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Clean Sand (clean + sand)
Selected AbstractsUse of GIS to predict effects of water level on the spawning area for smelt, Retropinna retropinna, in Lake Taupo, New ZealandFISHERIES MANAGEMENT & ECOLOGY, Issue 4 2002D. K. ROWE A GIS model of the littoral bathymetry and substrate composition of Lake Taupo was created using ArcInfo. Littoral substrates were mapped by aerial photography and confirmed by ground-truthing. Water depths were determined by echosounding linked to a differential GPS. These data were imported into ArcInfo where a 3D GIS model was used to calculate the total area of smelt, Retropinna retropinna Richardson, spawning habitat (i.e. clean sand between depths of 0.5,2.5 m) at each of five lake levels. There was little change in area over the first 50 cm below the natural maximum lake level, but spawning habitat decreased rapidly over the next 1.4 m such that a 30% reduction occurred at the natural minimum level. Anecdotal information on inter-annual variations in lake level and smelt abundance supported the notion that high lake levels in spring result in high recruitment of smelt. The GIS model also predicted effects of lake level change on areas of macrophyte cover and on other littoral substrates, and could be used to assess effects of lake level changes on the habitats of other biota. [source] Streaming potential dependence on water-content in Fontainebleau sandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010V. Allègre SUMMARY The electrokinetic potential results from the coupling between the water flow and the electrical current because of the presence of ions within water. The electrokinetic coefficient is well described in fluid-saturated media, however its behaviour under unsaturated flow conditions is still discussed. We propose here an experimental approach to investigate streaming potential variations in sand at unsaturated conditions. We present for the first time continuous records of the electrokinetic coefficient as a function of water content. Two drainage experiments have been performed within a column filled with a clean sand. Streaming potential measurements are combined with water pressure and water content measurements every 10 cm along the column. In order to model hydrodymanics during the experiments, we solve Richards equation coupled with an inverse problem to estimate the hydraulic parameters of the constitutive relations between hydraulic conductivity, water pressure and water content. The electrokinetic coefficient C shows a more complex behaviour for unsaturated conditions than it was previously reported and cannot be fitted by the existing models. The normalized electrokinetic coefficient increases first when water saturation decreases from 100 to about 65,80 per cent, and then decreases as the water saturation decreases, whereas all previous works described a monotone decrease of the normalized electrokinetic coupling as water saturation decreases. We delimited two water saturation domains, and deduced two different empirical laws describing the evolution of the electrokinetic coefficient for unsaturated conditions. Moreover, we introduce the concept of the electrokinetic residual saturation, Sr,ekw, which allows us to propose a new model derived from the approach of the relative permeability used in hydrodynamics. [source] Micro-environment of olive ridley turtle nests deposited during an aggregated nesting eventJOURNAL OF ZOOLOGY, Issue 4 2007S. Clusella Trullas Abstract The hatching success of nests deposited by olive ridley turtles Lepidochelys olivacea during aggregated nesting events (,arribada') is typically low and the underlying mechanisms are not clear. In this study, temperature, oxygen and carbon dioxide partial pressures (PO2 and PCO2) of in situ nests as well as nests relocated into a hatchery with clean sand were monitored throughout incubation. Hatching success of hatchery nests was significantly higher than in situ nests (83.1 vs. 21.6%) and mainly resulted from higher mortality of early-stage embryos. During the first half of incubation, temperature and PCO2 were higher (by 0.6°C and 0.7 kPa, respectively) and PO2 was lower (by 1.1 kPa) within in situ relative to hatchery nests. Because embryo metabolism does not interfere significantly with nest gas contents during the first half of incubation, these results suggest that the greater content of organic matter and/or microorganisms in the sand surrounding in situ nests had an effect on nest gas contents. As PO2 and PCO2 differences were relatively small, microbial activity (such as fungal and bacterial infection) may have caused the early embryo mortality found in situ. Moreover, our results suggest that during the second half of incubation, neither PO2 nor PCO2 reached threshold levels that resulted in the death of embryos or hatchlings. Overall, this study showed a clear benefit of using clean sand to increase hatchling production in arribada beaches and highlights the importance of further investigating the relationship between nest micro-environment, sand microbial activity and embryo development under natural conditions during these unique nesting events. [source] Promotion of 5-aminolevulinic acid on photosynthesis of melon (Cucumis melo) seedlings under low light and chilling stress conditionsPHYSIOLOGIA PLANTARUM, Issue 2 2004Liang Ju Wang When melon seedlings (Cucumis melo L. Ximiya No. 1) were cultured in a growth chamber with about 150 µmol m,2 s,1 photon flux density, the leaf photosynthetic ability reduced dramatically as leaf position decreased from the top. The application of 5-aminolevulinic acid (ALA) solutions significantly increased the net photosynthetic rate (Pn) as well as apparent quantum yield (AQY), carboxylation efficiency (CE) and stomata conductance (Gs). After irrigation with 10 ml of ALA solution (10 mg l,1 or 100 mg l,1) per container filled with approximately 250 g clean sand for 3 days, the leaf Pn was about 40,200% higher than that of controls, and AQY, CE and Gs increased 21,271%, 55,210% and 60,335%, respectively. Furthermore, ALA treatments increased leaf chlorophyll content and soluble sugar levels, as well as the rate of dark respiration, but decreased the rate of respiration under light. On the other hand, after melon seedlings that had been cultured in the chamber suffered chilling at 8°C for 4 h and then recovered at 25,30°C for 2 and 20 h, the Pn of the water-irrigated plants was only 12,18% and 37,47%, respectively, compared with the initial Pn before chilling treatment. If the seedlings underwent the same treatment but with ALA (10 mg l,1), the respective Pn was 22,38% and 76,101%, compared with that of the control before chilling stress. If chilling was prolonged for 6 h, the ALA-pre-treated plants only showed a few symptoms in the leaf margins whereas all water-irrigated plants died, which suggested that ALA presumably promoted chilling tolerance of the plants under low light. [source] Storegga tsunami sand in peat below the Tapes beach ridge at Harøy, western Norway, and its possible relation to an early Stone Age settlementBOREAS, Issue 3 2003STEIN BONDEVIK One of the early problems with the Storegga tsunami deposit was how to distinguish it from deposits of the midHolocene (Tapes) transgression. An excavation on Harøy, an island on the outermost western coast of Norway, shows a distinct, clean sand bed embedded in peat and clearly separated from the overlying Tapes beach deposits. This sand bed continues in the peat landwards of the beach ridge for at least 60 m. Radiocarbon dates of the peat show that the sand was deposited some time between 6900 and 7700 yr BP. The sedimentary structures of the bed, the 14C dates, and the fact that this is the only sand bed in the peat, suggest that the sand bed was deposited by a short-lived event, the Storegga tsunami. On the neighbouring island, Fjørtoft, a Stone Age settlement, dated to 7500 yr BP, was discovered in the early 1970s. The settlement was found underneath a sand bed that later had been covered by the Tapes beach ridge deposits. When discovered, the sand covering the settlement was inferred as eolian sand. However, this investigation shows that the Storegga tsunami deposited a widespread sand bed on the land surface around this time with a similar grain size distribution to eolian sand. It is therefore suggested that the sand bed covering this settlement was deposited from the Storegga tsunami. Both the stratigraphy and 14C dates demonstrate that the Tapes transgression maximum was reached well after the Storegga tsunami on Harøy, between 6500 and 6100 yr BP. [source] | |||||||||||||