Sediment Core Profiles Research Articles

Recent Anthropogenic Impacts on the Bilbao Estuary, Northern Spain: Geochemical and Microfaunal Evidence

The distributions of a range of elements (including137Cs and210Pb) have been studied in surface sediments and 0·5m cores from the Bilbao Estuary (Cantabrian coast, northern Spain) to determine recent and historical sediment contamination. Benthic foraminifera have also been examined to infer recent ecosystem changes. High concentrations of a range of metals are observed in three cores and in surface-scrapes. Observed concentrations depend on the proximity to sources of pollutants. Living foraminifera are absent from surface sediments in the upper estuary, and are scarce in the middle and lower estuary, due to persistent anoxia in the estuarine channel, and possibly, high pollutant concentrations. High metal concentrations in sediment core profiles, combined with the sporadic presence of foraminifera, indicate that environmental degradation has persisted in this estuary for at least the last 40 years. This degradation has been caused by the discharge of untreated industrial and domestic effluents. Surface sediments show a few transported living foraminifera of species that have been identified as dominant in nearby, less-polluted estuarine environments. Successful recolonization by these species may occur if the sediment conditions improve sufficiently. Foraminiferal assemblages could therefore be used as environmental quality indicators to assess the effectiveness of current regeneration schemes implemented under strategic local authority plans.

Transient salt transport modeling of shallow brine beneath a freshwater lake, the Sea of Galilee, Israel

During a lake highstand phase in the late Pleistocene the former saline Lake Lisan covered the topographic depression of Kinarot Basin currently occupied by the freshwater lake, Sea of Galilee. It was hypothesized that during this period, the dense saline waters of Lake Lisan percolated into the sediment. The recession of the saline lake from the basin and the rapid formation of a freshwater lake triggered solute transport from the sediment into the lake. A one‐dimensional numerical model of solute transport that considers sediment compaction was developed to simulate chloride transport from the sediment into the lake. Simulation results were compared with measured chloride concentration profiles in sediment cores. On the basis of a sensitivity analysis, results are in agreement with the hypothesis that Lake Lisan solutes are currently discharged into the Sea of Galilee. The calculated upward water velocity in the sediment ranges between 9 and 22 mm yr−1.

Groundtmthing Multibeam Bathymetric Surveys of Finfish Aquaculture Sites in the Bay d’Espoir Estuarine Fjord, Newfoundland

Current and potential salmonid aquaculture sites in the Bay d’Espoir estuarine fjord on the south coast of Newfoundland were surveyed using multibeam SWATH sonar. In 1997, shallow sites were surveyed using the CSS Puffin EM3000POS/MV system, and deeper sites were surveyed in 1998 using the CCGS Creed hull mounted EM 1000. Sediment cores from representative areas were collected during this period and analyzed for organic matter content, and pore water ammonium and sulfate. We discuss the correlation between the sediment core profiles and the results of the side scan and sun-illuminated bathymetric imagery. Bay d’Espoir is a natural depositional area, and that, coupled with the unique backscatter properties of fish farm wastes, increases the difficulty of interpreting these multibeam sonar images. A fairly accurate broad scale characterization of sediment quality can be made from high-resolution images. However’, much of the fine scale detail and inherent variation of sediment characteristics associated with impacts from aquaculture cannot be determined from multibeam imagery.

Accumulation of recent muds associated with coastal circulations, southeastern Korea Sea (Korea Strait)

