Fossil midge associations and the historical status of fish in acidified lakes     

M. G. Johnson  J. R. M. Kelso  O. C. McNeil  W. B. Morton 《Journal of Paleolimnology》1990,3(2):113-127

Chaoborid and chironomid (Diptera) fossils were examined in sediment cores form nine Ontario Precambrian Shield lakes that were fishless in 1979. An abundance of Chaoborus americamus (intolerant of predation by fish) throughout cores from four lakes indicated that they were fishless historically. Occurrence of Chaoborus punctipennis and C. flavicans and absence of C. americanus in cores, except near the surface in two cases, indicated that four other lakes were inhabited by fish historically. One of these was probably periodically fishless as suggested by fluctuations among these Chaoborus species. The ninth lake was not suitable for Chaoborus; only one specimen of C. trivittatus was found in this core. Chironomid fossil associations were substantially different in historically fishless and inhabited lakes. Fishless lakes had chironomids typical of eutrophic conditions indicating that seasonal oxygen depletion likely was inimical to fish. Chironomid associations of oligotrophic waters occurred in lakes historically inhabited by fish. Both good water quality and accessibility were required for long-term habitation by fish. Partial recovery of alkalinity and rise in pH were accompanied by substantial re-invasion by fish in two lakes which had been inhabited historically by fish. Diptera associations provide valuable information on the historical suitability of lakes for fish and the presence/absence of fish in regions where acidification of surface waters has occurred.  相似文献   

Effects of crustacean traps on benthic fauna     

Eno  N. Clare; MacDonald  David S.; Kinnear  Jim A. M.; Amos  S. Chris; Chapman  Colin J.; Clark  Robin A.; Bunker  Francis St P.D.; Munro  Colin 《ICES Journal of Marine Science》2001,58(1):11-20

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A 15-month study of zooplankton ingestion by farmed mussels (Mytilus edulis) in Bantry Bay, Southwest Ireland   总被引：4，自引：1，他引：4  

Clare Lehane  John Davenport 《Estuarine, Coastal and Shelf Science》2006,67(4):645-652

There is a growing body of evidence to suggest that bivalve molluscs routinely ingest zooplankton. To elucidate further these observations, a 15-month study of zooplankton ingestion by farmed mussels was conducted using mussel long-lines in Bantry Bay, Ireland. Stomach content analysis of the mussels showed that there was evidence of zooplankton ingestion throughout the sampling period, but that highest mean numbers of zooplankters were ingested by mussels in the spring and summer months. Various zooplankton species were present in mussel stomachs. Harpacticoid copepods were found more often in stomach contents than calanoid copepods, probably due to their proximity to the bivalves' inhalent siphons. Barnacle cyprids featured in large numbers in stomach contents, but only for a period of 3 months which broadly corresponded with their pelagic phase. Sizes of ingested zooplankton ranged from 126 μm to 6 mm, but more of the smaller zooplankters (e.g. crustacean nauplii) were ingested. When lengths of ingested copepods were compared with those found in plankton net samples, it was found that the net-sampled copepods were significantly larger than those found in mussel stomachs, suggesting that mussels select for smaller categories within the zooplankton available to them. Soft bodied zooplankton was rarely found in mussel stomachs but their absence may be due to rapid digestion or they may have been destroyed in the preservation process. Ingestion of zooplankton by bivalves is discussed in the context of the impacts mussel farms have on resident zooplankton populations.  相似文献   

Towards a method for postcolonial development geography? Possibilities and challenges   总被引：2，自引：0，他引：2  

Parvati Raghuram  Clare Madge 《Singapore journal of tropical geography》2006,27(3):270-288

