Home About us Contact
|
Home About us Contact | ||
|
|
||
M Depth (m + depth)
Selected AbstractsAeolian fetch distance and secondary airflow effects: the influence of micro-scale variables on meso-scale foredune developmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2008Kevin Lynch Abstract Unsuccessful attempts to use process-scale models to predict long-term aeolian sediment transport patterns have long been a feature of aeolian research. It has been proposed that one approach to overcome these problems is to identify micro-scale variables that are important at longer timescales. This paper assesses the contribution of two system variables (secondary airflow patterns and fetch distance) to medium-term (months to years) dune development. The micro-scale importance of these variables had been established during previous work at the site (Magilligan Strand, Northern Ireland). Three methods were employed. First, sand drift potentials were calculated using 2 years of regional wind data and a sediment transport model. Second, wind data and large trench traps (2 m length × 1 m width × 1·5 m depth) were used to assess the actual sediment transport patterns over a 2-month period. Third, a remote-sensing technique for the identification of fetch distance, a saltation impact sensor (Safire) and wind data were utilized to gauge, qualitatively, sediment transport patterns over a 1-month period. Secondary airflow effects were found to play a major role in the sediment flux patterns at these timescales, with measured and predicted rates matching closely during the trench trap study. The results suggest that fetch distance is an unimportant variable at this site. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigations regarding Alpine talus slopes using ground-penetrating radar (GPR) in the Bavarian Alps, GermanyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2001Oliver Sass Abstract The applicability of ground-penetrating radar (GPR) for the investigation of loose debris was tested at two sites (Viererkar and Zugspitzplatt). A pulseEKKO 100 GPR system equipped with 25 MHz antennae was utilized. The aim of the investigation was to record the base of the debris layer, and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls. The study areas are situated in the Northern Alps near the German,Austrian border. The sites are characterized by steep limestone rockwalls and extensive talus accumulations. A total of six profiles was surveyed. The method is suitable and effective for a quick survey in this dry, high-ohmic substrate. The GPR system was able to deliver information about the subsurface stratigraphy to c. 70 m depth. The boundary line to the bedrock was discovered , depending upon the profile surveyed ,5 to 25 m below the surface. The base of the debris material sometimes shows no distinct reflection. Buried features (V-shaped furrows, zones overdeepened by ice action, geological structures) could be detected. Arched structures well below the talus,bedrock interface can be interpreted as drainage systems in the karstic bedrock. A thick scree layer of Late Glacial age was separated from a thinner layer on the talus surface, which was related to the Holocene. The backweathering rates were fixed by a calculation of talus volume to c. 100 mm/103 a during the Holocene (Viererkar) and 150,300 mm/103 a (Zugspitzplatt). The detrital formation in north-exposed sites is twice as intense as in south-exposed sites. These results match the rates of recent rockfall in the same area of investigation. The calculated backweathering for the late glacial period is 150,730 mm/103 a. The magnitude of the calculated rockwall retreat lies well within the range of previous measurements. The discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated. Otherwise recent removal rates may be overestimated. Copyright © 2001 John Wiley & Sons, Ltd. [source] Spawning site selection by Eurasian perch (Perca fluviatilis L.) in relation to temperature and wave exposureECOLOGY OF FRESHWATER FISH, Issue 1 2009W. N. Probst Abstract,,, The selection of spawning depth by Eurasian perch Perca fluviatilis was investigated in an experiment using artificial substrata in Lake Constance during the spawning season of 2007. The experiment compared spawning behaviour at substrata between 0.5 and 15 m depth at two sites exposed to different regimes of ship-generated wave action. The total abundance of egg ribbons did not differ significantly between the two sites, but the preferred spawning depth was deeper at the wave exposed site (5 m) compared to the sheltered site (2 m). While water temperatures could not account for the observations, differences in wave exposure may explain the different spawning depth preferences. At both sites, large egg ribbons were generally found in deeper water, and large egg ribbons occurred more frequently at the sheltered site. Because the egg ribbons of perch are likely to have a size-dependent susceptibility to hydrodynamic stress, large females may be expected to select deeper spawning locations where the effects of surface waves are considerably attenuated. [source] Reproduction biology of pikeperch (Sander lucioperca (L.)) , a reviewECOLOGY OF FRESHWATER FISH, Issue 2 2003J. Lappalainen Abstract,,, The present review focuses on the reproduction biology of pikeperch (Sander lucioperca (L.)). Aspects like maturity, fecundity, spawning migrations, spawning habitats, onset of spawning, and development time of eggs were reviewed. The onset of maturity is reached at younger age in southern than northern populations due to higher growth rate in the south. Males mature at smaller size and are on average younger than females. Absolute fecundity is closely related to the length and weight, but no clear relationship could be found between relative fecundity and length. Statistically significant relationships were found between the onset of spawning and latitude, and between the duration of the development time of eggs and stable water temperature. Near the southern limits of distribution, the onset of spawning is in February while near the northern limits it is in June. The interannual variability in fecundity and in the onset of maturity and further the factors affecting them have not been studied much. Furthermore, it is not known whether these variations could affect the population dynamics of pikeperch. Little is also known about the actual spawning