Composition Of Surficial Sediments Research Articles

Influence of sediment sources, water mass, and physical processes on the dynamics of flocs at a location between the mouth of a river and the head of a submarine canyon

A field experiment was conducted in the summer of 2011 to obtain detailed process–response data to understand the dynamics of suspended sediment off the Gaoping River mouth near the head of the Gaoping Submarine Canyon in Southern Taiwan. An instrumented tetrapod and a collocated floating platform were used to record the temperature, salinity, current and wave fields. Additionally, the volume concentration (VC) and mass concentration (SSC) of suspended sediments were recorded. Temperature and salinity signals over a tidal cycle distinguished water masses originating from the river plume and the canyon, which alternately dominated the surface dynamics of suspended sediment at the study area. Terrestrial–sourced suspended sediments aggregated into larger flocs, characterized by high VC, SSC, and low effective density values. Conversely, marine–sourced suspended sediments generally had smaller grain sizes, characterized by lower VC, SSC, and high effective densities. In the surface water, the effective density of suspended sediments decreased exponentially with size. In the bottom water, values of VC and SSC were higher under energetic wave conditions and lower under nonenergetic wave conditions, whereas mean size of suspended sediments showed an opposite trend. The hydrodynamics also affected the sediment–water interface, which was reflected in the grain size composition of surficial sediments. The silt and clay content on the seabed was lower under energetic wave conditions and higher under nonenergetic conditions. According to process–responses characteristics, suspended sediments in the bottom water were associated with two regimes: smaller mean size with lower effective densities formed under energetic wave conditions and larger mean size with higher effective densities formed under nonenergetic wave conditions. In the former regime, waves–induced turbulence dominated suspended sediment dynamics by entraining seafloor sediments into the bottom water and aggregating them into microflocs (<~125 μm) and macroflocs (> ~ 125 μm). However, the size distribution of suspended sediment showed a bimodal distribution, and the larger peak is close to the Kolmogorov microscale (around 250 μm). It suggests that strong turbulence associated with significant sediment suspension and flocculation also resulted in disaggregation of macroflocs. As the wave energy dissipated, most of suspended sediments including all fine ones were removed from the bottom water, via flocculation and deposition. Under nonenergetic wave conditions, suspended sediments in the bottom water were contributed from upcanyon water and river plumes, controlled by semidiurnal tidal currents. The size distributions of suspended sediment under nonenergetic conditions were mostly unimodal, with peaks around 100–300 μm, less than the Kolmogorov microscales of turbulence flow (350 μm). Therefore, it could be concluded that turbulence strength plays a key role in flocculation of suspended sediment in the bottom water.

If you build it and they come, will they stay? Maturation of constructed fish spawning reefs in the St. Clair-Detroit River System

Constructed rock reefs have been used to remediate spawning habitat for Lake Sturgeon (Acipenser fulvescens) and other lithophilic spawning fishes in the St. Clair-Detroit River System, North America. Early projects used a cross-channel design and species-specific metrics (e.g., proximity to historical spawning locations) to guide reef placement. However, the Middle Channel Reefs and portions of other early projects were compromised by fine sediment accumulation. Therefore, geomorphological criteria were considered in siting reefs constructed after 2013 to avoid sediment sources and improve the likelihood of successful reef function. To evaluate the effectiveness of the revised placement process, we quantified physical maturation of constructed reefs using annual side-scan and down-looking sonar surveys beginning in 2014 and underwater video surveys beginning in 2015. Reef areas and hardness were measured from sonar surveys and underwater video was used to quantify surficial sediment composition. Size and hardness of reefs developed using geomorphological criteria decreased with time, but at rates slower than what was observed at the Middle Channel Reefs. Sediment composition of the reefs remained similar through 2017 and prevalence of reef rock was high, except at Hart's Light Reef, where dreissenid mussel shells composed 32% of the surficial substrate by age three. However, accumulation of fine sediments was documented at all reefs in 2018. Despite using geomorphic criteria to identify areas most suitable for reef construction, reef sediment composition has changed, and future reef restoration projects could benefit by incorporating methods for maintenance, in addition to using geomorphic criteria, to identify restoration sites.

