Maximum Sedimentation Rate Research Articles

Sediment transport in a cold climate salt marsh (St. Lawrence Estuary, Canada), the importance of vegetation and waves

Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations with sub-arctic winter conditions. The present paper explores sedimentary processes in the Pointe-aux-Épinettes marsh during the ice-free period. Currents, waves, suspended sediment, and sedimentation rates have been measured in June, August and October 2009. Vegetation growth was monitored during one year on a monthly basis to understand the seasonal impact on the marsh. Vegetation attenuates currents and waves, but this attenuation changes over the year as vegetation disappears along winter. Results show that suspended sediment transport and deposition are controlled by vegetation, wave height, currents, distance from the marsh edge and distance from sediment sources. Suspended sediment concentrations and sedimentation rates were significantly correlated to wave height, highlighting the importance of waves for sediment resuspension transport. Transport was lowest in August when vegetation was high and wave occurrence low. However, vegetation growth didn't change fundamentally sediments dynamic of the marsh. Within one tide, an important part of sediment transport is only local within the marsh, as shown by the maximum sedimentation rates occurring near unvegetated areas of the marsh. Data provide a spatial understanding of summer sedimentology on cold climate marshes.

Submarine structures in the Gulf of İzmit, based on multichannel seismic reflection and multibeam bathymetry

Multichannel seismic reflection and multi-beam bathymetry data were used to study the active tectonic and syn-tectonic stratigraphic setting of the Gulf of Izmit in the Marmara Sea (Turkey). The gulf and its near surroundings are deformed by the northern strand of the dextral North Anatolian Fault. Three connected basins of the gulf, the western (Darica), central (Karamursel) and eastern (Golcuk) basins are formed by active faults, as observed in the stacked and migrated seismic sections, as well as the bathymetry map. The main branch and its surrounding sedimentary strata are confined by normal faults to the north and south. These normal faults converge at depth towards the main fault, forming a negative flower structure in the gulf. The average maximum sedimentation rate is 0.4 mm/year according to the three most recent seismo-stratigraphic units that are located to the south of the main fault branch within the central basin. A 20° south-dipping major discontinuity along the northern shoreline of the gulf represents the top of Paleozoic basement.

Recent sedimentary study of the shelf of the Basque country

The Northern Iberian margin of the Spanish Basque country (provinces of Gipuzkoa and Viscaia) is characterized by a narrow continental platform, which receives inputs of riverine particulate matter from the numerous riverine systems located within the Basque country. This particulate matter is subsequently deposited within the Bay of Biscay, and Gouf de Capbreton [Frouin, R., Fiuza, A.F.G., Ambar, I., Boyd, T.J., 1990. Observations of a poleward surface current off the coasts of Portugal and Spain during winter. Journal of Geophysical Research 95 (C1), 679–691]. The main goal of this study is to establish a map of the surface sediment distribution of the Basque continental shelf and more specifically to map the muddy patch located at the eastern side of that continental shelf. Three oceanographic cruises were conducted in 2003 and 2004. From these campaigns 340 surface samples, 12 short cores and 3 gravity cores have been collected over the mid and outer shelf from depths ranging between 50 m and 150 m deep. 3 seismic profiles were obtained across the shelf mud patch using a Sparker device. Sediment grain-size analyses were performed by the classical physical method of sieving and use of settling columns. The POC (Particular Organic Carbon) amounts in sediment and water samples were determined using the Strickland and Parsons' method [Strickland, J.D.H., Parsons, T.R., 1972. Determination of particulate carbon. In : A practical handbook of seawater analysis. Fisheries ResearchBoard of Canada, Ottawa, pp. 207−211] as adapted by Etcheber [Etcheber, H., 1981. Comparaison des diverses méthodes d'évaluation des teneurs en matières en suspension et en carbone organique particulaire des eaux marines du plateau continental aquitain. Journal de Recherche Océanographique VI (2), 37−42]. Radioisotopic measurements ( 210Pb exc) were made using a semi-planar germanium detector coupled to a multichannel analyser. Radiographical analysis was performed with an X-ray equipment (SCOPIX®) coupled with a radioscopy instrumentation and processing unit. Firstly, a detailed sedimentological map of this shelf has been produced and secondly, geophysical surveys have precisely mapped the geometry of the main mud patch on the continental shelf. In the mud patch itself the rates of sedimentation are between 0.13 and 0.50 cm yr − 1 . The maximum rate of sedimentation is located in the central mud patch, whereas the minimum rate of deposition occurs close to the rocky outcrops. These results seem to be in agreement with the estimation of the total thickness of the mud patch revealed by seismic profiles. The central part corresponds to the maximum thickness of 7 m. Interpretations of the associated oceanic current forcing factors (current direction, wave fetch and wind directional modes) relating to the identified sediment depositional zones are also undertaken.

