A paleolimnological study of eutrophied Lake Arendsee (Germany)   总被引：1，自引：0，他引：1  

D. L. Findlay  H. J. Kling  H. Rönicke  W. J. Findlay 《Journal of Paleolimnology》1998,19(1):41-54

To study the algal microfossil assemblages of eutrophic Lake Arendsee (Germany) prior to the beginning of a restoration project, a 47-cm long freeze core, dating back to ca 1800, was taken from the deepest area of the lake. Based on the CRS modeled ²¹⁰Pb and ¹³⁷Cs profiles from the core, 1948 is around 15 cm and the sedimentation rate has increased from 21.2 mg cm^-2 yr^-1 in 1900 to 56.6 mg cm^-2 yr^-1 in 1986. The sediments were dominated by three centric diatoms. Stephanodiscus binatus, a species associated with eutrophic environments, dominated the upper 19 cm of the core. Cyclotella rossii, a species commonly found in less productive freshwater systems, was found to dominate the lower portion of the core and was absent above 16 cm. S. agassizensis was found throughout the core. In addition to the centric diatoms, three penate diatoms were found to be abundant. Fragilaria crotonensis was found throughout the core, but was most abundant from 19 cm to 16 cm. Asterionella formosa was prevalent below 15 cm, while Diatoma elongatum was found to be common from 17 cm to the surface. The abundances of algal remains of cyanobacteria, chlorophytes, cryptophytes and dinoflagellates decrease dramatically below 25 cm. Zooplankton remains were most abundant around 20 cm, with copepod spermatophores, fecal pellets and protozoa remains most common in the lower portion of the core. The major species shifts observed in the core from Lake Arendsee occur in a transition zone between 20 cm and 15 cm (1920–1940), a time when agricultural production was being increase with the use of inorganic fertilizer.  相似文献   

A diatom-inferred water depth reconstruction for an Upper Peninsula, Michigan, lake   总被引：2，自引：0，他引：2  

Richard B. Brugam  Kathleen McKeever  Lawrence Kolesa 《Journal of Paleolimnology》1998,20(3):267-276

Transects of surface sediment samples were taken in 4 lakes from the Sylvania Wilderness Area, Upper Peninsula of Michigan. These surface samples were compared with diatom samples from a core taken in the Northwest basin of Crooked Lake, also from the Sylvania Wilderness Area. Weighted Averaging calibration was used to reconstruct lake depths in Crooked Lake using the diatom microfossils from the core and the surface samples to infer past lake depth. During the early Holocene the lake was dominated by planktonic species and diatom-inferred water depth was large – approx. 13 m. At about 6700 BP inferred water depth was 2 m and samples were dominated by Fragilaria construens var. venter – a species characteristic of shallow parts of the surface sample transects. From 6700 to 5000 BP reconstructed water level was at its shallowest. From 5000 to 3000 BP it increased. This rise in water level was marked by increasing abundances of Aulacoseira ambigua and occurred at the same time increasing percentages of hemlock pollen indicate increasing available moisture. Modern water depth was reached about 3000 BP. The water level changes at Crooked Lake are consistent with regional climate changes in the Upper Midwest during the Holocene. The lake was shallowest during the mid-Holocene warm period documented by other investigators. It deepened as the Midwestern climate became cooler and wetter during the late Holocene.  相似文献   

The volume and paleobathymetry of glacial Lake Agassiz     

Jason D. Mann  David W. Leverington  John Rayburn  James T. Teller 《Journal of Paleolimnology》1999,22(1):71-80

During the last retreat of the Laurentide Ice Sheet in North America, many proglacial lakes formed as continental drainage was impounded against the southern and western ice margin. Lake Agassiz was the largest of these lakes. The bathymetry of Lake Agassiz at the Herman and Upper Campbell beach levels – formed at about 11.5–11.0 ka and 9.9–9.5 ka, respectively – was computer modelled in this study by first collecting data for the isostatically-deformed paleowater planes of the two lake levels (derived from isobase lines constructed from beach elevations), and then subtracting these from the modern topography of the former lake floor. Pixels with dimensions of 1/30 × 1/30 of a degree were used in the model. Using these data, the area and volume of the lake were also calculated: at the Herman level these were 152 500 km2 and 13 100 km3 respectively; at the Upper Campbell level these were 350 400 km2 and 38 700 km3. Contour maps showing the paleobathymetry of both periods in the lake's history were also constructed. Determining the paleobathymetry and volume of Lake Agassiz is an important step in understanding the impact that the lake had on its surrounding environment and on the rivers, lakes, and oceans into which it flowed.  相似文献   

