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1.
Dag Hongve 《Journal of Paleolimnology》2003,30(1):75-93
Cores of recent sediments were sampled along a depth gradient in a 23 m deep kettle lake with stagnant deep waters containing exceptionally high concentrations of dissolved iron and manganese. Sediment cores were taken on two occasions, in 1978 and 1997, before and after an incidence of full circulation. The aims of this study are to see how oxic and anoxic conditions in the water column influence stratigraphy and sediment focusing and, to compare cores from 1979 and 1998 to see how measured element fluxes and external events are reflected in the chemical stratigraphy. Element analyses show characteristic stratigraphic patterns that depend on the ability to undergo redox transformations, sorptive properties and chemical equilibria in the anoxic deep waters and porewaters. In sediments from the oxic part of the lake Al, Cr, Co, Ni, Zn Cu, Cd, and Pb were well correlated. Positive correlations are seen between elements associated with primary production and sulphur. In the anoxic part of the lake most metals were positively correlated with carbonate. Phosphorus correlated positively with iron in sediments from oxic waters and negatively with manganese and iron deep-water sediments. Porewater analyses indicate that recycling from the deep-water sediments was negligible. The stratigraphy of lead agrees with the historic variation in atmospheric input and is used as a chronological marker. Assessed deposition rates agree with measurements in sediment traps. Most elements more than double their rates of deposition towards the deepest point of the lake, while sulphur, manganese and carbonate had maxima around the depth of the redoxcline in the water. Variations in the external loading and variable redox conditions in the deep waters explain variations in the chemical composition of recent sediments. 相似文献
2.
A. Vuillemin D. Ariztegui A. S. De Coninck A. Lücke C. Mayr C. J. Schubert 《Journal of Paleolimnology》2013,50(3):275-291
Authigenic minerals can form in the water column and sediments of lakes, either abiotically or mediated by biological activity. Such minerals have been used as paleosalinity and paleoproductivity indicators and reflect trophic state and early diagenetic conditions. They are also considered potential indicators of past and perhaps ongoing microbial activity within sediments. Authigenic concretions, including vivianite, were described in late glacial sediments of Laguna Potrok Aike, a maar lake in southernmost Argentina. Occurrence of iron phosphate implies specific phosphorus sorption behavior and a reducing environment, with methane present. Because organic matter content in these sediments was generally low during glacial times, there must have been alternative sources of phosphorus and biogenic methane. Identifying these sources can help define past trophic state of the lake and diagenetic processes in the sediments. We used scanning electron microscopy, phosphorus speciation in bulk sediment, pore water analyses, in situ ATP measurements, microbial cell counts, and measurements of methane content and its carbon isotope composition (δ13CCH4) to identify components of and processes in the sediment. The multiple approaches indicated that volcanic materials in the catchment are important suppliers of iron, sulfur and phosphorus. These elements influence primary productivity and play a role in microbial metabolism during early diagenesis. Authigenic processes led to the formation of pyrite framboids and revealed sulfate reduction. Anaerobic oxidation of methane and shifts in pore water ion concentration indicated microbial influence with depth. This study documents the presence of active microbes within the sediments and their relationship to changing environmental conditions. It also illustrates the substantial role played by microbes in the formation of Laguna Potrok Aike concretions. Thus, authigenic minerals can be used as biosignatures in these late Pleistocene maar sediments. 相似文献
3.
Use of paleolimnology to document the effect of lake shoreland development on water quality 总被引：5，自引：0，他引：5
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
4.
Joyanto Routh Philip A. Meyers Tomas Hjorth Mark Baskaran Rolf Hallberg 《Journal of Paleolimnology》2007,37(4):529-545
Geochemical properties of sediments deposited in Lake Middle Marviken over the last 185 years record the impacts of a succession
of environmental changes that have occurred in the watershed. Clear-cutting of forests for wood and charcoal and extensive
water harnessing to support the local iron mills from 1897 to 1957 is recorded by low C/N ratios, high black carbon, and low
TOC and Ntotal accumulation rates. Larger δ13C and δ15N values in sediments deposited during this period imply higher productivity. Fluctuations in Ntotal and Ptotal accumulation rates show that the lake chemistry has varied between P or N-depleted systems that affected the δ15N values. Organic matter in the sediments is predominantly immature terrestrial material. Furthermore, hydrocarbon CPI, TAR,
and Paq values conform with the observed geochemical trends, variations in organic matter sources, and changes in the watershed.