Impact of Improvement of the Entrance Channel on the Rate of Sediment Deposition into the Dar es Salaam Harbour

The study reported here sought to investigate the effect that the dredging of the harbour basins and the entrance channel has had on sediment deposition rate into the Dar es Salaam harbour. Echo-sounding was carried out along berths No 2, 3, 4, 6, 7 and 8 as a means of detecting changes to their bathymetry in the four years since 1998, when the dredging commenced. Concentrations of transported sediments into and out of the harbour were determined using sediment traps. Short-term measurement of waves and currents were also carried out. Sediment traps, a wave-gauge and a current-meter were deployed in the entrance channel during the South East and North East monsoon seasons respectively. Our results reveal that the sedimentation rates after improvement of the channel are between 13 and 43 cm/year. Rates of sedimentation before dredging were relatively low, at between 7 and 25 cm/year. There are two reasons for the difference in rates. First, the settling of fine particles as a result of dredging activities, and second, the change of channel alignment and subsequent erosion on Ras Makabe. The eroded sediments were probably deposited into the harbour basin by the flood tide. This trend has the implication that the harbour basin will need more frequent dredging than it did before improvement of the entrance channel: In the past, with a maximum sedimentation rate of 25cm/year, it took 20 years before the harbour basin needed to be dredged. At the present sedimentation rate (maximum of 43cm/year), it will take only 11 years before re-dredging is necessary. Keywords : Dar es Salaam harbour, sediment deposition, entrance channel West Indian Ocean Journal of Marine Science Vol. 3 (2) 2004: pp. 105-112

Factors affecting seasonality of lithogenic and biogenic particle flux in a large estuarine ecosystem

Seasonal patterns of vertical flux over two years (2001–2003) at two stations in the Bras d'Or Lakes, a large estuary in Cape Breton Island, Nova Scotia, were determined using aluminum and organic carbon in settled particles collected in moored traps to calculate lithogenic (terrigenous) and marine biogenic fractions. On an annual basis, lithogenic material comprised 53% and 81% of dry weight and 48% and 66% of organic carbon in settled particles at the deep- (128 m) and shallow-water (41 m) locations, respectively. Peaks in runoff, inferred from rain and snowfall precipitation, ice cover and possible horizontal transport of resuspended sediment coincided with maximum sedimentation rates of lithogenic material during unstratified periods between October and March. Biological factors correlated with phytoplankton and ice algal primary production and seasonal changes in zooplankton grazing inferred from phaeopigments controlled biogenic particle fluxes under stratified conditions between June and September and during winter. Year-to-year variations in deposition of lithogenic and marine biogenic material depended on seasonal differences in stratification, precipitation, freeze/melt conditions and the extent of ice cover.

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr − 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr − 1 . Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr − 1 . Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr − 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the 210Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr − 1 ) exceeds the maximum sedimentation rate by 1.8 m kyr − 1 , which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.

Depositional environments of the Pleistocene loess-soil series inferred from sand grain morphoscopy—A case study of the East European Plain

Morphoscopy of sand grains from the Late Pleistocene loess–paleosol series exposed on the East European Plain along a longitudinal profile, from the southern limit of the Late Pleistocene ice sheet to the Azov Sea coasts is examined. The data presented refer to three main zones of the loess accumulation different in characteristics of the processes: the northern zone, including the vicinity of the Valdai ice sheet; the middle zone with the maximum sedimentation rate; and the southern zone adjoining seacoasts. The earlier part of the Valdai glacial epoch (before the Bryansk interstadial) was distinct for a rather moderate rate of subaerial processes without any noticeable spatial differentiation with respect to the latitudinal zones. In post-Bryansk time (after ∼24 ka BP) the most active dust accumulation is recorded in the middle zone. The maximum thickness of the Late Pleistocene loess has been recorded there, in the middle reaches of the Dnieper River. In the northern zone the rate of dust settling was not so high, presumably due to high speed of descending winds from the ice sheet. In the southern periglacial zone aeolian abrasion of sand grains was less pronounced as compared with areas farther to the north.

