevitable was inconsistent with information available to the committee. Hydrodynamic erosion was a likely culprit in the 1862 dam failure that seriously damaged the embankment. The Club’s substandard repair of this earlier breach sowed the seeds of its eventual destruction.

Hydrological analysis as a technical tool to support strategic and economic development: A case study of Lake Navaisha, Kenya

AbstractEffective integrated water resources management requires reliable estimation of an overall basin water budget and of hydrologic fluctuations between groundwater and surface‐water resources. Seasonal variability of groundwater‐surface water exchange fluxes impacts on the water balance. The long term lake water balance was calculated by Modflow using the stage‐volume rating curve of Lake Package LAK3. The long term average storage volume change is 8.4 × 108 m3/month. The lake water balances suggests that the lake is not in equilibrium with the inflow and outflow terms. Using field abstraction data analysis and model simulation, the combined volume of lake‐groundwater used for industrial abstraction since the last three decades was estimated. This requires an average abstraction amount of 7.0 × 106 m3/month with a long term trend of abstraction ratio 30% (groundwater) and 70% (lake water) since 1980. The amount resulted in a lake which might have been 4.8 m higher than was observed in the last stress period (2010).A long term regional groundwater budget is calculated reflecting all water flow in to and out of the regional aquifer. The model water balance suggests that lake Navaisha basin is in equilibrium with a net outflow about 1% greater than the inflow over the calibrated period of time (1932–2010). The regional model is best used for broad‐scale predictions and can be used to provide a general sense of groundwater to surface water and groundwater to groundwater impacts in the basin. A basin wide water resource management strategy can be designed by integrating the lake/wetland within the regional groundwater model to increase the level of sustainable production and good stewardship in Lake Navaisha. Such hydrological analysis is crucial in making the model serve as simulator of the response of lake stage to hydraulic stresses applied to the aquifer and variation in climatic condition.

Northern hemisphere climate control on the environmental dynamics in the glacial Black Sea “Lake”

The Marine Isotope Stage (MIS) 3 stands out due to its abrupt changes from cold and dry stadials to warm and humid interstadials, the so-called Dansgaard-Oeschger cycles that also affected temperature and rainfall in the Black Sea region. This study is based on a gravity core from the southeastern (SE) Black Sea that covers the last glacial lake stage from 64 to 20 ka BP. By using the composition of major and trace elements in the sediments, terrestrial plant-derived n-alkane flux, and Sr/Ca from benthic ostracods, we reconstruct the variability of riverine and aeolian input, salinity, and productivity in the SE Black Sea region in response to the Northern Hemisphere climate oscillations. During colder and drier stadials, the aeolian input increased relative to the riverine discharge, potentially due to southward shifted and/or stronger westerly winds and due to changes in the vegetation cover. An evaporation exceeding freshwater supply by rainfall and rivers possibly caused higher salinity and a lower lake level. The environmental status during MIS 4 and 2 is very much comparable with the stadial conditions during MIS 3. During warmer and more humid interstadials, lower salinity and presumably positive lake level changes most likely resulted from increased precipitation and river discharge. This likely increased primary productivity through an augmented nutrient supply. Lowest average salinities are suggested for the middle part of MIS 3 in response to enhanced meltwater from the disintegrating Fennoscandian Ice Sheet and/or by generally more humid conditions.

Hydroclimatological influences on recently increased droughts in China's largest freshwater lake