Accumulation rates of Cd, Pb, Zn, and S remained mostly unchanged throughout the period of mining, but an increase from 1957
to 1980 is most likely associated with air-borne industrial and fossil fuel emissions from regional urbanization. In situ
microbial processes, such as iron and manganese reduction, also appear to be important in carbon cycling and in affecting
the sediment and water chemistry of this lake. 相似文献
5.
异化铁还原是湿地土壤和沉积物中重要的生物地球化学过程,也是有机质矿化的主要途径之一。湿地干湿交替等过程会使土壤的氧化还原状态发生改变,影响铁元素及与其相关的元素的迁移和转化。总结了湿地土壤和沉积物中异化铁还原过程及其与碳、磷、硫等元素在生物地球化学循环关键过程中的相互作用,阐述了湿地土壤和沉积物中异化铁还原过程对微量金属元素迁移和转化的影响,分析了影响湿地土壤和沉积物异化铁还原过程的主要环境因子。未来相关研究应集中于湿地土壤和沉积物中异化铁还原微生物分析和纯化、不同有机质形式对异化铁还原过程的影响以及异化铁还原对土壤有机质矿化的贡献。 相似文献
6.
Richard L. Reynolds Jessica S. Mordecai Joseph G. Rosenbaum Michael E. Ketterer Megan K. Walsh Katrina A. Moser 《Journal of Paleolimnology》2010,44(1):161-175
Sediments in Marshall and Hidden Lakes in the Uinta Mountains of northeastern Utah contain records of atmospheric mineral-dust
deposition as revealed by differences in mineralogy and geochemistry of lake sediments relative to Precambrian clastic rocks
in the watersheds. In cores spanning more than a thousand years, the largest changes in composition occurred within the past
approximately 140 years. Many elements associated with ore deposits (Ag, As, Bi, Cd, Cu, In, Mo, Pb, S, Sb, Sn, and Te) increase
in the lake sediments above depths that correspond to about AD 1870. Sources of these metals from mining districts to the
west of the Uinta Mountains are suggested by (1) the absence of mining and smelting of these metals in the Uinta Mountains,
and (2) lower concentrations of most of these elements in post-settlement sediments of Hidden Lake than in those of Marshall
Lake, which is closer to areas of mining and the densely urbanized part of north-central Utah that is termed the Wasatch Front,
and (3) correspondence of Pb isotopic compositions in the sediments with isotopic composition of ores likely to have been
smelted in the Wasatch Front. A major source of Cu in lake sediments may have been the Bingham Canyon open-pit mine 110 km
west of Marshall Lake. Numerous other sources of metals beyond the Wasatch Front are likely, on the basis of the widespread
increases of industrial activities in western United States since about AD 1900. In sediment deposited since ca. AD 1945,
as estimated using 239+240Pu activities, increases in concentrations of Mn, Fe, S, and some other redox-sensitive metals may result partly from diagenesis
related to changes in redox. However, our results indicate that these elemental increases are also related to atmospheric
inputs on the basis of their large increases that are nearly coincident with abrupt increases in silt-sized, titanium-bearing
detrital magnetite. Such magnetite is interpreted as a component of atmospheric dust, because it is absent in catchment bedrock.
Enrichment of P in sediments deposited after ca. AD 1950 appears to be caused largely by atmospheric inputs, perhaps from
agricultural fertilizer along with magnetite-bearing soil. 相似文献
7.
8.
对托素湖沉积岩芯采用高分辨率XRF扫描分析法进行地球化学元素测试,运用多元统计分析法中的相关性分析、聚类分析及因子分析判别出不同沉积组分,揭示了托素湖沉积物中Si、Al、K、Ti、Ca、Sr、S、Cl、Br等元素的地球化学特征及其所指示的环境意义。同属强烈迁移型元素Ca、Sr在沉积物中主要受托素湖中内生碳酸盐的影响;而外源碎屑元素Si、Al、K、Ti主要受托素湖流域侵蚀的控制,其变化受托素湖流域降水量的控制,一定程度上指示了流域的干湿波动和极端气候事件发生的幅度与频率。 相似文献
9.
Veronika Gälman Johan Rydberg Andrei Shchukarev Staffan Sjöberg Antonio Martínez-Cortizas Richard Bindler Ingemar Renberg 《Journal of Paleolimnology》2009,42(1):141-153
Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H+, e?, Fe3+, SO4 2?, H2CO3 and included the formation of solid phases such as Fe(OH)3 (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO3. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)3/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves. 相似文献
10.
