Silicones in Chesapeake Bay sediments

Sediment samples from the upper reaches to the mouth of the Chesapeake Bay were analysed for extractable organic silicon (silicone) content. Organic silicon in the sediments ranged from less than 0.2 to some 36 ppm, w/w. In general, silicone tended to accumulate in high depositional areas: the northern bay, and along the shores to the south. While present, anthropogenic inputs in terms of defined source were not clear. It appears that processes in the bay act to rapidly remove silicone from the water column, probably on a function of the flocculation/precipitation of seston, especially in the northern area.     

Regularities of hydrological processes in the Chesapeake Bay (USA): Case study of a classical estuary

The main regularities of hydrological and hydrological-environmental processes occurring within the complex estuary, the Chesapeake Bay and the mouths of its tributaries, are discussed. The peculiarities of the estuary morphological structure, including the structures of tidal and net currents, salinity and water turbidity fields and their variability, the environmental conditions, and their human-induced changes. Using the Chesapeake Bay as an example, it became possible to reveal the basic features of classical estuaries subject to a considerable impact of river runoff and featuring mixing of river and sea water and moderate stratification of the water mass. It is shown that the regularities of hydrological processes in the Chesapeake Bay are typical of many mouth water bodies of estuarine type (inlets, drowned river valleys, lagoons, and tidal estuaries proper).     

The osmium isotopic composition of organic-rich marine sediments

The osmium (Os) concentration and¹⁸⁷Os/¹⁸⁶Os ratio of several recent, marine, organic-rich sediment samples from three widely separated sites have been measured. Os concentrations range from 0.095 to 0.212 ppb and¹⁸⁷Os/¹⁸⁶Os ratios range from 8.2 to 8.9. The calculated fraction of hydrogenous Os exceeds 78% in all samples. Thus, the¹⁸⁷Os/¹⁸⁶Os ratio of these samples reflects Os isotopic composition of seawater. The small range in measured¹⁸⁷Os/¹⁸⁶Os ratio indicates that the Os isotopic composition at these sites is fairly homogeneous. The large magnitude of the Os burial flux at these sites indicates the Os burial in association with organic-rich sediments is an important sink in the marine cycle of Os. These data also suggest that ancient organic-rich sediments may provide a record of past variations in the Os isotopic composition of seawater.     

A 130 year record of pollution in the Suances estuary (southern Bay of Biscay): implications for environmental management

Geochemical composition (Al, Zn, Pb, Cd, Cu, Ni, Cr and As) and foraminiferal assemblages in surface and core sediments were determined to assess the current situation and the recent environmental transformation of the Suances estuary (southern Bay of Biscay, Spain). Dating of the historical record has been achieved using isotopic analysis (²¹⁰Pb, ¹³⁷Cs) and two benchmark events such as the beginning of the mineral exploitation in the Reocín Pb-Zn deposits and the evolution of the chlor-alkali industry (inputs of Hg). Concentrations of Zn, Pb and Cd in both surface and core samples are remarkably higher than background values, reflecting the existence of significant amounts of polluted materials. The dramatic environmental impact of this pollution is clearly recorded by the change of the foraminiferal assemblages that even reach an afaunal stage during recent decades. Application of two different sets of Sediment Quality Guidelines confirm that they exert potential risk to the environment, and therefore if dredged they should need specific management measures.The results provide a reference database to monitor future environmental changes in the Suances estuary, particularly as regards the contaminated sediment storage and the re-colonization by autochtonous meiofauna.     

Lateral dynamics and associated transport of sediment in the upper reaches of a partially mixed estuary,Chesapeake Bay,USA

Data from time series of transects made over a tidal period across a section of the upper Chesapeake Bay, USA, reveal the influence of lateral dynamics on sediment transport in an area with a deep channel and broad extents of shallower flanks. Contributions to lateral momentum by rotation (Coriolis plus channel curvature), cross channel density gradients and cross channel surface slope were estimated, and the friction and acceleration terms needed to complete the balance were compared to patterns of observed lateral circulation. During ebb, net rotation effects were larger because of river velocity and reinforcement of Coriolis by curvature. During flood, stratification was greater because of landward advection of strong vertical density gradients. Together, the ebb intensified lateral circulation and flood intensified stratification focused sediment and sediment transport along the left side of the estuary (looking seaward). The tendency for greater stratification on flood and net sediment flux toward the left-hand shoal are contrary to more common models which, in the northern hemisphere, predict greater resuspension on flood and move sediment toward the right-hand shoal. These tidal asymmetries interact with the lateral circulation to focus net sediment flux on the left side of the estuary, and to produce net ebb directed sediment transport at the surface of the same order of magnitude as net flood directed sediment transport at the bottom.     