Siliceous microfossil distribution in the surficial sediments of Lake Baikal     

E. F. Stoermer  M. B. Edlund  C. H. Pilskaln  C. L. Schelske 《Journal of Paleolimnology》1995,14(1):69-82

Examination of surficial sediments at 16 stations shows minor, but consistent differences in the numbers and kinds of siliceous microfossils deposited in different regions of Lake Baikal. There is a general north-south decreasing trend in total microfossil abundance on a weight basis. Endemic plankton diatom species are the most abundant component of assemblages at all stations. Chrysophyte cysts are present at all stations, but most forms are more abundant at northern stations. Non-endemic plankton diatom species are most abundant at southern stations. Small numbers of benthic diatoms and sponge spicules are found in all samples. Although low numbers are present in offshore sediments, the benthic diatom flora is very diverse. Principal components analysis confirms primary north-south abundance trends and suggests further differentiation by station location and depth.  相似文献   

Relationships between sedimentary diatom assemblages and lakewater pH values in the Experimental Lakes Area     

D. L. Findlay  J. A. Shearer 《Journal of Paleolimnology》1992,7(2):145-156

Relationships between sedimentary diatom assemblages and lakewater pH values from 36 lakes and experimentally acidified Lake 223, in the Experimental Lakes Area, were analyzed. The relationships were used to assign diatoms in the 36 lakes into pH preference groupings. Based on their regional distribution Cyclotella stelligera and Tabellaria flocculosa strain IIIp were categorized as pH indifferent, in comparison to other areas were they have been categorized as acidophilic. Two models were then applied to calculate transfer coefficients which were used to calculate diatom-inferred pH values for Lake 223. Index B and a multiple linear regression of the pH groupings yielded similar correlations (r² 0.82 and 0.84 respectively, p=0.0001). The multiple linear regression inferred a pH of 5.36 for acidified Lake 223 compared to a measured pH of 5.46.  相似文献   

Fossil diatoms and the mid to late holocene paleolimnology of Lake Turkana,Kenya: a reconnaissance study     

John D. Halfman  David F. Jacobson  Carolyn M. Cannella  Kurt A. Haberyan  Bruce P. Finney 《Journal of Paleolimnology》1992,7(1):23-35

A 12 m sediment core recovered from the south basin of Lake Turkana, northwestern Kenya, reveals four major diatom assemblages that span approximately 5450 to 1070 years BP based on AMS radiocarbon analyses. The oldest assemblage, Zone D (5450 to 4850 yr BP), is dominated by Melosira nyassensis and Stephanodiscus spp. and is interpreted to reflect higher lake levels, fresher water and more variable seasonal mixing of the water column than the modern lake. Melosira dominates the assemblage in Zone C (4850 to 3900 yr BP) with some Surirella engleri and Stephanodiscus. This assemblage indicates a continuation of relatively high lake levels and seasonal mixing of a stratified lake. The brief peak of Surirella, interpreted as benthic, suggests an episode of slightly lower lake level. Thalassiosira rudolfi and Surirella predominate since the beginning of Zone B (3900 to 1900 yr BP), reflecting a decrease in lake level and increase in water column salinity. Increasing dominance of Surirella in Zone A (1900 to 1070 yr BP) may suggest that the lake continued to decrease in depth. Salinity probably rose to levels comparable with the modern lake. These results are consistent with paleoclimatic interpretations based on carbonate abundance, lamination thickness, oxygen isotope and bulk geochemistry profiles from this core and cores recovered from the north basin. It extends the known paleolimnology beyond 4000 yr BP of the earlier research to 5450 yr BP and into the early to mid Holocene pluvial phase in northern intertropical east Africa.  相似文献   

Diatom succession related to land use during the last 6000 years: a study of a small eutrophic lake in southern Sweden   总被引：1，自引：0，他引：1  

Hannelore Håkansson  Joachim Regnéll 《Journal of Paleolimnology》1993,8(1):49-69

Diatoms, pollen, physical and magnetic analyses of the sediments have been used to reconstruct the development over the last 6000 years of Lake Bussjösjön, a small lake in southern Sweden. Stratigraphic variations in a core of more than 15 m reveal changes in diatom assemblages, which correspond closely to changes in pollen, loss-on-ignition, and magnetic measurements that are related to land use and vegetation changes in the catchment. From ca 6000 BP to 2700 BP, a forest surrounded what was then a slightly eutrophic lake. The sudden appearance of Cyclostephanos dubius (Fricke) Round and several epiphytic/epipsammic diatoms at 2700 BP coincides with deforestation of the catchment (2700 BP to 2500 BP). A change in land use from predominantly pasture to arable land from 1300 BP to 1100 BP caused a high level of soil erosion with a decrease of C. dubius and the increase of Stephanodiscus species. An increase of epiphytic/epipsammic species coincides with increased arable farming and the change from a field-rotation to a crop-rotation system, and shows not only an increase in eutrophication but also changes in water depth. The influence of the catchment through time resulted in a smaller, shallower and eutrophic to hypertrophic lake.  相似文献   

