Determination of efficiency of Vaseline slide and Wilson and Cooke sediment traps by wind tunnel experiments

The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms⁻¹) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms⁻¹) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments, the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling to 2.2% for 400–500 μm particle size at 13.4 ms⁻¹. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5% at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms⁻¹, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms⁻¹, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind speed, and these could be helpful to increase the robustness of wind erosion measurements.     

The effect of grain size on the Cu, Pb, Ni, Cd speciation and distribution in sediments: a case study of Dongping Lake, China

This paper examines the surface sediments collected from Dongping Lake in China for speciation and distribution of toxic heavy metals (Cu, Pb, Ni, Cd) in different grain size fractions, and for the factors that need to be considered in potential hazard of metals to the environment. Four grain size fractions (<63, 63–78, 78–163 and 163–280 μm), divided in wet condition, and bulk samples less than 280 μm in diameter were analyzed for their distribution, density and appearance. A three-stage extraction procedure following the BCR protocol was used to chemically fractionate metals into “acid soluble”, “reducible”, “oxidizable” and “residual” fractions. Correlation analysis was used to analyze the datasets. The results showed that <63 μm grain size part constitutes the major proportion of the sediments, but its density is the smallest among the four grain size fractions. In general, the metal content curve against grain size presents “S” distribution, and the highest concentrations do not exist in <63 μm grain size. Appearance observation indicates that the adsorbed substance increases gradually along with the decreasing grain size. The dominant speciation of elements and the extent of pollution are responsible for the metal distribution in different grain size sediments. While studying bioavailability and mobilization of metals, it is advisable to take metal speciation, grain size distribution and density into consideration.     

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.     

Abundance and Chemical Speciation of Phosphorus in Sediments of the Mackenzie River Delta, the Chukchi Sea and the Bering Sea: Importance of Detrital Apatite

Utilizing a sequential extraction technique this study provides the first quantitative analysis on the abundance of sedimentary phosphorus and its partitioning between chemically distinguishable phases in sediments of the Bering Sea, the Chukchi Sea and the Mackenzie River Delta in the western Arctic Ocean. Total sedimentary phosphorus (TSP) was fractionated into five operationally defined phases: (1) adsorbed inorganic and exchangeable organic phosphorus, (2) Fe-bound inorganic phosphorus, (3) authigenic carbonate fluorapatite, biogenic apatite and calcium carbonate-bound inorganic and organic phosphorus, (4) detrital apatite, and (5) refractory organic phosphorus. TSP concentrations in surface sediments increased from the Chukchi Sea (18 μmol g⁻¹ of dried sediments) to the Bering Sea (22 μmol g⁻¹) and to the Mackenzie River Delta (29 μmol g⁻¹). Among the five pools, detrital apatite phosphorus of igneous or metamorphic origin represents the largest fraction (~43%) of TSP. The second largest pool is the authigenic carbonate fluorapatite, biogenic apatite as well as CaCO₃ associated phosphorus (~24% of TSP), followed by the Fe-bound inorganic phosphorus, representing ~20% of TSP. The refractory organic P accounts for ~10% of TSP and the readily exchangeable adsorbed P accounts for only 3.5% of TSP. Inorganic phosphorus dominates all of phosphorus pools, accounting for an average of 87% of the TSP. Relatively high sedimentary organic carbon and total nitrogen contents and low δ¹³C values in the Mackenzie River Delta together with the dominance of detrital apatite in the TSP demonstrate the importance of riverine inputs in governing the abundance and speciation of sedimentary phosphorus in the Arctic coastal sediments.     

Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain,Bangladesh

The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from 8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r ² = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top, passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and 5,000 years BP (¹⁴C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed onto Fe oxides in aquifer sediments.     