Strontium and its isotopic composition in interstitial waters of marine carbonate sediments

The concentrations and isotopic compositions of strontium in interstitial waters from several DSDP sites, where sediments consist chiefly of carbonate oozes and chalks, are used as indicators of carbonate diagenesis by reference to a recently-produced curve showing detailed variations in the⁸⁷Sr/⁸⁶Sr ratio of seawater with time. Carbonate sediments of the Walvis Ridge show increases in interstitial Sr²⁺ concentrations in the upper carbonate-ooze sections with the highest concentrations near the ooze-chalk boundary where maximum rates of carbonate recrystallization occur. Below this, in situ production of Sr²⁺ diminishes and there is a diffusive flux of Sr to an underlying sink, presumably volcanogenic sediments or basalts, leading to Sr isotopic disequilibrium between carbonates and interstitial waters. In some other sites, however, there is no apparent Sr sink at depth and isotopic equilibrium is retained. Overall, diffusive smoothing of profiles exerts an important control on the⁸⁷Sr/⁸⁶Sr ratios, although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of Mg²⁺ loss and reflect a combination of a flux of Sr²⁺ from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter.     

Mercury in sediments of Ulhas estuary

Hg levels in water, suspended particulate matter and sediment of the Ulhas estuary are under considerable environmental stress due to the indiscriminate release of effluents from a variety of industries including chlor-alkali plants. Concentration ranges of dissolved (0.04-0.61 micro gl(-1)) and particulate (1.13-6.43 micro gg(-1)) Hg reveal a definite enhancement of levels in the estuary. The Hg burden in sediment upstream of the weir that limits the tidal influence is low (0.08-0.19 micro gg(-1)) with low C(org) content (1.8-2.9%). The high Hg content of the sediment just below the weir varies seasonally (highest concentration recorded being 38.45 micro gg(-1)) due to incremental accretion of sediment as the fresh water flow over the weir progressively decreases. The 30 km segment of the estuary sustains markedly high levels of Hg in the sediment with an exponential decrease in the seaward direction from the weir. Higher concentrations than the expected background prevail in all the estuarine cores up to the bottom, though the overall concentration decreases from about 20 micro gg(-1) in core 7 (inner estuary) to 1 micro gg(-1) in core 31 (outer estuary). The Hg in sediment is associated with C(org), while its correlation with Al, Fe and Mn is poor. The Hg profiles in cores from the Arabian Sea (stations 34, 35 and 37) have a distinct horizon of enhanced concentration in the 5-60 cm segment. Based on 210Pb dating of core 37, the sediment at the bottom of this core is inferred to have been deposited in the year 1949, roughly two year prior to the establishment of the first chlor-alkali plant and represents the background (0.06-0.10 micro gg(-1)). The Hg profiles in the offshore cores indicate a marked increase in transfer of Hg to sediment subsequent to 1980, with a peak around 1990-1992. Based on the index of geoaccumulation it is considered that the estuarine segment between stations 4 and 23 is extremely polluted, while the sediment from the open coast is moderately polluted in the top 25-30 cm with respect to Hg. The enrichment factor of Hg in the sediment is 350-700 for core 4 and decreases to 0-7 for the open-shore cores.     

Anthropogenic lead concentrations and sources in Baltic Sea sediments based on lead isotopic composition

The Gulf of Gdańsk is influenced by heavy metals of anthropogenic origin. In this study, temporal concentration changes of Pb, Zn, Cd, and Cu were studied in six, 50 cm long sediment cores. The main aim of the study was to concentrate on the history of Pb fluxes and Pb isotopic composition (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) to trace Pb sources. The lowest Pb concentrations (19 μg g⁻¹) were measured in sediments deposited circa 1860, while the highest Pb concentrations (63–147 μg g⁻¹) were measured in sediments deposited between 1960s and 70s. Pre-industrial Pb fluxes were 7 Pb m² year⁻¹, while after WWII they reached 199 Pb m² year⁻¹. Highest ²⁰⁶Pb/²⁰⁷Pb ratios (∼1.22) were measured in the oldest sediment layers, and the lowest ²⁰⁶Pb/²⁰⁷Pb ratios (∼1.165) were measured in the sediments deposited in 1970s–90s. During the period of highest Pb contamination, the anthropogenic Pb fraction reached up to 93%. A general discussion of the Pb sources, emissions, and loads for Poland is included.     

