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Underlying Sediments (underlying + sediment)
Selected AbstractsThe dynamics of unattached benthic macroalgal accumulations in the Swan,Canning EstuaryHYDROLOGICAL PROCESSES, Issue 13 2001Helen Astill Abstract It has been suggested that macroalgal accumulations may impact on benthic nutrient cycling by promoting remineralization of sedimentary nutrients, otherwise inaccessible, and act as sinks/sources for dissolved nutrients in the water column. However, little consideration has been given to the time taken for these impacts to occur, and if accumulations persist long enough in a region for impacts to occur. In this study, accumulations were characterized seasonally, according to biomass, height relative to water depth, and organic content of the underlying sediment, from November 1996 to August 1997, in the Swan,Canning Estuary. Persistence of accumulations was measured from late summer to mid-winter in 1997, by tagging individual plants and recording the time tagged plants persisted at 10 sites. In summer 1998, physicochemical profiles of accumulations were measured over 24 h, at two locations: one with relatively low sediment organic content (SOCn) (1·5% LOI) and one with relatively high SOC (6% LOI). Accumulations rarely exceeded 25 cm in height, regardless of water column depth, and ranged between 100 and 500 g dwt m,2. Macroalgae persisted between one week, in relatively well-flushed regions, to one month in areas with poor flushing. Over the entire diurnal period, almost 100% of incident light was attenuated at the bottom of all accumulations. Dissolved oxygen levels at the bottom of accumulations were generally depressed, particularly at night, with hypoxia (1 mg l,1) recorded at the high SOC site at 03 : 00 h. No significant differences in FRP concentrations (approximately 30,60 µg l,1) were recorded between sites, or within accumulation profiles. Ammonium levels were greatly raised inside accumulations at the high SOC site by 03 : 00 h (10 and 300 µg l,1, inside and outside, respectively). The results show that, where SOC is high, conditions within accumulations are affected. Impacts occurred within 24 h; well within the period for which accumulations persist. These results also indicate that regulation of hydrological regimes in estuarine systems may result in increased persistence of macroalgal accumulations, and associated water quality problems. Copyright © 2001 John Wiley & Sons, Ltd. [source] A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black SeaENVIRONMENTAL MICROBIOLOGY, Issue 8 2008Martin Krüger Summary A novel microbially diverse type of 1- to 5-cm-thick mat performing anaerobic oxidation of methane (AOM) and covering several square metres of the seafloor was discovered in the Black Sea at 180 m water depth. Contrary to other AOM-mat systems of the Black Sea these floating mats are not associated to free gas and are not stabilized by authigenic carbonates. However, supply of methane is ensured by the horizontal orientation of the mats acting as a cover of methane enriched fluids ascending from the underlying sediments. Thorough investigation of their community composition by molecular microbiology and lipid biomarkers, metabolic activities and elemental composition showed that the mats provide a clearly structured system with extracellular polymeric substances (EPS) building the framework of the mats. The top black zone, showing high rates of AOM (15 ,mol gdw,1 day,1), was dominated by ANME-2, while the following equally active pink layer was dominated by ANME-1 Archaea. The lowest AOM activity (2 ,mol gdw,1 day,1) and cell numbers were found in the greyish middle part delimited towards the sediment by a second pink, ANME-1-dominated and sometimes a black outer layer (ANME-2). Our work clearly shows that the different microbial populations are established along defined chemical gradients such as methane, sulfate or sulfide. [source] High prokaryote diversity and analysis of community structure in mobile mud deposits off French Guiana: identification of two new bacterial candidate divisionsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2001Vanessa M. Madrid Abstract Bacterial and archaeal community compositions in highly mobile nearshore muds typical of the Guiana coastline of South America were examined by sequence analysis of a 16S rDNA clone library. DNA was extracted from a subsurface sediment layer (10,30 cm) collected at a subtidal (,1 m deep) mud wave site between Kourou and Sinnamary, French Guiana. Analysis of 96 non-chimeric sequences showed the majority to be bacteria (98%), that diversity was high with 64 unique sequences, and that proteobacteria were dominant (46%). Two crenarchaeota sequences were found (2%). Bacterial sequences belonged to the Cytophaga-Flexibacter-Bacteroides (18%), Actinobacteria (11.5%), Planctomycetes (6.3%), Cyanobacteria (3.2%), low-GC Gram-positive (1%), ,, , and , subdivisions of Proteobacteria (27%, 16%, and 9%, respectively). Additional bacterial sequences belonged to the candidate division TM6 (1%) and to two newly proposed candidate divisions: KS-A (2%) and KS-B (3%). A sizeable fraction (22%) of sequences from the Kourou,Sinnamary library are normally found in water column populations, reflecting frequent entrainment of suspended debris into physically reworked underlying sediments. Dominant sequences (56%) were related to Gelidibacter algens (Cytophaga-Flexibacter-Bacteroides group), Actinobacteria, Sulfitobacter