Selective Extraction Chemistry of Toxic Metal Sulfides from Sediments

Experimental evidence suggests that formation of metal sulfides in anoxic sediments limits the bioavailability of several toxic elements. Our ability to quantify the processes by which these metal sulfides form is dependent upon our ability to determine the speciation of solid phase metals in sediments. Our work indicates that an entire suite of Cu-Fe and Ni-Fe sulfide minerals can form upon the exposure of mackinawite to aqueous Cu and Ni. Furthermore, we have demonstrated that the solubility of pure metal sulfide minerals and their iron-metal derivatives in HCl directly correlates with the observed trends in the 'Degree of Trace Metal Pyritization' in natural sediments. Current extraction schemes cannot distinguish discrete trace metal sulfides from trace metals associated with pyrite.     

The Automatic Determination of the Location and Depth of Contacts and Dykes from Aeromagnetic Data

This paper demonstrates how to automatically obtain the location and depth of magnetic field sources of known structural index, such as contacts and dykes, for profile and map datasets. The method uses the analytic signal amplitude, and does not require that the magnetic data be pole-reduced or have a known magnetisation vector. The method is applied both to synthetic data and to aeromagnetic data from South Africa.     

WOODY VEGETATION AND DEBRIS FOR IN-CHANNEL SEDIMENT CONTROL

lINTRODUCTlONChanne1erosionandsedimentationareoftenproblemsinagriculturalwatersheds.Forexample,annualsuspendedsedimentyieldfrom8mixedcoverwatershedswithloessialsoilsinnorthwesternMississippi,U.S.A.ranginginsizetYom2lto622km2wasbetween7O4and1673tonnes(Shieldsetal.l995).ControlofchannelbankerosionintheU.S.hastraditionaIlybeenaddressedwithstructurescostingontheorderof$l5Om-1ofbankline.BecauseoftheecologicaIvalueandoftenlowercost(relativetononlivingstructure)ofvegetativetreatments,weargue…     

Organic carbon isotope ratios (δ13C) of Arctic Amerasian Continental shelf sediments

Organic matter origins are inferred from carbon isotope ratios ('¹³C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in '¹³C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment '¹³C, OC/N, and '¹⁵N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C₃ plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C₄ and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment '¹³C values (-16.5 to -13.6‰) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial-interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO₂ and pCO₂ in the Arctic Basin halocline.     

Filtering potential field data by modifying its amplitude and phase in the space domain

Potential field datasets are commonly broken down in the space domain into amplitude (total gradient, or analytic signal amplitude) and phase (tilt angle) components as part of the data processing and interpretation procedure. However, it is possible to reconstruct the data again in the space domain from the amplitude and phase, and if they have been modified then a filtered dataset will be produced. For example, modified derivatives and filters which are based on them (such as the tilt angle and the theta map) can be produced. In addition, the modification of the data amplitude prior to the reconstruction of the signal allows controllable automatic gain control filters to be designed. The procedures are demonstrated on aeromagnetic and gravity data from Southern Africa.     

The fetch effect on aeolian sediment transport on a sandy beach: a case study from Magilligan Strand,Northern Ireland

Experiments were conducted on Magilligan Strand, Northern Ireland, to assess the influence of the fetch effect on aeolian sediment transport. During each experiment surface sediments were uniformly dry and unhindered by vegetation or debris. The leading edge of erodible material was well defined, with the limit of wave up‐rush demarcating the wet–dry boundary; the work was conducted during low tides. A number of electronic and integrating traps were utilised, with two ultrasonic anemometers used to measure wind direction and velocity at 1 Hz. The combination of 1^o direction data and trap locations resulted in a range of fetch distances, from 2 to 26 m. Data integrated over 15‐minute intervals (corresponding to the integrating trap data) revealed a distinct trend for all the experiments. An initial rapid increase in the transport rate occurred over a short distance (4–9 m). This maximum transport rate was maintained for a further 5–6 m before a steady decay in the flux followed, as fetch distance increased. A measured reduction in wind speed (6–8%) across the beach suggests a negative feedback mechanism may be responsible for the diminishing transport rate: the saltating grains induce energy dissipation, thus reducing the capability of the wind to maintain transport. For one experiment, the presence of compact sediment patches may also have contributed to the reduction of the transport rate. The decay trend calls into question the utility of the fetch effect as an important parameter in aeolian studies that seek to understand sediment budgets of the foredune‐beach zone. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the equilibrium planform concept to natural beaches in Northern Ireland

The equilibrium planform concept (EPC) for bayed beaches has achieved wide currency in coastal morphodynamics. The north coast of Ireland comprises a series of discrete headland-embayment beaches within which waves and currents recycle a finite sediment volume. It is therefore an ideal setting in which to explore the applicability of the concept. Application of the approach to 9 embayment beaches on the north coast of Ireland provides some insights into the application of the concept. The planform of some beaches does correspond to that predicted while others do not. Those whose measured planform does not correspond to the predicted planform can be interpreted through, (a) difficulty in identifying the wave diffraction point, (b) disequilibrium on the beach (sediment scarcity or excess), (c) geological control of beach morphology. The subjectivity in selecting the diffraction point renders alternative explanations difficult and reduces the utility of the approach on natural shorelines, where significant irregularities render identification of such points difficult.     

Structure and sediment distribution in the western Bering Sea

Eleven seismic reflection profiles across Shirshov Ridge and the adjacent deep-water sedimentary basins (Komandorsky and Aleutian Basins) are presented to illustrate the sediment distribution in the western Bering Sea. A prominent seismic reflecting horizon, Reflector P (Middle—Late Miocene in age), is observed throughout both the Aleutian and Komandorsky Basins at an approximate subbottom depth of 1 km. This reflector is also present, in places, on the flanks and along the crest of Shirshov Ridge. The thickness of sediments beneath Reflector P is significantly different within the two abyssal basins. In the Aleutian Basin, the total subbottom depth to acoustic basement (basalt?) is about 4 km, while in the Komandorsky Basin the depth is about 2 km.Shirshov Ridge, a Cenozoic volcanic feature that separates the Aleutian and Komandorsky Basins, is an asymmetric bathymetric ridge characterized by thick sediments along its eastern flank and steep scarps on its western side. The southern portion of the ridge has more structural relief that includes several deep, sediment-filled basins along its summit.Velocity data from sonobuoy measurements indicate that acoustic basement in the Komandorsky Basin has an average compressional wave velocity of 5.90 km/sec. This value is considerably larger than the velocities measured for acoustic basement in the northwestern Aleutian Basin (about 5.00 km/sec) and in the central Aleutian Basin (5.40–5.57 km/sec). In the northwestern Aleutian Basin, the low-velocity acoustic basement may be volcaniclastic sediments or other indurated sediments that are overlying true basaltic basement. A refracting horizon with similar velocities (4.6–5.0 km/sec) as acoustic basement dips steeply beneath the Siberian continental margin, reaching a maximum subbottom depth of about 8 km. The thick welt of sediment at the base of the Siberian margin may be the result of sediment loading or tectonic depression prior to Late Cenozoic time.