1,943 research outputs found
NERC - GEOPASS mid project review: GR3/10529: minutes of Workshop 1
No full textThe mid-term project review meeting took place at the Environmental Change Research Centre, UCL between 6th - 8th April inclusive. All but one of the active participants in the project were present:
Prof. Rick Battarbee (RWB): Principal Investigator
Dr. Roger Flower (RJF): Principal Investigator
Dr. David Jewson (DJ): Principal Investigator
Dr. Dave Ryves (DBR): PORA
Dr. Anson Mackay (AWM): Associated personnel
Dr. Mike Sturm (MS): Senior Visiting Fellow
Dr. Joan Lees (JL): Associated personnel
Apologies: Dr Anna Kuzmina (Senior Visiting Fellow)
Day 1 of the meeting was used as an opportunity for the project team to update each other on work progress to date, and to exhange & harmonise data already collected.
Day 2 focused on the NERC proposal, specifically what we have acheived so far, and what remains to be done to fulfill project requirements.
Day 3 focused firstly on what types of data would need to be collected to create a diatom transfer function for Lake Baikal. In the afternoon, new ideas for future projects and co-operation were discussed between the 4 groups: ECRC, University of Ulster, EAWAG & the Limnological Institute at Irkuts
Influence of temperature and sliding speed on the subsurface microstructure evolution of EN AW-6060 under sticking friction conditions
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1896, 140012 (2017) and may be found at https://doi.org/10.1063/1.5008168.The microstructure evolution of the friction boundary layer of the aluminum alloy EN AW-6060 was investigated. Sticking friction tests at different temperatures and sliding speeds were carried out. A severe deformation below the friction surface was observed by means of LOM and EBSD mapping. Thus, the thickness variation and the grain structure of the high deformation zone could be described. Fibrous structure was observed at 300 °C and 400 °C, while equiaxed grains with high misorientation angle (>15°) were generated at higher temperatures. Additionally, abnormal grain growth and coarse grains were detected at high sliding speeds (10 mm/s, 42 mm/s) at 450°C and 500 °C respectively
Biodiversity and biomass of algae in the Okavango Delta (Botswana), a subtropical flood-pulsed wetland
No full textIn freshwater bodies algae provide key ecosystem services such as food and water purification. This is the first systematic assessment of biodiversity, biomass and distribution patterns of these aquatic primary producers in the Okavango Delta (Botswana), a subtropical flood-pulsed wetland in semiarid Southern Africa. This study delivers the first estimate of algal species and genera richness at the Delta scale; 496 species and 173 genera were observed in 132 samples. A new variety of desmid (Chlorophyta) was discovered, Cosmarium pseudosulcatum var. okavangicum, and species richness estimators suggest that a further few hundred unidentified species likely live in this wetland. Rare species represent 81% of species richness and 30% of total algal biovolume. Species composition is most similar within habitat types, thus varying more significantly at the Delta scale. In seasonally inundated floodplains, algal species / genera richness and diversity are significantly higher than in permanently flooded open water habitats. The annual flood pulse has historically allowed more diverse algal communities to develop and persist in these shallower and warmer environments with higher mean nutrient levels and more substrata and more heterogenous habitats for benthic taxa. These results support the Intermediate Disturbance Hypothesis, Species-Energy Theory and Habitat Heterogeneity Diversity hypotheses. Higher algal biodiversity supports higher algal biomass in the floodplains, where species form three-dimensional communities of attached and periphytic algae requiring more nutrients than phytoplankton assemblages. Multivariate analyses demonstrate that habitat type, flooding frequency and conductivity most importantly influence the relative abundance of algal species, genera and phyla in the Okavango Delta. This study’s findings highlight how the preservation of water level fluctuations and habitat heterogeneity is crucial to maintaining biodiverse and thus resilient food webs in this unique ecosystem which faces increasing anthropogenic threats, such as global warming and upstream water abstraction plans
Plio-Pleistocene reconstruction of East African and Arabian Sea palaeoclimate
No full textSuperimposed upon a long-term trend of aridification, the climate history of Africa was punctuated by episodes of extreme climate variability, characterised by the precessionally-forced appearance and disappearance of large lake systems within the East African Rift Valley. In order to investigate the nature of low-latitude climate variability during the Late Pliocene and Early Pleistocene, this thesis combines high-resolution analyses from one of the lake phases in the Central Kenyan Rift with the reconstruction of long-term changes in the transport of wind-borne terrigenous dust to the Arabian Sea. Climate in both regions is strongly influenced by relative changes in the strength of the Indian Ocean monsoons, which determine rainfall distribution in equatorial East Africa and generate the low-level winds which transport dust offshore from the Arabian Peninsula. In the Baringo-Bogoria basin in the Central Kenyan Rift, a well-dated package of fluvio-lacustrine sediments and diatomite units documents a major humid phase between 2.7 and 2.55 million years ago (Ma), coincident with the intensification of glaciation in the Northern Hemisphere. Stable oxygen isotope measurements of diatom silica, combined with the XRF analysis of whole-sample geochemistry, reveal that the deep lake phase was characterised by wet-dry cycles lasting, on average, 1,400 years. Over longer timescales, variations in the aeolian delivery of lithogenic matter to the Arabian Sea, reflected in normalised flux of titanium, show that monsoonal circulation prior to 2.6 Ma was highly variable and primarily driven by orbitally-forced changes in tropical summer insolation, modulated by the 400,000 year cycle of orbital eccentricity. Millennial-scale fluctuations in the dust record also support the evidence of abrupt wet-dry cycles in East Africa. Such high-resolution cycles are rarely found in older records, thus giving a valuable insight to the nature of short-term fluctuations in Plio-Pleistocene climate
A rationale for the use of artificial substrata to enhance diatom-based monitoring of eutrophication in lowland rivers
No full textWith the introduction of new European directives governing water quality, the need to monitor
eutrophication in rivers has been recognized. The inclusion of a reliable biotic component in any such
monitoring scheme is considered necessary. Diatoms have been shown to display a direct response to
trophic status and are therefore being used in preliminary work in this field. The sampling of river
diatoms has relied on the river site having clean cobbles, or other solid substrata, from which to collect
the epilithon. From a total of 58 lowland river sites visited only 31 had a good epilithic community . The
need therefore exists for a more reliable sampling method in these systems. Artificial substrata have a
number of reported advantages over the natural communities : lower sample variability, consistency
between sites, placement at the point of interest and ease of use. Data are presented here to compare three
different types of artificial substrata (rough tile, smooth tile and rope) with the natural communities
(epilithon epipelon and epiphyton) at two eutrophic river sites. Within sample variation is shown to be
lower on the artificial substrata while a high diversity is maintained on the rope and rough tiles. Further
ad vantages of using artificial substrata are described and the logistics of their applied use are discussed
The impact of carp stocking on fresh water Sites of Special Scientific Interest in southern England
No full textCarp have been introduced to ponds throughout
Britain because they are favoured by anglers.