and Ruegeria spp. (,-proteobacteria), all of which are chemoorganotrophs, consistent with abundant labile organic carbon. The presence of sequences from potential sulfate reducers and sulfide oxidizers suggests the likelihood of sulfur cycling in these sediments, despite the dominance of suboxic (iron-reducing), non-sulfidic diagenetic properties. Rarefaction analysis indicated that bacterial diversity in the French Guiana library is not only unusually high in comparison with other marine sedimentary environments, but among the most diverse of all environments reported to date. [source] The Tortonian reference section at Monte dei Corvi (Italy): evidence for early remanence acquisition in greigite-bearing sedimentsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009S. K. Hüsing SUMMARY The reliability of primary natural remanent magnetization (NRM) signals in greigite-bearing sediments has been frequently questioned. Here, we show that the stable NRM in the deep marine Middle to Late Miocene sediments at Monte dei Corvi, northern Italy, is mainly carried by greigite. Combined rock magnetic experiments and scanning electron microscopy successfully enabled discrimination between two greigite populations. One fine-grained and relatively well-dispersed greigite population (grain size between 60 and 200 nm) is most likely of magnetotactic origin. The second greigite population with larger grain sizes (typically 700 nm to 1 ,m) is most likely of authigenic (bacterially mediated) origin, and is related to post-depositional sulphidization processes. Greigite is the main magnetic remanence carrier in the older part of the section (12.8 to 8.7 Ma), whereas greigite and fine-grained (presumably magnetotactic) magnetite are present in the younger part of the section (8.7 to 6.9 Ma). Similar remanent magnetization directions of the magnetite and greigite components, and the likelihood of a magnetotactic origin, suggests that the NRM is of syn-depositional age. We suggest that moderate methane seepage from the underlying sediments may have occurred that resulted in the preservation of pristine greigite. This corroborates the reliability of the previously established magnetostratigraphy at Monte dei Corvi. [source] HYDROLOGICAL EFFECTS OF AN UNCONTROLLED FLOWING WELL, RED RIVER VALLEY, NORTH DAKOTA, USA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2004Philip J. Gerla ABSTRACT: In areas of the Red River Valley that overlie permeable Paleozoic sediments, wetlands and salinization have developed where unregulated flowing wells discharge brackish water. Field data were collected to assess the fate of water and salt from a well 25 km northwest of Grand Forks. Drilled during the drought of the 1930s, discharge was used to replenish water in a small oxbow pond used by livestock. The unregulated well discharges about 56 m3/day, measured since 1993. This discharge exceeds ground water flow from the site, thereby forming a ground water mound with a maximum height of 1 m and a diameter of about 300 m. Most soil and underlying sediments near the well have a hydraulic conductivity of 0.3 m3/day. Flow net analysis suggests that less than 25 percent infiltrates, with the remaining water lost to surface flow and evapotranspiration (ET). Evapotranspiration and slow infiltration has led to increased salinization, with shallow soils exhibiting EC to 500 milliSiemens/m. The most pronounced soil salinization occurs along the margins of the oxbow pond and meander scars. Wetland vegetation with low diversity comprises three zones, with species associations similar to those of closed basin prairie potholes to the west. [source] Pilot-scale demonstration of in situ capping of PCB-containing sediments in the lower Grasse RiverREMEDIATION, Issue 1 2003James D. Quadrini A fish-consumption advisory is currently in effect in a seven-mile stretch of the Grasse River in Massena, New York, due to elevated levels of PCBs in fish tissue. One remedial approach that is being evaluated to reduce the PCB levels in fish from the river is in situ capping. An in-river pilot study was conducted in the summer of 2001 to assess the feasibility of capping PCB-containing sediments of the river. The study consisted of the construction of a subaqueous cap in a seven-acre portion of the river using various combinations of capping materials and placement techniques. Optimal results were achieved with a 1:1 sand/topsoil mix released from a clamshell bucket either just above or several feet below the water surface. A longer-term monitoring program of the capped area commenced in 2002. Results of this monitoring indicated: 1) the in-place cap has remained intact since installation; 2) no evidence of PCB migration into and through the cap; 3) groundwater advection through the cap is not an important PCB transport mechanism; and 4) macroinvertebrate colonization of the in-place cap is continuing. Additional follow-up monitoring in the spring of 2003 indicated that a significant portion of the cap and, in some cases, the underlying sediments had been disturbed in the period following the conclusion of the 2002 monitoring work. An analysis of river conditions in the spring of 2003 indicated that a significant ice jam had formed in the river directly over the capping pilot study area, and that the resulting increase in river velocities and turbulence in the area resulted in the movement of both cap materials and the underlying sediments. The pilot cap was not designed to address ice jam,related