Sedimentation and subsidence rate in the Gulf of Corinth: what we learn from the Marion Dufresne's long-piston coring

Abstract Long-piston coring in the central Gulf of Corinth Basin was performed in 2001 on board the RSS Marion Dufresne , enabling the recovery of lacustrine sediments buried at 12–13.5 mbsf below Holocene marine sediments. The lacustrine sequence consists of varve-like muddy, organically rich, layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine-lacustrine interface at 13 kyr BP. Vertical fault slip rates were measured by using fault offsets of correlated reflectors. The maximum subsidence rate of the depocentre (3.6 mm yr −1 ) exceeds the maximum sedimentation rate by 1.8 mm yr −1 , which, consequently, corresponds to the rate of deepening of the basin floor. Data on the water level during the last glacial period indicate that the Corinth–Lake level was about 80 m lower than the present sea level. Inflow of seawater through the Rio–Antirio sill, as a consequence of the last eustatic sea level rise, may have caused catastrophic marine flooding phenomena in the Gulf of Corinth, similar to the one reported from the Black Sea. To cite this article: I. Moretti et al., C. R. Geoscience 336 (2004).

Numerical modelling of drainage basin evolution and three-dimensional alluvial fan stratigraphy

A forward numerical model is presented to study the effects of bedrock erodability, thrust displacement rate, pulsating tectonic activity and sea-level fluctuations on drainage basin morphology and stratigraphy of large alluvial fan systems. A low value of the bedrock erodability coefficient Kb (0.5×10−4 year−2/3) vs. thrust rate (2.0 m/ky) is associated with a time lag between cessation of tectonic activity and maximum sedimentation rates observed on the alluvial fans. Applying higher Kb values, ranging between 1.0 and 8.0×10−4 year−2/3, results in higher sediment yields due to more rapid headward catchment erosion and elaborate sideways branching of drainage networks. Pulsating tectonic activity is reflected in a stratigraphic alternation of prograding and retrograding alluvial fan gravels. During tectonic activity, fan gravel fronts and coastlines retreat because catchment yields are insufficient to fill the accommodation space created by the flexural response due to thrust loading. Phases of tectonic quiescence and cessation of flexural subsidence are indicated by progradation of the gravel front. Depending on the position in the basin, the lag time for arrival of the gravel associated with tectonic cessation is several tens to hundred thousands of years. A combination of pulsed tectonic activity with sinuous sea-level fluctuation leads to a more complex stratigraphic pattern. In that case, stratigraphic response to tectonic pulses is masked by a similar but higher-order frequency-stacking pattern, especially in the more distal parts.

Sedimentation rates and fluxes in the continental shelf mud fields in the Bay of Biscay (France)

Sedimentation rates in shelf mud fields of the Bay of Biscay (the Gironde shelf mud patches and “La Grande Vasière”) were investigated for a 100-yr time scale, using 210Pb geochronology of nine cores. The distribution of apparent sedimentation rates reveals a general trend along the terrigenous dispersal system from the Gironde outlet of: no or negligible (<0.1 cm yr −1) cumulative sedimentation in the inner zone of the mud fields; 0.1–0.2 cm yr −1 in the outer zone where the supply is reduced; and a maximum value of about 0.5 cm yr −1 in the depocentre of the main mud field. Except for the latter value, the 210Pb sedimentation rates are of the same magnitude as longer-term rates based on 14C, and although slightly higher, are in good agreement with an earlier estimation determined for the rate of accumulation of surficial sediments, using pollen analyses. These differences are interpreted as being due to an increase in the supply of fine-grained sediment over the last century (from 0.2 to 0.5 cm yr −1), perhaps as a result of an intensification of estuarine suspended matter supply to the shelf. Compilation of a sediment budget shows that about one third of the annual Gironde solid discharge is trapped in the Gironde nearshore shelf mud fields. The mid-shelf muddy belt (i.e. “La Grande Vasière”) is the site of accumulation of fine-grained material from various terrigenous sources (mainly from the Gironde and Loire rivers). Two cores from the latter area yielded a maximum rate of sedimentation of 0.2 cm yr −1. Mixing processes dominate in this open middle shelf, due to the periodic sediment removal by long-period swells and bioturbation.