behaviour of pikeperch in natural habitats. This is probably due to the typical spawning habitats located at 1,3 m depth in waters with high turbidity and low visibility. Even though the homing behaviour to the same spawning areas is well developed in adults, it is not known whether the adults were actually born in the same area. [source] Dynamics of the SAR11 bacterioplankton lineage in relation to environmental conditions in the oligotrophic North Pacific subtropical gyreENVIRONMENTAL MICROBIOLOGY, Issue 9 2009Alexander Eiler Summary A quantitative PCR assay for the SAR11 clade of marine Alphaproteobacteria was applied to nucleic acids extracted from monthly depth profiles sampled over a 3-year period (2004,2007) at the open-ocean Station ALOHA (A Long-term Oligotrophic Habitat Assessment; 22°45,N, 158°00,W) in the oligotrophic North Pacific Ocean. This analysis revealed a high contribution (averaging 36% of 16S rRNA gene copies) of SAR11 to the total detected 16S rRNA gene copies over depths ranging from the surface layer to 4000 m, and revealed consistent spatial and temporal variation in the relative abundance of SAR11 16S rRNA gene copies. On average, a higher proportion of SAR11 rRNA gene copies were detected in the photic zone (< 175 m depth; mean = 38%) compared with aphotic (> 175 m depth; mean = 30%), and in the winter months compared with the summer (mean = 44% versus 33%, integrated over 175 m depth). Partial least square to latent structure projections identified environmental variables that correlate with variation in the absolute abundance of SAR11, and provided tools for developing a predictive model to explain time and depth-dependent variations in SAR11. Moreover, this information was used to hindcast temporal dynamics of the SAR11 clade between 1997 and 2006 using the existing HOT data set, which suggested that interannual variations in upper ocean SAR11 abundances were related to ocean-climate variability such as the El Niño Southern Oscillation. [source] Comparative analysis of genome fragments of Acidobacteria from deep Mediterranean planktonENVIRONMENTAL MICROBIOLOGY, Issue 10 2008Achim Quaiser Summary Acidobacteria constitute a still poorly studied phylum that is well represented in soils. Recent studies suggest that members of this phylum may be also abundant in deep-sea plankton, but their relative abundance and ecological role in this ecosystem are completely unknown. A recent screening of three metagenomic deep-sea libraries of bathypelagic plankton from the South Atlantic (1000 m depth), the Adriatic (1000 m depth) and the Ionian (3000 m depth) seas in the Mediterranean revealed an unexpected relative proportion of acidobacterial fosmids, which affiliated to the Solibacterales (Group 3), to the Group 11 and, most frequently, to the Group 6 of this diverse phylum. Here, we present the comparative analysis of 11 acidobacterial genome fragments containing the rrn operon from these Mediterranean libraries. A highly conserved syntenic region spanning up to 30 kb and containing up to 25 open reading frames was shared by Group 6 Acidobacteria. Synteny was also partially conserved in distantly related acidobacterial genome fragments derived from a metagenomic soil library, indicating a remarkable conservation of this genomic region within these Acidobacteria. A search for Acidobacteria -specific hits in directly comparable, available fosmid-end sequences from soil and marine metagenomic libraries showed a significant increase of their relative proportion in plankton libraries as a function of increasing depth reaching, at high depth, levels nearly comparable to those of soil. Thus, our results suggest that Acidobacteria are abundant and represent a significant proportion of the microbial community in the deep-sea ecosystem. [source] Phylogenetic analyses of ribosomal DNA-containing bacterioplankton genome fragments from a 4000 m vertical profile in the North Pacific Subtropical GyreENVIRONMENTAL MICROBIOLOGY, Issue 9 2008Vinh D. Pham Summary High-throughput identification of rRNA gene-containing clones in large insert metagenomic libraries is difficult, because of the high background of host ribosomal RNA (rRNA) and rRNA genes. To address this challenge, a membrane hybridization method was developed to identify all bacterial small subunit rRNA-containing fosmid clones of microbial community DNA from seven different depths in the North Pacific Subtropical Gyre. Out of 101,376 clones screened, 751 rDNA-containing clones were identified that grouped in ,60 different clades. Several rare sequences only remotely related to known groups were detected, including a Wolbachia -related sequence containing a putative intron or intervening sequence, as well as seven sequences from Order Myxococcales not previously detected in pelagic habitats. Stratified, depth-specific population structure was evident within both cultured and uncultured lineages. Conversely, some eurybathyal members of the genera Alcanivorax and Rhizobium shared identical small subunit ribosomal DNA sequences that were distributed from surface waters to the 4000 m depth. Comparison with similar analyses in Monterey Bay microbial communities revealed previously recognized, as well as some distinctive, depth-stratified partitioning that distinguished coastal from open ocean bacterioplankton populations. While some bias was evident in fosmid clone recovery in a few particular lineages, the overall phylogenetic group recovery and distributions were consistent with previous studies, as well as with direct shotgun sequence data from the same source DNA. [source] Abundance and activity of Chloroflexi -type SAR202 bacterioplankton in the meso- and bathypelagic waters of the (sub)tropical AtlanticENVIRONMENTAL MICROBIOLOGY, Issue 7 2008Marta M. Varela Summary The contribution of Chloroflexi -type SAR202 cells to total picoplankton and bacterial abundance and uptake of d - and l -aspartic acids (Asp) was determined in the different meso- and bathypelagic water masses of the (sub)tropical Atlantic (from 35°N to 5°S). Fluorescence in situ hybridization (FISH) revealed that the overall abundance of SAR202 was , 1 × 103 cells ml,1 in subsurface waters (100 m layer), increasing in the mesopelagic zone to 3 × 103 cells ml,1 and remaining fairly constant down to 4000 m depth. Overall, the percentage of total picoplankton identified as SAR202 increased from < 1% in subsurface waters to 