Relative Contributions Of Sediment Research Articles

Stromatolite branching in the Neoproterozoic of the Centralian Superbasin, Australia: an investigation into sedimentary and microbial control of stromatolite morphology

The extensive and well-preserved Neoproterozoic Acaciella australica Stromatolite assemblage of Australia is ideal for examining the relative roles of microbial and environmental influences on stromatolite branching and stromatolite macrostructure across a wide geographical area. Detailed sedimentological analyses indicate that the basal hemispheroidal section of bioherms contains abundant sediment. By contrast, the columnar sections of bioherms are composed almost exclusively of micritic laminae. These micritic laminae display little evidence for environmental, especially sedimentary, control over stromatolite morphology. The change from a hemispheroidal morphology to branching morphology is linked to variations in the relative contributions of sediment and framework growth. The shift to columns appears to be closely linked to a decrease in sediment supply that resulted in a more stable environment in which microbially mediated framework growth began to control stromatolite morphology. Branching in the A. australica assemblage stromatolites appears to be caused by shifting sedimentary and microbial control on stromatolite morphology.

HISTORICAL TRENDS IN SEDIMENTATION RATES AND SEDIMENT PROVENANCE, FAIRFIELD LAKE, WESTERN NORTH CAROLINA

: Sedimentation rates and sediment provenance were examined for lacustrine sediments deposited in Fairfield Lake, western North Carolina, during the past 111 years. Stratigraphic, radionuclide, and cartographic data indicate that sedimentation rates have increased several fold during the past three decades in response to localized development. The magnitude of increased sedimentation was surprising given limited development within the basin: 0.12 to 0.68 buildings/ha in 2000 in those parts directly delivering sediment to the dated cores. Thus, the analysis illustrates the potential sensitivity of watersheds in the southern Appalachians to changes in land cover. An approach that combined geochemical fingerprinting with sediment mixing models was subsequently evaluated to determine its ability to accurately estimate the contribution of sediment from (1) major bedrock formations that underlie the watershed and (2) potential sources associated with four land cover categories. Sediment sources in both analyses proved difficult to geochemically fingerprint to greater than 90 percent accuracy using data on acid-soluble metals and selected isotopes of lead (Pb). The relative contributions of sediment from delineated sources, estimated by the mixing models, generally corresponded with known temporal and spatial patterns of land cover. However, the models were plagued by two significant problems — the chemical alteration of sediments as they were transported through upland streams to depositional sites within the lake and the loss of elemental mass. Thus, future investigations using the fingerprinting approach in this area of intense weathering, and presumably others, will need to modify the existing methods to more accurately elucidate changes in sediment provenance related to development.

Sediment source identification by using137Cs and210Pb radionuclides in a small catchment of the Hilly Sichuan Basin, China

Double radionuclide tracers of137Cs and210Pb were used to investigate sediment sources in the Wujia Gully, a small catchment in the Hilly Sichuam Basin in 2002. Average137Cs and210Pb concentrations in the source soils of the steep forest slopes, gentle cultivated terraces and bare slopes were 7.15 ±0.40 and 162.01 ±3.86 Bq·kg-1, 4.01 ±0.31 and 70.96 ±2.65 Bq · kg-1, and 0 and 15.12 ±1.22 Bq · kg-1, respectively, while those concentrations in the recently deposited sediments in the reservoir were 3.06 ±0.23 and 72.66 ±1.61 Bq · kg-1, respectively. By using the mixing model, the relative sediment contributions from steep forest slopes, gentle cultivated terraces and bare slopes (including channel banks) were estimated to be 18%, 46% and 36%, respectively. Cultivated terraces and bare slopes (including channel banks) were the first and the second important sediment sources in catchment. Specific sediment yield in the catchment was 642 t · km-2 · a-1 from the deposited sediment volume in the reservoir since 1956. Soil erosion rates for the forest slopes and cultivated terraces, which accounted for 2/3 and 1/3 of the drainage area in the catchment, were estimated to be 173 and 886 t · km-2 · a-1, respectively.

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using 137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and 137Cs contents of the deposited sediments before and after 1993, changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully, in the Rolling Loess Plateau, are analyzed in this paper. Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield of the catchment, in sharp decrease of the sediment yield and the relative sediment contribution of the inter-gully area, and in increase of the sediment yield and the contribution of the gully area, for a short term. The mean specific sediment yield of 29650 t km−2 a−1 of 1994–1996 in the catchment was 2.2 times the average value of 13413 t km−2 a−1 for a long term. The specific sediment yield of the inter-gully area decreased from the 14335 t km−2 a−1 in 1994 to 7034 t km−2 a−1 in 1995 and 3517 t km−2 a−1 in 1996, while the yield of the gully area varied between 44944 and 62136 t km−2 a−1 during the period of 1994–1996 which was much greater than the value of 21118 t km−2 a−1 before 1993. The relative sediment contribution from the inter-gully area decreased from 23% in 1994 to 15% in 1995 and 6% in 1996, while the contribution from the gully area increased from 77% in 1994 to 85% in 1995 and 94% in 1996. It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration, therefore, the soil erosion reduced but the runoff amount increased on the inter-gully area. Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements, consequently, in increase of the total sediment yield from the catchment.