TOPSAR wave spectra model and coastal erosion detection

This paper presents work done utilizing TOPSAR data to detect shoreline change along the Terengganu coast (Malaysia). TOPSAR data were used to extract information on wave spectra. This wave spectra information was then used to model shoreline changes by investigating the wave refraction patterns. From these patterns, the volume transport at several locations was estimated. The shoreline change model developed was designed to cover a 20 km stretch of shoreline of Kuala Terengganu. The model utilized data from aerial photographs, TOPSAR data and ground truth data. The location of sedimentation and erosion along the shoreline of Kuala Terengganu was estimated. The wave spectra extracted from TOPSAR data showed wavelengths ranging from 20 m to 175 m. The main direction of the waves given by the spectra was from the northeast. The wave refraction patterns varied, showing both convergence and divergence, indicating erosion and sedimentation locations, respectively. A comparison between the TOPSAR shoreline change model and aerial photographs and ground truth data showed a significant relationship. Finally, the regression model showed that erosion occurred particularly at Sultan Mahmed Airport, at a rate of −1.5 m/year. The maximum rate of sedimentation along the 20 km stretch was 1 m/year.

Neotectonic movements, sedimentation and water-level fluctuation of the Lake Vegoritis in Upper Quaternary

Lake Vegoritis is a 20km long lake located within the NE-SW oriented, Late Pliocene - Quaternary Vegoritis neotectonic depression. More than 200km of high resolution Boomer profiles provided valuable data on the recent evolution of the area. Two main seismic units separated from each other by an erosional surface (Reflector "W") were recognized in the upper 50-60m below the lakebed. The upper seismic unit is an onlapping basin fill characterized by parallel, sub-horizontal internal reflectors. The thickness of the unit reaches 15-20m in the deeper part of the lake. The lower seismic unit is a parallel-stratified unit with continuous internal reflections, slightly folded or inclined. We interpret Reflector "W" as the peri-lake land-surface during the last lake-level low stand, i.e. during the last glacial maximum. The lake has amassed on average 15-20m of sediments since the end of Wurm Glacial Period with a mean sedimentation rate of about lm/kyr. 210Pb geochronology applied on a sediment core recovered in front of the main water stream outflow yielded maximum sedimentation rate of 0.4cm/y for the time before 1956 and 0.6cm/y since 1956. The later is attributed to the dramatic man-induced lowering of the lake level by more than 30m between 1956-1990. Both the lakebed and the sediments below dip gently westwards, towards the SW-NE trending Vegoritis marginal fault. Slope failure phenomena occur in various stratigraphie levels along the fault-controlled western steep slope. The newly discovered E-W trending Ag Panteleimon fault divides Vegoritis fault into a northern active segment and a southern less effective one. On the seismic profiles the southern fault block subsides forming a 2m high morphological step on the lakebed, while the lake sediments are slightly folded. Further to the west Ag. Panteleimon fault separates Jurassic marbles to the north from Pleistocene conglomerates to the south and divides the NE-SW trending Petron-lake fault into two segments. We interpret Ag. Panteleimon fault as a dextral strike slip fault with minor normal component. In conclusion, strike slip movements have significantly influenced the formation and evolution of the Late Pliocene-Quaternary Vegoritis asymmetric graben and possibly of other basins in NW Greece. Despite the "suspicious" very low seismicity of the area, both normal and strike slip faults remain presently active with high seismic potential

A simple model of flow patterns in overpressured sedimentary basins with heat transport and fracturing