Abstract. Lake droughts are the consequence of climatic, hydrologic and anthropogenic influences. Quantification of droughts and estimation of the contributions from the individual factors are essential for understanding drought features and their causation structure. This is also important for policymakers to make effective adaption decisions, especially under changing climate. This study examines Poyang Lake, China's largest freshwater lake, which has been undergoing drastic hydrological alternation in the past decade. Standardized lake stage is used to identify and quantify the lake droughts, and hydroclimatic contributions are determined with a water budget analysis, in which absolute deficiency is defined in reference to normal hydrologic conditions. Our analyses demonstrate that in the past decade the lake droughts worsened in terms of duration, frequency, intensity and severity. Hydroclimatic contributions to each individual drought varied between droughts, and the overall contribution to the lake droughts in the past decade came from decreased inflow, increased outflow, and reduced precipitation and increased evapotranspiration in the lake region. The decreased inflow resulted mainly from reduced precipitation and less from increased evapotranspiration over the Poyang Lake basin. The increased outflow was attributable to the weakened blocking effects of the Yangtze River, which the Three Gorges Dam (TGD) established upstream. The TGD impoundments were not responsible for the increased number of drought events, but they may have intensified the droughts and changed the frequency of classified droughts. However, the TGD contribution is limited in comparison with hydroclimatic influences. Hence, the recently increased droughts were due to hydroclimatic effects, with a less important contribution from anthropogenic influences.

GIS‐based multiproxy coastline reconstruction of the eastern Gulf of Riga, Baltic Sea, during the Stone Age

We present early to mid‐Holocene palaeocoastline reconstructions for the Tolkuse‐Rannametsa area on the eastern coast of the Gulf of Riga. Radiocarbon‐dated sediment stratigraphies and diatom analyses, supported by ground‐penetrating radar data and GIS‐based modelling, were used in the palaeogeographical reconstructions to strip back younger sediments and landforms from the LiDAR‐derived digital elevation model. The reconstructions show an open coast environment during the Ancylus Lake stage and the formation of a peatland after the lake drainage at about 9000–8600 cal. a BP. The waters of the Litorina Sea flooded the study area between 8200 and 7700 cal. a BP, forming a 25‐km‐long and up to 5.5‐m‐deep lagoon with two connections to the sea. This brackish water lagoon existed in the area for about 4000 years and terminated around 3800–3500 cal. a BP as a result of isostatic uplift and growth of the barrier spit. The reconstructions illustrate the relationships between the lagoonal system and three Mesolithic and Neolithic settlement sites found in the study area. A comparative analysis which besides palaeogeographical and ecological data included a data set with more than 100 Stone Age sites from the eastern Baltic region, was used to propose the most suitable locations for coastal settlements in the Tolkuse‐Rannametsa area. However, some of these areas are presently covered by a peat layer that is several metres thick, which may explain the relative scarcity of the archaeological finds on the shores of the palaeo‐lagoon. The proposed multiproxy approach has the capability to delimit the areas that would have been favourable for prehistoric habitation, but might not be observable in the present‐day topography. In return, this increases the likelihood of locating any well‐preserved preserved settlement sites and artefacts that are buried under the protective sediment layer.

Quantifying the Response Time of a Lake–Groundwater Interacting System to Climatic Perturbation

Response time, describing how quickly a disturbed system would reach a new equilibrium, has been helpful to hydrogeologists in characterizing and understanding the hydrogeological systems. This study examined the complex response times associated with lake–groundwater perturbed by climate. Simulated hydraulic heads and lake stage values derived from a 3-D, MODFLOW-based model were used to calculate the response times for a closed, groundwater-fed lake system. Although obviously coupled, the response times of the lake and groundwater systems were different from one another. Typically, the adjustments in hydraulic heads occurred more rapidly than lake stage. Response times for groundwaters close to the lake were controlled by the lake because of the slow transient response in stage. However, the influence of the lake declined toward the basin boundaries. This behavior occurred because critical parameters controlling the response-time behavior of the groundwater system (e.g., recharge rate) differed from those controlling the response-time behavior of the lake (e.g., bed leakance). An improved understanding of lake–groundwater behaviors have the potential to evaluate how lakes function as systems for recording paleoclimates.