forces on the cap, as the occurrence of ice jams in this section of the river had not been known prior to the observations conducted in the spring of 2003. These findings will preclude implementation of the longer-term monitoring program that had been envisioned for the pilot study. The data collected immediately after cap construction in 2001 and through the first year of monitoring in 2002 serve as the basis for the conclusions presented in this article. It should be recognized that, based on the observation made in the spring of 2003, some of these conclusions are no longer valid for the pilot study area. The occurrence of ice jams in the lower Grasse River and their importance on sediments and PCBs within the system are currently under investigation. © 2003 Wiley Periodicals, Inc. [source] Geoarchaeology of the Milfield Basin, northern England; towards an integrated archaeological prospection, research and management frameworkARCHAEOLOGICAL PROSPECTION, Issue 2 2002David G. Passmore Abstract This paper presents the results of geoarchaeological investigations undertaken on the valley floor of the Milfield Basin in Northumberland, northern England. The area has a regionally and nationally important archaeological record, including a series of major neolithic and Anglian settlements, but has hitherto lacked archaeological assessment and management guidelines appropriate to the wide range of late-glacial and post-glacial environmental settings in the basin. This project has used geomorphological techniques to delimit and classify a total of nine valley floor landform elements in terms of their geomorphology and their known and potential archaeological and palaeoenvironmental associations. Terraced glaciodeltaic and glaciofluvial sand and gravel landforms comprise the oldest landform elements described here and have formed the primary regional focus for prehistoric and early historic settlement and associated subsistence and ritual activity. These landforms have experienced little post-glacial geomorphological activity, but their multiperiod archaeological landscapes lie beneath a shallow soil cover and are vulnerable to land-use activities that disturb terrace soils and underlying sediments. A second group of landform elements are of Holocene age and include localized surface peats, alluvial fans, colluvial deposits and extensive deposits of terraced alluvium. Archaeological landscapes in these environments may lie buried intact and unrecorded beneath protective covers of sediment although locally they may have been subject to erosion and reworking by fluvial and slope processes. Holocene alluviation may account, at least in part, for the paucity of recorded archaeology in these parts of the basin. However, peat and organic-rich sedimentary sequences identified here (including four 14C dated peat sequences) offer an opportunity to elucidate the environmental context and land-use histories of local prehistoric and early historic communities in the basin, and hence also should be regarded as an archaeological resource. Discussion of landform elements and their archaeological associations is followed by a brief outline of evaluation criteria developed with the aim of ensuring effective long-term management of archaeological and palaeoenvironmental resources. It is concluded that geoarchaeological analysis of landform elements may be considered central to development of frameworks intended to underpin future programmes of archaeological research and the development of cultural resource management and evaluation strategies. Copyright © 2002 John Wiley & Sons, Ltd. [source] Middle Weichselian glacial event in the central part of the Scandinavian Ice Sheet recorded in the Hitura pit, Ostrobothnia, FinlandBOREAS, Issue 1 2008VELI-PEKKA SALONEN The Hitura open pit exposes a sedimentary sequence up to 50 m thick representing Late Saalian to Holocene glacial and non-glacial sediments. The sequence was investigated using sedimentological methods, OSL-dating and pollen and diatom analyses to reconstruct the Middle Weichselian (MWG) glacial event in the central part of the Scandinavian Ice Sheet (SIS). The results indicate that the sediment succession represents two entire glacial advance and retreat cycles. The lowermost deposits are Late Saalian esker and delta sediments overlain by sediments that correlate with the early Eemian lacustrine phase. Remnants of the Eemian soil post-dating the lacustrine phase were also observed. The area was ice-free during the entire Early Weichselian (EWG). The first glacial advance recorded in the sediments is related to the MWG. It started 79 kyr ago, deformed underlying sediments and deposited an immature till, including large detached sediment pods containing remains of organic material, soils and fluvial sediments representing allochthonous material from EWG ice-free stadials and interstadials. The glacial deposits are conformably overlain by glaciolacustrine and littoral accumulations, indicating MWG deglaciation between 62 and 55 kyr ago. Based on the fabric measurements from the till unit overlying the MWG sediments, ice advance during the Late Weichselian (LWG) was initially from the west and later from a north-northwesterly direction. The Hitura strata provide the first dating of the MWG deglaciation (55 to 62 kyr ago) from central parts of the SIS. It can be considered as a key site for studying the growth and decay of SIS during the poorly known early parts of the glaciation. [source] | ||||||||||||||||