Overpressure zones in sedimentary basins are defined as sediments where the fluid pore pressure is substantially higher than hydrostatic. Chief among the causes for the formation of overpressure is the rapid deposition of low‐permeablity sediments so that compaction and dewatering are inhibited. This results in the support of the overlying material in part by the fluid, rather than by grain to grain contact. Many overpressure zones also have associated geothermal anomalies whereby the geotherms are hotter than normal. In this paper, we present a one‐dimensional model of overpressure generation and dissipation, with hydraulic fracture. The fluid flow is coupled to the fluid temperature field and to the motion of the solid sediment matrix. Compacted coordinates are introduced to decouple the fluid velocity and temperature from the solid matrix velocity. Using a maximum sedimentation rate of 1 km Myr−1 and a hydraulic conductivity at the top of the layer equal to 5×10−12 m s−1, 3 km of partially compacted sediment are deposited in 5 Myr, generating an overpressure of 0.81 of the lithostatic pressure at the bottom of the sediment layer. An undercompaction of 19% relative to normally compacted sediment is developed at a final depth of 3.66 km by the end of sedimentation. Dissipation of the overpressure takes place on a timescale of the order of 40 Myr. The equilibrium temperature generates thermal gradients in excess of 38°C km−1 at shallow depths. Fast sedimentation rate and high permeability in the fractured state favor oscillating behavior and propagation of fracture waves. Overpressure zones may constitute a proximal source of hydrothermal fluids for the genesis of ore deposits in sedimentary basins.

Problems of core correlation, sediment source ascription and yield estimation in Ponsonby Tarn, West Cumbria, UK

A suite of 27 short cores, 10 of which have been used for magnetic measurements and four for radiometric dating, provides a framework for reconstructing the processes, patterns and rates of sedimentation in Ponsonby Tarn, a small artificial impoundment created towards the end of the 19th century, close to the Sellafield nuclear reprocessing plant in NW England. Spatial and temporal changes in sedimentation are reconstructed and evidence presented for non-synchroneity in magnetic property changes from core to core in the upper part of the sequence, as a result of sorting and selective deposition at different distances from the inflow to the Tarn. Magnetic measurements alone are therefore not a secure basis upon which to quantify sediment yield for defined time intervals at this site. The chronology, established mainly from 210Pb and 134Cs analyses, allows estimates of mean sediment yield per annum for four periods: prior to AD 1940, 1940–1964, 1964–1986 and 1986–1991. The rates of sediment accumulation have increased in recent times, especially since 1964, with evidence for input from both magnetically enhanced soils and gleyed alluvial and/or podsolized subsoil sources. Pre-1940 mean annual deposition within the present area of the lake is calculated as 19·5 t a−1 and for the period since 1986 (the period of maximum sedimentation rates), as 111·3 t a−1. These represent yields of 7·0 t km−2 a−1 and 39·8 t km−2 a−1, respectively, for the catchment as a whole. Rock magnetic evidence, based on measurements of both bulk samples and the finest particle size separates, suggests that bacterial magnetite, formed within the lake, contributes to the magnetic properties of the sediments, thus modifying the signatures relating to allochthonous sediment input. Copyright © 1999 John Wiley & Sons, Ltd.

Problems of core correlation, sediment source ascription and yield estimation in Ponsonby Tarn, West Cumbria, UK

A suite of 27 short cores, 10 of which have been used for magnetic measurements and four for radiometric dating, provides a framework for reconstructing the processes, patterns and rates of sedimentation in Ponsonby Tarn, a small artificial impoundment created towards the end of the 19th century, close to the Sellafield nuclear reprocessing plant in NW England. Spatial and temporal changes in sedimentation are reconstructed and evidence presented for non-synchroneity in magnetic property changes from core to core in the upper part of the sequence, as a result of sorting and selective deposition at different distances from the inflow to the Tarn. Magnetic measurements alone are therefore not a secure basis upon which to quantify sediment yield for defined time intervals at this site. The chronology, established mainly from 210Pb and 134Cs analyses, allows estimates of mean sediment yield per annum for four periods: prior to AD 1940, 1940–1964, 1964–1986 and 1986–1991. The rates of sediment accumulation have increased in recent times, especially since 1964, with evidence for input from both magnetically enhanced soils and gleyed alluvial and/or podsolized subsoil sources. Pre-1940 mean annual deposition within the present area of the lake is calculated as 19·5 t a−1 and for the period since 1986 (the period of maximum sedimentation rates), as 111·3 t a−1. These represent yields of 7·0 t km−2 a−1 and 39·8 t km−2 a−1, respectively, for the catchment as a whole. Rock magnetic evidence, based on measurements of both bulk samples and the finest particle size separates, suggests that bacterial magnetite, formed within the lake, contributes to the magnetic properties of the sediments, thus modifying the signatures relating to allochthonous sediment input. Copyright © 1999 John Wiley & Sons, Ltd.