10,20% in the bathypelagic waters. On average, members of the SAR202 cluster accounted for about 30% of the Bacteria in the bathypelagic waters, whereas in the mesopelagic and subsurface waters, SAR202 cells contributed < 5% to total bacterial abundance. The ratio of d -Asp : l -Asp uptake by the bulk picoplankton community increased from the subsurface layer (d -Asp : l -Asp uptake ratio , 0.03) to the deeper layers reaching a ratio of ,1 at 4000 m depth. Combining FISH with microautoradiography to determine the proportion of SAR202 cells taking up d -Asp versus l -Asp, we found that ,,30% of the SAR202 cells were taking up l -Asp throughout the water column while d -Asp was essentially not taken up by SAR202. This d -Asp : l -Asp uptake pattern of SAR202 cells is in contrast to that of the bulk bacterial and crenarchaeal community in the bathypelagic ocean, both sustaining a higher fraction of d -Asp-positive cells than l -Asp-positive cells. Thus, although the Chloroflexi -type SAR202 constitutes a major bathypelagic bacterial cluster, it does not contribute to the large fraction of d -Asp utilizing prokaryotic community in the meso- and bathypelagic waters of the North Atlantic, but rather utilizes preferentially l -amino acids. [source] Ecotype diversity in the marine picoeukaryote Ostreococcus (Chlorophyta, Prasinophyceae)ENVIRONMENTAL MICROBIOLOGY, Issue 6 2005Francisco Rodríguez Summary The importance of the cyanobacteria Prochlorococcus and Synechococcus in marine ecosystems in terms of abundance and primary production can be partially explained by ecotypic differentiation. Despite the dominance of eukaryotes within photosynthetic picoplankton in many areas a similar differentiation has never been evidenced for these organisms. Here we report distinct genetic [rDNA 18S and internal transcribed spacer (ITS) sequencing], karyotypic (pulsed-field gel electrophoresis), phenotypic (pigment composition) and physiological (light-limited growth rates) traits in 12 Ostreococcus strains (Prasinophyceae) isolated from various marine environments and depths, which suggest that the concept of ecotype could also be valid for eukaryotes. Internal transcribed spacer phylogeny grouped together four deep strains isolated between 90 m and 120 m depth from different geographical origins. Three deep strains displayed larger chromosomal bands, different chromosome hybridization patterns, and an additional chlorophyll (chl) c -like pigment. Furthermore, growth rates of deep strains show severe photo-inhibition at high light intensities, while surface strains do not grow at the lowest light intensities. These features strongly suggest distinct adaptation to environmental conditions encountered at surface and the bottom of the oceanic euphotic zone, reminiscent of that described in prokaryotes. [source] Percolation characteristics of a water-repellent sandy forest soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008G. Wessolek Summary In a tracer experiment TDR transect measurements were made to study percolation behaviour in a 120-year-old pine stand (Pinus sylvestris) on a water-repellent sandy soil (Haplic Arenosol). The experiment (with potassium iodide) showed an 80% labelling of the total flow in organic layers, whereas the area of transport in the mineral soil was sharply reduced to 12,30%. The average diameters of these preferential flow paths were about 8,15 cm. The TDR measurements indicate a homogeneous flow only for a short period from February until April. At this time of the year preferential flow is insignificant, because the soil is at approximately field capacity and not repellent to water. During summer (May to September) the soil dries out, and most precipitation results in preferential flow during this period. For any daily rainfall exceeding 10 mm, water infiltrates down to 1 m depth in the soil, which nevertheless, is still within the root zone. This kind of deep percolation results in the subsoil's wetting to field capacity (pF 1.8) earlier than the topsoil. A one-dimensional numerical model (SWAP) was used to simulate mean water balance with hydraulic functions with and without a water-repellency term. From the results of our tracer experiment we showed that the de-watering process in spring could be simulated well using the traditional piston flow concept, while the rewetting behaviour could be described more realistically using the mobile,immobile concept for water repellency. [source] Influence of water flow velocity, water depth and colony distance on distribution and foraging patterns of terns in the Wadden SeaFISHERIES OCEANOGRAPHY, Issue 3 2009PHILIPP SCHWEMMER Abstract Surface-feeding seabirds, such as Common (Sterna hirundo) and Arctic Terns (Sterna paradisaea) in the German Wadden Sea, are dependent on biological and physical processes that affect prey availability close to the water surface. We proposed the following four hypotheses: (i) relationships should exist between high water flow velocity and foraging activity of terns, as turbulence should enhance prey availability at the surface; (ii) the areas of highest foraging success should be located within areas of low water depth, due to enhanced biological productivity; (iii) as terns are known to have small foraging radii, the location of their breeding grounds should be related to the location of their foraging grounds; (iv) terns should forage intensely in river estuaries, as these should hold ample food supplies. The time between terns leaving the colony and their first foraging attempt differed significantly among different tidal stages: the time was shortest during flood and ebb tides (i.e., highest water flow velocities). Modelling of a long-term data set revealed the highest probability of foraging activity in conditions of high water currents, in both shallow areas and in areas of around 15,20 m depth. Foraging activity was negatively correlated with distance from colony. The distance to the closest estuary had no significant effect on foraging behaviour. Our findings emphasize the physical,biological coupling in the Wadden Sea and highlight the overall importance of small-scale physical processes in directly influencing prey availability for surface-feeding seabirds. [source] Larval fish assemblages and water mass structure off the oligotrophic south-western Australian coastFISHERIES OCEANOGRAPHY, Issue 1 2008B. A. MUHLING Abstract Larval fish assemblages were