Stratigraphic control on earthquake-induced liquefaction: A case study from the Central Po Plain (Italy)

Studies on earthquake-induced liquefaction tied to high-resolution stratigraphic analysis have been rarely undertaken. We report the results of a multidisciplinary study from the Quistello–Moglia area, in the central Po Plain (northern Italy). In this region, combined stratigraphic, sedimentological, geotechnical, and geochemical data allowed assessment of liquefaction potential and identification of the primary source for liquefaction, following the second main shock (Mw~6) of the 2012 Po Plain earthquake. Using Cone Penetration Test (CPT)-based simplified procedures for liquefaction hazard evaluation, we assessed the highest liquefaction potential of Holocene, fluvial-channel and related (crevasse/levee) fine sand-silt facies encased in thick, mud-prone floodplain and swamp successions. The liquefaction potential, and the intensity of the manifestations induced on the ground surface, decreased for the vertically-amalgamated, sheet-like Pleistocene sandy fluvial units encountered at depths greater than 13m. Floodplain and swamp deposits were virtually non-liquefiable. In the Quistello area, the compositional characterization of sands that were liquefied and extruded during the 2012 earthquake reveals the diagnostic geochemical fingerprint of sediment carried by the Po River, as opposed to the Apennine composition of surficial sediments. These data rule out proximity of liquefied layers to the surface, and attest the buried, meandering Po River system at depths of ~7–10m most likely representing the source for the liquefied sand that vented to the surface. Similarly, at Moglia, liquefied sands were likely sourced from loose and saturated, ribbon-shaped, fluvial sand bodies encased in mud, though at shallower (4–7m) depths. Pronounced liquefaction phenomena in alluvial plain systems are commonly believed to be associated primarily with elongate topographic ridges following paleo-river courses. Here, we document that under favorable stratigraphic conditions liquefaction may also occur away from surficial channel–levee systems, in areas dominated superficially by overbank fines. Combining subsurface stratigraphic analysis with geotechnical data, thus, is critical to investigate liquefaction patterns and delineate liquefaction hazard zones.

Spatial sediment variability in a tropical tide dominated estuary: Sources and drivers

Surficial sediment composition and spatial variability reflect the dynamics and level of natural and anthropogenic impact in estuarine systems. The aim of this study is to evaluate some key environmental and sedimentary variables, as well as to evaluate the current environmental quality in the tide-dominated Caravelas estuarine system (Brazil). Sixty-five surficial sediment samples were studied for grain size as well as calcium carbonate, total organic carbon, total nitrogen, metals, semi-metals and rare earth elements and for organic matter δ13C. Based on the spatial distribution of these data and summarizing our findings, three sectors can be individualized in the Caravelas estuarine system: i. Barra Velha inlet; ii. the main channel of the Caravelas estuary, and iii. the channel interconnecting Caravelas and Nova Viçosa estuaries. In the inlet the sedimentary organic matter is provided essentially by marine sources, which corroborates the small continental input. Freshwater dissolved organic carbon and particulate organic carbon occur in the interconnecting channel, proving the occurrence of the residual transport towards the Caravelas estuary, with continental contribution towards Caravelas River. The geochemical fingerprint indicates that the Barreiras Group, composed by Neogene terrigenous deposits, located west of the study area, as an important source of terrigenous material to the entire Caravelas estuary system. The higher values of heavy rare earth elements (between 20 and 30 mg kg−1) in the northern sector of the study area may be related to the high degree of chemical weathering in magmatic or metamorphic rocks, which occur to the north of the study area.

Interannual heavy element and nutrient concentration trends in the top sediments of Venice Lagoon (Italy)

The elemental composition of surficial sediments of Venice Lagoon (Italy) in 1987, 1993, 1998 and 2003 were investigated. Zn and Cr concentrations resulted in higher than background levels, but only Cd and Hg were higher than legal quality standards (Italian Decree 2010/260 and Water Framework Directive 2000/60/EC). Contaminants with similar spatial distribution are sorted into three groups by means of correlation analysis: (i) As, Co, Cd, Cu, Fe, Pb, Zn; (ii) Ni, Cr; (iii) Hg. Interannual concentrations are compared by applying a factor analysis to the matrix of differences between subsequent samplings. A general decrease of heavy metal levels is observed from 1987 to 1993, whereas particularly high concentrations of Ni and Cr are recorded in 1998 as a consequence of intense clam fishing, subsequently mitigated by better prevention of illegal harvesting. Due to the major role played by anthropogenic sediment resuspension, bathymetric variations are also considered.