Evidence for an eolian origin for the silt-enriched soil mantles on the glaciated uplands of eastern Upper Michigan, USA 总被引：1，自引：0，他引：1
We provide textural, geochemical, and mineralogical data on a thin, silty deposit that unconformably mantles glaciated uplands in the eastern Upper Peninsula of Michigan. Previous research on this deposit, which we hypothesize to be loess, is nonexistent. The uplands were islands or narrow peninsulas within one or more glacial lakes. We compare the distribution, likely source and nature of the 20–60 cm thick silty mantle by using the loess formation model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223–236], which focuses on the generation of eolian silt by saltating sand across upwind, barren surfaces. Parabolic dunes, with arms open to the NW, are common on former lake floors upwind of the silt-mantled uplands, attesting to the strength and direction of paleowinds. The abrupt termination of the dunes at the footslopes of the uplands, associated with silt deposition on upland soil surfaces in downwind locations, are both consistent with the model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223−236]. Sediments on former lake floors contain abundant strata of fine/medium sand and silt, and thus are likely sources for the silt and dune sand. The cap, dune and lake sediments are similar along many different geochemical axes, whereas the substrate sediment, i.e., the drift below the cap, is unique. Cap sediments, normally containing roughly 30% silt, are enriched in quartz and depleted in Ti and Zr, relative to dune sediment. The dune sediment, a more residual eolian deposit, is enriched in Ti and Zr, relative to the cap, probably due to its greater abundance of heavy minerals. Therefore, we conclude that the silty cap is loess that was deflated from abandoned lake floors after nearby glacial lakes drained, probably contemporaneously with dune migration across the former lake floors. 相似文献
11.
Meromixis has several powerful effects on lakes, yet there is no single definitive sediment indicator of meromixis. In this study three sediment indicators of meromixis were compared in Brownie Lake, Minneapolis, Minnesota, a small eutrophic lake that became meromictic around 1925. The results show that in Brownie the onset of laminations and changes in the iron to manganese ratio most likely occurred before the development of permanently anoxic bottom water and that changes in the diatom assemblage occurred later, most likely only when meromixis was well developed.This is the 11th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers. 相似文献
12.
柴达木盆地那棱格勒河流域是我国目前最大的盐湖型锂矿区和工业设施最为完备的卤水锂工业基地,长期以来关于其尾闾盐湖区锂的物源问题备受关注。尽管目前的众多研究已经对流域内地表水体及尾闾区盐湖中锂的物源有了较为一致的看法,但盆地周缘围岩风化过程在其中起到的作用仍缺乏系统性认识。基于部分保守性微量元素在物源示踪研究中的重要作用,本文通过对流域内河流表层沉积物中的REEY、Li、Sc、Co、Nb、Ta、Th等微量元素开展其地球化学行为方面的分析,讨论了沉积物的物源属性特征及其中锂的来源特征,为深入认识盐湖区游离态锂资源的物源提供了新的证据。结果表明,那棱格勒河流域与毗邻的东、西对比区河流沉积物有着相似的化学风化背景和基岩类型,源岩具有显著的长英质岩和基性岩的二元混合特征,且基性源岩所占比重更大;而沉积物中的锂除尾闾盐湖区明显受到富锂孔隙水体夹带的影响外,其它地区锂的来源特征与沉积物的物源特征相同,表明地表迁移过程对介质中锂的通量影响较弱,沉积物中的锂更多的是以赋存在相关矿物结构中的形式存在;研究区来自源岩风化作用提供的游离态锂的量较为有限,尾闾盐湖中的锂资源主要以昆仑山深大断裂带涌出的热泉水的长年补给为主。 相似文献
13.
沉积岩中的微量元素对沉积环境水介质的变化较为敏感,是研究沉积物沉积时古气候、古环境的有效手段。选取了对沉积环境介质较为敏感的锶(Sr)、钡(Ba)、铜(Cu)、铀(U)、钒(V)、镍(Ni)、钍(Th)等元素作为判别指标,对柴达木盆地西部上新统油砂山组、狮子沟组和更新统七个泉组三套富锶岩层的古气候和古沉积环境特征进行了研究。结果表明,柴达木盆地西部从油砂山组到七个泉组沉积时总体上为干旱的气候环境;湖盆水体的盐度较高,表现为咸水环境,且从油砂山组到七个泉组随着地层变新,盐度有逐渐增大的趋势;油砂山组、狮子沟组和七个泉组沉积时湖盆水体均表现为中等分层、湖水循环较为顺畅的氧化环境。 相似文献
14.