Recent muds accumulating in the southeastern Korea Sea (Korea Strait) are mostly derived from the Nakdong River discharge and can be divided into the Proximal Mud Deposits (PMD) and the Distal Mud Deposits (DMD). The PMD show a relatively well- or weakly stratified subbottom on high-resolution seismic profiles (3.5 kHz and Uniboom), whereas the DMD are acoustically characterized by a transparent subbottom and the extensive occurrence (about 900 km 2 in area) of acoustic turbidity in shallow sediments. 210Pb excess activity profiles of sediment cores yield apparent sediment accumulation rates of 1.8–4.4 mm/yr. On the basis of an average sediment accumulation rate, suspended-sediment budget in the PMD and the DMD was calculated, which provides important information about distribution patterns and transport directions. The PMD are a direct sink of about 35% (1.65×10 6 t/yr) of total fine-grained sediments released from the Nakdong River. The remaining riverine sediments are transported farther to northeastward in response to the strong coastal front between the coastal circulation and the offshore Tsushima Current. An annual sink of sediments in the DMD is estimated to be 2.9×10 6 t/yr that are approximately 63% of the annual discharge of suspended sediments by the Nakdong River. Additionally, average contents of organic carbon and nitrogen in the DMD are about two times of those in the PMD, reflecting high biological productivity associated with coastal upwelling process in this area. The coastal upwelling process is also supported by C/N ratio, sea-surface temperatures and chlorophyll pigment concentrations.

Sediment ages and flux variations from depth profiles of 210Pb: lake and marine examples

Sediment accumulation rates are redetermined for several freshwater and marine settings to demonstrate the application of a new methodology for interpreting sediment core profiles of radioisotope activity versus depth. Depositional histories were reconstructed using the sediment isotope tomography (SIT) methodology, which abandons the stringent requirement of current methods that sediment accumulation rates and isotopic fluxes may not both vary with time. Using inverse numerical analysis techniques in conjunction with a predictive model, the SIT method is able to separate the effects of sediment accumulation from flux variations to determine age-to-depth relationships. Cumulative probability procedures provide a framework for interpreting the sensitivity and accuracy of the model-determined age-to-depth relationships. Restrictions applied to previous methods on interpreting sediment profiles affected by mixing must also be adhered to when using the SIT method. Previously published data from two Estonian lakes, Kurtna and Nômmejärv, from Rockwell Reservoir in Northeastern Ohio and from Cape Lookout Bight, NC, are examined to demonstrate the broad applicability of the methodology. With the exception of one location, the resultant age-to-depth relationships determined by the model agree with earlier interpretations. In the Estonian Lake Nômmejärv, previous use of the Constant Flux model overestimates sediment ages for two known time horizons, giving ages of 43 yr at 22 cm and 111 yr at 45 cm. The age-to-depth relationship determined by the SIT method reproduces satisfactorily the time horizons of 16±1 yr at 22 cm and 35±2 yr at 45 cm, in agreement with the onset of industrial activities in the region. These examples illustrate the suitability of this new methodology for application in a variety of complex depositional environments.

A record of hydrocarbon input to San Francisco Bay as traced by biomarker profiles in surface sediment and sediment cores

San Francisco Bay is one of the world's largest urbanized estuarine systems. Its water and sediment receive organic input from a wide variety of sources; much of this organic material is anthropogenically derived. To document the spatial and historical record of the organic contaminant input, surficial sediment from 17 sites throughout San Francisco Bay and sediment cores from two locations—Richardson Bay and San Pablo Bay—were analyzed for biomarker constituents. Biomarkers, that is, `molecular fossils', primarily hopanes, steranes, and n-alkanes, provide information on anthropogenic contamination, especially that related to petrogenic sources, as well as on recent input of biogenic material. The biomarker parameters from the surficial sediment and the upper horizons of the cores show a dominance of anthropogenic input, whereas the biomarker profiles at the lower horizons of the cores indicate primarily biogenic input. In the Richardson Bay core the gradual upcore transition from lower maturity background organics to a dominance of anthropogenic contamination occurred about 70–100 years ago and corresponds to the industrial development of the San Francisco Bay area. In San Pablo Bay, the transition was very abrupt, reflecting the complex depositional history of the area. This sharp transition, perhaps indicating a depositional hiatus or erosional period, dated at pre-1952, is clearly visible. Below, the hiatus the biomarker parameters are immature; above, they are mature and show an anthropogenic overlay. Higher concentrations of terrigenous n-alkanes in the upper horizons in this core are indicative of an increase in terrigenous organic matter input in San Pablo Bay, possibly a result of water diversion projects and changes in the fresh water flow into the Bay from the Delta. Alternatively, it could reflect a dilution of organic material in the lower core sections with hydraulic mining debris.