sampled using replicated oblique bongo net tows along a five-station transect extending from inshore (18 m depth) to offshore waters (1000 m depth) off temperate south-western Australia. A total of 148 taxa from 93 teleost families were identified. Larvae of Gobiidae and Blenniidae were abundant inshore, while larvae of pelagic and reef-dwelling families, such as Clupeidae, Engraulidae, Carangidae and Labridae were common in continental shelf waters. Larvae of oceanic families, particularly Myctophidae, Phosichthyidae and Gonostomatidae, dominated offshore assemblages. Multivariate statistical analyses revealed larval fish assemblages to have a strong temporal and spatial structure. Assemblages were distinct among seasons, and among inshore, continental shelf and offshore sampling stations. Inshore larval fish assemblages were the most seasonal, in terms of species composition and abundance, with offshore assemblages the least seasonal. However, larval fish assemblages were most closely correlated to water mass, with species distributions reflecting both cross-shelf and along-shore oceanographic processes and events. Similarity profile (SIMPROF) analysis suggested the presence of twelve distinct larval fish assemblages, largely delineated by water depth and season. The strength and position of the warm, southward flowing Leeuwin Current, and of the cool, seasonal, northward flowing Capes Current, were shown to drive much of the variability in the marine environment, and thus larval fish assemblages. [source] Spatial distribution and feeding habits of Pacific cod (Gadus macrocephalus) larvae in Mutsu Bay, JapanFISHERIES OCEANOGRAPHY, Issue 2 2002Tetsuya Takatsu The spatial distributions and feeding habits of Pacific cod (Gadus macrocephalus) larvae, and the spatial distributions of copepod nauplii and copepodites, their main prey, were examined in Mutsu Bay from February to March during 1989,92. Yolk-sac larvae were caught at 30,45 m depth at the bay mouth. Larvae without yolk were collected at 8,45 m depth at the bay mouth and the inner part of the bay, and large larvae were chiefly found in the bay. This geographical pattern in larval size may have been because of transport to the inner part of Mutsu Bay by the Tsugaru Warm Current. The dominant taxa of copepod nauplii and copepodites in the diet and the environment changed each year. Larvae fed mainly on abundant taxa in the environment, suggesting that larvae are opportunistic feeders. Nauplii and copepodites were abundant in the bay, especially in 1992. Copepodites were slightly more abundant in the diet of cod larvae in 1992 than in 1991, but this difference was smaller than in the environment. In addition, larvae with empty digestive tracts were scarce in 1991 and 1992. Prey concentrations in the bay in 1991 and 1992 seem to have been high enough to sustain most Pacific cod larvae. [source] Effects of temperature and sediment properties on benthic CO2 production in an oligotrophic boreal lakeFRESHWATER BIOLOGY, Issue 8 2010IRINA BERGSTRÖM Summary 1. Temperature and many other physical and chemical factors affecting CO2 production in lake sediments vary significantly both seasonally and spatially. The effects of temperature and sediment properties on benthic CO2 production were studied in in situ and in vitro experiments in the boreal oligotrophic Lake Pääjärvi, southern Finland. 2. In in situ experiments, temperature of the water overlying the shallow littoral sediment varied seasonally between 0.5 and 15.7 °C, but in deep water (,20 m) the range was only 1.1,6.6 °C. The same exponential model (r2 = 0.70) described the temperature dependence at 1.2, 10 and 20 m depths. At 2.5 and 5 m depths, however, the slopes of the two regression models (r2 = 0.94) were identical but the intercept values were different. Sediment properties (wet, dry, mineral and organic mass) varied seasonally and with depth, but they did not explain a significantly larger proportion of variation in the CO2 output rate than temperature. 3. In in vitro experiments, there was a clear and uniform exponential dependence of CO2 production on temperature, with a 2.7-fold increase per 10 °C temperature rise. The temperature response (slope of regression) was always the same, but the basic value of CO2 production (intercept) varied, indicating that other factors also contributed to the benthic CO2 output rate. 4. The annual CO2 production of the sediment in Lake Pääjärvi averaged 62 g CO2 m,2, the shallow littoral at 0,3 m depth releasing 114 g CO2 m,2 and deep profundal (>15 m) 30 g CO2 m,2. On the whole lake basis, the shallow littoral at 0,3 m depth accounted for 53% and the sediment area in contact with the summer epilimnion (down to a depth c. 10 m) 75% of the estimated total annual CO2 output of the lake sediment, respectively. Of the annual production, 83% was released during the spring and summer. 5. Using the temperature-CO2 production equations and climate change scenarios we estimated that climatic warming might increase littoral benthic CO2 production in summer by nearly 30% from the period 1961,90 to the period 2071,2100. [source] Increase in photosynthetic efficiency as a strategy of planktonic organisms exploiting deep lake layersFRESHWATER BIOLOGY, Issue 2 2004Beatriz Modenutti Summary 1. The photosynthetic efficiencies of the mixotrophic ciliate Ophrydium naumanni and the autotrophic dinoflagellate Gymnodinium paradoxum were investigated using laboratory and field experiments in Lake Moreno Oeste (41°5,S and 71°33,W, 758 m a.s.l.), in the Nahuel Huapi System (North Patagonia, Argentina). 2. The effect of different underwater light intensities on net primary production (NPP) was assessed during one summer. Additionally, laboratory experiments were carried out to obtain photosynthesis-irradiance response curves for each species. 3. Ophrydium naumanni and G. paradoxum dominated the metalimnetic (30 m depth) deep chlorophyll maximum (DCM) in the lake. 4. Despite these deep higher abundances, the cell-specific production of both species was higher at 10 m than at 30 m (DCM) depth. In addition, at 5 m depth, NPP was reduced by PAR + UV-A radiation. 5. Both species exhibited a positive NPP at very low irradiance but the mixotrophic ciliate was more efficient in exploiting the DCM irradiance level both in situ and at comparable light intensities in laboratory experiments. Light acclimatised O. naumanni showed a higher NPP at lower irradiances and photoinhibition at medium and high irradiances. 