Artificial mouth opening fosters anoxic conditions that kill small estuarine fish     

Alistair Becker  Laurie J.B. Laurenson  Kylie Bishop   《Estuarine, Coastal and Shelf Science》2009,82(4):566-572

Fish kills are not uncommon within estuaries in many regions of the world. In seasonally open systems, which are common in temperate areas, they are often associated with mouth openings. Such a kill occurred in July 2005 in the Surrey Estuary following a closed mouth period of seven months resulting in the loss of many thousands of fish. At the time the fish community within the estuary was under investigation which provided comprehensive data of this population prior to the kill. Monthly water quality monitoring was also being conducted prior to the kill and also carried out on a daily basis following the mouth opening. The Surrey was stratified during the closed mouth phase, isolated waters below the halocline had stagnated and become anoxic. As a result only waters above the halocline contained oxygen concentrations capable of sustaining most fish. It appears that if a mouth opening happens under low flow conditions, a shearing effect occurs within the water column where surface waters flow out to sea leaving deeper waters behind. This resulted in only anoxic waters being present for in excess of six days and was responsible for the fish kill. Fish sampling of the Surrey Estuary was conducted three and six months following the kill and those data were compared to that collected in the 12 months prior to the event. Three months after the kill few fish were collected within the estuary and included marine opportunists near the mouth and estuarine resident species in the far upper reaches of the system. However six months following the kill large numbers of estuarine resident species were collected throughout the Surrey Estuary. As many species were euryhaline, it is believed that some individuals migrated into freshwater reaches of the Surrey to escape the anoxic conditions within the estuary. As conditions improved they recolonised the Surrey Estuary. The high fecundity and rapid growth of these small, short lived species probably aided in their re-establishing populations within the estuary. It is clear from this research that artificial openings of estuaries should be avoided during low flow periods when oxygen concentrations are low. It also appears that many of the small estuarine resident species common in seasonally open estuaries are capable of recolonising estuaries following fish kills. The effects on larger, longer lived resident species are not known but likely to be more detrimental due to longer time required for them to reach sexual maturity.  相似文献   

A re-examination of the mechanism and human impact of catastrophic mass flows originating on Nevado Huascarán, Cordillera Blanca, Peru in 1962 and 1970     

Stephen G. Evans  Nicholas F. Bishop  Lionel Fidel Smoll  Patricio Valderrama Murillo  Keith B. Delaney  Anthony Oliver-Smith 《Engineering Geology》2009,108(1-2):96-118

The 1962 and 1970 Huascarán mass movements, originated as rock/ice falls from the mountain's North Peak, transformed into higher-volume high-velocity mud-rich debris flows by incorporation of snow from the surface of a glacier below Huascarán and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus. Water for fluidization of the entrained material originated in the melting of incorporated snow and the liberation of soil moisture contained within the entrained materials. Eyewitness reports indicate very high mean velocities for the events; 17–35 m/s (1962) and 50–85 m/s (1970). The runout distances and velocity profiles of both events were simulated using DAN/W. Both mass movements continued downstream in the Rio Santa as debris floods (aluviones) that in 1970 reached the Pacific at a distance of 180 km. In strong contrast to publications in the geosciences literature, 1961 Peru Census data indicates that the death toll of the 1970 event is ca. 6000 and that total life loss in the two events did not exceed 7000 people.  相似文献   

Reduced removal of bacteriophage MS2 in during basin infiltration managed aquifer recharge as basin sand is exposed to infiltration water          下载免费PDF全文

Jean‐Marc Mayotte  Lisanne Hölting  Kevin Bishop 《水文研究》2017,31(9):1690-1701

Basin infiltration managed aquifer recharge (MAR) is a commonly used method for storing and treating surface water to be used as drinking water. This study examined how the removal of bacteriophage MS2 was affected by the relative age of the sand used for basin infiltration MAR at 4 °C using batch experiments (static and agitated) and column experiments. The sand and the water used in all experiments were characteristic of that used at a basin infiltration MAR scheme in Uppsala, Sweden. Experimental data was fit with numerical models describing the fate and transport of virus in soil—water systems. The “used” sand that had been subjected to intermittent infiltration over a period of 8 years had 15 times the amount of organic carbon than the “new” sand, which had yet to be used for infiltration. Results showed that attachment of MS2 to the new sand in batch experiments was relatively irreversible. Attachment to the used sand was reversible. Inactivation of MS2 was slowed when it was attached to the used sand. Results for the column experiments showed that the removal rate of MS2 was significantly lower in columns of used sand than in columns of new sand. Simulations indicated that MS2 would be entirely removed in the infiltration basins with new sand. Less than 3 log removals was estimated for basins with used sand. Reduced removal of MS2 by the used sand was deemed to be most likely due to organic coatings on the used sand. Results of this study give deeper insight into the mechanisms responsible for removing virus in infiltration basins and how those mechanisms will change as the sand in the basin is exposed to infiltration water.  相似文献   

Episodic stream water pH decline during autumn storms following a summer drought in northern Sweden     

Hjalmar Laudon  Kevin Bishop 《水文研究》2002,16(9):1725-1733

The sources of episodic pH decline in four streams from northern Sweden during the autumn of 1996 were quantified. The events, in which pH dropped by between 1·0 and 2·4 units, were preceded by an extensive summer drought. Total organic carbon, which increased 100% to 160% during peak flow, was the most important driving mechanism of the episodic pH decline. Sulphate, however, was relatively more important during these autumn events than during spring flood. In the sites where past and present anthropogenic deposition were believed to be the main source of sulphate in stream water, sulphate contributed less than 0·3 pH units to the pH decline. In catchments where natural sources of sulphate are known to be important, sulphate contributed up to 0·6 units of pH decline. The export of sulphate during the episodes was two to nine times higher than what was expected from deposition only. The drought preceding the study episodes resulted in some of the lowest ground water levels during the 1990s in that region. The large export of sulphate was probably due to oxidation of natural sulphate bearing minerals in the soil and/or previously deposited sulphate driven by the low ground water level preceding the episodes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Geomorphic change in high mountains: a western Himalayan perspective   总被引：1，自引：0，他引：1  

