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Lake Basins (lake + basin)

Distribution by Scientific Domains

Life Sciences	41%
Humanities and Social Sciences	29%
Earth and Environmental Science	29%

Kinds of Lake Basins

great lake basin

Selected Abstracts

Effects of high-magnitude/low-frequency fluvial events generated by intense snowmelt or heavy rainfall in arctic periglacial environments in northern Swedish Lapland and northern Siberia

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2004
A. A. Beylich
Abstract In the Latnjavagge drainage basin (68°21,N, 18°29,E), an arctic-oceanic periglacial environment in northernmost Swedish Lapland, the fluvial sediment transport and the characteristics and importance of high-magnitude/low-frequency fluvial events generated by intense snowmelt or heavy rainfall have been investigated and compared with snowmelt- and rainfall-induced discharge peaks in the Levinson-Lessing Lake basin (Krasnaya river system) on the Taimyr Peninsula, an arctic periglacial environment in northern Siberia (74°32,N, 98°35,E). In Latnjavagge (9 km2) the intensity of fluvial sediment transport is very low. Most of the total annual sediment load is transported in a few days during snowmelt generated runoff peaks. Due to the continuous and very stable vegetation covering most areas below 1300 m a.s.l. in the Latnjavagge catchment, larger rainfall events are of limited importance for sediment transport in this environment. Compared to that, in the c. 40 times larger Krasnaya riversystem rainfall-generated runoff peaks cause significant sediment transport. The main sediment sources in the Latnjavagge drainage basin are permanent ice patches, channel debris pavements mobilized during peak discharges and exposing fines, and material mobilized by slush-flows. In the Krasnaya river system river bank erosion is the main sediment source. In both periglacial environments more than 90% of the annual sediment yield is transported during runoff peaks. The results from both arctic periglacial environments underline the high importance of high-magnitude/low-frequency fluvial events for the total fluvial sediment budgets of periglacial fluvial systems. Restricted sediment availability is in both arctic environments the major controlling factor for this behaviour. [source]

Factors affecting abundance and distribution of submerged and floating macrophytes in Lake Naivasha, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
A. N. Ngari
Abstract Macrophytes have been shown to perform important ecological roles in Lake Naivasha. Consequently, various studies regarding the impact of biotic factors on the macrophytes have been advanced but related studies on environmental parameters have lagged behind. In an attempt to address this gap, sampling on floating species and submergents was carried out in eight sampling sites in 2003 to investigate how they were influenced by a set of environmental factors. Soil texture (sandy sediments; P < 0.05, regression coefficient = ,0.749) and wind were the most important environmental parameters influencing the distribution and abundance of floating macrophytes. Combination of soil texture and lake-bed slope explained the most (86.3%) variation encountered in the submergents. Continuous translocation of the floating dominant water hyacinth to the western parts by wind has led to displacement of the submergents from those areas. In view of these findings, the maintenance and preservation of the steep Crescent Lake basin whose substratum is dominated by sand thus hosting most submergents remain important, if the whole functional purpose of the macrophytes is to be sustained. Résumé On a montré que les macrophytes jouent un rôle économique important dans le lac Naivasha. Par conséquent, diverses études ont été réalisées sur l'impact des facteurs biotiques sur les macrophytes, mais les études correspondantes sur les paramètres environnementaux sont à la traîne. Pour essayer de compenser cette lacune, en 2003, on a réalisé un échantillonnage des espèces flottantes et submergées sur huit sites d'échantillonnage pour étudier comment elles étaient influencées par un ensemble de facteurs environnementaux. La texture du sol (sédiments sableux, P < 0,05, coefficient de régression = 0,749) et le vent étaient les paramètres environnementaux les plus important quant à l'influence sur la distribution et l'abondance des macrophytes flottants. La combinaison de la texture du sol et de la pente du fond du lac expliquait la plus grande partie (86,3%) de la variation rencontrée chez les espèces submergées. Le déplacement continuel des jacinthes d'eau, qui est la plante flottante dominante, vers la partie ouest par le vent a entraîné le déménagement des espèces submergées hors de cette partie du lac. Au vu de ces résultats, il est important d'assurer l'entretien et la préservation de la pente raide du bassin du lac en forme de croissant si l'on peut conserver l'ensemble de la fonction des macrophytes. [source]