Modelling the Influence of Groundwater Abstractions on the Water Level of Lake Naivasha, Kenya Under Data-Scarce Conditions

This study presents the state-of-the-art understanding of the data-scarce and hydrogeologically complex groundwater system of Lake Naivasha, Kenya, with the particular aim of exploring the influence groundwater abstractions have on Lake Naivasha’s water level. We developed multiple alternative but plausible parameterizations for a MODFLOW groundwater model, based on literature, existing models and available data, while trying not to over-complicate the model. In doing so, we illustrate a possible strategy of going about data-scarce regions in modelling in general. Processes encountered in the calibrated parameterizations show groundwater flows laterally from the escarpments to the valley floor and axially from the lake along the Rift, with a larger portion flowing out southward than northward. Extraction of groundwater interrupts the flow from the northwestern highlands to the lake, leading to a lake stage reduction of 0.7–7.5 cm due to abstractions at our target farm (Flower Business Park) or an implied 7–75 cm due to total groundwater abstractions in the area. Although this study demonstrates our understanding of Naivasha’s groundwater system remains fragile and the current model cannot be embedded in operational water management yet, it (i) reflects the contemporary understanding of the local groundwater system, (ii) illustrates how to go about modelling in data-scarce environments and (iii) provides a means to assess focal areas for future data collection and model improvements.

Non-Pollen Palynomorphs Characteristic for the Dystrophic Stage of Humic Lakes in the Wigry National Park, Ne Poland

Abstract The numerous dystrophic (humic) lakes are a very important feature of Wigry National Park, NE Poland. As the most recent palaeoecological data indicate, at the beginning of its development (in the Late Glacial and Early and Middle Holocene) these water bodies functioned as harmonious lakes, and their transformation into dystrophic lakes and the stabilization of the trophic state took place at the beginning of the Subboreal. Palynological analysis of sediments from two such lakes (Lake Ślepe and Lake Suchar II), with special emphasis on non-pollen palynomorphs (NPPs), was aimed at a detailed biological characterization of dystrophic lakes during their long-lasting existence. The obtained results allowed for the designation of organisms characteristic for dystrophic lakes, of which representatives appeared with the decreasing pH of the water and the formation of Sphagnum peat around lakes. These organisms were divided into four groups: algae, fungi, testate amoebas, and animals. Their representatives appear invarious developmental stages of dystrophic lakes.

Processes that control water chemistry and stable isotopic composition during the refilling of Lake Ngami in semiarid northwest Botswana

Summary Lake Ngami in semiarid Botswana was dry until 2009 when it began filling with water because of regional increases in precipitation and from redirection of water to the lake from distributaries of the Okavango River. We measured the physical, chemical and stable isotopic composition of lake water collected at 25 cm below the surface along a ∼18 km axial transect from the inflow river to the distal end of the lake. Our objective was to determine the processes that control water properties and to establish baseline values for future temporal and spatial comparisons. The major ionic concentrations (e.g., Cl−, Na+, Ca2+) and the stable oxygen (δ18O) and hydrogen (δD) isotope ratios show three distinct regions of increasing concentrations and isotopic enrichment, respectively along the transect. The δ18O vs. δD data plot along the Okavango Delta evaporation line and suggest modification of lake water by evaporation. The proportions of the major ions in the inlet water and in the lake were similar and log Cl− vs. log Na+ suggests an evaporative enrichment of solutes. The segmentation of the major solutes and the δ18O and δD into three regions along the axial transect results from differential evaporation of lake recharge from 2010, 2011 and 2012, and are thus controlled by the residence time of recharge in the lake. Unlike the major ions, the dissolved inorganic carbon (DIC) concentrations and the stable carbon isotopic ratios (δ13C) of DIC increase along the axial transect to about midway in the lake, and then reach steady state. The δ13C of dissolved organic matter in the inlet river and lake averaged ∼−25.7 ± 0.3‰ while that for particulate organic carbon decreased from ∼−24‰ in the inlet river to ∼−28‰ in the lake from water column productivity. Carbon cycling in Lake Ngami is controlled by evaporation which increase DIC concentrations and equilibration between carbon in DIC and atmospheric CO2(g). The results show the importance of evaporation and residence time in controlling the solute chemistry and the dominance of atmospheric CO2(g) in controlling carbon cycling during the filling stages of lakes in arid environments.

