68 research outputs found
Water chemistry and endangered white-clawed crayfish: A literature review and field study of water chemistry association in Austropotamobius pallipes
No full textPopulations of the endangered white-clawed crayfish (Austropotamobius pallipes) have rapidly declined in distribution and density in recent decades as a result of invasive crayfish, disease and habitat degradation. The species is thought to be particularly sensitive to water chemistry, and has been proposed as a bio-indicator of water quality. Here we detail the results of a systematic review of the literature regarding the chemistry of waterbodies inhabited by white-clawed crayfish, along with a wide-scale field study of the chemistry of crayfish-inhabited waterbodies in the UK. We use these data to examine potentially significant variables influencing crayfish distribution. Several variables appear to have thresholds that affect crayfish distribution; crayfish presence was associated with high dissolved oxygen, low conductivity, ammonium, sodium, and phosphate, and to a lesser extent low sulphate, nitrate, and total suspended solids. Some variables (magnesium, potassium, sodium, sulphate, nitrate, and total suspended solids) may be tolerated at moderate to high concentrations in isolation (indicated by the presence of some populations in high levels of these variables), but suites of chemical conditions may act synergistically in situ and must be considered together. Recent efforts to conserve white-clawed crayfish have included relocations to Ark Sites; novel protected habitats with reduced risk of the introduction of disease, invasive crayfish and habitat degradation. We use our findings to propose the first detailed guidelines for common water chemistry variables of potential Ark Sites for the conservation of the species throughout its European range
Bacterially mediated removal of phosphorus and cycling of nitrate and sulfate in the waste stream of a "zero-discharge" recirculating mariculture system
No full textSimultaneous removal of nitrogen and phosphorus by microbial biofilters has been used in a variety of water treatment systems including treatment systems in aquaculture. In this study, phosphorus, nitrate and sulfate cycling in the anaerobic loop of a zero-discharge, recirculating mariculture system was investigated using detailed geochemical measurements in the sludge layer of the digestion basin. High concentrations of nitrate and sulfate, circulating in the overlying water (∼15 mM), were removed by microbial respiration in the sludge resulting in a sulfide accumulation of up to 3 mM. Modelling of the observed S and O isotopic ratios in the surface sludge suggested that, with time, major respiration processes shifted from heterotrophic nitrate and sulfate reduction to autotrophic nitrate reduction. The much higher inorganic P content of the sludge relative to the fish feces is attributed to conversion of organic P to authigenic apatite. This conclusion is supported by: (a) X-ray diffraction analyses, which pointed to an accumulation of a calcium phosphate mineral phase that was different from P phases found in the feces, (b) the calculation that the pore waters of the sludge were highly oversaturated with respect to hydroxyapatite (saturation index = 4.87) and (c) there was a decrease in phosphate (and in the Ca/Na molar ratio) in the pore waters simultaneous with an increase in ammonia showing there had to be an additional P removal process at the same time as the heterotrophic breakdown of organic matter
Evaluating feedback mechanisms in the School of Earth and Environment
No full textAssessment feedback plays a crucial role in the learning experience. However, recent National Student Survey (NSS) results have shown there to be a large degree of student dissatisfaction regarding assessment feedback right across the Higher Education sector in the UK. Evaluating feedback mechanisms in the School of Earth and Environment was a project at the University of Leeds, designed to evaluate the provision of assessment feedback through in-depth consultation with staff and students about current practices, with a view to building upon good practice and creating a strategy for further improvement. Data gathered via focus groups and questionnaires was distilled into a key set of recommendations for ways forward. The recommendations focused on two main strategies: a) the creation of a new comprehensive feedback code of practice for staff, and b) raising student awareness of their rights regarding feedback provision as well as their responsibility to engage with feedback and how to get the most from it. These initiatives have been supported by a distinct, highly visual and sustained advertising campaign designed to act as a corollary to raising staff and student awareness of assessment feedback
Phanerozoic Vertical Movements in Morocco
No full textOur understanding of the Earth’s interior is limited by the access we have of its deep layers, while the knowledge we have of Earth’s evolution is restricted to harvested information from the present state of our planet. We therefore use proxies, physical and numerical models, and observations made on and from the surface of the Earth. The landscape results from a combination of processes operating at the surface and in the subsurface. Thus, if one knows how to read the landscape, one may unfold its geological evolution.In the past decade, numerous studies have documented km-scale upward and downward vertical movements in the continental rifted margins of the Atlantic Ocean and in their hinterlands.These movements, described as exhumation (upward) and subsidence (downward), have been labelled as “unpredicted” and/or “unexpected”. ‘Unpredicted’ because conceptual, physical, and numerical models that we dispose of for the evolution of continental margins do not generally account for these relatively recent observations. ‘Unexpected’ because the km-scale vertical movements occurred when our record of the geological history is insufficient to support them. As yet, the mechanisms responsible for the km-scale vertical movements remain enigmatic.One of the common techniques used by geoscientists to investigate the past kinematics of the continental crust is to couple ‘low-temperature thermochronology’ and ‘time-temperature modelling’. In Morocco alone, over twenty studies were conducted following this approach. The reason behind this abundance of studies and the related enthusiasm of researchers towards Moroccan geology is due to its puzzling landscapes and complex history. In this Thesis, we investigate unconstrained aspects of the km-scale vertical movements that occurred in Morocco and its surroundings (Canary Islands, Algeria, Mali, and Mauritania). Applied Geolog
A Structural Modeling Approach on Timing & Evolution of Mesozoic Anticlines in the Western High Atlas, Morocco