Chronology of latest Pleistocene lake-level fluctuations in the pluvial Lake Chewaucan basin, Oregon, USA

JOURNAL OF QUATERNARY SCIENCE, Issue 6 2001
Joseph M. Licciardi
Abstract New accelerator mass spectrometer radiocarbon ages from gastropods in shore deposits within the pluvial Lake Chewaucan basin, combined with stratigraphical and geomorphological evidence, identify an abrupt rise and fall of lake level at ca. 12 14C ka. The lake-level high is coeval with lake-level lows in the well-dated records of palaeolakes Bonneville and Lahontan, and with a period of relatively wet conditions in the more southerly Owens Lake basin. This spatial pattern of pluvial lake levels in the western USA at 12 14C ka indicates a variable synoptic response to climate forcing at this time. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Characteristics of Important Stopover Locations for Migrating Birds: Remote Sensing with Radar in the Great Lakes Basin

CONSERVATION BIOLOGY, Issue 2 2009
DAVID N. BONTER
ave terrestre migratoria; migración; radar; sitios de escala temporal; WSR-88D Abstract:,A preliminary stage in developing comprehensive conservation plans involves identifying areas used by the organisms of interest. The areas used by migratory land birds during temporal breaks in migration (stopover periods) have received relatively little research and conservation attention. Methodologies for identifying stopover sites across large geographic areas have been, until recently, unavailable. Advances in weather-radar technology now allow for evaluation of bird migration patterns at large spatial scales. We analyzed radar data (WSR-88D) recorded during spring migration in 2000 and 2001 at 6 sites in the Great Lakes basin (U.S.A.). Our goal was to link areas of high migrant activity with the land-cover types and landscape contexts corresponding to those areas. To characterize the landscapes surrounding stopover locations, we integrated radar and land-cover data within a geographic information system. We compared landscape metrics within 5 km of areas that consistently hosted large numbers of migrants with landscapes surrounding randomly selected areas that were used by relatively few birds during migration. Concentration areas were characterized by 1.2 times more forest cover and 9.3 times more water cover than areas with little migrant activity. We detected a strong negative relationship between activity of migratory birds and agricultural land uses. Examination of individual migration events confirmed the importance of fragments of forested habitat in highly altered landscapes and highlighted large concentrations of birds departing from near-shore terrestrial areas in the Great Lakes basin. We conclude that conservation efforts can be more effectively targeted through intensive analysis of radar imagery. Resumen:,Una etapa preliminar en el desarrollo de planes de conservación integrales implica la identificación de áreas utilizadas por los organismos de interés. Las áreas utilizadas por aves terrestres migratorias durante escalas temporales en la migración (períodos de parada) han recibido relativamente poca atención de investigación y conservación. Hasta hace poco, las metodologías para la identificación de sitios de parada en áreas geográficas extensas han sido escasas. Ahora, los avances en la tecnología de radar meteorológico permiten la evaluación de patrones de migración de aves en escalas espaciales grandes. Analizamos datos de radar (WSR-88D) registrados en seis sitios en la cuenca de los Grandes Lagos (E.U.A.) durante la migración en las primaveras de 2000 y 2001. Nuestra meta fue relacionar áreas con gran actividad migratoria con los tipos de cobertura de suelo y los contextos del paisaje correspondientes a esas áreas. Para caracterizar los paisajes circundantes a las localidades de parada, integramos los datos de radar y de cobertura de suelo a un sistema de información geográfica. Comparamos las medidas del paisaje en un radio de 5 km en las áreas que consistentemente albergaron a grandes números de migrantes con los paisajes circundantes a áreas seleccionadas aleatoriamente y que eran utilizadas por relativamente pocas aves durante la migración. Las áreas de concentración se caracterizaron por tener 1.3 veces más cobertura forestal y 9.3 veces más cobertura de agua que las áreas con poca actividad migratoria. Detectamos una fuerte relación negativa entre la actividad de las aves migratorias y los usos de suelo agrícolas. El examen de eventos migratorios individuales confirmó la importancia de los fragmentos de hábitat boscoso en paisajes muy alterados y resaltó las grandes concentraciones de aves partiendo de áreas terrestres cercanas a la costa en la cuenca de los Grandes Lagos. Concluimos que los esfuerzos de conservación pueden ser abordados más efectivamente mediante el análisis intensivo de imágenes de radar. [source]