梵净山九龙池沉积物氮同位素组成与全新世气候演变过程

湖泊沉积物氮同位素(δ¹⁵N)在古环境、古气候变化方面有着指示气候干湿变化的重要作用,但目前学界对于δ¹⁵N记录作为气候代用指标所指示的气候干湿变化特征仍缺乏深入探索。本文以贵州省梵净山九龙池湖泊沉积物为研究对象,分析并探讨δ¹⁵N所记录的梵净山地区气候干湿变化过程与特征,并结合总有机碳(TOC)、总氮(TN)和碳氮比值(C/N)数据进行对比研究,结果表明:(1)由于九龙池湖泊沉积物有机质受流域输入影响,气候湿润时,陆生植物增多,土壤湿度增大,外源输入对湖泊沉积物有机质影响增大,沉积物δ¹⁵N值偏负;气候干旱时,陆生植物减少,土壤湿度降低,外源输入对湖泊沉积物有机质影响减小,沉积物δ¹⁵N值偏正;(2)九龙池湖泊沉积物δ¹⁵N记录很好地揭示了梵净山地区全新世的气候干湿变化过程,即早期(11.5—9.2 ka B.P.)亚洲夏季风增强,气候从干旱期向湿润期转变,中期(9.2—3.0 ka B.P.)亚洲夏季风强盛,气候整体处于湿润期,晚期(3.0—2.2 k...     

Evaluation of butyltin compounds in Maryland waters of Chesapeake Bay

A monthly sampling programme for dibutyltin (DBT), tributyltin (TBT) and tetrabutyltin (TTBT) was initiated for a period of one year (July 1985–June 1986) in the Maryland waters of Chesapeake Bay. Concentrations of the above butyltin species were evaluated in the microlayer and water column of eight sampling stations representing two small and two large marinas, a large harbour, two major river systems and a heavily used shipping channel. DBT concentrations in the microlayer were generally higher in the four marinas when compared with the other stations. The highest DBT concentration reported in the microlayer was 1156 ng l⁻¹. Mean microlayer TBT concentrations ranged from 54–310 ng l⁻¹ in the four marinas. Three TBT concentrations ranging from 1049–1171 ng l⁻¹ were reported in the microlayer of the marinas. TBT concentrations of 41 and 29 mg l⁻¹ were detected in the microlayer of a heavily used shipping channel (C & D Canal) during May and June. TTBT concentrations were not detected in the microlayer at most stations during the 12 month sampling period.Mean DBT concentrations in the water column ranged from 23–145 ng l⁻¹ in the four marinas. DBT concentrations in the water column of the other stations were < 35 ng l⁻¹. Mean water column concentrations of TBT ranged from 51–408 ng l⁻¹ in all four marinas. Peak concentrations of TBT were reported in May and June for the various marinas. The highest TBT concentration reported in the water column was 998 ng l⁻¹. TBT concentrations of 20–24 ng l⁻¹ were reported in one of the river systems (Potomac River). TTBT concentrations were not detected in the water column at most of the stations.     

ENAA Studies of pollution in anoxic Black Sea sediments

The vertical distributions of five potential pollutants - Zn, As, Br, Sn, and Sb - were determined via epithermal neutron activation in the upper 50 cm of unconsolidated sediments from the Black Sea, which were collected 600 m below sea surface. This analysis demonstrated increasing concentrations towards the upper limits of sediments, which were greater than alert concentrations in the case of As and Br, and in accordance with Romanian Environment Regulations. The utilization of Chernobyl ¹³⁷Cs as a time marker allowed for dating of this region to the last 100 years.     