Modelling cadmium accumulation by benthic invertebrates in situ: The relative contributions of sediment and overlying water reservoirs to organism cadmium concentrations

An in situ experiment was designed (1) to determine the relative importance of Cd in the sediment versus Cd in the overlying water for its accumulation in benthic animals and (2) to test in situ the acid volatile sulfide (AVS) model. Sediments of a low‐Cd shield lake were artificially contaminated with various amounts of Cd and placed at a littoral site in open plastic containers in the lake bottom for 11 months to allow colonization by indigenous lake bcnthos. Gradients in sedimentary and interstitial water Cd concentrations were, thus, created in situ, although Cd concentrations in the overlying water remained low. Accumulation of Cd by benthic invertebrates was significantly and linearly correlated with sediment Cd concentrations across treatment levels for most taxa. The magnitude of the response to the sediment Cd gradient was taxon specific and consistent with differences in animal ecology. Despite the high Cd contamination levels attained in the experiment, the population densities of most taxa appear to have been unaffected by the presence of Cd. We used the results from the experimental containers to predict the sources of Cd for benthic animals in the environs. For almost all of the taxa studied, individuals living in the low‐Cd sediments outside the experimental containers accumulated their Cd almost exclusively from the overlying water; only the burrowing, sediment‐feeding taxa Chironomus stuegeri and members of the Tubificidae obtained substantial Cd from the sediment. Cadmium activities in the pore waters of the containers were in agreement with the AVS model, but the Cd concentrations found in the benlhic organisms did not. Our results from this shield lake suggest that predictions of Cd concentrations in most benthic animals would be more accurate if they were based on water column rather than on sedimentary Cd concentrations.

The significance of various sediment magnetic mineral fractions for tracing sediment sources in Killimicat Creek

The mineral magnetic properties of sediment are increasingly being used to determine the sources of sediment, and associated nutrients and contaminants in drainage basins. This study was undertaken to measure the relative contributions of the magnetic mineral components in sediment (i.e., components associated with surface bound Fe, the heavy mineral fraction, and as inclusions in particles) to determine the extent to which they represent the bulk of the sediment. Deposited channel sediment samples from the tributaries and downstream reach at the first major confluence in the headwaters of Killimicat Creek, New South Wales, were sieved to separate 6 particle size fractions, and the mineral magnetic properties measured to determine the relative contribution of sediment from the smaller tributary basin. The finest sand component (63–125 μm) was then separated into light and heavy mineral fractions, and magnetic measurements made on each fraction. Magnetic parameter data from the 63–125 μm fraction, measured before density separation, show a dominance of sediment (70±12%) derived from the smaller tributary basin. Measurements of the light sediment fraction give a similar result (73±13%). The proportion of the heavy mineral fraction delivered from the smaller tributary is 78±38%. The light mineral fraction of all of the samples were treated with HCl to remove surface bound Fe, and subsequent magnetic measurements show that 41–94% of the mass specific magnetic susceptibility is attributable to magnetic minerals associated with surface bound Fe. The heavy mineral component, while <4% by weight of the 63–125 μm fraction, contributes 5–40% of the total magnetic susceptibility. The results show that most of the magnetic mineral component (>60%) is associated with sediment particles, rather than the discrete heavy mineral component.

USE OF RESERVOIR DEPOSITS AND CAESIUM-137 MEASUREMENTS TO INVESTIGATE THE EROSIONAL RESPONSE OF A SMALL DRAINAGE BASIN IN THE ROLLING LOESS PLATEAU REGION OF CHINA

This paper reports the results of an investigation of the erosional response of the 3.86 km(2) Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China . In the absence of direct measurements , information derived from reservoir deposits and from caesium - 137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin . Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km(-2) year(-1), 8584 t km(-2) year(-1) and 15851 t km(-2) year(-1) respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits year in the two sediment-trap reservoirs ranged between 4627 and 32472 t km(-2) year(-1). Almost all the sediment transported from the catchment was contributed by 2-4 large floods each year. Measurements of the caesium - 137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973-1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium - 137 content of the sediment deposited in this sediment-trap reservoir , the relative contributions of sediment from the rolling plateau and gully areas over the period 1973-1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium - 137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin . (C) 1997 by John Wiley & Sons, Ltd.

Bioavailability of six organic chemicals toChironomus Tentanslarvae in sediment and water

Uptake and elimination of 14C-labeled terbutryn, fluridone, triphenyl phosphate (TPP), trans-permethrin, methoxychlor and 2,4,5,2′,4′,5′-hexachlorobiphenyl (HCBP) by Chironomus tentans larvae were studied in sediment-water systems. Animals were exposed to three different sediments containing 50 to 500 μg/kg (wet weight) of each chemical, or were held in screened containers in water above the treated sediment for 24 or 96-h. Elimination of radioactivity was determined over a 48-h interval. Results were analyzed by use of a one-compartment kinetic model. Larvae exposed in sand or in water above sand had significantly higher concentrations of each chemical than those exposed in or above river (silty) or pond (silty clay) sediments. Uptake of terbutryn and fluridone, two hydrophilic compounds, was similar (24-h exposure) to that of methoxychlor and greater than that for TPP, trans-permethrin or HCBP, due to much greater partitioning of the former compounds into water above each sediment. TPP, trans-permethrin, methoxychlor and HCBP concentrations were significantly higher in larvae from sediment than in animals held in water above sediment. Uptake rate constants from water for each chemical were much greater than those for sediment, but due to the relatively large sediment-to-water ratio (1:5) and the high proportion of chemical in sediment, relative contributions of sediment and water uptake to body burden were similar. Assimilation of each compound by larvae from ingested sediments appeared to be negligible except for TPP and HCBP. Estimates of assimilation of TPP and HCBP in sand-water systems were much greater than those for sediments with higher organic matter content.