Sedimentation, bioturbation, and Hg uptake in the sediments of the estuary and Gulf of St. Lawrence

Sedimentation rates and mixing depths have been estimated from the application of a two‐layer biodiffusion model to 210Pb profiles in sediment cores collected in the Laurentian Trough in the Estuary and Gulf of St. Lawrence. Sedimentation rates decrease exponentially with distance seaward from 0.70 cm yr−1 (0.47 g cm−2 yr−1) near the head of the Trough to 0.04 cm yr−1 (0.03 g cm−2 yr−1) in the Gulf of St. Lawrence. Mercury (Hg) sediment profiles exhibit subsurface maxima that decrease from concentrations of 0.6 ug g−1 near the entrance to the Saguenay Fjord to 0.04 µg g−1 in the central part of the Gulf. Hg release data for a chloralkali plant on the Saguenay River were used as the input function for the biodiffusion model and provided accurate simulation of measured profiles when mixing was permitted to extend into the deep (>10 cm) sediment layer. Estimates of Hg sediment inventories indicate that 100–130 tonnes (t) of Hg have been retained within the sediments of the St. Lawrence Estuary, which, combined with an Hg inventory of 30 t estimated for the sediments of the Saguenay Fjord, approximately balance the 136 t of Hg released from the chloralkali plant since 1947. 137Cs and 239,240Pu sediment‐depth profiles were also simulated by the biodiffusion model using input functions based on atmospheric fallout modified by radionuclide transport through the St. Lawrence River drainage basin.

Bulk density calibration for X-ray tomographic analyses of marine sediments

A calibration procedure is presented for generating bulk density profiles of intact marine sediment cores using X-ray computed tomography (CT). Developed using both artificial and natural marine sediment samples, the correlation is strong with an R2 value of 0.98. Similar experiments with carbonate sediments were also strongly linear, but offset from the terrigenous curve, illustrating the influence of sediment chemistry on scanner response. Comparison between newly computed densities for both sediment types with those from individually calibrated cores during our previous CT studies reveals good correspondence between the data sets.

Chemical Contaminants in Fish and Sediment Core Samples from the Dnipro River, Ukraine, 1994

Abstract Some aspects of the quality of fish and sediment samples with respect to contamination with organochlorine compounds, polycyclic aromatic hydrocarbons and several metals are addressed. Fish were obtained from three reservoirs: Kyiv, Kremenchuk and Kakhovka. Sediment cores were obtained from Kremenchuk, Zaporizhzhia and Kakhovka. Levels of contaminants in fish showed differences among species within a reservoir and among reservoirs within a species. The major organochlorine compounds found in the fish were DDT and PCBs with levels in the low ng/g range. Fish PCB levels generally tended to be higher in the Upper Kakhovka reservoir than in the other reservoirs and the congener profile suggested a local source of PCBs to that reservoir. Bream from the Kyiv reservoir had higher levels of mercury than bream from the other reservoirs even though they were of relatively small size. Lead-210 profiles in sediment cores suggested that all three cores sampled only recent time; two of the cores extended deeply enough to capture the large increase in cesium-137 from Chernobyl in 1986, and the third consisted only of material deposited after that event. Inputs of cesium-137 were high and there was no indication of decreases since 1986. Polycyclic aromatic hydrocarbons in sediments were also high, especially in the Zaporizhzhia reservoir where concentrations consistently exceeded Canadian sediment quality guidelines by sever-alfold. Concentrations were lower in the Kakhovka reservoir but still in excess of guidelines, and they were lower yet at the most upstream core from Kremenchuk reservoir. A similar pattern was evident with several metals in sediments. Concentrations in the core from Zaporizhzhia exceeded those from Kakhovka which in turn exceeded those from Kremenchuk. Concentrations in both Zaporizhzhia and Kakhovka generally exceeded Canadian sediment quality guidelines. The general picture that emerges is one of a system of widespread chemical contamination not only with Chernobyl byproducts but also with hydrocarbons, metals and organochlorines, with significant sources downstream from the Kremenchuk site.