Fluxes and budget of [formula omitted] on the continental margin of the Bay of Biscay (northeastern Atlantic)

As part of the ECOFER experiment (ECOMARGE program, JGOFS-France), concentrations of the natural radionuclide 210 Pb were measured in particulate matter collected by sediment traps deployed for a 14-month period (June 1990–August 1991) on two mooring lines within the Cap-Ferret Canyon, on the French continental slope of the Bay of Biscay (northeastern Atlantic). 210 Pb concentrations (range 63–218 dpm g −1) and fluxes (range 0.1–11.2 dpm cm −2 yr −1) displayed typical gradients, increasing with depth at both mooring sites. Also, at equivalent trap depths, 210 Pb activities were systematically higher on the deep slope mooring (3000 m) compared to the shallow one (2300 m). Fluxes of 210 Pb generally decreased seaward and exhibited temporal variations, but with no marked seasonal trend, essentially matching variations in total mass flux. Various correlations between 210 Pb activities and major constituents of trapped particles were examined. 210 Pb activities were independent of the particle composition, indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles. The 210 Pb budget, as determined by the balance of local supply flux and fluxes to sediment traps and sediments, implies important lateral inputs to both mooring sites (65–89% of the flux measured by traps), a feature typical of continental margin environments. On the basis of annual mean 210 Pb activity in traps of the two mooring sites, two particle sources are hypothesized. The first source, located in shallow waters of the shelf and upper slope, supplies the entire slope region. The second source, probably composed of resuspended particles from upper slope sediments, feeds essentially the upper and intermediate slope region. Maximum sedimentation rates, determined on seven box-cores, decreased with bottom depth, from 0.3 to 0.4 cm yr −1 at the canyon heads down to 0.06 cm yr −1 at 3000 m. A good agreement was observed, at both mooring sites, between 210 Pb fluxes registered by the near-bottom traps and excess 210 Pb inventories within the underlying sediments, suggesting that nuclide fluxes measured by traps during this experiment are representative of fluxes on a longer time scale (10–100 yr). Nevertheless, total mass fluxes measured by traps were 3–4 times lower than 210 Pb -determined sediment accumulation rates, a discrepancy that may be more apparent than real, given the possible errors in the latter due to bioturbation.

The chronology of Holocene alluvial sediments from the Wetterau, Germany, provided by optical and 14C dating

Holocene floodplain chronologies are often hard to establish, the principal limitation being the scarc ity of organic remains. In the present study, optical dating of flood loam was carried out in addition to 14C dating of organics. The results show that silty distal alluvial sediments can successfully be dated by means of infrared-stimulated luminescence (IRSL). Through the use of complementary dating techniques, a detailed chronology was obtained for the floodplain sediments of the Wetter, a small river in central Germany, where Holocene sediments overlay Lateglacial channel fills. The early-Holocene sediments consist of sandy loams, followed by the so-called black meadow soil–a dark layer rich in organic matter. Our chronology puts the soil development in the interval 9.8 ka to 3.5 ka, interrupted only by shorter phases of silt deposition. Considerable sedimentation occurred during the Late Iron Age/Roman Period, when the deposition of the younger flood loam first began. This deposit, which is up to 2.5 m thick, forms the youngest bed, with maximum sedimentation rates occurring 1300 to 900 a ago (Middle Ages), and slowing down since that time.