Metals in Sediment Cores from Nine Coastal Lagoons in Central Vietnam

Problem statement: After being dramatically hit by war events, Vietnam is presently experiencing a huge economical and social development. However, very few data, relative to pollution levels and trends, are available for the correct management of critical areas such as coastal lagoons, where many economical activities are linked to high value environmental features. Approach: A set of sediment cores from nine coastal lagoons of central Vietnam (Lang Co, Truong Giang, An Khe, Nuoc Man, Nuoc Ngot, Thi Nai, O Loan, Thuy Trieu and Dam Nai) were sampled in 2008 and analyzed to assess metal and (Al, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb, V, U and Zn) and As levels and historical trends. Results: Concentrations are generally low, with the exception of As, which often exceeds ERL guidelines and Ni that does the same at O Loan. In some cases, concentrations-depth profiles account for recent increasing trends but surficial values are still low when compared to both international guidelines and polluted sediments all around the world. Sediment grain size seems to affect the depth distribution of a number of metals and when normalized to the content of silt and clay, values are particularly high at Dam Nai and Thi Nai, due to the very coarse composition of surficial sediments. Conclusion: Metal concentrations in lagoon sediments derive from the composition of rocks and soils in the watersheds. However, recent increasing trends need for further monitoring.

First recognition of a Laurentide Ice Stream : Robert Bell on Hudson Strait

In papers published in 1895 and 1901, and in undated notes for a 1907 paper he did not deliver or publish, Robert Bell of the Geological Survey of Canada interpreted the pattern of glacial striae, stossing of rock knobs, and surficial sediment composition along the margins of Hudson Strait, between Labrador, Ungava Bay and Baffin Island, as evidence of what he called an ice-stream, a long river-like glacier, fed from Hudson Bay and Foxe Basin, that had moved eastward along the Strait during the Late Glacial period. This was the earliest mention of such a glaciological feature within the Laurentide Ice Sheet (LIS). It was not until ice-streams were recognized in the West Antarctic Ice Sheet in the 1970’s that Bell’s concept was revived in the next decade and subsequently, in recognition of several ice-streams within the Late Wisconsinan LIS.

Surficial sediment phosphorus fractions along a biogeochemical gradient in Nyanza (Winam) Gulf, northeastern Lake Victoria and their possible role in phosphorus recycling and internal loading

Different phosphorus fractions and metal element composition of surficial sediments were measured on three occasions in 2005 and 2006 along a transect between Nyanza Gulf and offshore Lake Victoria, in order to assess the potential for sediments to contribute to the water column P concentrations in Lake Victoria. Total phosphorus (TP), apatite phosphorus (AP), inorganic phosphorus (IP) and organic phosphorus (OP) increased in sediments along the gulf towards the main lake while the non-apatite inorganic phosphorus (NAIP) increases were less defined. The longitudinal gradient of sediment TP and its fractions in Nyanza Gulf is a result of high rates of terrigenous input and resuspension and transport of the light, phosphorus rich inorganic and organic matter towards the main lake. TP in the sediment ranged from 812.7 to 1,738 mg/kg dry weight (DW) and was highest in the Rusinga Channel, the exchange zone between the gulf and the main lake. AP was the most important TP fraction, contributing between 35 and 57.3% of TP. Ca content in the sediment was strongly associated with TP and AP in the sediment (r2 = 0.92 and 0.98, respectively) in the gulf and the channel, indicating the importance of apatite in controlling P availability in these zones. In the gulf and the Rusinga Channel, the less bioavailable apatite phosphorus dominated, whereas in the deeper main lake OP was the major fraction illustrating the importance of anaerobic release of P from sediments and acceleration of internal P loading in the main lake.