Heavy meals in urban roadside soils, part 1: effect of particle size fractions on heavy metals partitioning

Urban roadside soils are important environmental media for assessing heavy metal concentrations in urban environment. However, among other things, heavy metal concentrations are controlled by soil particle grain size fractions. In this study, two roadside sites were chosen within the city of Xuzhou (China) to reflect differences in land use. Bulk soil samples were collected and then divided by particle diameter into five physical size fractions, 500–250, 250–125, 125–74, 74–45, < 45 μm. Concentrations of metals (Ti, Cr, Al, Ga, Pb, Ba, Cd, Co, Cu, Mn, Ni, V, Zn, Mo, As, Sb, Se, Hg, Bi, Ag) were determined for each individual fraction. These metals could be roughly classified into two groups: anthropogenic element (Pb, Ba, Cd, Cu, Zn, Mo, As, Sb, Se, Hg, Bi, Ag) and lithophile element (Ti, Cr, Al, Ga, Co, Mn, Ni, V) in terms of values of enrichment factor. As expected, higher concentrations of anthropogenic heavy metals (Cu, Zn, Mo, As, Hg, Bi, Ag) are observed in the finest particle grain size fraction (i.e. < 45 μm). However, heavy metals Se, Sb and Ba behave independently of selected grain size fractions. From the viewpoint of mass loading, more than 30% of the concentrations for all anthropogenic heavy metals are contributed by the particle grain size fractions of 45–74 μm at site 1 and more than 70% of the concentrations for all heavy metals are contributed by the particle grain size fractions of 45–74 and 74–125 μm at site 2. These results are important for transport of soil-bound heavy metals and pollution control by various remedial options.     

Pyritization of trace metals in estuarine sediments and the controlling factors: a case in Jiaojiang Estuary of Zhejiang Province,China

Three undisturbed sediment samples were collected from the intertidal zone of the Jiaojiang Estuary of Zhejiang Province, China. The sediments were found to contain remarkably low concentrations of organic carbon (<0.6%) and acid volatile sulfide (AVS) (<30 μmol g⁻¹). The availability of these two substrates likely constrained sulfate reduction and pyritization of several trace metals, respectively. This was especially true at one station where AVS concentrations in the upper 20 cm averaged less than 0.05 μmol g⁻¹. Although the depth dependence of the degree of trace metal pyritization was generally consistent with expectations based on redox conditions, depth profiles of reactive-metal and pyrite-metal concentrations in several cases revealed more complex behavior and a positive correlation between reactive-metal concentrations and pore water metal concentrations.     

Distribution and enrichment of trace metals in marine sediments of Bay of Bengal,off Ennore,south-east coast of India

In order to avoid the pollution of trace metals in marine environment, it is necessary to establish the data and understand the mechanisms influencing the distribution of trace metals in marine environment. The concentration of heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Zn, Co and Cd) were studied in sediments of Ennore shelf, to understand the metal contamination due to heavily industrialized area of Ennore, south-east coast of India. Concentration of metals shows significant variability and range from 1.7 to 3.7% for Fe, 284–460 μg g⁻¹ for Mn, 148.6–243.2 μg g⁻¹ for Cr, 385–657 μg g⁻¹ for Cu, 19.8–53.4 μg g⁻¹ for Ni, 5.8–11.8 μg g⁻¹ for Co, 24.9–40 μg g⁻¹ for Pb, 71.3–201 μg g⁻¹ for Zn and 4.6–7.5 μg g⁻¹ for Cd. For various metals the contamination factor (CF) and geoaccumulation index (I _geo) has been calculated to assess the degree of pollution in sediments. The geoaccumulation index shows that Cd, Cr and Cu moderately to extremely pollute the sediments. This study shows that the major sources of metal contamination in the Ennore shelf are land-based anthropogenic ones, such as discharge of industrial wastewater, municipal sewage and run-off through the Ennore estuary. The intermetallic relationship revealed the identical behavior of metals during its transport in the marine environment.     

