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Substrate Composition (substrate + composition)
Selected AbstractsMacro-scale bed roughness of the siple coast ice streams in West AntarcticaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2004Martin J. Siegert Abstract Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness re,ecting substrate composition and ,ow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow-,owing Ice Stream C (,10 000 km2) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic in,uence on ice stream position. Bed roughness increases up-,ow of ice streams, which, unless the bed is modi,ed, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd. [source] Use 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] Response of secondary production by macroinvertebrates to large wood addition in three Michigan streamsFRESHWATER BIOLOGY, Issue 8 2009SALLY A. ENTREKIN Summary 1.,We measured responses in macroinvertebrate secondary production after large wood additions to three forested headwater streams in the Upper Peninsula of Michigan. These streams had fine-grained sediments and low retention capacity due to low amounts of in-channel wood from a legacy of past logging. We predicted that wood addition would increase macroinvertebrate secondary production by increasing exposed coarse substrate and retention of organic matter. 2.,Large wood (25 logs) was added haphazardly to a 100-m reach in each stream, and a 100-m upstream reach served as control; each reach was sampled monthly, 1 year before and 2 years after wood addition (i.e. BACI design). Macroinvertebrate secondary production was measured 1 year after wood addition in two habitat types: inorganic sediments of the main channel and debris accumulations of leaf litter and small wood. 3.,Overall macroinvertebrate production did not change significantly because each stream responded differently to wood addition. Production increased by 22% in the main-channel of one stream, and showed insignificant changes in the other two streams compared to values before wood addition. Changes in main-channel macroinvertebrate production were related to small changes in substrate composition, which probably affected habitat and periphyton abundance. Macroinvertebrate production was much greater in debris accumulations than in the main-channel, indicating the potential for increased retention of leaf litter to increase overall macroinvertebrate production, especially in autumn. 4.,Surrounding land use, substrate composition, temperature and method of log placement are variables that interact to influence the response of stream biota to wood additions. In most studies, wood additions occur in altered catchments, are rarely monitored, and secondary production is not a common metric. Our results suggest that the time required for measurable changes in geomorphology, organic matter retention, or invertebrate production is likely to take years to achieve, so monitoring should span more than 5 years, and ecosystem metrics, such as macroinvertebrate secondary production, should be incorporated into restoration monitoring programs. [source] Effect of Drought Stress on Yield and Quality of Maize/Sunflower and Maize/Sorghum Intercrops for Biogas ProductionJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2010S. SchittenhelmArticle first published online: 16 FEB 2010 Abstract Intercropping represents an alternative to maize (Zea mays L.) monoculture to provide substrate for agricultural biogas production. Maize was intercropped with either sunflower (Helianthus annuus L.) or forage sorghum [Sorghum bicolor (L.) Moench] to determine the effect of seasonal water supply on yield and quality of the above-ground biomass as a fermentation substrate. The two intercrop partners were grown in alternating double rows at plant available soil water levels of 60,80 %, 40,50 % and 15,30 % under a foil tunnel during the years 2006 and 2007 at Braunschweig, Germany. Although the intercrop dry matter yields in each year increased with increasing soil moisture, the partner crops responded quite differently. While maize produced significantly greater biomass under high rather than low water supply in each year, forage sorghum exhibited a significant yield response only in 2006, and sunflower in none of the 2 years. Despite greatly different soil moisture contents, the contribution of sorghum to the intercrop dry matter yield was similar, averaging 43 % in 2006 and 40 % in 2007. Under conditions of moderate and no drought stress, sunflower had a dry matter yield proportion of roughly one-third in both years. In the severe drought treatment, however, sunflower contributed 37 % in 2006 and 54 % in 2007 to the total intercrop dry matter yield. The comparatively good performance of sunflower under conditions of low water supply is attributable to a fast early growth, which allows this crop to exploit the residual winter soil moisture. While the calculated methane-producing potential of the maize/sorghum intercrop was not affected by the level of water supply, the maize/sunflower intercrop in 2006 had a higher theoretically attainable specific methane yield under low and medium than under high water supply. Nevertheless, the effect of water regime on substrate composition within the intercrops was small in comparison with the large differences between the intercrops. [source] Effect of strain and alloy composition inhomogeneity on the electronic and optical properties of III-nitride semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2008Nikos Skoulidis Abstract Using the empirical tight binding method with a sp3s* basis for the first neighbour interactions and only p,p interactions for the second neighbours, we calculated the optical properties near the fundamental gap of cubic GaxAl1,xN alloys for x<0.33 grown on a substrate whose lattice constant varies from the lattice constant of cubic AlN to GaN. We found that the spectra of the fully relaxed alloy have a tail with onset energy at the indirect gap of AlN and an edge at the direct gap of the alloy which follows the Vegard's law within 0.1 eV. The maximum of band gap for each alloy composition is found for a substrate with the lattice constant of the fully relaxed alloy. When the substrate composition is such that induces negative tetragonal strain on the alloy (,xx<0) the energy band gap is mainly affected by the alloy composition while for ,xx>0 the alloy composition has a limited effect. The total effect of substrate and alloy composition in the calculated range on the band gap can be as much as 0.4 eV and is mainly due to the valence band shift as the conduction band is only slightly affected by the substrate or the alloy composition. This band gap change is adequate to explain the experimentally observed double photoluminescence peak of open quantum dots. The energy separation of the double peak is 0.1 eV and one peak can be attributed to the tetragonically strained wetting layer and the other to the fully relaxed quantum dots. Furthermore the present results can be used to estimate any possible stoichiometric inhomogeneity and help design structures with specific energies for the pair of peaks. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||