A dynamic mass budget for toxaphene in North America

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2002
Matthew MacLeod
Abstract A continental-scale dynamic mass budget for toxaphene in North America is presented, based on available information on physicochemical properties, usage patterns, and reported environmental concentrations and using the Berkeley-Trent North American mass balance contaminant fate model (BETR North America). The model describes contaminant fate in 24 ecological regions of North America, including advective transport between regions in the atmosphere, freshwater, and near-shore coastal water. The dynamic mass budget accounts for environmental partitioning, transport, and degradation of the estimated 534 million kg of toxaphene that were used in North America as an insecticide and piscicide between 1945 and 2000. Satisfactory agreement exists between model results and current and historically reported concentrations of toxaphene in air, water, soil, and sediments throughout North America. An estimated 15 million kg of toxaphene are believed to remain in active circulation in the North American environment in the year 2000, with the majority in soils in the southern United States and Mexico, where historic usage was highest. Approximately 70% of total toxaphene deposition from the atmosphere to the Great Lakes is attributed to sources outside the Great Lakes Basin, and an estimated total of 3.9 million kg of toxaphene have been transported to this region from other parts of the continent. The toxaphene mass budget presented here is believed to be the first reported continental-scalemultimedia mass budget for any contaminant. [source]

Characteristics of Important Stopover Locations for Migrating Birds: Remote Sensing with Radar in the Great Lakes Basin

Biological attributes of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2006
A. C. Benson
Summary Lake sturgeon Acipenser fulvescens are imperiled throughout the Laurentian Great Lakes basin. Efforts to restore this species to former population levels have been ineffective due in part to limited information regarding its early life history. The objectives of this study were to characterize the larval drift and biological attributes of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin. Lake sturgeon larvae were captured from May to June 2002 and 2003 using drift nets, while age-0 juveniles were captured from June through October 2002 and 2003 using wading, snorkeling, backpack electrofishing, and haul-seine surveys. Larval drift occurred within 14 days of adult spawning and extended from 1 to 3 weeks in duration, with two peaks in the number of fish drifting downstream each year. Larvae had a median total length (TL) of 19 mm (range: 13,23; N = 159) in 2002 and 18 mm (range: 13,24; N = 652) in 2003. Catch-per-unit-effort for larvae was 0.18 fish h,1 m2 and 0.94 fish h,1 m2 in 2002 and 2003, respectively. Age-0 juvenile lake sturgeon exhibited rapid growth (i.e. 2.57 mm day,1 in TL and 0.66 g day,1 in wet weight) throughout summer and fall months; relative condition of fish in both years was approximately 100, indicating good condition. Absolute abundance of age-0 juveniles in 2003 was estimated at 261 fish using the Schnabel estimator. The results from this study indicate that the lower Peshtigo River contains important nursery habitats suitable for age-0 lake sturgeon. [source]

Impact of a rock avalanche on a moraine-dammed proglacial lake: Laguna Safuna Alta, Cordillera Blanca, Peru