Jean-Luc Loizeau Daniel Span Véronique Coppee Janusz Dominik 《Journal of Paleolimnology》2001,25(2):205-214
Lake Annecy sediments have been studied to provide an insight into the evolution of the lake trophic state in response to climate changes during the Holocene. Determination of the concentration of carbonate, Fe, Mn, and different forms of P in conjunction with total sediment fluxes derived from 14C ages allows an estimation of yearly fluxes of these sediment components. High fluxes of endogenic carbonate occur during the early to middle Holocene. Non apatitic inorganic phosphorus flux is variable but shows some higher-than-present values during this period. These observations are interpreted as being a result of enhanced productivity by favourable conditions for phytoplankton development. In addition, the low Mn/Fe ratio of the redox-sensitive forms of these elements recorded during this period suggests low oxygen concentrations in the bottom waters. Therefore it appears that the lake may have undergone oxygen depletion in the bottom water during the warmer-than-present periods, due to increased productivity and subsequent oxygen consumption from the decay of organic matter. With future climate changes, this suggests that lake water quality may likely degrade under global warming. 相似文献
15.
哈拉湖岩芯XRF扫描元素统计分析及其环境意义 总被引：3，自引：0，他引：3
青藏高原东北缘高山湖泊哈拉湖是位于季风与西风影响的交汇带的封闭深水湖泊,是区域环境和气候变化的良好记录载体。目前对该湖的研究还较少,缺乏对沉积物中元素环境意义的系统认识。通过高分辨率XRF岩芯扫描,用相关、聚类和因子分析的方法对哈拉湖沉积岩芯地球化学元素进行分析。结果显示Ti、K、Si、Al、Fe、Mn等元素变化一致,相关性高,归为同一类,即径流输入的陆源碎屑组分,反映了流域水文状况如径流量的变化。Sr、Zr元素相关性高,为赋存在粗颗粒沉积物中的元素,根据哈拉湖实际,应为冬季湖泊冰面风力搬运,反映了湖区冬季风力强度的变化。Ca元素既与径流输入元素总体变化一致,也与Sr、Zr元素显著相关,且在第一和第二主成分(径流和风力)上的载荷相当,表明哈拉湖沉积物中的碳酸盐既有粗颗粒的外源碎屑,也有湖泊自生的组分,这在利用碳酸盐进行地球化学研究时应重视,注意去除外源碎屑碳酸盐的影响。可溶元素S和Cl可能反映了入湖水量与蒸发对比情况,与湖泊盐度有关。 相似文献
16.
20 0 0年 1月 1 9日至 2 7日在 70°3 0′E- 75°3 0′E,6 2°S以南的南极普里兹湾近岸陆架区的陆隆向深海区设三条纵断面进行浮游生物现存量、真光层深度和光合作用速率的现场观测。并在冰间湖站 - 1 2进行连续昼夜观测。结果表明 ,观测海区叶绿素 a浓度高值位于近岸海湾、冰间湖和测区中部的陆坡区 ;陆坡中部站 - 6和 - 8,0 - 5 0 m的浅水层为叶绿素 a高值区 (2 .1 6- 5 .0 8μg/dm3 )。各测站平均叶绿素 a浓度 2 5 m次表层 (1 .49± 1 .6 1 μg/dm3 )高于表层 (1 .1 4±1 .1 9μg/dm3 ) ,5 0 m以下更深层的浓度随深度的增加而降低 ,2 0 0 m层叶绿素 a浓度仅 0 .0 3±0 .0 2μg/dm3 。昼夜观测结果表明表层叶绿素 a浓度在南极夏季的午后出现最大值 ,晨间出现最小值 ;2 5 m以浅水层的叶绿素 a浓度明显高于深层水 ,与封冰消融冰藻的释放有关。测区真光层潜在初级生产力为 0 .76 - 1 2 .5 9mg C/(m3· h) ,平均值为 4.0 1± 4.0 7mg C/(m3· h) ;海湾和陆架区现场生产力均超过 1 .5 g C/(m2 · d) ,陆坡、深海区约 0 .5 g C/(m2 · d)。高生产力位于高生物量的近岸海湾、陆架冰间湖区。光合作用同化数在 0 .88- 3 .1 0 mg C/(mg Chla· h)。表层叶绿素a浓度与海水中溶解氧浓度呈紧密相关 (Y=0 .0 5 9X 相似文献
17.