Needle in a Haystack: Predicting the Occurrence of Wetland Invertebrates on the Basis of Simple Geographical Data. A Case Study on Two Threatened Micro-Mollusc Species (Gastropoda: Vertiginidae) from Poland

The aim of this study was to evaluate whether simple geographical data can be used to predict the probability of the presence of two threatened snail species: Vertigo angustior and V. moulinsiana, occurring within wetland areas across their central European range. Our research was based on data from 226 localities across Poland fitting with the species requirements according to the current literature. We used Canonical Variance Analysis with variance partitioning and tree classifications to model relationships between the species presence/absence and rough geographic features describing each locality (landscape and geomorphological types and hydrography). Our results have shown that the localities of the studied species are related to particular types of landform and landscape and are not distributed uniformly. Both species occur predominantly in young postglacial lowland landscapes and are usually associated with particular succession stages of lakes, with V. moulinsiana occurring in earlier phases of habitat evolution. Results from modelling show that cost- and time effectiveness of surveying for these species could be substantially increased by avoiding particular location types. The prediction models presented will be a useful tool for planning future surveys of the vertiginids and in studies on their ecology and distribution.

Hydrographs of a Martian flood from the breach of Galilaei Crater

Spectacular floods were spawned on Mars when large craters filled to overtopping and catastrophically breached. The wealth of data now available permits quantitative analysis of these ancient floods. Galilaei Crater is examined here, along with the likely sources of its water and the processes that formed Tana Vallis, its 1-km-deep outflow channel. Laser altimetry data, stereo-photogrammetry, and scaled images are used to reconstruct the lake volume and the geometry of the preserved breach. It is theorized that surface flows from Hydaspis Chaos eroded the rim and floor of Galilaei Crater and partly filled the basin, leading to degradation of the underlying cryosphere. Groundwater released from a confined aquifer then slowly filled Galilaei Crater until the enclosed lake overtopped its rim. The resulting flood breached the crater wall, rapidly drained the lake, and eroded Tana Vallis. The drainable lake volume was ≥1.110×1013m3, based on laser altimetry data from Mars Global Surveyor. This volume was 90% of the volume in Lake Superior in the Great Lakes. Using the reconstructed breach and channel geometry, methods used to analyze terrestrial dam breaches were applied to produce hydrographs of lake stage and discharge. Peak flood discharge in Tana Vallis likely ranged from 1.5 to 4.7×107m3s−1. Mean channel incision rates are estimated at 0.333, 0.133, and 0.0667mmin−1 for scenarios in which Tana Vallis formed in 2, 5, and 10days. For the 5-day breach erosion scenario, stream power per unit streambed area at the time of peak discharge was estimated at >3.5×105Wm−2. The volume of material eroded to form the vallis was only ~3% of the lake volume that drained in 5days. Open-channel calculations were performed to compare with the dam breach hydrographs for Tana Vallis. The channel as seen today never flowed bank full or even at three-fourths its maximum depth because the implied flows would have exceeded peak discharges from the crater breach. I also evaluate an alternative model (catastrophic ice lake collapse) for the morphology and breach of Aram Chaos, a large crater near Galilaei Crater. That model has fundamental difficulties because of improbable assumptions and inadequate consideration of the knowledge base of terrestrial basalt hydrology. The model of ice lake collapse fails to explain the breach and outflow of crater lakes like those that existed in Aram Chaos and Galilaei Crater. The present analysis supports a simpler model of groundwater inflow that fills a crater to overtopping. This model harmonizes with the low elevations of Aram Chaos and Galilaei Crater and is more consistent with extensive evidence of fluid breakouts in this region and with theoretical and terrestrial knowledge.