Metal concentrations in surface sediments of boston harbor—Changes with time

The concentrations of metals in surface sediments of Boston Harbor have decreased during the period 1977–1993. This conclusion is supported by analysis of: (1) surface sediments collected at monitoring stations in the outer harbor between 1977 and 1993; (2) metal concentration profiles in sediment cores from depositional areas of the harbor; and (3) historical data from a contaminated-sediment database, which includes information on metal and organic contaminants and sediment texture. The background and matrix-corrected concentrations of lead (Pb) measured in the surficial layer (0–2cm) of cores decreased by an average of 46%±12% among four locations in the outer harbor during the 16y period. Chromium (Cr), copper (Cu), mercury (Hg), silver (Ag), and zinc (Zn) exhibited similar trends. Results from our sediment sampling are supported by historical data that were compiled from diverse sources into a regional sediment database. This sediment database contains approximately 3000 samples; of these, about 460 samples were collected and analyzed for Cu, Hg, or Zn and many other sediment parameters in Boston Harbor surface sediments between 1971–1993. The database indicates that the concentrations of these three metals also decreased with time in Boston’s Inner Harbor. The decreases in metal concentrations that are observed in more recent years parallel a general decrease in the flux of metals to the harbor, implemented by: (1) ending the sewage sludge discharge to the Harbor in December, 1991; (2) greater source reduction (e.g. recovery of silver from photographic processing) and closing or moving of industries; (3) improvements in wastewater handling and sewage treatment; and (4) diminishing use of lead in gasoline beginning about 1973. Despite the general decrease in metal concentrations in Boston Harbor surface sediments, the concentrations of Ag and Hg measured at some outer harbor stations in 1993 were still at, or above, the level associated with frequent adverse effects to marine organisms (guidelines are: Ag 3.7μg g−1, Hg 1.17μg g−1, from Long et al., 1995). Concentrations of the other metals listed were in the range considered to occasionally induce adverse biological effects.

Reconstitution of Biogenic Particle Flux in the Indian Sector of the Southern Ocean During the Last 140 Kyrs Deduced from 230Th Profiles in Sediment Cores

Ice core records show that the atmospheric concentration of carbon dioxide decreased during past glacial periods (Barnola et al., 1987). Southern Ocean seems to be a key area to explain these Isotopic stage I 2 observations. Series of papers attributed the glacial lowering of atmospheric C O 2 either to enhanced MD94102 T.z 'biological pump' or to a change in oceanic i,o 0.8 circulation (Broeker et al., 1986). However, estimates of past changes in Southern Ocean produc~ 0.6 tivity are still discussed, In order to answer this ~ 0.4 problem, we have chosen to study spatial and o.2 temporal variations of the biogenic particle flux in 0.0 the Indian sector of the Southern Ocean deduced MD88769 from 23~ profiles in sediment cores. ~.2

Long-range atmospheric transport of mercury to ecosystems, and the importance of anthropogenic emissions—a critical review and evaluation of the published evidence