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2005
Bryn Hubbard
Abstract Moraines that dam proglacial lakes pose an increasing hazard to communities in the Andes and other mountain ranges. The moraines are prone to failure through collapse, overtopping by lake waters or the effect of displacement waves resulting from ice and rock avalanches. Resulting floods have led to the loss of thousands of lives in the Cordillera Blanca mountains of Peru alone in the last 100 years. On 22 April 2002 a rock avalanche occurred immediately to the south-west of Laguna Safuna Alta, in the Cordillera Blanca. The geomorphic evidence for the nature, magnitude and consequences of this event was investigated in August 2002. Field mapping indicated that the avalanche deposited 8,20 × 106 m3 of rock into the lake and onto the surface of the frontal region of Glaciar Pucajirca, which flows into the lake. Repeated bathymetric surveying indicated that ,5 × 106 m3 of this material was deposited directly into the lake. The immediate effect of this event was to create a displacement wave that gained in height as it travelled along the lake basin, overtopping the impounding moraine at the lake's northern end. To achieve overtopping, the maximum wave height must have been greater than 100 m. This, and subsequent seiche waves, caused extensive erosion of both the proximal and distal faces of the impounding terminal moraine. Further deep gullying of the distal face of this moraine resulted from the supply of pressurized water to the face via a relief overflow tunnel constructed in 1978. Two-dimensional, steady-state analysis of the stability of the post-avalanche moraine rampart indicates that its proximal face remains susceptible to major large-scale rotational failure. Copyright © 2005 John Wiley & Sons, Ltd. [source]

,Land Moves and Behaves': Indigenous Discourse on Sustainable Land Management in Pichataro, Patzcuaro Basin, Mexico

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2003
Narciso Barrera-Bassols
ABSTRACT An ethnoecological study was carried out in the Purhepecha community of San Francisco Pichataro, west central Mexico, with the purpose of investigating how land degradation, in terms of soil erosion and fertility depletion, was (and still is) handled by indigenous farmers so that traditional agriculture could remain sustainable over centuries. After briefly reviewing opposite views on the land degradation issue in the regional context of the Patzcuaro lake basin, the paper focuses on land management at local level. The indigenous concept of land is discussed as an integrated whole, including water cycle, climate, relief and soils. Indigenous people venerate land as the mother of all living beings, including humans. Therefore, people's health and survival require good land care and management. Local knowledge on land management is organized around four basic principles: land position, land behaviour, land resilience and land quality. Fanners recognize land as a dynamic subject, a concept reflected in the expression ,land moves and behaves'. Soil erosion and fertility depletion are perceived as ,normal' processes the farmers control by means of integrated management practices. Farmers recognize several land classes, primarily controlled by landscape position, which require different land care. The example of San Francisco Pichataro demonstrates that traditional agriculture does not necessarily lead to land degradation. But the collective knowledge, or social theory, on land management is increasingly exposed to be fragmented as the community undergoes structural changes and loses its social cohesion under the pressure of externalities such as off-farm activities, out-migrations and governmental intervention, among others. [source]

A late Holocene record of arid events from the Cuzco region, Peru

JOURNAL OF QUATERNARY SCIENCE, Issue 6 2003
Alex Chepstow-Lusty
Abstract The small recently infilled lake basin of Marcacocha (13°13,S, 72°12,W, 3355,m) in the Cuzco region of Peru has a morphology and location that renders it extremely sensitive to environmental change. A record of vegetation, human impact and climatic change during the past 4200,yr has been obtained from a highly organic core taken from the centre of the basin. Sustained arid episodes that affected the Peruvian Andes may be detectable using the proxy indicator of sedge (Cyperaceae) pollen abundances. As the lake-level was lowered during sustained drier conditions, the local catchment was colonised by Cyperaceae, whereas during lake floods, they retreated or were submerged and pollen production was correspondingly reduced. Drier episodes during prehistoric times occurred around 900,bc, 500,bc, ad 100 and ad 550, with a longer dry episode occurring from ad 900 to 1800. Evidence from the independently derived Quelccaya ice-core record and the archaeological chronology for the Cuzco region appears to support the climatic inferences derived from the sedge data. Many of these aridity episodes appear to correspond with important cultural changes in the Cuzco region and elsewhere in the Central Andes. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Fine-scale population structure and dispersal in Biomphalaria glabrata, the intermediate snail host of Schistosoma mansoni, in Venezuela