Palaeohydrology of the Quaternary saline Lake Ballivian (southern Bolivian Altiplano) based on diatom studies     

S. Servant-Vildary  S. H. Mello e Sousa 《International Journal of Salt Lake Research》1993,2(1):69-85

Diatoms are usually used for reconstructing variations in past lacustrine depth. In a small endorheic basin located in the southern Bolivian Altiplano, we used a comparative method based on basin morphology, stratigraphy, sediment samples, altitude and diatom ecology to infer depth variations more precisely in both marginal and central parts of the basin. Beforeca. 22,000 yr BP, the general tendency was a progressive increase in water-level from 4,135 to 4,155 m altitude, but Lake Ballivian rose to 4,160 m twice, and dropped below 4,135m twice. After ca. 22,000 yr BP, a long dry period occurred, as indicated by a sedimentation hiatus. Atca. 13,000 yr BP, the water-level slightly increased again but the lake stayed very shallow, at less than 4,125 m altitude. *** DIRECT SUPPORT *** A02GG003 00005  相似文献   

Diatom-salinity relationships in 111 lakes from the Interior Plateau of British Columbia,Canada: the development of diatom-based models for paleosalinity reconstructions   总被引：2，自引：0，他引：2  

Susan E. Wilson  Brian F. Cumming  John P. Smol 《Journal of Paleolimnology》1994,12(3):197-221

Diatoms were identified and enumerated from the surface sediments of 111 lakes, 45 from the Kamloops region and 66 from the Cariboo/Chilcotin region, located on the southern Interior Plateau of British Columbia, Canada. This paper is an extension of another study which investigated the relationship of diatoms to salinity and ionic composition in 65 lakes from the Cariboo/Chilcotin region. The 111 lakes spanned a large gradient in salinity, ranging from fresh through hypersaline (late-summer salinity values ranged from 0.04 to 369 g l^–1), and included both carbonate- and sulphate-dominated lakes with sodium and magnesium as the dominant cations. The Kamloops region had more sulphate-dominated, hypersaline lakes and fewer carbonate-rich lakes than the Cariboo/Chilcotin region. Most lakes had higher salinities in the late-summer compared to the spring.Both salinity and brine-type were important variables that could explain the different diatom assemblages present in the lakes. The majority of diatom taxa had salinity optima in the freshwater to subsaline range (<3 g l^–1), and the taxa displayed a range of both narrow and broad tolerances along the salinity gradient. Weighted-averaging regression and calibration, and maximum likelihood techniques were used to develop salinity inference models from the diatom assemblages based on their relationship to the spring, late-summer and average lakewater salinity measurements. Simple weighted-averaging (WA) models generally produced the same or lower bootstrapped RMSEs of prediction than weighted-averaging with tolerance downweighting (WA(tol)) in the two regional and the combined datasets. Weighted averaging partial least squares (WA-PLS) showed little or no improvement in the predictive abilities of the datasets, as judged by the jackknifed RMSE of prediction. In all cases, the combined dataset of 102 lakes performed better than either of the smaller regional datasets, with relatively little difference between spring, average and late-summer salinity models. The maximum likelihood models gave lower apparent RMSEs of prediction in comparison to other methods; however, independent validation of this technique using methods such as bootstrapping were not undertaken because of the computer intensive nature of such analyses. These diatom-based salinity models are now available for reconstructing salinity and climatic trends from appropriately chosen closed-basin lakes in the Interior region of British Columbia.This is the second in a series of papers published in this issue on the paleolimnology of arid regions. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. R. Chivas served as guest editor for these papers.  相似文献   

Mucus Aggregates in the Adriatic Sea: An Overview of Stages and Occurrences   总被引：2，自引：0，他引：2  

Michael Stachowitsch  Neda Fanuko  Marjan Richter 《Marine Ecology》1990,11(4):327-350

Abstract. The wide range of macroscopic mucus aggregates in the Adriatic Sea is documented. These structures arc considered to be initially produced by diatoms. A differentiation into five states or stages: macroflocs, stringers, clouds, creamy surface layers, and gelatinous surface layers is proposed. This classification is based not only on size and shape, but also takes relative position in the water, stability, behavior, and effect on benthos into consideration. An interrelationship between these aggregates - as different manifestations or phases of the same phenomenon - is postulated.
Macroflocs and stringers arc more common. Larger aggregates (clouds, creamy layers, gelatinous layers) arc less frequent. The general term "marine snow" is inadequate to describe the entire range of aggregate sizes and shapes, while the Italian designation "mare sporco" (dirty sea) is misleading. Two massive occurrences of dense clouds coupled with surface accumulations were recorded in the Adriatic in 1988 and 1989. The effect of the various stages on the shallow coastal ecosystem of the Northern Adriatic Sea is discussed.  相似文献