Importance of porosity and transfer of matter in the rock weathering processes: two examples in central Spain

Some physical properties (bulk and free porosity, pore size distribution), and the chemical composition and mass balance of two deeply weathered profiles one developed on Hercynian granodiorite and the other on pre-Cambrian slates were studied. Hydric and mercury porosimetry, nitrogen adsorption techniques, chemical analyses and XRD techniques were used. On granodiorite, weathering has created increased porosity with a pore diameter <5 μm, whereas on slates the weathering has produced of ca. 1 μm in diameter. These pore sizes have played an important role in the weathering processes. Assuming that weathering preserves volumes, except in the uppermost part of the profiles, it brought about a loss of matter of more than 12% (~300 kg/m³) on granodiorite and ca. 30% (~800 kg/m³) on slates. These changes are related to shifts in the mineralogical evolution, with the appearance of new 2:1 and 1:1 phyllosilicates and Fe oxy-hydroxides as the main authigenic minerals. The release of matter, at least since the upper Neogene until the present, has led to the lowering of relief in a more or less homogeneous way, giving rise to gentle hillsides and flat surfaces below which the current river networks are incised. Porosity studies have the potential to explain several specific landforms as well as affecting landscape development in general.     

Environmental and health risk assessment in abandoned mining area, Zlata Idka, Slovakia

The Zlata Idka village is a typical mountainous settlement. As a consequence of more than 500 years of mining activity, its environment has been extensively affected by pollution from potentially toxic elements. This paper presents the results of an environmental-geochemical and health research in the Zlata Idka village, Slovakia. Geochemical analysis indicates that arsenic (As) and antimony (Sb) are enriched in soils, groundwater, surface water and stream sediments. The average As and Sb contents are 892 mg/kg and 818 mg/kg in soils, 195 mg/kg and 249 mg/kg in stream sediments, 0.028 mg/l and 0.021 mg/l in groundwater and 0.024 mg/l and 0.034 mg/l in surface water. Arsenic and Sb concentrations exceed upper permissible limits in locally grown vegetables. Within the epidemiological research the As and Sb contents in human tissues and fluids have been observed (blood, urine, nails and hair) in approximately one third of the village’s population (120 respondents). The average As and Sb concentrations were 16.3 μg/l and 3.8 μg/l in blood, 15.8 μg/l and 18.8 μg/l in urine, 3,179 μg/kg and 1,140 μg/kg in nails and 379 μg/kg and 357 μg/kg in hair. These concentrations are comparatively much higher than the average population. Health risk calculations for the ingestion of soil, water, and vegetables indicates a very high carcinogenic risk (>1/1,000) for as content in soil and water. The hazard quotient [HQ=average daily dose (ADD)/reference dose (RfD)] calculation method indicates a HQ>1 for groundwater As and Sb concentrations.     

High arsenic contents in groundwater of central Spain

The chemical and microbiological characteristics of groundwater from two provinces of central Spain were studied. In some zones of this area, the concentrations of As in groundwater exceed the guideline concentrations, set internationally between 10 g/l and 50 g/l, reaching levels over 100 g/l. A narrow correlation between the contents of arsenic and HCO₃^– was observed. These data suggest a possible mechanism of the As mobilization from aquifer sediments to groundwater: the bicarbonate ions could displace HAsO₄^2– adsorbed on aquifer oxyhydroxides. Sediments containing relatively high contents of adsorbed arsenic are deposited in surface water environments with low carbonate concentrations. Subsequently, the sediments become exposed to groundwater with highly dissolved carbonate content, and arsenic can be mobilized by displacement from mineral surfaces. In addition, the presence of Pseudomonas genera bacteria, which secrete siderophores (Fe chelating agents) could mobilize As adsorbed on Fe oxides through their dissolution. These combined microbiological and chemical processes might have increased the natural mobility of As.     