MOLECULAR ECOLOGY, Issue 5 2002
J. Mavárez
Abstract Biomphalaria glabrata is the main intermediate host of Schistosoma mansoni in America and one of the most intensely studied species of freshwater snails, yet very little is known about its population biology. Here, we used seven highly polymorphic microsatellite loci to analyse genetic diversity in the Valencia lake basin, which represents the core of the endemic area for schistosomiasis in Venezuela. Populations were sampled at short spatial scale (a few kilometres), both inside the lake and in ponds or rivers near the lake. Our results indicate that B. glabrata essentially cross-fertilizes, with little variation in selfing rates among populations. Our markers detected considerable genetic variation, with an average heterozygosity of 0.60. More diversity per population was found within than outside the lake, suggesting an influence of connectivity among populations on the levels of genetic diversity. A marked population structure was detected and lake populations were less structured than other populations. Most individuals were assigned to their population of origin using an assignment test. No strong demographic signal (e.g. bottleneck) was detected, though lake populations are likely to experience bottlenecks more frequently than the other populations analysed. Differences in gene flow therefore seem to play an important role in population differentiation and in the restoring of genetic diversity in demographically unstable populations. [source]

Hydrologic and geomorphic effects of temporary ice-dammed lake formation during jökulhlaups

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2003
Matthew J. Roberts
Abstract Glacial outburst ,oods (jökulhlaups) occur frequently in glaciated environments, and the resultant ,ooding causes geomorphic change and, in some instances, damage to local infrastructure. During some jökulhlaups, ,oodwater is stored temporarily in ice-marginal locations. In July 1999, a linearly rising jökulhlaup burst from Sólheimajökull, Iceland. During this remarkable event, subglacial ,oodwater pooled transiently in two relict ice-dammed lake basins, before draining suddenly back into Sólheimajökull. The signi,cance of such rapid formation and attendant drainage of temporary ice-dammed lakes during jökulhlaups has not been addressed. Consequently, this paper: (i) assesses the hydrologic and geomorphic effects of temporary ice-dammed lake formation caused by lake-basin ,retro-,lling'; and (ii) discusses the impact and signi,cance of transient retro-,lling under jökulhlaup conditions. Pre- and post-,ood ,eldwork at Sólheimajökull enabled the impact and signi,cance of lake-basin retro-,lling to be assessed. Field evidence demonstrates that the July 1999 jökulhlaup had an unusually rapid rise to peak discharge, resulting in subglacial ,oodwater being purged to ice-marginal locations. The propensity for temporary retro-,lling was controlled by rapid expulsion of ,oodwater from Sólheimajökull, coincident with locations suitable for ,oodwater storage. Floodwater inundated both ice-marginal lake basins, permitting signi,cant volumes of sediment deposition. Coarse-grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro-,lling. The depositional characteristics of lake-basin deposits at Sólheimajökull are similar to jökulhlaup sediments documented in proglacial settings elsewhere; however, their depositional setting and association with ice-marginal landforms is distinctive. Findings suggest that temporary ice-dammed lake formation and drainage has the capacity to alter the shape of the ,ood hydrograph, especially if drainage of a temporary lake is superimposed on the original jökulhlaup. Deposits associated with lake-basin retro-,lling have a long-term preservation potential that could help to identify temporary ice-dammed lake formation in modern and ancient glacial environments. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Phosphorus decrease and climate variability: mediators of synchrony in phytoplankton changes among European peri-alpine lakes

FRESHWATER BIOLOGY, Issue 10 2005
ORLANE ANNEVILLE
Summary 1. In an attempt to discern long-term regional patterns in phytoplankton community composition we analysed data from five deep peri-alpine lake basins that have been included in long-term monitoring programmes since the beginning of the 1970s. Local management measures have led to synchronous declines in phosphorus concentrations by more than 50% in all four lakes. Their trophic state now ranges from mesotrophic to oligotrophic. 2. No coherence in phytoplankton biomass was observed among lakes, or any significant decrease in response to phosphorus (P)-reduction (oligotrophication), except in Lakes Constance and Walen. 3. Multivariate analyses identified long-term changes in phytoplankton composition, which occurred coherently in all lakes despite the differing absolute phosphorus concentrations. 4. In all lakes, the phytoplankton species benefiting from oligotrophication included mixotrophic species and/or species indicative of oligo-mesotrophic conditions. 5. A major change in community composition occurred in all lakes at the end of the 1980s. During this period there was also a major shift in climatic conditions during winter and early spring, suggesting an impact of climatic factors. 6. Our results provide evidence that synchronous long-term changes in geographically separated phytoplankton communities may occur even when overall biomass changes are not synchronous. [source]