Literature on the long-range atmospheric transport of both anthropogenic and naturally occurring mercury (Hg) to terrestrial and aquatic ecosystems was reviewed for the purpose of assessing the quantitative importance and environmental significance of the anthropogenic emissions. The weight of evidence, comprising many different kinds of data that corroborate each other independently, supports the following conclusions. (i) Approximately 5000 t of anthropogenic Hg are introduced into the atmosphere every year, both by direct emission from sources of pollution and by reemission of previously deposited Hg from diffuse secondary sources in the environment. The primary emissions ( 4000 t) result from various human activities, especially the combustion of fossil fuels (notably coal) and solid wastes. Natural emissions amount to about 2000 t/year. (ii) Although some of the annual anthropogenic Hg output (about half the quantity emitted by primary sources) is deposited near its point sources, the rest (a total of 3000 t) is subject to transport over great distances by atmospheric circulation, resulting in measurable contamination of terrestrial and aquatic environments and organisms up to several thousand kilometers from the points of origin. Indeed, a number of remote ecosystems receive most of their Hg input from the atmosphere. (iii) The available evidence supports the generally accepted conclusion that the Hg enrichment commonly seen in the uppermost horizons of sediment cores from remote lakes is due primarily to contamination by airborne anthropogenic Hg in the recent past, rather than postdepositional redistribution of Hg. Although postdepositional alteration may result in detectable remobilization of sedimentary Hg, its effects on total Hg profiles in lake sediment cores have been found, thus far, to be negligible. (iv) Atmospheric transport of anthropogenic Hg to aquatic and terrestrial ecosystems is a cause for concern, as the Hg is accumulating, to a greater or lesser extent, in organisms (e.g., fish in remote lakes). Moreover, the Hg is associated with, and interacts with, other by-products of fossil fuel combustion, including the strong acids responsible for acid precipitation. The acids aggravate the effects of Hg pollution by furthering the accumulation of methyl Hg in fish inhabiting ill-buffered lakes. Contamination of the atmosphere with Hg and associated pollutants is a serious international problem that calls for reduction or elimination of emissions.

Radiocesium sorption-desorption processes in lake sediments

The kinetics of radiocesium sorption and desorption by cation solutions and the corresponding radiocesium distribution profiles in sediment cores were investigated. The results have shown that a significant percentage of radiocesium is adsorbed in the sediments during the first 3 d. Radiocesium reaches rapidly (< than 5 d) at a depth which does not exceed 3.5 cm. The desorption of radiocesium was found to depend on cation concentrations. Empirical laws are derived both for cesium adsorption and desorption.

Seasonal sediment storage on mudflats adjacent to the Amazon River

210Pb and 234Th activity profiles in sediment cores from underconsolidated mudflats 300 km downdrift of the Amazon river mouth record an ephemeral surface layer of fine-grained sediment up to 1.5 m thick. This layer contains about l.5 × 10 8 tons of Amazon sediment deposited rapidly (~1 cm/d) from a fluid-mud suspension (10–400 g/l) during the months between January and June. Virtually the entire layer is remobilized in July–December and the sediment is advected alongshore to the northwest. Seasonal variations in trade-wind strength and in supply of Amazon shelf sediment are thought to control emplacement, and removal of this ephemeral deposit. Solitary surface gravity waves characteristic of this setting generate a net landward sediment flux, which, with shore-normal tidal currents, controls spatial geometry of the surface layer. The resultant lens-shaped deposit dissipates incident wave energy and provides a substrate above mean high water for mangrove colonization and irregular shoreline progradation of meters per year. Macroscale (sand/silt laminations) and microscale (plasmic fabric) sedimentary structures in the ephemeral layer record diverse temporal variations (e.g., tidal and wave-induced) in bottom shear stress and sediment supply. Ephemeral deposition of 10 8 tons is inferred to be common in coastal areas associated with large and energetic river dispersal systems.

Nondestructive density determination on marine sediment cores from gamma-ray attenuation measurements

We describe an improved nondestructive technique for density measurement based on gamma-ray absorption that permits construction of high-resolution density profiles of marine sediment cores. The system is capable of resolving vertical density variations with a spatial resolution of 4 mm and absolute accuracy of ± 1%. Comparison with conventional density determination on samples confirms the absolute accuracy. In addition to standard vertical profiling, a core rotation option is included to measure density as a function of rotation angle. This allows the quantification of the variability of density within a layer and detection of inhomogenities like icerafted debris or biogenic structures.