Domestic and international arrivals of NOBOB (no ballast on board) vessels to lower Chesapeake Bay

In examining ship-mediated biological invasions, most research and treatment development has focused on ballast water. Another vector that has gained attention recently is vessels arriving in a "no ballast on board" (NOBOB) condition. Such ships retain relatively small, unpumpable volumes of water and sediment in their ballast tanks. Nonetheless, these unpumpable portions can represent great ecological risk. This scenario is relevant in the Great Lakes, which have experienced a dramatic series of introductions, despite most vessels arriving there as NOBOBs since 1994. We examined shipping patterns of NOBOBs arriving to lower Chesapeake Bay to begin evaluating their risk of biopollution. Only 14% of ships arrive as NOBOBs, and of those, 17% depart to another port in the upper bay. Most NOBOBs arrive from or leave for other US ports; proximate trans-Atlantic crossings are few. Given the nature of their operations, we conclude NOBOBs may represent a risk for aquatic nuisance species invasions to Chesapeake Bay.     

Lead isotopic composition of the potassic rocks from Roccamonfina (South Italy)

Pb isotope data are presented for the potassic rocks from Roccamonfina and some other Campanian volcanoes. Pb isotope variations for Roccamonfina fall within the previously found range of values for the Italian potassic volcanism and form similar shallow regression lines in the Pb-Pb diagrams. Their interpretation as two-component mixing lines is well supported by other geochemical evidence. The relation of the mixing processes deduced for Roccamonfina and for the wider regional volcanism is discussed. The enriched and anomalous mantle under Italy is proposed to be a result of various degrees of metasomatism of a range of “Atlantic island” type mantle compositions by an LIL-element-enriched mantle “fluid”. The mantel “fluid” may either derive its isotope and trace element characteristics from an old LIL-element-enriched mantle source or from continental crust which has to some extend retained its geochemical identity in the upper mantle.     

Long-term trends in the macrobenthos and water quality of the lower Chesapeake Bay (1985–1991)

Long-term trends in macrobenthic communities of the lower Chesapeake Bay, USA, were examined using data collected quarterly (March, June, September and December) from 1985 to 1991 at 16 stations along a salinity gradient from tidal freshwater regions of the major tributaries (James, York and Rappahannock rivers) to the polyhaline region of the main-stem of Chesapeake Bay. A non-parametric trend analysis procedure was applied to five parameters characterizing macrobenthic community structure: community biomass, species richness, abundance of individuals, proportion of biomass composed of opportunistic species (opportunistic biomass composition) and proportion of biomass composed of equilibrium species (equilibrium biomass composition). For the parameters tested 36 trends were detected. For community biomass, five trends were significant; all had positive slopes and occurred in the James and York rivers. For species richness, six trends were significant; all had positive slopes with three trends in the James River, two trends in the York River and one trend in the main-stem of Chesapeake Bay. For abundance of individuals, 17 trends were detected; all abundance trends were seasonally dependent, had positive slopes and occurred at 12 of the 16 stations. For opportunistic biomass composition, four trends were significant; all had positive slopes with one trend in the lower Rappahannock River and three trends in the main-stem of Chesapeake Bay. For equilibrium biomass composition four trends were significant; two trends had positive slopes (one in the James River and one in the York River) and two trends had negative slopes (one in the Rappahannock River and one in the main-stem of Chesapeake Bay). Trends in the James and York rivers were considered to indicate improving conditions for the benthos, while trends in the lower Rappahannock River and the main-stem of the Chesapeake Bay were considered to indicate deteriorating conditions. Deteriorating conditions for the benthos were associated with regions exposed to summer, low dissolved oxygen events. The trends in the indicators of benthic biological community health were inferentially related to trends observed in water quality conditions in the tributaries and main-stem of Chesapeake Bay. All major water quality and biotic trends appeared to correspond in an ecologically meaningful manner.     

Distributions of polychlorinated biphenyls in the Daliao River estuary of Liaodong Bay,Bohai Sea (China)

The distributions of 41 polychlorinated biphenyls (PCBs) were determined in the aqueous phase, suspended particulate matter (SPM), and sediment of the Daliao River estuary in Liaodong Bay, Bohai Sea (China). The total PCB concentrations ranged from 5.51 to 40.28 ng L⁻¹ in the surface water, from 6.78 to 66.55 ng L⁻¹ dry weight in the SPM, and from 0.83 to 7.29 ng g⁻¹ dry weight in the sediment. The PCB concentrations in water, SPM, and sediment were moderate relative to those reported for other estuary and marine systems around the world. Sedimentary PCB concentrations decreased offshore due to the active deposition of laterally transported river-borne particles. The predominance of the highly chlorinated congeners for the water, SPM, and sediment samples are an indication of either a lack of degradation or the presence of nearby or recent releases into the environment.     

Distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in sediments from Zhanjiang Bay and Leizhou Bay, South China

The concentrations and spatial distribution of polycyclic aromatic hydrocarbons have been investigated in two adjacent bays of Zhanjiang and Leizhou, China. The total concentrations of the 16 USEPA priority PAHs were ranged from 41.96 to 933.90ng/g dry weight with an average concentration of 315.98ng/g and ranged from 21.72 to 319.61ng/g with an average concentration of 103.91ng/g in Zhanjiang and Leizhou Bays, respectively. The spatial distribution of PAHs was site-specific and appeared to be somewhat positively correlated with TOC and negatively correlated with sediment grain size in the two bays. The values of Phe/Ant, BaA/228 and InP/276 were higher than 10, less than 0.2, and from 0.2 to 0.5, respectively, indicating that the sources of PAHs in the two bays were mainly from petroleum and its combustion, which predominantly originated from those ships and boats coming and going in the two bays.     

Distribution and sources of organochlorinated contaminants in sediments from Izmir Bay (Eastern Aegean Sea)

Eighteen surface sediment samples representative of the entire Izmir Bay were analyzed for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). This was in order to provide extensive information concerning the recent deposition of these compounds in this area, together with levels, distribution, possible sources and potential biological risk. Sites that were contaminated by high concentrations of organochlorine compounds were associated with dense population, such as the harbour and the Gediz River estuary. Relatively higher ΣDDT concentrations and high DDT/DDE + DDD ratios in the Gediz River estuary indicated DDT usage, probably linked to public health emergencies. According to the established guidelines for sediment quality, the risk of adverse biological effects from such levels of OCPs and PCBs as recorded at most of the study sites was insignificant. But the higher concentrations in Inner bay and in the Gediz River estuary could cause biological damage.     

Study on nutrient distribution and interaction with sediments in a macro-tidal estuary

An integrated hydro-environmental model has been developed for predicting the distribution of nutrients in estuarine and coastal waters. This paper also reports on an application of the model to the Loughor Estuary in the UK, which has a high tidal range. The horizontal two-dimensional model considers the hydrodynamic, sediment transport, dissolved oxygen and nutrient cycling processes. In particular, the effect of sediment suspension and deposition on the nutrient distribution in the water column has been included in the model. A TVD-MacCormack scheme has been adopted to numerically solve the coupled partial differential equations. Field surveys and laboratory experiments in connection with the Loughor Estuary were conducted to obtain measured data for model calibration and verification. It was found that the linear isotherm model gave a good approximation of the adsorption/desorption processes over the range of nitrogen and phosphorus concentrations measured in the natural estuary. Through experiments on the collected soil samples, the salinity-dependent partition ratios between the adsorbed and dissolved nutrients were determined. The results of the established model showed good agreement with the measured data. Finally, the model was used to examine the implications of changing the sewage effluent discharge scheme on the nutrient distributions in the estuary.     

Nitrogen and carbon isotopic composition in the diamonds of Mbuji Mayi (Zaïre)

The concentration and isotopic composition of nitrogen, measured in large diamonds (gram size) from the Mbuji Mayi kimberlite district (Zaïre) show a large range of variation (100<N<2100 ppm, ?11.2<δ¹⁵N< +6.0). The¹⁵N-depleted nitrogen is associated with the higher nitrogen concentrations. The large diamonds are individually rather homogeneous in¹³C (range ofδ¹³C < 0.9‰) while variations occur within small octahedral diamonds from the same district (range up to 5.8‰). The total range ofδ¹³C variation is about the same for the large diamonds (?10.5 <δ¹³C < ?5.5), the small octahedral diamonds (?10 <δ¹³C < ?4.6), and the carbonates from local kimberlites (?11.8 < δ¹³C < ?5.5). The diamond carbon isotopic data could indicate a complex story of crystallization within a deep-seated system fractionating its carbon isotopes.The nitrogen results indicate that nitrogen in diamonds is, on the average, markedly depleted in¹⁵N (weighted average ?5.15‰) relative to atmosphere, sediments and upper mantle.