Sandwaves on the Southeast Vietnam Shelf recorded by high resolution seismic profiles: formation and mechanism

The application of high resolution seismic data using boomer sound source has revealed a wide distribution of large-scale bedforms (sandwaves) on the Southeast Vietnam continental shelf. Bedforms that are a few meters high in wave height and hundreds of meters long in wavelength are primarily developed in the inner shelf (20–40 m) and considered to be formed under the present-day marine hydrodynamic conditions. Those bedforms developed in the deeper water (120 m) of the northernmost part of the continent can be interpreted as the relict morphological features formed during the latest sea-level lowstand of the late Pleistocene period. Two sediment transport paths have been identified on the basis of the bedform’s leeward orientation: northeast-southwest (along-shore) and north-south (cross-shore). A quantitative bottom current map is constructed from sandwave dimensions, surface sediments and measurement data. The strongest current velocities that gradually decrease toward the southwest are indicated by large sandwaves in the north (field B). Water depth, surficial sediment composition and bottom current are three factors that control the development of bedforms.

Spatial models as a tool to identify spatial patterns of surficial sediment composition and their contributing factors in the littoral zone of Lake Constance (Germany)

Spatial models as a tool to identify spatial patterns of surficial sediment composition and their contributing factors in the littoral zone of Lake Constance (Germany)

Spatial models as a tool to identify spatial patterns of surficial sediment composition and their contributing factors in the littoral zone of Lake Constance (Germany)

For a lake-wide investigation of littoral surface sediments, we collected approximately 800 samples from Lake Constance along 235 parallel transects of 1 km distance along the shore at water depths of 1, 2, 4 and 8 m. Sediment samples were analyzed for the presence of spatial patterns in mineralogical and granulometric composition and contents of carbon and sulphur, with the purpose of identifying general and lake specific processes that contribute to the observed patterns. In particular, we wanted to test if the general factors known for contributing to littoral sediment composition could be revealed by spatial modeling of a dataset based on a systematic sampling scheme. Explanatory variables for a regression model were derived from GIS-analyses of the dataset, and also from other available data on Lake Constance. Highest levels of variance explained by the model (30–40%) were reached for the parameters calcite, clay minerals, sulphur and inorganic carbon content. Regional patterns in sediment composition, described by the proportion of explained between-transect variance (VE t ) in the model, are explained by up to 70%. The observed east-west gradient of mineralogical sediment composition is ascribed to the respective regional patterns of allogenic and endogenic sources. Allogenic minerals such as clay, dolomite and quartz dominate the littoral surface sediments of the eastern part of the lake and the areas near river mouths. Endogenic minerals like calcite dominate the littoral sediments of the western parts of the lake, reflecting internal process of biogenic carbonate precipitation that corresponds to the distribution patterns of submersed macrophytes (particularly Charophytes).

The Nature of Organic Matter in the Danube River Particles and North-western Black Sea Sediments

Suspended matter and sediments from the Danube River and the adjacent north-western Black Sea were analysed for organic carbon, nitrogen and biogenic carbonate and silica, as well as for different fractions of organic matter such as amino acids and carbohydrates. In addition, the nitrogen isotopic composition of surficial sediments of the NW Black Sea was examined. Particulate organic carbon (POC) contents decrease with total suspended solid (TSS) concentration due to dilution by mineral matter derived from upstream and riverbed erosion. The contribution of labile constituents such as amino acids and carbohydrates to POC remains uniform across the measured TSS contents. This suggests that any possible decrease in labile POC (LPOC) from dilution with refractory organic matter is masked by inputs of fresh organic matter from tributaries downstream. Comparison of TSS, POC and LPOC leaving the Iron Gate I barrier at the head of the Danube delta shows that the bulk of material currently entering the Black Sea is derived from inputs from tributaries and riverbed erosion, downstream of the Iron Gate I. The nature and distribution of organic matter in the surface sediments of the Black Sea are influenced by mixing between Danube-derived material and freshly produced organic matter on the shelf and in the open sea, on the one hand, and by oxic degradation during transport from the shelf to the abyssal Black sea, on the other. Preliminary data on the stable isotopic composition of nitrogen in surface sediments of the Black Sea further suggest that organic matter production on the shelf and the adjacent north-western Black Sea is fuelled by different nitrogen sources.