Hydrothermal input into sediments of the Mid-Atlantic Ridge

Abstract The analysis of geochemical profiles in metalliferous sediment cores obtained from the Mid-Atlantic Ridge rift valley at the TAG, MARK and 15°N hydrothermal vent fields and near 27°10′N allowed a study of the history of hydrothermal processes. Of the three hydrothermal zones of the TAG field, the North hydrothermal zone reached its maximum activity between 6000 and 25 000 years ago, the MIR Mound 10 000 years ago and the Active mound 15 000 years ago. Evidence of intensive hydrothermal sedimentation is not seen near the MARK field. The MARK sulphide mounds were probably formed in the course of a single hydrothermal episode that began 4000 years ago. Most of the sulphides of the newly found hydrothermal field near 15°N were formed in the course of an event traced by a Fe-enriched layer 70–90 cm below the seafloor. At present, this field is only slightly hydrothermally active. Three Fe-enriched layers correspond to the possible stages of ore formation at a site of presumed hydrothermal activity near 27°10′N. Their relative intensity is decreasing with time.

Origin and early diagenesis of arborinone/isoarborinol in sediments of a highly productive freshwater lake

This paper reports on the presence of arborinone, isoarborinol and some of their early diagenetic degradation products in a tropial lake. Isoarborinol and arborinne, two 3-oxygenated pentacyclic triterpenes whose origin was initially ascribed to higher plants, were found to be highly abundant in Lake Valencia (Venezuela) surface sediments. The primarily autochthonous origin of the organic matter in sediments from this hypereutrophic lake seems to indicate a microbial source for these compounds, as previously suggested by other authors. The structures of two novel tetracyclic aliphatic alkene degradation products of arborinone/isoarborinol are also proposed, and sediment core profiles for both parent and degradation products are discussed.

Origin and early diagenesis of arborinone/isoarborinol in sediments of a highly productive freshwater lake

This paper reports on the presence of arborinone, isoarborinol and some of their early diagenetic degradation products in a tropial lake. Isoarborinol and arborinne, two 3-oxygenated pentacyclic triterpenes whose origin was initially ascribed to higher plants, were found to be highly abundant in Lake Valencia (Venezuela) surface sediments. The primarily autochthonous origin of the organic matter in sediments from this hypereutrophic lake seems to indicate a microbial source for these compounds, as previously suggested by other authors. The structures of two novel tetracyclic aliphatic alkene degradation products of arborinone/isoarborinol are also proposed, and sediment core profiles for both parent and degradation products are discussed.

Radiochronology of sediments from the Mediterranean Sea using natural210Pb and fallout137Cs

The210Pb and137Cs profiles of sediment cores from two locations in southern Spain, three locations in southern Turkey and two locations in northern Cyprus were determined by direct γ-ray spectroscopy. Sedimentation rates were derived for all locations using the210Pb data. The rates range from 1.39±0.12 cm · y−1 (0.50±0.04 g · cm−2 · y−1) to 0.08±0.01 cm · y−1 (0.039±0.003 g · cm−2 · y−1). Except for one core, the137Cs profiles were also used to compute sedimentation rates. The results are in good agreement with those of210Pb values. The results of the Constant Initial Concenration and Constant Rate of Supply dating models are in good agreement with each other. The flux of unsupported210Pb varies between 0.11±0.03 to 0.74±0.01 pCi · cm−2. The average depositional flux was found to be considerably lower for cores from the Eastern Mediterranean.

Kinetics of Radiocesium Sorption in Lake Sediments

The sorption of radiocesium (137Cs) in sediments sampled from Lake Pamvotis of Ioannina was studied in a laboratory simulation. In a series of experiments, the kinetics of 137Cs sorption and 137Cs distribution profiles in sediment cores were investigated. The results have shown that a significant percentage of 137Cs (35%) is adsorbed in the sediments during the first 3 d, at a rate of 0.41 +/- 0.05 d-1. The rest of 137Cs is adsorbed with the slower rate of 0.024 +/- 0.004 d-1. 137Cs rapidly reaches (< 5 d) a depth that does not exceed 3.5 cm. The sorption of 137Cs was found to follow Freundlich's empirical law, which describes the adsorption of most substances in solution to solids.