Seasonal variations of phosphorus species in sediment from the middle Adriatic Sea

Phosphorus (P) species concentrations in 0–2 cm surface sediment layer were investigated monthly from November 2001 to December 2002 at the bay, channel and open sea stations in the middle Adriatic. Modified SEDEX method was used for inorganic phosphorus species determination [P in biogenic (P-FD), authigenic (P-AUT), detrital apatite (P-DET) and P adsorbed on to iron oxides and hydroxides (P–Fe)], and organic phosphorus (P-ORG). P-FD, P-AUT and P-DET concentration ranges (1.5–5.4, 0–2.7 and 0.4–3.4 μmol g⁻¹, respectively) were similar at all stations, and showed no obvious common trend of seasonal changes. P–Fe ranged from 1.9 to 11.9 μmol g⁻¹ with the highest values at bay station and higher seasonal oscillations than other inorganic P forms. P-ORG ranged from 0.3 to 18.7 μmol g⁻¹ with higher concentrations at stations of fine-sized sediments and showed increased concentrations in warm part of the year at all stations. Correlation between concentrations of P–Fe in the surface sediment layer and orthophosphate sediment-water interface concentration gradients at bay and channel stations indicated to P–Fe importance in the orthophosphate benthic flux. For the bay station, linkage between sediment P-ORG and chlorophyll a concentrations, primary production and microzooplankton abundance was established, indicating a 1 month delay of sediment response to production fluctuations in the water column.     

Detrital,metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ ¹¹B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ ¹¹B ≈ +0.9‰). The varying δ ¹¹B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ ¹¹B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ ¹¹B values (up to +7.7‰) towards the margins of the grains. The δ ¹¹B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.     

Inorganic phosphorus uptake in a carbonate-dominated seagrass ecosystem

Seasonal phosphate (Pi) uptake kinetics were determined using chambers encompassing the water column, sediment and the entire system (water column + sediment + seagrass/epiphyte) in Florida Bay (FB) during 2003–2006 and on the Little Bahama Bank (LBB) during a cruise June, 2004. Pi uptake was a linear function of concentration at low Pi levels (< 2 μmo11^-1). Applying the Pi system rate constant (S_p) from western (177 ±50 x 10^-6 m s^-1) and eastern (272 ±66 x 10^-6 m s^-1) bay sites, and using Pi measured during the study (0.02 to 0.177 μmol Pi 1^-1), we calculated a Pi uptake rate of 0.30 to 2.62 mmol Pi m^-2 d^-1 for western and 0.47 to 4.16 mmol Pi m^-2 d^-1 for eastern bay sites which includes phytoplankton uptake (0.455 m height). During non-bloom conditions, phytoplankton dominated Pi uptake in the east (46%) and both phytoplankton and the seagrass-epiphyte consortium in the west (32 and 52%, respectively), with a smaller contribution by the sediment (15–20%). On LBB interior sites, the water column always dominated (≽94%) Pi uptake with a higher S_p (573-881 x 10^-6 m s^-1) than FB. During cyanobacterial blooms in FB (chla 17 μg 1^-1), the water column dominated Pi uptake (100%) and S_p was the highest (>2,800 x 10^-6 m s^-1) measured. Phytoplankton accounted for 88% of this sequestered Pi with only 12% in the acid extractable fraction, likely as calcium bound and/or adsorbed P, and only 1% attributable to small heterotrophs. When chl α levels declined (2 μg I^-1) Pi uptake was still dominated by phytoplankton (77%), the acid extractable pool increased (18%) and the heterotrophic community became more important (22%). In carbonate-dominated seagrass systems, Pi is primarily taken up by the water column biota and is subsequently remineralized/hydrolyzed in the water column or settles to the benthos where it becomes available to benthic primary producers.     

Mapping of accumulated nitrogen in the sediment pore water of a eutrophic lake in Iowa, USA

A large pool of nitrogen in the sediment pore fluid of a eutrophic lake in Iowa, USA, was mapped in this study. Previously, the lake had supported fishing and boating, but today it no longer supports its designated uses as a recreational water body. In the top 5 cm of the lake bottom, the pore water nitrogen ranges between 3.1 and 1,250 μg/cm³ of sediments, with an average of 160.3 μg/cm³. Vertically, nitrate concentrations were measured as 153 μg/cm³ at 0–10 cm, 162 μg/cm³ at 10–20 cm, and 32 μg/cm³ at 20–30 cm. Nitrate mass distribution was quantified as 3.67 × 10³ kg (65%) in the bottom sediments, 172 kg (3%) in suspended particulates, and 1.83 × 10³ kg (32%) in the dissolved phase. Soil runoff nutrients arrive at the lake from the heavily fertilized lands in the watershed. Upon sedimentation, a large mass of nitrogen desorbs from mineral particles to the relatively immobile pore fluid. Under favorable conditions, this nitrogen diffuses back into the water column, thereby dramatically limiting the lake’s capability to process incoming nutrients from farmlands. Consequently, a condition of oxygen deficiency disrupts the post-season biological activities in the lake.     