Recycling of manganese from anoxic sediments in stagnant basins by seawater inflow: a study of surface sediments from the Gotland Basin, Baltic Sea

Abstract The occurrence of Mn carbonates in sapropelic sediments has been proposed to indicate that the host sediment originally accumulated under oxygenated bottomwaters. In the central Baltic Sea, Ca-rich rhodochrosite layers in sapropelic sediments have been related to inflows of oxic seawater from the North Sea into the brackish, predominantly anoxic, deeps of the central Baltic. This study attempts to verify the model of authigenic Mn carbonate formation by comparing oceanographic records directly with the composition of surficial sediments of the Gotland Basin. Surface sediments of the Gotland Deep sampled in 1997 displayed significant Ca-rich rhodochrosite enrichments at 6.5, 11 and 15 cm sediment depth which reflect periods of intense seawater inflows in 1969–76, 1948–56, and 1931–39, respectively. However, the latest major seawater inflow detected in 1993 was not reflected in the surface sediment. The topmost 6 cm of the sediment was totally depleted in Mn and 210Pb data implied a disturbed top layer down to 5 cm. Calculations of saturation indices indicate that the porewaters were undersaturated with respect to Mn and Ca carbonate phases in the uppermost 8 cm in 1997. At greater depths, the porewaters were close to equilibrium with respect to calcite and rhodochrosite. The Ca-rhodochrosite layers corresponded well to a sediment core sampled at the same location in 1994, but that core displayed a further enrichment of Ca-rich rhodochrosite close to the sediment surface, which can be related to a major inflow of North Sea water in 1993. The significant decrease of about 2.3 mol/m2 Mn in the uppermost 6 cm of a disturbed sediment surface from 1994 to 1997 corresponds to an enrichment of about 20 μmol/l of dissolved Mn within the 90 m thick anoxic water column in 1997. We conclude that several inflows of dense seawater into the Gotland Deep, monitored between 1994 and 1997, led to a resuspension of the unstable, fluffy surface sediment layer. Authigenic Ca-rich rhodochrosite which had formed immediately after the major inflow of oxic seawater in 1993 was therefore redissolved in undersaturated bottomwaters and Mn was recycled from surficial sediments into the water column. This in turn means that, in contrast to the established model of Ca-rhodochrosite formation as a result of seawater inflow, the occurrence of mixed, Mn-depleted layers does not prove that seawater inflow has not occurred during the deposition of these sediments.

Modern Sedimentation on the Shoreface and Inner Continental Shelf at Wrightsville Beach, North Carolina, U.S.A.

ABSTRACT The geologic framework and surficial morphology of the shoreface and inner continental shelf off the Wrightsville Beach, North Carolina, barrier island were mapped using high-resolution sidescan-sonar, bathymetric, and seismic-reflection surveying techniques, a suite of over 200 diver vibracores, and extensive seafloor observations by divers. The inner shelf is a sediment-starved, active surface of marine erosion; modern sediments, where present, form a patchy veneer over Tertiary and Quaternary units. The lithology of the underlying units exerts a primary control on the distribution, texture, and composition of surficial sediments, as well as inner-shelf bathymetry. The shoreface is dominated by a linear, cross-shore morphology of rippled scour depressions (RSDs) extending from just seaward of the surf zone onto the inner shelf. On the upper shoreface, the RSDs are incised up to 1 m below surrounding areas of fine sand, and have an asymmetric cross section that is steeper-sided to the north. On the inner shelf, the RSDs have a similar but more subdued cross-sectional profile. The depressions are floored primarily by shell hash and quartz gravel. Vibracore data show a thick (up to 1.5 m) sequence of RSD sediments that unconformably overlies ancient coastal lithosomes. In this sediment-starved inner shelf setting, rippled scour depressions probably form initially on preexisting coarse-sediment substrates such as modern lag deposits of paleofluvial channel lithosomes or ancient tidal inlet thalwegs. Interannual observations of seafloor morphologic change and the longer-term record contained in vibracores suggest that the present seafloor morphology is either relatively stable or represents a recurring, preferential morphologic state to which the seafloor returns after storm-induced perturbations. The apparent stability is interpreted to be the result of interactions at several scales that contribute to a repeating, self-reinforcing pattern of forcing and sedimentary response which ultimately causes the RSDs to be maintained as sediment-starved bedforms responding to both along-shore and across-shore flows. Sediment accumulation from over 30 years of extensive beach nourishment at Wrightsville Beach appears to have exceeded the local shoreface accommodation space, resulting in the leaking of beach and shoreface sediment to the inner shelf. A macroscopically identifiable beach nourishment sediment on the shoreface and inner shelf was used to identify the decadal-scale pattern of sediment dispersal. The nourishment sediment is present in a seaward-thinning wedge that extends from the beach over a kilometer onto the inner shelf to waters depths of 14 m. This wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach nourishment.