In this paper we explore the contours of a 'method' for postcolonial development geography, which makes it possible to imagine another 'world-picturing'. We suggest three steps towards such a method. First, we propose that a postcolonial method involves thinking about why we are doing research in the south in the first place; how we come to and produce our questions; and how we analyze and represent our findings based on our subject positionings. Second, that we need to recognize theorization as an inherent part of method, rethink how we currently theorize and reconfigure our methods of theorization to address wider political aims. Problematizing theorization helps challenge the universalism of Eurocentric theories, thus enabling development geography to move towards more decolonized versions and visions. Finally, that this must be accompanied by firmer recognition of our multiple investments – personal, institutional and geopolitical – and how they frame the possibilities for change. These are some possible steps that we think can reconfigure the 'scholarly track' that postcolonial development geographers traverse.  相似文献   

A space-based decametric wavelength radio telescope concept     

K. Belov  A. Branch  S. Broschart  J. Castillo-Rogez  S. Chien  L. Clare  R. Dengler  J. Gao  D. Garza  A. Hegedus  S. Hernandez  S. Herzig  T. Imken  H. Kim  S. Mandutianu  A. Romero-Wolf  S. Schaffer  M. Troesch  E. J. Wyatt  J. Lazio 《Experimental Astronomy》2018,46(2):241-284

This paper reports a design study for a space-based decametric wavelength telescope. While not a new concept, this design study focused on many of the operational aspects that would be required for an actual mission. This design optimized the number of spacecraft to insure good visibility of approx. 80% of the radio galaxies– the primary science target for the mission. A 5,000 km lunar orbit was selected to guarantee minimal gravitational perturbations from Earth and lower radio interference. Optimal schemes for data downlink, spacecraft ranging, and power consumption were identified. An optimal mission duration of 1 year was chosen based on science goals, payload complexity, and other factors. Finally, preliminary simulations showing image reconstruction were conducted to confirm viability of the mission. This work is intended to show the viability and science benefits of conducting multi-spacecraft networked radio astronomy missions in the next few years.  相似文献   

The Dynamics of Benthic Respiration at a Mid-Shelf Station Off Oregon     

Clare E. Reimers  H. Tuba Özkan-Haller  Rhea D. Sanders  Kristina McCann-Grosvenor  Peter J. Chace  Sean A. Crowe 《Aquatic Geochemistry》2016,22(5-6):505-527

Mid-shelf sediments off the Oregon coast are characterized as fine sands that trap and remineralize phytodetritus leading to the consumption of significant quantities of dissolved oxygen. Sediment oxygen consumption (SOC) can be delayed from seasonal organic matter inputs because of a transient buildup of reduced constituents during periods of quiescent physical processes. Between 2009 and 2013, benthic oxygen exchange rates were measured using the noninvasive eddy covariance (EC) method five separate times at a single 80-m station. Ancillary measurements included in situ microprofiles of oxygen at the sediment–water interface, and concentration profiles of pore water nutrients and trace metals, and solid-phase organic C and sulfide minerals from cores. Sediment cores were also incubated to derive anaerobic respiration rates. The EC measurements were made during spring, summer, and fall conditions, and they produced average benthic oxygen flux estimates that varied between ?2 and ?15 mmol m^?2 d^?1. The EC oxygen fluxes were most highly correlated with bottom-sensed, significant wave heights (H _s). The relationship with H _s was used with an annual record of deepwater swell heights to predict an integrated oxygen consumption rate for the mid-shelf of 1.5 mol m^?2 for the upwelling season (May–September) and 6.8 mol m^?2 y^?1. The annual prediction requires that SOC rates are enhanced in the winter because of sand filtering and pore water advection under large waves, and it counters budgets that assume a dominance of organic matter export from the shelf. Refined budgets will require winter flux measurements and observations from cross-shelf transects over multiple years.  相似文献   

Aspiration and reality: flood policy, economic damages and the appraisal process   总被引：1，自引：0，他引：1  