Michael P. Bishop  John F. Shroder  Jr.  Radoslav Bonk  Jeffrey Olsenholler 《Global and Planetary Change》2002,32(4)

Globally significant interactions between climate, surface processes, and tectonics have recently been proposed to explain climate change and mountain building. Assessing climate-driven erosion processes and geomorphic change in high-mountain environments, however, is notoriously difficult. In the western Himalaya, the coupling of climate, surface processes, and tectonics results in complex topography that frequently records the polygenetic nature of topographic evolution over the last 100 ka. Depending upon the erosional history of a particular landscape, temporal overprinting of geomorphic events can produce unique topographic properties which define the spatial complexity of the topography. Field work coupled with analysis of the topography using digital elevation models (DEMs) enable low- and high-frequency spatial patterns and scale-dependent properties of the topography to be detected and associated with geomorphic events caused by climate and tectonic forcing. We conducted spatial analysis of the topography at Nanga Parbat in northern Pakistan to demonstrate the utility of geomorphometry and to characterize dramatic geomorphic change over the past 100 ka. Results indicate rapid river incision, extensive glaciation, and variable denudation rates by mass movement, glaciation, and catastrophic flood flushing. Furthermore, topographic and chronologic evidence indicate that glaciation is strongly controlled by the southwestern monsoon, and that modern fluvial systems are still responding to tectonic forcing and deglaciation. Scale-dependent analysis of the topography revealed that different erosion processes uniquely alter the spatial complexity of the topography, such that the greatest mesoscale relief appears to be caused by glaciation. Collectively, our results indicate that topographic development in the western Himalaya is inherently polygenetic in nature, with glaciation, fluvial and slope processes all playing important roles at different times, and that they can do so sequentially on the same portion of the landscape. Given the rapidity of major changes in climate and glaciation over the last 100 ka, the landscape cannot be in steady-state.  相似文献   

Coastal inundation under concurrent mean and extreme sea-level rise in Coral Gables,Florida, USA     

Alarcon  Vladimir J.  Linhoss  Anna C.  Kelble  Christopher R.  Mickle  Paul F.  Sanchez-Banda  Gonzalo F.  Mardonez-Meza  Fernando E.  Bishop  Joseph  Ashby  Steven L. 《Natural Hazards》2022,111(3):2933-2962

Natural Hazards - Southeast Florida (SF) is among the most vulnerable regions to sea-level rise in the United States of America. The consequences associated with sea-level rise (SLR) are already...  相似文献   

Seasonal variation of crescentic dune morphology and morphometry,Strzelecki–Simpson Desert,Australia     

Mark A. Bishop 《地球表面变化过程与地形》2001,26(7):783-791

The general absence of contemporary dune building in the Australian arid zone finds the occurrence of crescentic dune genesis and evolution at Gurra Gurra waterhole, a somewhat enigmatic event amongst prevalent inactive linear dunescapes. Crescentic dune construction is geographically restricted to areas of dominant unidirectional high windiness and minimal vegetation, parameters that are generally uncommon in arid Australia today. The influence of seasonal multidirectional winds can see dune form undergo continual transition between quasi‐equilibrium and disequilibrium. Such dynamic antithesis is depicted in seasonal mathematical comparisons of the planimetric attributes, length and width. Dimensional equilibrium is a transient feature at Gurra Gurra waterhole and not characteristic of this dunescape. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Meeting the Need for GIS Skills in Developing Countries: The Case of Informal Settlements     

Ian D. Bishop  Mike Barry  Elsworth McPherson  Joiana Nascarella  Karen Urquhart  & Francisco Escobar 《Transactions in GIS》2002,6(3):311-326

Informal settlements are a chronic issue in developing countries. Management and formalisation processes require good spatial data and analytical tools. While software such as geographic information systems (GIS) are widely available, access to good data and skilled users may be limited. In this paper we suggest that digital multimedia learning tools, accessible via the World Wide Web (WWW) may be part of the solution. We present the rationale for, and structure of, a suite of prototype learning modules for neighbourhood operations. We illustrate the use of these operations by converting shack locations into population density maps for the Imizamo Yethu settlement near Cape Town, South Africa. This prototype forms a part of a larger web site that also includes background information, data sources and software.  相似文献   

Numerical Ground-Water Flow Modeling of the Snake River Plain Aquifer Using the Superposition Technique     

J. M. Hubbel  C. W. Bishop  G. S. Johnson  J. G. Lucas 《Ground water》1997,35(1):59-66

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There and back again: Epiphany, disillusionment, and rediscovery in political ecology     

Paul Robbins  Kristina Monroe Bishop 《Geoforum》2008,39(2):747-755

This paper reviews the experience of discovering, abandoning, and rediscovering elements of the work of political ecologist Piers Blaikie from the period spanning 1992-2006. In the process, we analyze the cyclic fate of critical ideas in the field of political ecology, including especially the “chain of explanation,” during a tumultuous period where materialist and constructivist theorists encountered one another. The paper concludes with a specific discussion of the power of traditional tools in political ecology for addressing current socio-ecological crises, specifically HIV/AIDS in southern Africa.  相似文献