6. Under the strong wind-driven turbulence commonly found in Patagonian lakes, organisms cannot select their position in the epilimnetic water column and will be dragged to potentially harmful UV radiation levels. Thus, metalimnetic DCM colonisation by these two species represents a tradeoff between higher survival and lower cell-specific NPP. [source] Wave and sediment dynamics along a shallow subtidal sandy beach inhabited by modern stromatolitesGEOBIOLOGY, Issue 1 2008J. E. ECKMAN ABSTRACT To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1,2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas , the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s,1), wave conditions remain comparatively calm until local winds increase above speeds of ,3,4 m s,1 at which point maximum wave speeds rapidly increase to 50,80 cm s,1. Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7,10 g cm,2 day,1 (,4,6 cm day,1). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions. [source] Microbial diversity of a sulphide spire located in the Edmond deep-sea hydrothermal vent field on the Central Indian RidgeGEOBIOLOGY, Issue 2 2003Joost Hoek ABSTRACT A culture-independent molecular phylogenetic survey was carried out for a bacterial and archaeal community of a mineralized crust coating a sulphide spire, which was collected from the Edmond vent field (23° S, 69° E, 3300 m depth) on the Central Indian Ridge. Small-subunit rRNA genes (16S rDNA) were amplified from environmental DNA by PCR utilizing Bacteria-specific, and Archaea-specific 16S rDNA primers. PCR products were cloned and 26 bacterial and nine archaeal unique sequence types (phylotypes) were identified from 150 clones analysed by restriction fragment length polymorphism, representing eight and four distinct lineages, respectively. The majority (>90%) of the bacterial phylotypes group with the ,-Proteobacteria and confirms the global prevalence of ,-Proteobacteria in deep-sea hydrothermal environments. Among the ,-Proteobacteria, >40% of the phylotypes were closely related to the recently isolated deep-sea vent thermophilic chemolithoautotrophic sulphur-reducer, Nautilia lithotrophica. A single bacterial sequence was nearly identical (99% similarity) to the thermophilic hydrogen-oxidizing Hydrogenobacter thermolithotrophum, and is the first report of Hydrogenobacter at deep-sea hydrothermal vents. A majority (97%) of the archaeal phylotypes grouped with the ,Deep-sea Hydrothermal Vent Euryarchaeotal Group', a phylogenetic lineage of uncultured Archaea that have only been reported from other deep-sea hydrothermal vents on the Mid-Atlantic Ridge, East Pacific Rise, Juan de Fuca Ridge, Isu,Ogasawara Arc, Okinawa Trough and the Manus Basin. A single sequence was closely related to the hyperthermophilic sulphur-reducing Thermococcales frequently found in diverse deep-sea vent environments. Scanning electron micrographs of the mineralized crust reveal abundant filamentous, rod and coccoidal forms encased in sulphur and sulphide mineral precipitate, suggesting that the thermophilic chemolithoautorophs and sulphide-producing heterotrophs may influence the architecture and sulphur cycling of the sulphide spire. [source] Hydraulic observations from a 1 year fluid production test in the 4000 m deep KTB pilot boreholeGEOFLUIDS (ELECTRONIC), Issue 1 2006W. GRÄSLE Abstract A long-term pump test was conducted in the KTB pilot borehole (KTB-VB), located in the Oberpfalz area, Germany. It produced 22 300 m3 of formation fluid. Initially, fluid production rate was 29 l min,1 for 4 months, but was then raised to an average of 57 l min,1 for eight more months. The aim of this study was to examine the fluid parameters and hydraulic properties of fractured, crystalline crusts as part of the new KTB programme ,Energy and Fluid Transport in Continental Fault Systems'. KTB-VB has an open-hole section from 3850 to 4000 m depth that is in hydraulic contact with a prominent continental fault system in the area, called SE2. Salinity and temperature of the fluid inside the borehole, and consequently hydrostatic pressure, changed significantly throughout the test. Influence of these quantities on variations in fluid density had to be taken into account for interpretation of the pump test. Modelling of the pressure response related to the pumping was achieved assuming the validity of linear Darcy flow and permeability to be independent of the flow rate. Following the principle ,minimum in model dimension', we first examined whether the pressure response can be explained by an equivalent model where rock properties around the borehole are axially symmetric. Calculations show that the observed pressure data in KTB-VB can in fact be reproduced through such a configuration. For the period of high pumping rate (57 l min,1) and the following recovery phase, the resulting parameters are 2.4 × 10,13 m3 in hydraulic transmissivity and 3.7 × 10,9 m Pa,1 in storativity for radial distances up to 187 m, and 4.7 × 10,14 m3 and 6.0 × 10,9 m Pa,1, respectively, for radial distances between 187 and 1200 m. The former pair of values mainly reflect the hydraulic properties of the fault zone SE2. For a more realistic hydraulic study on a greater scale, program FEFLOW was used. Parameter values were obtained by matching the calculated induced pressure signal to fluid-level variations observed in the KTB main hole (KTB-HB) located at 200 m radial distance from KTB-VB. KTB-HB is uncased from 9031 to 9100 m and shows indications of leakage in the casing at depths 5200,5600 m. Analysis of the pressure record and hydraulic modelling suggest the existence of a weak hydraulic communication between the two boreholes, probably at depths around the leakage. Hydraulic modelling of a major slug-test in KTB-HB that was run during the pumping in KTB-VB reveals the effective transmissivity of the connected formation to be 1 to 2 orders of magnitude lower than the one determined for the SE2 fault zone. [source] Origin of deep saline groundwaters in the Vienne granitic rocks (France): constraints inferred from boron and strontium isotopesGEOFLUIDS (ELECTRONIC), Issue 2 2001J. Casanova Abstract As part of a preliminary geological characterization programme to assess the feasibility of an underground laboratory in granitic rock, a series of 17 deep boreholes (maximum depth, 900 m) was