However, carp feeding is known to have a detrimental
effect on submerged macrophytes and so could reduce
the conservation status of inland water Sites of
Special Scientific Interest. Five SSSI sites where
symptoms of nutrient enrichment are attributed to the
effects of common carp and common bream
(Carvalho & Moss 1995) together with a sixth,
national nature reserve site, form the basis for this
study. Data was gathered on fish stocking densities,
water chemistry and submerged plant cover. The
range of degradation in the lakes was related to fish
stocking densities. Two sites were chosen for a
detailed study of the calculation of a TP budget for the
period March - July 1996, thereby allowed a compar ison
of carp P release rates to other P loadings. The
results of this study show that at a stocking density of
200 kg ha· 1, carp fisheries can be compatible with
SSSI conservation. At higher stocking densities,
degradation of the sites can occur due to carp feeding
ecology, interactions with other fish species and manmade
changes to the lake. No general model of the
effects of carp on ponds can be built due to the
variety of factors which interact with the species in
these lakes
Author-Suggested, Weighted Citation Index: A Novel Approach for Determining the Contribution of Individual Researchers
No full textA novel scientometric index, named ‘author-suggested, weighted citation index’ (Aw-index) is proposed to indicate the scientific contribution of any individual researcher. For calculation of the Aw-index, it is suggested that during the submission of a scholarly article, the corresponding author would provide a statement, agreed upon by all the authors, containing weightage factors against each author of the article. The author who contributed more to the article would secure a higher weightage factor. The summation of the weightage factors of all the authors of an article should be unity. The citation points a researcher receives from a scholarly publication is the product of his/her weightage factor for that article and the total number of citations of the article. The Aw-index of any individual researcher is the summation of the citation points he/she receives for all his/her publications as an author. The Aw-index provides the opportunity to the group of authors of a multi-authored article to determine the quantum of partial citations to be attributed to each of them. Through an illustrative example, a comparison of the proposed index with the major scientometric indexes is presented to highlight the advantages of the Aw-index
Further high resolution analyses of surface sediment cores taken from Lake Baikal
No full textFollowing up our work reported in the year pilot study report (Mackay et al. 1993), a total
of 31 surface sediment cores were collected from Lake Baikal in the summer of 1993, in
accordance with the original project proposals. Of these only 22 are suitable for quality
stratigraphic work at the ECRC. These cores were taken from selected sites along the length
of the lake, but owing to problems with ship-time and equipment, the southern basin was not
fully sampled at this time. Consequently, earlier this year in March, we undertook a further
expedition to collect more cores from the southern basin. This involved working from the lake
whilst frozen. and hence necessited new techniques: 1700 m 'Kevlar' rope was purchased and
a new winch refurbished, the latter being funded by The Royal Society. A further 7 cores
were collected, 6 of which are suitable for stratigraphic work. These cores will also be used
to check core replicability. There now remains one area, approximately 5 km from the eastern
shore of the southern basin, following a transect towards the middle of that basin, where we
still need to collect several cores (ca. 3) and this will be done early next year in March 1995
Influence of Process Parameters on the Quality of Aluminium Alloy EN AW 7075 Using Selective Laser Melting (SLM)
No full textAbstractSelective laser melting (SLM) is an additive manufacturing process, forming the desired geometry by selective layer fusion of powder material. Unlike conventional manufacturing processes, highly complex parts can be manufactured with high accuracy and little post processing. Currently, different steel, aluminium, titanium and nickel-based alloys have been successfully processed; however, high strength aluminium alloy EN AW 7075 has not been processed with satisfying quality. The main focus of the investigation is to develop the SLM process for the wide used aluminium alloy EN AW 7075. Before process development, the gas-atomized powder material was characterized in terms of statistical distribution: size and shape. A wide range of process parameters were selected to optimize the process in terms of optimum volume density. The investigations resulted in a relative density of over 99%. However, all laser-melted parts exhibit hot cracks which typically appear in aluminium alloy EN AW 7075 during the welding process. Furthermore the influence of processing parameters on the chemical composition of the selected alloy was determined
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