Water Flow and Clay Retention in Submerged Macrophyte Beds

The effect of aboveground plant structure on near-bottom water flow and surficial sediment composition was evaluated in Lake Memphremagog (Quebec–Vermont) at 34 nearshore sites within three mixed-species macrophyte beds. Plant surface area accounted for 70% of the variance in flow reduction when the effect of changing water depth was removed. Relationships between plant surface area and surficial sediment clay content were evident within each of the three multispecies beds. The equations predicting within-bed clay concentrations were not significantly different from a general among-bed model (r2 = 0.74) developed at 25 sites of high biomass from other nearshore locations in Lake Memphremagog. The study provides quantitative evidence for the importance of macrophytes as sites of sedimentation of fine particles and their associated nutrients and contaminants.

Predictions of surficial sediment composition in the littoral zone of lakes

Lacustrine sediment focusing presumes the removal of fine‐grained littoral particles (silt and clay) to storage sites in the deeper, less productive zone of a lake. In the littoral zone, shorter term sediment storage, on the time scale of biological transfers, demands attention as these clays and silts represent potential vectors in aquatic contaminant transfers. Two empirical models that predict surficial fine‐grained sediment composition of the littoral were developed in Lake Memphremagog, Quebec. A 5‐variable model explained 67% of the variance in the proportion of clay at 62 nearshore sites. A 3‐variable model including measures of fetch, depth, and slope explained 58% of the variance while the additional variables of plant presence or absence and sediment organic matter contributed the remaining 9% of explained variation. The two models performed exceedingly well when tested at 41 sites not used in the original derivation of the model. Of these 41 test sites, 13 represent samples from littoral zones of five eastern Canadian lakes (maritime provinces) representing different geologies and morphologies.

Effect of wood waste dumping on organic matter in seawater and surficial sediments of Alberni Inlet, British Columbia

Distribution of particulate organic carbon (POC) and dissolved organic carbon (DOC) in seawater, and chemical composition of surficial sediments were studied in relation to pulpmill effluent and dumping of dredge spoil containing wood debris in Alberni Inlet, British Columbia, Canada. The maximum concentration of POC (377–584µg Cl−1) was observed at the surface around the dumping area (5–7 km seaward of the inlet's head), and at the location immediately adjacent to the dump site POC was elevated throughout the water column (50 m). While POC tended to decrease in the surface layer for a distance of about 25km down-inlet, measureable effects of POC in the deeper water did not extend beyond 600m from the dump site. The dump site was conspicuous by the large maximum in C:N ratio (46.3). In contrast, DOC was observed to be highest (4.25mg Cl−1) at the head of the inlet where pulpmill effluent was being discharged and a secondary maximum was found about 10km down-inlet from the dump site. The data suggest that a considerable proportion of the dredge spoil sinks rapidly near the dump site, probably within several hundred metres. Some of the spoil, perhaps low density wood debris may travel considerably further with the surface water where by leaching it may contribute to some extent to the surface DOC before sinking into deeper water.

Survey of metals in sediments near Quonset Point, Rhode Island

Elevated levels of silver, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead and zinc were observed in sediments collected from Narragansett Bay off Quonset Point during autumn of 1973. The probable source of the metals contamination was an electroplating facility on Quonset Point, in continuous operation from 1943 until it was closed in spring of 1973. Data on elemental composition of surficial sediments collected from various geographical locations reported by other investigators are presented and compared to those reported herein.