drilled by ANDRA in the Vienne district, France. A salinity gradient was demonstrated in the granitic waters with concentrations varying from approximately 1 g L,1 at 150 m depth at the top of the basement (beneath the sedimentary cover) to 10 g L,1 in the deeper part (from 400 to 600 m depth). Sr and B isotope ratios were measured in order to better understand the origin of the salinity and to evaluate the degree of water,rock interaction in the system. The results obtained were compared to those of mineral spring waters emerging from the granitic basement in the Massif Central. Evidence in support of a significant marine contribution include: (i) the Cl,Br investigations agree with a marine origin for the saline groundwaters without evolution from seawater; (ii) the 87Sr/86Sr ratio of the Vienne deep groundwaters (0.7078,0.7084) is in agreement with a palaeo-seawater isotopic signature; (iii) measured ,11B values for the deepest brine samples are enriched in 11B (up to 36.1,) relative to the granitic springs. The combined use of ,11B, Cl, B, Br, Sr contents and 87Sr/86Sr ratios makes it possible to define and quantify a mixing model between marine and crustal end-members in order to explain the origin of the deep saline groundwaters in the Vienne granitic rocks. [source] A radiomagnetotelluric survey on an oil-contaminated area near the Brazi Refinery, RomaniaGEOPHYSICAL PROSPECTING, Issue 3 2005B. Tezkan ABSTRACT Scalar radiomagnetotelluric measurements were carried out on a contaminated test area close to the Brazi Refinery in Romania in order to detect and to monitor a 1 m thick oil layer expected at 5 m depth. Radio transmitters broadcasting in a frequency range from 10 kHz to 300 kHz were selected to observe the apparent resistivity and the phase data associated with the E- and B-polarizations. They were located parallel and perpendicular to the assumed strike direction of the contamination plume. The data were interpreted by a 2D inversion technique from which the conductivity structure of the area was derived. The 2D inversion models of all profiles on the contaminated area show a poor-conductivity zone above the groundwater table which could be associated with the oil contamination. A first attempt was also made to monitor the contaminated layer: the radiomagnetotelluric measurements were repeated on the same profiles a year later, but this time in a dry period, not in a rainy one. The 2D inversion results of the measurements in the dry period indicate that the high-resistivity layer moved closer to the surface. Additional reference measurements were then carried out on a non-contaminated area situated at a distance from the refinery, in the opposite direction to the flow of the groundwater. These reference measurements were used for the derivation of the unperturbed geology and they were also compared with the measurements of the contaminated test area. There is a significant difference in the frequency dependences of the apparent resistivities of the reference and contaminated areas, which could indicate a contamination at shallow depth. The 2D inversion results show the increase of resistivity at a depth of about 5 m beneath the contaminated area where the oil contamination is expected according to the information from the boreholes. [source] Use of low frequencies for sub-basalt imagingGEOPHYSICAL PROSPECTING, Issue 3 2003Anton Ziolkowski ABSTRACT Many prospective passive ocean margins are covered by large areas of basalts. These basalts are often extremely heterogeneous and scatter the seismic energy of the conventional seismic reflection system so that it becomes difficult to obtain information on deeper reflectors. Since high frequencies are scattered more than low frequencies, we argue that the acquisition system for sub-basalt targets should be modified to emphasize the low frequencies, using much larger airguns, and towing the source and receivers at about 20 m depth. In the summer of 2001 we obtained seismic reflection data over basalt in the northeast Atlantic using a system modified to enhance the low-frequency energy. These new data show deep reflections that are not visible on lines shot in the same places with a conventional system. [source] On removing the primary field from fixed-wing time-domain airborne electromagnetic data: some consequences for quantitative modelling, estimating bird position and detecting perfect conductorsGEOPHYSICAL PROSPECTING, Issue 4 2001Richard Smith In the process of removing the primary field from fixed-wing time-domain airborne EM data, the response is decomposed into two parts, which are referred to here as the time-domain ,in-phase' and ,quadrature' components. The time-domain in-phase component is dominated by the primary field, which varies significantly as the transmitter,receiver separation changes. The time-domain quadrature component comes solely from the secondary response associated with currents induced in the ground and this is the component that has traditionally been used in the interpretation of data from fixed-wing towed-bird time-domain EM systems. In the off-time, the quadrature response is very similar to the total secondary response. However, there are large differences in the on-time and even some small differences in the off-time.One consequence of these differences is that when airborne EM data are to be interpreted using a synthetic mathematical model, the synthetic data calculated should also be the quadrature component. A second consequence relates to the time-domain in-phase component which is sometimes used to estimate the receiver-sensor (bird) position. The bird-position estimation process assumes there is no secondary field in the in-phase component. If the ground is resistive, the secondary contained in the in-phase component is small, so the bird-position estimate is accurate to about 30 cm, but in highly conductive areas the secondary contribution can be large and the position estimate can be out by as much as 5 m. A third consequence arises for highly conductive bodies, the response of which is predominantly in-phase. This means that any response from these types of body is lost in the component that has been removed in the primary-field extraction procedure. However, if the bird position is measured very accurately, the actual free-space primary field can be estimated. If this is then subtracted from the estimated primary (actually free-space primary