Aminopeptidase and phosphatase activities in basins of Lake Hiidenvesi dominated by cyanobacteria and in laboratory grown Anabaena

FRESHWATER BIOLOGY, Issue 9 2002
JAANA VAITOMAA
1.,Extracellular enzyme activities were examined in freshwater basins representing a transition from hypertrophy to mesotrophy and in axenic cyanobacterial cultures to evaluate the ecological role of extracellular enzyme activities of cyanobacteria. 2.,Aminopeptidase activity was related to the trophic status of the lake basins. The activity was highest in the most eutrophic basin and decreased in the less nutrient-rich basins. Cyanobacteria were the most important autotrophic organisms and aminopeptidase activity was positively associated with cyanobacterial biomass. 3.,In an axenic Anabaena batch culture, nitrogenase activity was several orders of magnitude higher than leucine aminopeptidase activity. Nitrate did not have an effect on aminopeptidase activity or growth, but significantly reduced the rate of nitrogen fixation. A high phosphorus concentration at the beginning of the Anabaena batch-culture experiment resulted in reduced phosphatase activity. 4.,In Lake Hiidenvesi, aminopeptidase activity probably originated mostly from attached bacteria and less so from cyanobacteria. [source]

Temporal coherence of two alpine lake basins of the Colorado Front Range, U.S.A.

FRESHWATER BIOLOGY, Issue 3 2000
J. I. L. L. S. Baron
1. Knowledge of synchrony in trends is important to determining regional responses of lakes to disturbances such as atmospheric deposition and climate change. We explored the temporal coherence of physical and chemical characteristics of two series of mostly alpine lakes in nearby basins of the Colorado Rocky Mountains. Using year-to-year variation over a 10-year period, we asked whether lakes more similar in exposure to the atmosphere be-haved more similarly than those with greater influence of catchment or in-lake processes. 2. The Green Lakes Valley and Loch Vale Watershed are steeply incised basins with strong altitudinal gradients. There are glaciers at the heads of each catchment. The eight lakes studied are small, shallow and typically ice-covered for more than half the year. Snowmelt is the dominant hydrological event each year, flushing about 70% of the annual discharge from each lake between April and mid-July. The lakes do not thermally stratify during the period of open water. Data from these lakes included surface water temper-ature, sulphate, nitrate, calcium, silica, bicarbonate alkalinity and conductivity. 3. Coherence was estimated by Pearson's correlation coefficient between lake pairs for each of the different variables. Despite close geographical proximity, there was not a strong direct signal from climatic or atmospheric conditions across all lakes in the study. Individual lake characteristics overwhelmed regional responses. Temporal coherence was higher for lakes within each basin than between basins and was highest for nearest neighbours. 4. Among the Green Lakes, conductivity, alkalinity and temperature were temporally coherent, suggesting that these lakes were sensitive to climate fluctuations. Water tem-perature is indicative of air temperature, and conductivity and alkalinity concentrations are indicative of dilution from the amount of precipitation flushed through by snowmelt. 5. In Loch Vale, calcium, conductivity, nitrate, sulphate and alkalinity were temporally coherent, while silica and temperature were not. This suggests that external influences are attenuated by internal catchment and lake processes in Loch Vale lakes. Calcium and sulphate are primarily weathering products, but sulphate derives both from deposition and from mineral weathering. Different proportions of snowmelt versus groundwater in different years could influence summer lake concentrations. Nitrate is elevated in lake waters from atmospheric deposition, but the internal dynamics of nitrate and silica may be controlled by lake food webs. Temperature is attenuated by inconsistently different climates across altitude and glacial meltwaters. 6. It appears that, while the lakes in the two basins are topographically close, geologically and morphologically similar, and often connected by streams, only some attributes are temporally coherent. Catchment and in-lake processes influenced temporal patterns, especially for temperature, alkalinity and silica. Montane lakes with high altitudinal gradients may be particularly prone to local controls compared to systems where coherence is more obvious. [source]

Population characteristics of Oreochromis esculentus in the Victoria and Kyoga lake basins.