Clare Johnson  Edmund Penning-Rowsell  Sue Tapsell 《Area》2007,39(2):214-223

Research shows that flood damage potential has increased significantly in the last 15 years. At the same time, flood policy has shifted away from simplistic flood defence towards 'living with floods' and 'making space for water'. This paper explores the mis-match between the aspiration in policy ideals, the reality of rising potential economic damages and the inability of the flood risk appraisal process to match the aspiration with the reality. Unless investment appraisal procedures are changed, the increase in damages will undermine policy changes that seek a different pattern of flood risk management, away from economically dominated decision-criteria towards more sustainable objectives.  相似文献   

Predation on soft-shell clams,Mya arenaria,by the common mummichog,Fundulus heteroclitus     

William E. Kelso 《Estuaries and Coasts》1979,2(4):249-254

Invertebrate predation has been cited as the major factor determining post-settling survival of the soft-shell clam, Mya arenaria. Feeding studies on common mummichogs, Fundulus heteroclitus, in Essex Bay, Massachusetts, from July 1976 to June 1978 showed soft-shell clams to be an important diet item in fish greater than 55 mm TL. Biweekly quantitative seining from 16 April to 24 September 1977 revealed predation peaks in the spring and fall corresponding to March–April and June–July spawning periods for M. arenaria. In spring and fall 1977 and spring 1978, 38.5% of the male and 52.8% of the female mummichogs sampled over 55 mm TL averaged 6.77 and 7.32 clams per stomach respectively. The maximum number of clams per stomach was 49 (108 mm female), and 47 (100 mm male). Quantitative seining at low tide yielded mummichog densities from 0.35 to 6.04 fish/m². Combining mummichog density estimates with soft-shell clam predation data gave a possible consumption of 546,000 M. arenaria per km low tide shoreline per day during peak predation periods. Results indicate mummichog predation may equal or exceed invertebrate predation as a major cause of small (<12 mm) soft-shell clam mortality in the Gulf of Maine.  相似文献   

Multi-proxy summer and winter precipitation reconstruction for southern Africa over the last 200 years     

Raphael Neukom  David J. Nash  Georgina H. Endfield  Stefan W. Grab  Craig A. Grove  Clare Kelso  Coleen H. Vogel  Jens Zinke 《Climate Dynamics》2014,42(9-10):2713-2726

This study presents the first consolidation of palaeoclimate proxy records from multiple archives to develop statistical rainfall reconstructions for southern Africa covering the last two centuries. State-of-the-art ensemble reconstructions reveal multi-decadal rainfall variability in the summer and winter rainfall zones. A decrease in precipitation amount over time is identified in the summer rainfall zone. No significant change in precipitation amount occurred in the winter rainfall zone, but rainfall variability has increased over time. Generally synchronous rainfall fluctuations between the two zones are identified on decadal scales, with common wet (dry) periods reconstructed around 1890 (1930). A strong relationship between seasonal rainfall and sea surface temperatures (SSTs) in the surrounding oceans is confirmed. Coherence among decadal-scale fluctuations of southern African rainfall, regional SST, SSTs in the Pacific Ocean and rainfall in south-eastern Australia suggest SST-rainfall teleconnections across the southern hemisphere. Temporal breakdowns of the SST-rainfall relationship in the southern African regions and the connection between the two rainfall zones are observed, for example during the 1950s. Our results confirm the complex interplay between large-scale teleconnections, regional SSTs and local effects in modulating multi-decadal southern African rainfall variability over long timescales.  相似文献   

The Oxford Principles     

Steve Rayner  Clare Heyward  Tim Kruger  Nick Pidgeon  Catherine Redgwell  Julian Savulescu 《Climatic change》2013,121(3):499-512

Scientific momentum is increasing behind efforts to develop geoengineering options, but it is widely acknowledged that the challenges of geoengineering are as much political and social as they are technical. Legislators are looking for guidance on the governance of geoengineering research and possible deployment. The Oxford Principles are five high-level principles for geoengineering governance. This article explains their intended function and the core societal values which they attempt to capture. Finally, it proposes a framework for their implementation in a flexible governance architecture through the formulation of technology-specific research protocols.  相似文献