plus secondary in-phase response), then the residual is the secondary in-phase response of the ground. Using this methodology, very conductive ore bodies could be detected. However, a sensitivity analysis shows that detection of a large vertically dipping very conductive body at 150 m depth would require that the bird position be measured to an accuracy of about 1.4 cm and the aircraft attitude to within about 0.01°. Such tolerances are very stringent and not easily attainable with current technology. [source] Seismic anisotropy in granite at the Underground Research Laboratory, ManitobaGEOPHYSICAL PROSPECTING, Issue 3 2000Gordon M. Holmes The Shear-Wave Experiment at Atomic Energy of Canada Limited's Underground Research Laboratory was probably the first controlled-source shear-wave survey in a mine environment. Taking place in conjunction with the excavation of the Mine-by test tunnel at 420 m depth, the shear-wave experiment was designed to measure the in situ anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any in situ shear-wave survey to date. Inversion of the shear-wave polarizations shows that the anisotropy of the in situ rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023° and dip 35°. The in situ anisotropy is probably due to microcracks with orientations governed by the in situ stress field and to mineral alignment within the weak gneissic layering. However, there is no unique interpretation as to the cause of the in situ anisotropy as the fabric orientation agrees approximately with both the orientation expected from extensive-dilatancy anisotropy and that of the gneissic layering. Eight raypaths with shear waves propagating wholly or almost wholly through granodiorite, rather than granite, do not show the expected shear-wave splitting and indicate a lower in situ anisotropy, which may be due to the finer grain size and/or the absence of gneissic layering within the granodiorite. These results suggest that shear waves may be used to determine crack and mineral orientations and for remote monitoring of a rockmass. This has potential applications in mining and waste monitoring. [source] Amazon drought and its implications for forest flammability and tree growth: a basin-wide analysisGLOBAL CHANGE BIOLOGY, Issue 5 2004Daniel Nepstad Abstract Severe drought in moist tropical forests provokes large carbon emissions by increasing forest flammability and tree mortality, and by suppressing tree growth. The frequency and severity of drought in the tropics may increase through stronger El Niño Southern Oscillation (ENSO) episodes, global warming, and rainfall inhibition by land use change. However, little is known about the spatial and temporal patterns of drought in moist tropical forests, and the complex relationships between patterns of drought and forest fire regimes, tree mortality, and productivity. We present a simple geographic information system soil water balance model, called RisQue (Risco de Queimada , Fire Risk) for the Amazon basin that we use to conduct an analysis of these patterns for 1996,2001. RisQue features a map of maximum plant-available soil water (PAWmax) developed using 1565 soil texture profiles and empirical relationships between soil texture and critical soil water parameters. PAW is depleted by monthly evapotranspiration (ET) fields estimated using the Penman,Monteith equation and satellite-derived radiation inputs and recharged by monthly rain fields estimated from 266 meteorological stations. Modeled PAW to 10 m depth (PAW10 m) was similar to field measurements made in two Amazon forests. During the severe drought of 2001, PAW10 m fell to below 25% of PAWmax in 31% of the region's forests and fell below 50% PAWmax in half of the forests. Field measurements and experimental forest fires indicate that soil moisture depletion below 25% PAWmax corresponds to a reduction in leaf area index of approximately 25%, increasing forest flammability. Hence, approximately one-third of Amazon forests became susceptible to fire during the 2001 ENSO period. Field measurements also suggest that the ENSO drought of 2001 reduced carbon storage by approximately 0.2 Pg relative to years without severe soil moisture deficits. RisQue is sensitive to spin-up time, rooting depth, and errors in ET estimates. Improvements in our ability to accurately model soil moisture content of Amazon forests will depend upon better understanding of forest rooting depths, which can extend to beyond 15 m. RisQue provides a tool for early detection of forest fire risk. [source] Ground Water Discharge and Nitrate Flux to the Gulf of MexicoGROUND WATER, Issue 3 2004Carolyn B. Dowling Ground water samples (37 to 186 m depth) from Baldwin County, Alabama, are used to define the hydrogeology of Gulf coastal aquifers and calculate the subsurface discharge of nutrients to the Gulf of Mexico. The ground water flow and nitrate flux have been determined by linking ground water concentrations to 3H/3He and 4He age dates. The middle aquifer (A2) is an active flow system characterized by postnuclear tritium levels, moderate vertical velocities, and high nitrate concentrations. Ground water discharge could be an unaccounted source for nutrients in the coastal oceans. The aquifers annually discharge 1.1 ± 0.01 × 108 moles of nitrate to the Gulf of Mexico, or 50% and 0.8% of the annual contributions from the Mobile-Alabama River System and the Mississippi River System, respectively. In southern Baldwin County, south of Loxley, increasing reliance on ground water in the deeper A3 aquifer requires accurate estimates of safe ground water withdrawal. This aquifer, partially confined by Pliocene clay above and Pensacola Clay below, is tritium dead and contains elevated 4He concentrations with no nitrate and estimated ground water ages from 100 to 7000 years. The isotopic composition and concentration of natural gas diffusing from the Pensacola Clay into the A3 aquifer aids in defining the deep ground water discharge. The highest 4He and CH4 concentrations are found only in the deepest sample (Gulf State Park), indicating that ground water flow into the Gulf of Mexico suppresses the natural gas plume. Using the shape of the CH4 -He plume and the accumulation of 4He rate (2.2 ± 0.8 ,cc/kg/1000 years), we estimate the natural submarine discharge and the replenishment rate for the A3 aquifer. [source] Infiltration pattern in a regolith,fractured bedrock profile: field observation of a dye stain patternHYDROLOGICAL PROCESSES, Issue 2 2006Jae Gon Kim Abstract We examined the infiltration pattern of water in a regolith,bedrock profile consisting of two overburdens (OB1 and OB2), a buried rice paddy soil (PS), two texturally distinctive weathered materials (WM1 and WM2) and a fractured sedimentary rock (BR), using a Brilliant Blue FCF dye tracer. A black-coloured coating in conducting fractures in WM1, WM2 and BR was analysed by X-ray diffraction and scanning electron microscopy. The dye tracer penetrated to greater than 2 m depth in the profile. The macropore flow and saturated interflow were the major infiltration patterns in the profile. Macropore flow and saturated interflow were observed along fractures in WM1, WM2 and BR and at the dipping interfaces of PS,WM1, PS,WM2 and PS,BR respectively. Heterogeneous matrix flow occurred in upper overburden (OB1) and PS. Compared with OB1, the coarser textured OB2 acted as a physical barrier for vertical flow of water. The PS with low bulk density and many fine roots was another major conducting route of water in the profile. Manganese oxide and iron oxide were positively identified in the black coating material and had low crystallinity and high surface area, indicating their high reactivity with conducting contaminants. Copyright © 2006 John Wiley & Sons, Ltd. [source] Energy, exergy and uncertainty analyses of the thermal response test for a ground heat exchangerINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2009M. H. Sharqawy Abstract This paper presents energy, exergy and uncertainty analyses for the thermal response test of a ground heat exchanger. In this study, a vertical U-shaped ground heat exchanger with 80,m depth and 20,cm borehole diameter is installed for the first time at the university premises in Saudi Arabia. A mobile thermal response apparatus is constructed and used to measure the performance of the ground heat exchanger. The thermal response test was carried out four times at different thermal loads from September 2007 to April 2008. The energy and exergy transports of these thermal response tests were analyzed using the experimental results obtained in this period. The analysis provides a better understanding of the overall performance of vertical ground heat exchangers, verifies the thermal response test results and improves the experimental setup. Copyright © 2008 John Wiley & Sons, Ltd. [source] Thermal modelling and experimental validation of ground temperature distribution in greenhouseINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2004M.K. Ghosal Senior Research Fellow Abstract A periodic analysis for daily and monthly variations of ground temperature with depths is presented both under greenhouse and bare surface conditions of Delhi and for bare surface condition in other climates of India in order to design an efficient earth to air heat exchanger for greenhouse system. Calculations were carried out for a typical winter and summer day of Delhi in year 2000. Predicted values of ground temperature at 1 m depth were in fair agreement with experimental values under both conditions. Ground temperatures at various depths inside greenhouse were found to be on an average 7,9°C and 3,6°C higher than bare surface for daily and monthly variations respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source] Abundance and clonal replication in the tropical corallimorpharian Rhodactis rhodostomaINVERTEBRATE BIOLOGY, Issue 4 2000Nanette E. Chadwick-Furman Abstract. The corallimorpharian Rhodactis rhodostoma appears to be an opportunistic species capable of rapidly monopolizing patches of unoccupied shallow substrate on tropical reefs. On a fringing coral reef at Eilat, Israel, northern Red Sea, we examined patterns of abundance and clonal replication in R. rhodostoma in order to understand the modes and rates of spread of polyps across the reef flat. Polyps were abundant on the inner reef flat (maximum 1510 polyps m,2 and 69% cover), rare on the outer reef flat, and completely absent on the outer reef slope at >3 m depth. Individuals cloned throughout the year via 3 distinct modes: longitudinal fission, inverse budding, and marginal budding. Marginal budding is a replicative mode not previously described. Cloning mode varied significantly with polyp size. Approximately 9% of polyps cloned each month, leading to a clonal doubling time of about 1 year. The rate of cloning varied seasonally and depended on day length and seawater temperature, except for a brief reduction in cloning during midsummer when polyps spawned gametes. Polyps of R. rhodostoma appear to have replicated extensively following a catastrophic low-tide disturbance in 1970, and have become an alternate dominant to stony corals on parts of the reef flat. [source] Consequences of introducing the invasive amphipod Gmelinoides fasciatus into large shallow Lake Peipsi: present distribution and possible effects on fish foodJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2010K. Kangur Summary The objective of the study was to assess the effect of the Baikalian amphipod Gmelinoides fasciatus, a successful invader into Europe, as a fish food source in Lake Peipsi to where it was introduced in the 1970s. In 2002,2006, the littoral macrozoobenthos was studied along 17 transects (0.1,4 m depth, 384 quantitative samples) to determine the recent distribution of G. fasciatus and its share in the benthic community. Earlier records on the littoral macrozoobenthos from the years 1970, 1980, 1990 and 2000 were also used for comparison. Our results indicate that the invasive G. fasciatus is the dominant species (about 43% of total macrozoobenthos abundance) in the littoral zone of Lake Peipsi, while the native gammarids Gammarus lacustris and Pallasea quadrispinosa appear to be extinct and oligochaetes seem to have declined. G. fasciatus preferred hard substrates and it was mainly distributed close to water shallow beach areas (water depth <0.2 m), where its abundance reached locally up to 29 000 ind. m,2 (97% of total macrozoobenthos abundance). This distribution pattern of the invader in summer makes it mostly inaccessible for adult fish and increases its survival rate. Being highly mobile, G. fasciatus is not sensitive to water level fluctuations in shallow lakes. These behavioural characteristic increase its population success. [source] | |||||||||||||||||||||||||||||||