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2006
Implications for conservation, improvement of the stocks
First page of article [source]

Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods,

JOURNAL OF QUATERNARY SCIENCE, Issue 4 2006
B. Wohlfarth
Abstract The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution 14C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono- and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and ,realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for over-dependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age,depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Morphometric and spatial analysis of thaw lakes and drained thaw lake basins in the western Arctic Coastal Plain, Alaska

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2005
K. M. Hinkel
Abstract Landsat-7 ETM,+ scenes were acquired for the western Arctic Coastal Plain of Alaska extending from 152° to 162° W longitude. A segmentation algorithm was used to classify lakes and drained thaw lake basins (DTLBs) exceeding 1,ha in size. A total of 13,214 lakes and 6539 DTLBs were identified. Several indices were obtained from the image processing software and used for a comparative analysis of lakes and basins including object size, goodness of elliptic fit, shape complexity, shape asymmetry, and orientation of the major axis. Nonparametric statistical analyses indicate that lakes and basins share similar orientation only. Three subregions of the western Arctic Coastal Plain were identified based on landscape age, as demarcated by ancient shorelines. The surfaces become progressively older inland and include the Younger Outer Coastal Plain, the Outer Coastal Plain, and the oldest Inner Coastal Plain. Lakes and basins in all subregions have statistically similar orientation, indicating that summer wind direction has not changed appreciably over the past several thousand years. Basin orientation is less clustered than lake orientation. Lakes are highly elliptical, while basins have more complex shapes. Lake coverage (%) is fairly constant across the three subregions, while DTLB coverage decreases on older surfaces. Lake and basin size decreases on progressively older surfaces, but the number of features per unit area increases. It is uncertain if surface age is responsible for differences in regional metrics as an analysis of the Inner Coastal Plain demonstrates significant internal variation. Distance from the coast, ground ice content, surficial sediments, and local relief may also influence lake morphometry. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Ostracoda (Crustacea) from the Turkish Ramsar site of Lake Ku, (Manyas Gölü)

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2001
Selçuk Alt, nsaçl
Abstract 1.,Lake Ku, (Manyas Gölü), an important bird conservation area, was sampled in the summer, autumn, winter and spring of 1997, and the seasonal and spatial distributions of ostracods were investigated. Many of the taxa collected are useful indicator species for monitoring conditions within lake basins. 2.,The findings suggest that the L. Ku, ecosystem is already substantially degraded. Pollution, coupled with extensive water abstraction for irrigation, have damaged the value of the lake, both commercially (as an inland waters fishery), and as an important site for wetland bird conservation. 3.,This work shows that ostracod faunal analysis has value in the study of such sites, particularly where more formal physical, chemical and biological monitoring methods are inappropriate or unavailable. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Oil and Gas Accumulation in the Foreland Basins, Central and Western China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010
Yan SONG
Abstract: Foreland basin represents one of the most important hydrocarbon habitats in central and western China. To distinguish these foreland basins regionally, and according to the need of petroleum exploration and favorable exploration areas, the foreland basins in central and western China can be divided into three structural types: superimposed, retrogressive and reformative foreland basin (or thrust belt), each with distinctive petroleum system characteristics in their petroleum system components (such as the source rock, reservoir rock, caprock, time of oil and gas accumulation, the remolding of oil/gas reservoir after accumulation, and the favorable exploration area, etc.). The superimposed type foreland basins, as exemplified by the Kuqa Depression of the Tarim Basin, characterized by two stages of early and late foreland basin development, typically contain at least two hydrocarbon source beds, one deposited in the early foreland development and another in the later fault-trough lake stage. Hydrocarbon accumulations in this type of foreland basin often occur in multiple stages of the basin development, though most of the highly productive pools were formed during the late stage of hydrocarbon migration and entrapment (Himalayan period). This is in sharp contrast to the retrogressive foreland basins (only developing foreland basin during the Permian to Triassic) such as the western Sichuan Basin, where prolific hydrocarbon source rocks are associated with sediments deposited during the early stages of the foreland basin development. As a result, hydrocarbon accumulations in retrogressive foreland basins occur mainly in the early stage of basin evolution. The reformative foreland basins (only developing foreland basin during the Himalayan period) such as the northern Qaidam Basin, in contrast, contain organic-rich, lacustrine source rocks deposited only in fault-trough lake basins occurring prior to the reformative foreland development during the late Cenozoic, with hydrocarbon accumulations taking place relatively late (Himalayan period). Therefore, the ultimate hydrocarbon potentials in the three types of foreland basins are largely determined by the extent of spatial and temporal matching among the thrust belts, hydrocarbon source kitchens, and regional and local caprocks. [source]

