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Glacial Lakes (glacial + lake)
Selected AbstractsHabitat characteristics at bluegill spawning colonies in a South Dakota glacial lakeECOLOGY OF FRESHWATER FISH, Issue 4 2006N. J. C. Gosch Abstract,,, Bluegill (Lepomis macrochirus) primarily reproduce in spawning colonies. We assessed habitat characteristics at 15 bluegill spawning colonies in a South Dakota glacial lake. Nesting sites were visually identified and angling was used to verify the species of nesting fish. Habitat characteristics were measured at each nesting site and compared with those measured at 75 randomly selected sites. In Lake Cochrane, mean water depth of spawning colonies was 1.0 m. Of the 13 habitat characteristics measured, four (substrate type, substrate firmness, vegetation density and dissolved oxygen levels) were significantly different (P , 0.05) between nesting and random sites. Every bluegill nest site contained gravel substrate, despite the availability of muck, sand and rock. Substrate firmness was indexed at 0-cm penetration and vegetation density was low at all nesting sites. Additionally, bluegills selected nesting locations with relatively moderate dissolved oxygen levels. Lake Cochrane bluegill nest sites consisted of shallow, gravel areas with short, low-density, live submergent Chara vegetation. [source] Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North SeaBOREAS, Issue 3 2010SANDRA PASSCHIER Passchier, S., Laban, C., Mesdag, C.S. & Rijsdijk, K.F. 2010: Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea. Boreas, Vol. 39, pp. 633,647. 10.1111/j.1502-3885.2009.00138.x. ISSN 0300-9483. Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice-stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice-sheet reconstructions. [source] Influence of hatch duration and individual daily growth rates on size structure of age-0 smallmouth bass cohorts in two glacial lakesECOLOGY OF FRESHWATER FISH, Issue 3 2008Q. E. Phelps Abstract,,, We assessed hatch dates and daily growth rates of age-0 smallmouth bass from two glacial lakes over a 3-year period. Hatching durations (19,27 days among years) of smallmouth bass occurred from late May until late June. Mean daily growth rate of age-0 smallmouth bass ranged from 0.56 to 1.56 mm·day,1. Correlation analysis indicated that hatch date had little effect on daily growth rates. Hatch date was significant in explaining variation in total length (TL) of age-0 smallmouth bass at time of capture in only three of six cases and hatch date never explained >50% of the variation in bass length. Daily growth rate significantly explained variation in smallmouth bass TL at time of capture in all six models, accounting for 31,86% of the variability in bass length. Our findings suggest that size structure of age-0 cohorts in some populations may be more strongly regulated by variation in individual daily growth rate than by hatch timing. [source] Factors influencing the temporal coherence of five lakes in the English Lake DistrictFRESHWATER BIOLOGY, Issue 3 2000D. G. George 1. The lakes in the Windermere catchment are all deep, glacial lakes but they differ in size, shape and general productivity. Here, we examine the extent to which year-to-year variations in the physical, chemical and biological characteristics of these lakes varied synchronously over a 30,40-year period. 2. Coherence was estimated by correlating time-series of the spring, summer, autumn and winter characteristics of five lakes: Esthwaite Water, Blelham Tarn, Grasmere and the North and South Basins of Windermere. Three physical, four chemical and two biological time-series were analysed and related to year-to-year variations in a number of key driving variables. 3. The highest levels of coherence were recorded for the physical and chemical variables where the average coherence was 0.81. The average coherence for the biological variables was 0.11 and there were a number of significant negative relationships. The average coherence between all possible lake pairs was 0.59 and average values ranged from 0.50 to 0.74. A graphical analysis of these results demonstrated that the coherence between individual lake pairs was influenced by the relative size of the basins as well as their trophic status. 4. A series of examples is presented to demonstrate how a small number of driving variables influenced the observed levels of coherence. These range from a simple example where the winter temperature of the lakes was correlated with the climatic index known as the North Atlantic Oscillation, to a more complex example where the summer abundance of zooplankton was correlated with wind-mixing. 5. The implications of these findings are discussed and a conceptual model developed to illustrate the principal factors influencing temporal coherence in lake systems. The model suggests that our ability to detect temporal coherence depends on the relative magnitude of three factors: (a) the amplitude of the year-to-year variations; (b) the spatial heterogeneity of the driving variables and (c) the error terms associated with any particular measurement. [source] Contrasts in the Quaternary of mid-North America and mid-Eurasia: notes on Quaternary landscapes of western Siberia,JOURNAL OF QUATERNARY SCIENCE, Issue 7-8 2005H. E. Wright Abstract The West Siberian Plain was formed by marine deposits that extended from the Mediterranean basin to the arctic. Tectonic action later produced a striking series of long straight NE,SW grabens in the southern part of the plain. Pleistocene advance of the Kara ice sheet onto the continent resulted in blockage of the Ob and Yenisey rivers to form huge proglacial lakes that drained through these grabens south via the Turgay Pass and the Aral, Caspian, Black and Mediterranean seas to the North Atlantic Ocean, but during the Last Glacial Maximum (late Weichselian, isotope stage 2), the Kara ice sheet did not advance onto the continent in northwestern Siberia. The Altai Mountains, which bound the West Siberian Plain on the south, contained large deep intermontane ice-dammed lakes, which drained catastrophically when the ice dams broke, forming giant ripples on the basin floors. Pollen studies of glacial lakes indicate that the Lateglacial steppe vegetation and dry climatic conditions continued into the early Holocene as summer insolation maintained high levels. Permafrost development on a drained lake floor in the western Altai Mountains resulted in the formation of groups of small pingos. In North America the growth and wastage of the huge Laurentide ice sheet had an indirect role in the climatic history of western Siberia during the Glacial and Lateglacial periods, after which the climate was more affected directly by insolation changes, whereas in North America in the early Holocene the insolation factor was coupled with the climatic effects of the slow wastage of the ice sheet, and the time of maximum dryness was postponed until the mid-Holocene. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||