鄱阳湖自然保护区湿地植被生物量空间分布规律

PDF HTML阅读 XML下载 导出引用 引用提醒 鄱阳湖自然保护区湿地植被生物量空间分布规律 DOI: 10.5846/stxb201307301983 作者: 作者单位: 中国科学院南京地理与湖泊研究所;湖泊与环境国家重点实验室,中国科学院南京地理与湖泊研究所;湖泊与环境国家重点实验室,中国科学院南京地理与湖泊研究所;湖泊与环境国家重点实验室,中国科学院南京地理与湖泊研究所;湖泊与环境国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院南京地理与湖泊研究所"一三五"战略发展规划项目(NIGLAS2012135001);国家自然科学基金项目(41401506) Spatial distribution of wetland vegetation biomass in the Poyang Lake National Nature Reserve, China Author: Affiliation: Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:探明区域湿地植被生物量的空间分布规律及其变化趋势,对于更好地保护候鸟生境、制定合理的湿地保护政策具有重要的意义。以鄱阳湖国家级自然保护区为研究对象,基于2000-2011年研究区MODIS植被指数产品和同期的植被生物量调查资料,建立了湿地植被生物量的遥感估算模型。在此基础上利用GIS空间分析方法,系统分析了保护区近10年来湿地植被生物量的空间分布规律及其季节变化特征。研究结果表明:(1)MODIS增强型植被指数的乘幂模型可以较好地模拟研究区湿地植被生物量的鲜重,拟合模型总体精度达到91.7%。(2)多年平均生物量呈现"岛屿型"空间分布模式:各子湖泊及洼地中心处,表现为水生植被群落为主的低生物量区(<285 g/m2);湖心水体外围14-15m的高程区域,分布着以苔草群落为主的中生物量区(285-830 g/m2);高程位于16-18m的河口三角洲及天然堤坝区域,表现为以蒿、荻和芦苇群落为主的高生物量区。(3)保护区植被群落分布具有特定的季相变化特征,高、中、低生物量区在不同的月份呈现出不同的空间生消和演进规律,鄱阳湖水位的周期性涨落是影响其变化的一个重要扰动因子。 Abstract:Vegetation is one of the important components of wetland, and vegetation biomass is a key indicator of the health status of the wetland ecosystem. Comphrehensive understanding of spatial distribution of vegetation biomass and its temporal variation is a pre-requirement for effective protection of bird habitats and scientific planning of wetland conservation. In this regard, it has been one of central topics in hydro-ecology, wetland ecology and vegetation ecology in past decades. In recent years, vegetation change has become one of major concerns with frequently occurred extreme droughts in the Poyang Lake National Nature Reserve (PLNRR) of China. To investigate the spaital changes of vegetation, MODIS (Moderate resolution Imaging Spectrordiometer) vegetation index products (MOD13Q1) were used to construct a model for retrieval of vegetation biomass with the coincident field data in PLNRR for the period from 2000-2011. GIS spatial analysis techniques were used to analyze the spatial patterns and seasonal variations of wetland vegetation biomass. Our findings can be summerizes as follows: (1) the power function best describe the relationship between MODIS-EVI (Enhanced Vegetation Index) and green yield of vegetaiton in PLNRR, with an overall accuracy of 91.7%. (2) Multi-year average of vegetation biomass displayed an island-like spatial pattern and can be classified into three zones. Vegetation biomass was lower than 285g/m2, dominant with aquatic vegetation communities, for the bottom areas near the center of lakes. It ranged from 285 to 830 g/m2, dominant with sedge communities, for the periphery of the lakes with an elevation of 14-15 m. The biomass was higher than 830 g/m2 dominant with wormwood and reed communities, for surrounding delta or dyke areas with an elevation of 16-18 m. (3) Vegetation biomass showed different seasonal variations in each zone, which was jointly affected by multiple factors. Lake stage is the most important factor in regulating the spatial development of the vegetation biomass. Overall, the results should be not only helpful for understanding the change in biodiversity and ecosystem stability, but also provide a scientific basis for effective management and protection of wetland resources in the PLNRR. 参考文献 相似文献 引证文献