Sediment retention in a bottomland hardwood wetland in Eastern Arkansas

One of the often-stated functions of wetlands is their ability to remove sediments and other particulates from water, thus improving water quality in the adjacent aquatic system. However, actual rates of suspended sediment removal have rarely been measured in freshwater wetland systems. To address this issue, suspended sediment dynamics were measured in a 85-km2 bottomland hardwood (BLH) wetland adjacent to the highly turbid Cache River in eastern Arkansas during the 1988–1990 water years. A suspended sediment mass balance was calculated using depth-integrated, flow-weighted daily measurements at wetland inflow and outflow points. Over the three-year period, suspended sediment load decreased an average of 14% between upstream and downstream sampling points. To test the idea that the suspended sediments were retained by the adjacent wetland and to determine what portion of the BLH forest was most responsible for retaining the suspended sediments, concurrent measurements of sediment accretion were made at 30 sites in the wetland using feldspar clay marker horizons, sedimentation disks, the137cesium method, and dendrogeomorphic techniques. Sedimentation rates exceeding 1 cm/yr were measured in frequently flooded areas dominated byNyssa aquatica andTaxodium distichum. Maximum sedimentation rates did not occur on the natural levee, as would be predicted by classical fluvial geomorphology, but in the “first bottom,” where retention time of the water reached a maximum. Multiple regression was used to relate sedimentation rates with several physical and biological factors. A combination of distance from the river, flood duration, and tree basal area accounted for nearly 90% of the variation in sedimentation rates.

Patterns of Mass Sedimentation and of Deposition of Sediment Contaminated by PCBs in Green Bay

Almost one thousand sediment samples were collected from many sediment depths at sixty-four sampling stations in Green Bay as part of the Green Bay Mass Balance Study. The samples were analyzed for Pb-210 and Cs-137, and PCB congeners. Mass sedimentation rates and mixed depths were calculated from radionuclide profiles constructed for each sampling station. Most of the mass sedimentation in Green Bay occurs in the southern bay. Maximum sedimentation rates reach levels above 150 mg/cm 2/yr. Three distinct sedimentation zones exist. The main sedimentation zone, located between the Peshtigo River and Sturgeon Bay, receives sediment from throughout the southern bay. South of this zone, the Oconto River helps to create a second smaller zone of sedimentation. The Fox River supports a much larger zone which is focused at its southern end, located along the eastern shore of Green Bay about 35 Km from the mouth of the Fox River. Maximum depth-averaged sediment PCB concentrations are about 1500 ng/g dry. By combining sedimentation data and measured sediment PCB concentrations, it was possible to calculate the mass of PCBs in Green Bay sediment. Green Bay contains about 8500 Kg of PCBs, and PCB-contaminated sediment is not uniformly distributed over the bay. Instead, the most contaminated sediments, as well as the greatest mass of sediment-bound PCBs, are located in the Fox River deposition zone. Sediment from the other three major rivers entering the bay dilutes the contaminated Fox River sediment. Highly contaminated sediment is found only in the Fox River deposition zone. About 50% of the total mass of PCBs in Green Bay sediments is found within 10 Km of this zone, in an area equal to about 3% of the total area of the bay. Despite this fact, eliminating PCBs from Green Bay would require the removal of large amounts of sediments.

PURIFICATION OF CELLULASE FROM FUSARIUM MONILIFORME AND ITS APPLICATION TO THE PRODUCTION OF RED BEAN STARCH PRECIPITATE

To investigate the effect of cellulase on increase of recovery of red bean starch precipitate, cellulases from Fusarium moniliforme were purified and applied to the production of red bean starch precipitate. Onea-glucosidase, two filter paper degradation enzymes (FPase), one endo-a-glucanase (endo-Cx) and one exo-a-glucanase (exo-Cx) were purified by ammonium sulfate fractionation, gel filtration and ion-exchange chromatography. Optimum temperature and time of submersion of red beans for reduction of hardness was 50°C and 2 h. Maximum sedimentation rate of starch was obtained when the red bean was incubated in a mixture of 0.004 units/mL of FPase and 0.3 units/mL of CMCase, and maximum recovery of red bean starch precipitate was obtained with 0.004 units/mL of FPase and 0.2 units/mL of CMCase. Enzyme treatment reduced suspended solids about 40% in waste water compared with control. A little hydrolysis in cell wall, intercellular space and interstarch granular space was observed.