Fluvial dissolved Fe concentrations decrease upon mixing with seawater, resulting in the formation of Fe-floccules. However, a clear understanding of the fate of these floccules has yet to be established. Assessing how tidal processes affect the formation of Fe-colloids in the Leirárvogur estuary, SW Iceland, is an important step in understanding the formation and potential deposition of estuarine Fe-rich minerals within this estuarine system. The Leirárvogur estuary drains predominately Fe-rich basalt, increasing the likelihood of detecting changes in Fe-phases. Fluvial waters and local lake waters that drain into the estuary were compared and the effects of seasonal changes were considered, in an attempt to understand how varying end-members and external factors play a role in Fe-rich mineral formation. Aqueous and colloidal Fe concentrations were found to be greater towards the head of the Leirárvogur estuary, suggesting that potential Fe-rich minerals and complexes are forming at sites of fluvial input. Increasing suspended colloidal Fe towards the estuary mouth suggests that Fe-colloids are readily transported seaward. 相似文献
Two scales of levee confinement are commonly recognised from submarine channel-levee systems on the seafloor and in the subsurface. Large-scale external levees bound the entire system whilst smaller-scale internal levees bound individual thalweg channels within the channel-belt. Although thin beds are commonly identified in core and well logs, their origin, and consequently their stratigraphic significance is currently poorly understood. This knowledge gap stems, in part, from the lack of unambiguously identified outcrop analogues of channel-levees, and in particular the lack of identifiable internal and external levees. Here we report from two exhumed channel-levee systems where both scales of confinement can be recognised: the Rosario Fm. of Baja California, and the Fort Brown Fm. of South Africa. A suite of characteristic sedimentary features are recognised from internal and external levees respectively: internal levees are characterised by structures indicative of complexity in the waxing-waning style of overspill, interactions with topography and flow magnitude variability; in contrast, external levees are characterised by structures indicative of simple surge-like waning flows, relatively uniform flow directions, laterally extensive beds, and a lack of erosive events. Using these observations, together with published literature, we propose a simple nomenclatural scheme for levee sub-environments, and criteria to differentiate between levee sub-environments in core or outcrop. 相似文献
We present a relative sea-level (RSL) history, constrained by AMS radiocarbon-dated marine-freshwater transitions in isolation basins from a site adjacent to the Lambert Glacier, East Antarctica. The RSL data suggest an initial ice retreat between c. 15,370 and 12,660 cal yr B.P.. Within this period, meltwater pulse IA (mwp IA, between c. 14,600-14,200 and 14,100-13,700 cal yr B.P.) occurred; an exceptionally large ice melting event, inferred from far-field sea-level records. The RSL curve shows a pronounced highstand of approximately 8 m between c. 7570-7270 and 7250-6950 cal yr B.P. that is consistent with the timing of the RSL highstand in the nearby Vestfold Hills. This is followed by a fall in RSL to the present. In contrast to previous findings, the isolation of the lakes in the Larsemann Hills postdates the isolation of lakes with similar sill heights in the Vestfold Hills. An increase in RSL fall during the late Holocene may record a decline in the rate of isostatic uplift in the Larsemann Hills between c. 7250-6950 and 2847-2509 cal yr B.P., that occurred in response to a documented mid-Holocene glacier readvance followed by a late-Holocene retreat. 相似文献
In order to improve understanding of the fate of septic tank or individual sewage disposal system (ISDS) effluent in regolith overlying fractured-rock aquifers, effluent from an ISDS in such a setting was tracked via geophysical, hydrological, and geochemical methods. Under typical precipitation conditions, the effluent entered the fractured bedrock within 5 m of the boundary of the constructed infiltration area. During a period of unusually high spring recharge, the plume migrated between 50 and 100 m within the regolith before infiltrating the fractured bedrock. The chemical signature of the effluent is similar to that required to account for the decline in water quality, suggesting a causative relationship (as estimated from mass-balance models of the surface-water chemistry near the mouth of the basin). The elevated salt content of the effluent during periods of high natural recharge to the infiltration area correlates with elevated salt concentrations in surface and groundwater at the basin scale, suggesting that some of the effluent salt load may be stored in the unsaturated zone during dry periods and flushed during periods of elevated natural recharge. 相似文献