民勤盆地位于石羊河下游,现今大面积地区已被风沙覆盖.前人的研究报道了在民勤盆地的东部曾经发育过一个面积巨大的"腾格里古大湖",然而尚不明确民勤盆地是否也曾被湖水覆盖.为此,本文收集整理了民勤盆地中8个水文地质钻孔的地层资料,利用GIS技术重现了研究区地表以下50 m深度内的湖相地层的空间分布特征.分析发现,在盆地的不同地区普遍发育了2~3层深湖亚相地层,部分地区甚至多达4层,各湖相层厚度介于0.5~32 m.区域地层对比结果显示,在某个时段研究区大范围地区普遍发育了深水湖泊,而其他时段则在不同地区零星发育了小湖泊.结合研究区已有的测年资料,本文认为在晚第四纪某个时段(倒数第二层深湖亚相发育阶段),整个研究区内曾经存在一个规模较大的连通湖泊;但民勤盆地晚第四纪不同阶段深湖亚相地层差异明显的空间分布特征,可能反映了湖盆沉积中心自东向西、再向北东的迁移过程. 相似文献
18.
Harris Lake, a small, groundwater fed lake in the Cypress Hills area of Saskatchewan, is one of the few lacustrine basins in the Great Plains that contains a complete, uninterrupted record of Holocene sedimentation. The lithostratigraphy and variation in the mineralogical composition of the sediments in this basin provide insight into the paleolimnology and paleohydrology of the lake and surrounding watershed. Although there is no evidence that the basin was dry for extended periods during the Holocene, the lake did experience numerous short-lived episodes of high salinity, as well as significant changes in solute composition during the early to mid-Holocene. An abrupt change, from a lake dominated by detrital sediments to one characterized almost entirely by endogenic deposition, occurred about 4000 years ago in response to the combined influence of forestation of the watershed and diversion of major fluvial and detrital influx by landsliding. These adjustments to the Harris Lake drainage basin were likely the result of the onset of cooler and wetter climatic conditions after 4500 B.P. During the late Holocene, slope failure continued to sporadically provide fresh clastic material to the otherwise endogenic-sediment dominated lake. 相似文献
19.
作者首次在南极洲万达盐湖底部现代沉积物中发现了自生的黄铁矿颗粒。该发现对解释万达湖还原层湖水中铁离子的垂直迁移具有重要地球化学意义。基于1.目前万达湖还原层湖水的FeS_2活度积(IAP)大于它的热动力溶度积(Ksp)2.该湖还原层湖水的pH—pE数据组落在黄铁矿的pH—pE相图中的黄铁矿相区。相图预测到现在万达湖还原层湖水有析出自生黄铁矿的可能性,而且进一步被X射线衍射分析及电镜扫描等资料证实,湖底沉积物中存在黄铁矿矿物。这样,就有力地解释了还原层湖水中铁离子浓度降低的原因—由于黄铁矿颗粒的形成而迁出了水中铁离子。 相似文献
20.
Cladocera as indicators of trophic state in Irish lakes 总被引：1，自引：0，他引：1
We examined the impact of lake trophic state on the taxonomic and functional structure of cladoceran communities and the role
of nutrient loading in structuring both cladoceran and diatom communities. Surface sediment assemblages from 33 Irish lakes
were analysed along a gradient of total phosphorus concentration (TP; 4.0–142.3 μg l−1), using a variety of statistical approaches including ordination, calibration and variance partitioning. Ordination showed
that the taxonomic structure of the cladoceran community displayed the strongest response to changes in lake trophic state,
among 17 measured environmental variables. Trophic state variables chlorophyll-a and TP explained about 20% of the variance in both cladoceran and diatom assemblages from a set of 31 lakes. Procrustes analysis
also showed significant concordance in the structure of cladoceran and diatom communities (P < 0.001). Thus, lake trophic state affects the taxonomic structure of both primary and secondary producers in our study lakes.
We also found a significant decrease in relative abundance of taxa associated with both macrophytes and sediments, or sediments
only, along the TP gradient (r = −0.49, P = 0.006, n = 30), as well as an increase in the proportion of the planktonic group (r = 0.43, P = 0.017, n = 30). This suggests that cladoceran community structure may also be shaped by lake trophic state indirectly, by affecting
habitat properties. We found no relationship between lake trophic state and the relative abundance of each of three cladoceran
groups that display different body size. We compared community structure between bottom and top sediment samples in cores
from six Irish lakes. Results revealed similar trajectories of nutrient enrichment over time, as well as a strong shift in
cladoceran functional structure in most systems. This study confirms that Cladocera remains in lake sediments are reliable
indicators of lake trophic state. This study also highlights the fact that taxonomic and functional structure should both
be considered to account for the multiple factors that shape cladoceran communities. 相似文献