Results of paleoecological studies in the loess region of Szeged-Öthalom (SE Hungary)

New results of sedimentological, Magnetic Susceptibility, geochemical, radiocarbon and malacological analysis from a typical and an infusion loess section are presented from SE Hungary. The geologic and geomorphologic value of the area is that aeolian (typical) loess accumulated on sand dunes that formed during MIS3, while in the interdune depressions on the top of lacustrine deposit series, infusion loess developed. As the two types of loess interfinger, it is the first demonstration that the two types of loess formed during the same time period (isochron) in different environments (heterotype). At the end of MIS3 and during MIS 2 between 33,000–13,000 cal BP, a temperate steppe-forest steppe environment characterized the loess surface of the SE Great Hungarian Plain. During the first interstadial phase of MIS2 a Pinus sylvestris charcoal rich paleosol layer developed on the loess covered surface of a wind-blown sand hummock, while in the interdune depressions a pond phase developed. After the formation of the paleosol layer on the surface of the loess covered wind-blown sand hummock during the Heinrich 2 event, Vertigo modesta-Vallonia tenuilabris indicate a cold steppe-forest steppe environment and a deeper and colder lake phase in the interdune depressions. After that, a short microinterstadial phase developed and a Pupilla triplicata-Chondrula tridens dominated temperate steppe-forest steppe environment evolved on the terrestrial surface between 23,000–21,000 cal BP. After 21,000 cal BP, in the Last Glacial Maximum (LGM) the environment completely changed. The average dust accumulation accelerated and coarse silt (0.02–0.06 mm) became dominant. As a result, the lake stage transformed to a marshy environment, while on the land area shade-loving, including closed forest environment-preferring mollusca taxa appeared, such as Vestia turgida, Vitrina pellucida and Mastus venerabilis. Based on the mollusca fauna composition, humidity increased during the cooling of the LGM horizon, forestation started and a boreal forest-steppe evolved at the study site. During the post LGM, the interdune depressions filled and aeolian loess layers developed. Formation of the infusion loess occurred between 24,000–17,000 cal BP. Loess formation lasted until the beginning of the Late Glacial Maximum (Last Permafrost Maximum) and ended in a forest steppe environment with boreal, Central European, holarctic, palearctic and continental mollusc fauna elements.

Refining the pattern and style of Cordilleran Ice Sheet retreat: palaeogeography, evolution and implications of lateglacial ice‐dammed lake systems on the southern Fraser Plateau, British Columbia, Canada

Decay of the last Cordilleran Ice Sheet (CIS) near its geographical centre has been conceptualized as being dominated by passive downwasting (stagnation), in part because of the lack of large recessional moraines. Yet, multiple lines of evidence, including reconstructions of glacio‐isostatic rebound from palaeoglacial lake shoreline deformation suggest a sloping ice surface and a more systematic pattern of ice‐margin retreat. Here we reconstructed ice‐marginal lake evolution across the subdued topography of the southern Fraser Plateau in order to elucidate the pattern and style of lateglacial CIS decay. Lake stage extent was reconstructed using primary and secondary palaeo‐water‐plane indicators: deltas, spillways, ice‐marginal channels, subaqueous fans and lake‐bottom sediments identified from aerial photograph and digital elevation model interpretation combined with field observations of geomorphology and sedimentology, and ground‐penetrating radar surveys. Ice‐contact indicators, such as ice‐marginal channels, and grounding‐line moraines were used to refine and constrain ice‐margin positions. The results show that ice‐dammed lakes were extensive (average 27 km2; max. 116 km2) and relatively shallow (average 18 m). Within basins successive lake stages appear to have evolved by expansion, decanting or drainage (glacial lake outburst flood, outburst flood or lake maintenance) from southeast to northwest, implicating a systematic northwestward retreating ice margin (rather than chaotic stagnation) back toward the Coast Mountains, similar in style and pattern to that proposed for the Fennoscandian Ice Sheet. This pattern is confirmed by cross‐cutting drainage networks between lake basins and is in agreement with numerical models of North American ice‐sheet retreat and recent hypotheses on lateglacial CIS reorganization during decay. Reconstructed lake systems are dynamic and transitory and probably had significant effects on the dynamics of ice‐marginal retreat, the importance of which is currently being recognized in the modern context of the Greenland Ice Sheet, where &gt;35% of meltwater streams from land‐terminating portions of the ice sheet end in ice‐contact lakes.