The fossil diatom records preserved in radiometrically dated sediment cores from four shallow lakes in the Norfolk Broads, UK (Barton Broad, Rollesby Broad, Wroxham Broad and Upton Broad) were analysed. A weighted-averaging partial least squares (WA-PLS) diatom-total phosphorus (TP) transfer function, based on a training set of 152 mostly shallow (maximum depth < 3 m) lakes in northwest Europe, was applied to the full diatom dataset for each core to reconstruct the past TP concentrations of the lakes. Owing to the dominance of non-planktonic Staurosira, Pseudostaurosira and Staurosirella spp. (formerly classified in the genus Fragilaria) throughout the diatom records, the quantitative diatom inferred TP (DI-TP) concentrations did not adequately reflect the changes that occurred in the lakes as indicated by shifts in the other diatom taxa, or as reported in the literature. This was most apparent at Barton Broad and Rollesby Broad, where there was a marked increase in the importance of planktonic taxa associated with highly nutrient-rich waters but no increase in DI-TP. The modern and fossil data were thus square-root transformed to downweight the dominant taxa and the new transfer function was applied to the cores. An improvement was seen only in the reconstruction for Barton Broad. Finally, the Staurosira, Pseudostaurosira and Staurosirella spp. were removed from the modern and fossil diatom data, and the transfer function was re-applied. The trends in DI-TP became less clear, particularly for Upton Broad and Barton Broad, owing to a paucity of data for calibration once these taxa were deleted from the counts data. The problems associated with reconstructing trophic status and determining TP targets for restoration from fossil diatom assemblages in these systems are discussed. 相似文献
Summary The aim of this paper is to contribute towards a better understanding of the contemporary position of commons as a land resource, and to evaluate whether commons have a distinct role to play in today's 'post-productivist' countryside. Following the government's recent recognition of the multi-functional role of commons, the paper sets out to investigate whether this can be achieved through existing agri-environmental schemes. A case study of commons in the Cambrian Mountains (Wales) enables an assessment of the compatibility of one recent agri-environmental scheme, the ESA scheme, with commons management. It is concluded that new legislation and policy are needed, and that agri-environmental policy may provide an opportunity to develop a framework within which the management of common land can be improved to meet conservation and amenity as well as farming objectives. 相似文献
The seaward end of modern rivers is characterized by the interactions of marine and fluvial processes, a tract known as the fluvial to marine transition zone, which varies between systems due to the relative strength of these processes. To understand how fluvial and tidal process interactions and the fluvial to marine transition zone are preserved in the rock record, large‐scale outcrops of deltaic deposits of the Middle Jurassic Lajas Formation (Neuquén Basin, Argentina) have been investigated. Fluvial–tidal indicators consist of cyclically distributed carbonaceous drapes in unidirectional, seaward‐oriented cross‐stratifications, which are interpreted as the result of tidal modulation of the fluvial current in the inner part of the fluvial to marine transition zone. Heterolithic deposits with decimetre‐scale interbedding of coarser‐grained and finer‐grained facies with mixed fluvial and tidal affinities are interpreted to indicate fluvial discharge fluctuations (seasonality) and subordinate tidal influence. Many other potential tidal indicators are argued to be the result of fluvial–tidal interactions with overall fluvial dominance or of purely fluvial processes. No purely tidal or tide‐dominated facies were recognized in the studied deposits. Moreover, fluvial–tidal features are found mainly in deposits interpreted as interflood (forming during low river stage) in distal (delta front) or off‐axis (interdistributary) parts of the system. Along major channel axes, the interpreted fluvial to marine transition zone is mainly represented by the fluvial‐dominated section, whereas little or no tide‐dominated section is identified. The system is interpreted to have been hyposynchronous with a poorly developed turbidity maximum. These conditions and the architectural elements described, including major and minor distributary channels, terminal distributary channels, mouth bars and crevasse mouth bars, are consistent with an interpretation of a fluvial‐dominated, tide‐influenced delta system and with an estimated short backwater length and inferred microtidal conditions. The improved identification of process interactions, and their preservation in ancient fluvial to marine transition zones, is fundamental to refining interpretations of ancient deltaic successions. 相似文献
GEOMORPHOLOGY by R. J. Chorley, S. A. Schumm and D. E. Sugden.’ 19 × 25 cm, xxiii and 605 pages. Methuen: London 1984 (ISBN 0 416 32590 4) $A39.95 (cloth).
THEMES IN GEOMORPHOLOGY edited by A. F. Pitty. 13 × 21 cm, 280 pages. Croom Helm: London 1985 (ISBN 0 7099 2066 0) $A49.50 (cloth).
DESERTS AND ARID LANDS edited by F. El‐Baz. 16 × 25 cm, vi and 222 pages. Nijhoff: The Hague 1984 (ISBN 90 247 2850 9) $US46.00 (cloth).
COASTAL GEOMORPHOLOGY IN AUSTRALIA edited by B. G. Thorn. 16 × 24 cm, xv and 349 pages. Academic Press: Sydney 1984 (ISBN 0 12 687880 3) $A49.50 (cloth).
KWONGAN: Plant Life on the Sandplain edited by J. S. Pate and J. S. Beard. University of Western Australia Press: Nedlands 1984 (ISBN 0 85564 230 0) $A25.00 (limp).
THEMES IN BIOGEOGRAPHY edited by J. A. Taylor. 22 × 14 cm, xxvii and 404 pages. Croom Helm: London 1984 (ISBN 0 7099 2428 3) $A25.95 (limp).
ENVIRONMENTAL IMPACT ASSESSMENT: A Practical Guide by C. F. Porter. 22 × 15 cm, xiii and 269 pages. University of Queensland Press: St Lucia 1985 (ISBN 0 7022 1699 2) $A35.00 (cloth).
THE CLIMATIC SCENE edited by M. J. Tooley and G. M. Sheail. 16 × 24 cm, xx and 306 pages. George Allen and Unwin: London 1985 (ISBN 0 04 551089 X) $A59.95 (cloth).
VOLCANIC HAZARDS: A Sourcebook on the Effects of Eruptions by R. J. Blong. 24 × 15 cm, xvi and 424 pages. Academic Press: Sydney 1984 (ISBN 0 12 107180 4) $A68.00 (cloth).
THE ECONOMICS OF BUSHFIRES: The South Australian Experience edited by D. T. Healey, F. G. Jarrett and J. M. McKay. 22 × 15 cm, x and 152 pages. Oxford University Press: Melbourne 1985 (ISBN 0 19 554669 5) $A19.99 (cloth). 相似文献