The Late Weichselian sea level history of the Kullen Peninsula in northwest Skåne, southern Sweden

BOREAS, Issue 2 2001
PER SANDGREN
The Kullen Peninsula in northwest Skåne, at the time of the Weichselian deglaciation an island surrounded by the Kattegat Sea, is the earliest known deglaciated area in Sweden. Sediment stratigraphic and mineral magnetic properties, combined with radiocarbon dating, were used to determine and date the isolation of present-day lake basins from the sea. Significant environmental changes, which reflect the isolations, are supported by previously published palaeoecological data and cannot be related to climate changes. Basins situated above the marine limit (ML) have short (in the order of centimetres) minerogenic sequences that are magnetically characterized by low concentrations of detrital magnetite. In contrast, the pre-isolation sediments in basins below the ML, especially those deposited in sheltered positions in the landscape, have thick sequences (in the order of metres) of authigenic greigite-bearing sediments. Age determinations of the isolation level are based on the AMS radiocarbon dating of terrestrial plant macrofossil remains and previously published pollen stratigraphical investigations. Supported by the upper level of a sandy beach deposit preserved on the generally steep till covered slopes, the marine limit can be determined to 88,89 m a.s.l., which developed at the regional deglaciation c. 17000 calendar years ago. The results indicate that the deglaciation shoreline level remained fairly constant, relative to the sea level, for c. 1000 years and was followed by a gentle regression. The presented shoreline displacement curve from the Kullen Peninsula extends c. 1000 calendar years further back in time than any previously published records from the Swedish west coast. [source]

Tectonic Landform of Quaternary Lakes and Its Implications for Deformation in the Northern Qinghai-Tibet Plateau

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2009
An WANG
Abstract: The Hohxil region in the northern Qinghai-Tibet Plateau is occupied by numerous plateau lakes, which have long been inferred as being tectonic products. However, so far little evidence has been found to support this tentative inference. Field survey and morphotectonic analysis of TM satellite images in the eastern segment of the Hohxil region revealed that Kusai Lake and Yelusu Lake are S-shaped pull-apart basins, which were dominated by left strike-slip master faults trending WNW-ESE. The pull-apart distances of the two lakes are analyzed to be <15,20 km and 15 km respectively. Based on studies of the faulting rate, the initiation ages of the pull-apart basins are suggested to be approximately in the Early Pleistocene. The pull-apart basin tectonics is further regarded as a common mechanism for the widely distributed large lake basins in the northern Qinghai-Tibet Plateau. Regional distribution of these pull-apart basins and their substantial intra-block slip suggest that a sinistral shear stress, which is independent of the distinguished strike-slip faults, has been imposed on across the northern Qinghai-Tibet Plateau. Thus, the intra-block slip may be an important expression of the eastward extrusion of the Plateau crustal material in accommodating the ongoing continent-continent convergence between India and Eurasia. The revelation of pull-apart tectonics within the Plateau hinterland provides field evidence and a possible style of deformation for the newly proposed continuous deformation by the global positioning system (GPS) measurement across the northern Qinghai-Tibet Plateau. A model, with respect to systematic tectonic landform development, for pull-apart basins is finally proposed. [source]