Stratigraphic and chronologic analysis of the Warren Beach, northwest Ohio, USA

The current understanding of Lake Warren as a proglacial lake stage in the Lake Erie basin during the last deglaciation is based on limited stratigraphic information from strandlines and a wide range of radiocarbon ages. The purpose of this study is to use ground-penetrating radar (GPR) and optically stimulated luminescence (OSL) dating to reconstruct the stratigraphy, depositional environment, and age of the Oak Openings Ridge (OOR), a former strandline of Lake Warren in northwestern Ohio. Both sedimentary exposures and &gt;4 km of GPR data were used to demonstrate that the OOR is a barrier spit that migrated from the northeast to the southwest, and is currently blanketed by an aeolian sheet. Sediments observed in exposures show a shallowing-up sequence attributed to the retreat of proglacial lakes from the area. Corresponding GPR data reveal three distinct GPR facies. The lowermost radar facies 1 (RF1) is a sandy barrier spit platform of a lower beach face prograding across finer-grained lacustrine mud or till. Eroded into RF1 is an upper beach face of RF2, the top of which is visible in cutbank and borrow pit exposures. Overlying the RF2 beach face is uppermost unit RF3, consisting of low-relief, aeolian parabolic dunes and sand sheets. Four OSL ages from a climbing ripple sequence in RF2 average 14.2 ± 0.5 ka, consistent with an earlier published OSL age of 14.1 ± 1.0 ka (Campbell et al. in 2011) from the same unit. From earlier work, the overlying aeolian dunes (RF3) record westerly winds after formation of the OOR, and OSL dating records episodic activity from the Younger Dryas chronozone to ∼8000 years ago. The results suggest that the OOR formed in two phases. First, a barrier spit prograded into Lake Warren from the northeast. Second, parabolic sand dunes and a sand sheet formed episodically for ∼5000 years thereafter. The sediment source for the sand body is from southeast Michigan, but it is of uncertain origin.

Hydrologic modelling for Lake Basaka: development and application of a conceptual water budget model.

Quantification of fluxes of water into and out of terminal lakes like Basaka has fundamental challenges. This is due to the fact that accurate measurement and quantification of most of the parameters of a lake's hydrologic cycle are difficult. Furthermore, quantitative understanding of the hydrologic systems and hence, the data-intensive modelling is difficult in developing countries like Ethiopia due to limitation of sufficient recorded data. Therefore, formulation of a conceptual water balance model is extremely important as it presents a convenient analytical tool with simplified assumptions to simulate the magnitude of unknown fluxes. In the current study, a conceptual lake water balance model was systematically formulated, solved, calibrated, and validated successfully. Then, the surface water and groundwater interaction was quantified, and a mathematical relationship developed. The overall agreement between the observed and simulated lake stage at monthly time step was confirmed based on the standard performance parameters (R(2), MAE, RMSE, E(f)). The result showed that hydrological water balance of the lake is dominated by the groundwater (GW) component. The net GW flux in recent period (post-2000s) accounts about 56% of the total water inflow. Hence, GW plays a leading role in the hydrodynamics and existence of Lake Basaka and is mostly responsible for the expansion of the lake. Thus, identification of the potential sources/causes for the GW flux plays a leading role in order to limit the further expansion of the lake. Measurement of GW movement and exchange in the area is a high priority for future research.