No full textThe Moroccan passive margin has been the objective of a variety of studies to investigate the petroleum potential and to locate play systems in the offshore and partly onshore Agadir-Essaouira basin. These basins are largely dependent on the structural development of Atlas mountains, being characterised by different phases of tectonic rifting, regional shortening and differential exhumation and subsidence patterns. The evolution of salt-cored anticlines in the Western High Atlas are possibly a key in understanding the tectonic history of the area especially in the context of the observed vertical movements. This study has the aim to provide additional information on timing and evolution of salt-cored anticlines in the Western High Atlas, to get a better understating of folding mechanisms related to vertical movements in the hinterland. Their role in controlling sedimentation pathways is investigated, since the basin links the paleozoic massifs as a sediment source and the offshore as sediment sink system. A new modeling technique was applied to two salt-cored anticlines, the Jbel Amsittene and the Imouzzer anticline, combining remote sensing geological and structural data, integrated in a 3D structural modeling environment (Gocad). This allows for the extraction of the thickness distribution for the identification of pre-Alpine locations of sediment depocenters. Further, the tectonic history of folding, using 2D section balancing (Move) and 3D unfolding and strain analysis (Gocad), is investigated. In a small field study, the large scale modeling results are compared to small scale field observations. Salt and folding mechanisms in the context of the geological setting and history are discussed and their impact on Jurassic to Early Cretaceous sediment pathways are outlined. The expression of folding on the sea-floor and the impact of the presence of pre-orogenic anticlines on the Alpine folding processes are debated. The results suggest Early to Middle Jurassic salt activities potentially initiated by pre-orogenic exhumation in the hinterland and subsidence towards the offshore, resulting in a hydraulic head gradient causing salt flow. Another scenario are pre-orogenic phases of tectonic shortening or salt flow by increased thermal activities. The topography that was created certainly controlled the sediment distribution of passive margin sands into the offshore basin. Jurassic salt mobilisation also had an impact on the Alpine-folding process which might have resulted in a connection of smaller isolated salt diapirs leading to a variety of strike orientations of folds in the basins.Civil Engineering and GeosciencesGeoscience & EngineeringApplied Geolog
Vergelijking van gemeentelijke verkoopmethodes voor transformaties van voormalige schoolgebouwen naar woningen middels (C)PO
No full textTijdens dit onderzoek wordt een vergelijking gemaakt tussen gemeentelijke verkoopmethodes die worden gebruik voor het verkopen van voormalige schoolgebouwen als (C)PO-project. Deze schoolgebouwen worden verkocht aan particulieren die deze schoolgebouwen vervolgens transformeren naar woningen. Er wordt een vergelijking gemaakt van zes verkoopmethodes die zijn gebruikt in de gemeentes Rotterdam, Amsterdam en Den Haag. Tijdens deze vergelijking wordt gekeken naar vier variabelen waaruit de verkoopmethodes zijn samengesteld: de toewijzingssystematiek, verkaveling, investeringen en de randvoorwaarden. Hierbij wordt onderzocht wat de redeneringen zijn geweest van de gemeentes om voor deze methode te kiezen. Vervolgens wordt bepaald of deze redeneringen zijn te herleiden tot de doelstellingen die de gemeentes hebben voor deze transformatie-(C)PO-projecten.Management in the Built EnvironmentArchitecture and The Built Environmen
Mobilisation of arsenic from bauxite residue (red mud) affected soils: Effect of pH and redox conditions
No full textThe tailings dam breach at the Ajka alumina plant, western Hungary in 2010 introduced ∼1 million m3 of red mud suspension into the surrounding area. Red mud (fine fraction bauxite residue) has a characteristically alkaline pH and contains several potentially toxic elements, including arsenic. Aerobic and anaerobic batch experiments were prepared using soils from near Ajka in order to investigate the effects of red mud addition on soil biogeochemistry and arsenic mobility in soil–water experiments representative of land affected by the red mud spill. XAS analysis showed that As was present in the red mud as As(V) in the form of arsenate. The remobilisation of red mud associated arsenate was highly pH dependent and the addition of phosphate to red mud suspensions greatly enhanced As release to solution. In aerobic batch experiments, where red mud was mixed with soils, As release to solution was highly dependent on pH. Carbonation of these alkaline solutions by dissolution of atmospheric CO2 reduced pH, which resulted in a decrease of aqueous As concentrations over time. However, this did not result in complete removal of aqueous As in any of the experiments. Carbonation did not occur in anaerobic experiments and pH remained high. Aqueous As concentrations initially increased in all the anaerobic red mud amended experiments, and then remained relatively constant as the systems became more reducing, both XANES and HPLC–ICP-MS showed that no As reduction processes occurred and that only As(V) species were present. These experiments show that there is the potential for increased As mobility in soil–water systems affected by red mud addition under both aerobic and anaerobic conditions
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Evidence for suboxic nitrification in recent marine sediments
No full textThe classical scheme of biogeochemical zones (BGZ) is known to be an oversimplification
of the microbial processes that occur in organic-rich marine sediments. Results from a coupled
deployment of pore-water gel probes in Loch Duich, Scotland, provide direct evidence for rapid
recycling within the iron reduction (FeR) and sulphate reduction (SR) zones. High resolution porewater
profiles obtained using diffusive equilibrium in thin films (DET) gel probes found a nitrate peak
at the boundary between the FeR and SR zones. This non-steady state feature is consistent with recycling
of reduced N occurring throughout the FeR zone. Both conventional pore-water iron profiles
and results from diffusive gradient in thin films (DGT) probes indicate that iron is solubilised and precipitated
in rapid Fe/S recycling reactions throughout the SR zone. The presence of such complex
recycling reactions confirms the oversimplification of the classical BGZ scheme
Optimising the usability of the innovation partnership procedure for contracting authorities
No full textCivil Engineering and GeosciencesStructural EngineeringConstruction Management and Engineerin
Bereiding van acetyleen S.B.A. proces
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
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