Large tank experiment on nitrate fate and transport: the role of permeability distribution

A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted within a large tank (4 × 8 × 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m³), used to fill the tank, were excavated from an unconfined alluvial aquifer near Ferrara (Northern Italy); the field site was connected to a pit lake located in a former agricultural field. To evaluate spatial heterogeneity, the tank’s filling material was characterized via slug tests and grain-size distribution analysis. The investigated sediments were characterized by a large spectrum of textures and a heterogeneous hydraulic conductivity (k) field. Initial tank pore water composition exhibited high concentration of nitrate (NO₃ ⁻) sulfate (SO₄ ²⁻) calcium (Ca²⁺), and magnesium (Mg²⁺), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO₃ ⁻ and SO₄ ²⁻ was heterogeneous and not related to the finer grain-size content (<63 μm). The tank’s material was flushed with purified tap water for 800 days in steady-state conditions; out flowing water was regularly sampled to monitor the migration rate of fertilizer by-products. Complete removal of NO₃ ⁻ and SO₄ ²⁻ took 500 and 600 days, respectively. Results emphasized organic substrate availability and spatial heterogeneities as the most important constraints to denitrification and nitrogen removal, which increase the time required to achieve remediation targets. Finally, the obtained clean-up time was compared with a previous column experiment filled with the same sediments.     

Elemental chemistry and geochemical partitioning of heavy metals in road dust from Dhanbad and Bokaro regions,India

Road dust collected from India’s richest and oldest coal mining belt of Dhanbad and Bokaro regions was analysed for particle size characteristics and elemental composition. The particle size distribution pattern shows dominance of 500–250 μm and 250–125 μm size fractions, constituting 45–58% of the mass size spectrum. Si is the most dominant element and its concentration varied between 29.3 and 36.4% with the average value 34.3%. Fe, Ti and Mn are the dominant heavy metals followed by Zn, Cr, Pb, Cu, Ni and Co. No significant differences concentration of metals between sampling sites was apparent; however, some sites tend to accommodate relatively higher metals due to its proximity to industrial and mining sites. In general, finer fraction (<63 μm) tend to contain 1–3 times higher metals as compared with the bulk composition. Except Pb and Mn all the measured metals are generally lie below grade zero, suggesting that there is no pollution threat with respect to these metals in roadway dust from the studied sites. Geochemical speciation study shows that the lithogenic phase is the major sink for heavy metals. Fe–Mn oxide and organic are the major non-lithogenic phases and Pb and Zn are the major elements of the non-lithogenic phase.     

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (S^o), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol⁻¹) than at station A (Ea=110 kJ mol⁻¹). The maximum SRR values observed equalled 14 μmol cm⁻³ d⁻¹ at station B and 1 μmol cm⁻³ d⁻¹ at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and S^o were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m⁻² yr⁻¹, and at station A of the order of 12 mol m⁻² yr⁻¹. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.     

Trace Metals (Cd,Cu, Hg,and Pb) Accumulation Recorded in the Intertidal Mudflat Sediments of Three Coastal Lagoons in the Gulf of California,Mexico

²¹⁰Pb geochronologies of Cd, Cu, Hg, and Pb fluxes were obtained from the intertidal mudflat sediments of the coastal lagoons Chiricahueto, Estero de Urías, and Ohuira in the Mexican Pacific. The Cu and Hg sediment concentrations at the three lagoons fell within the ranges of 6–76 μg g⁻¹ and 0.1 to 592 ng g⁻¹, respectively; Chiricahueto and Estero de Urías sediments had comparable Cd and Pb concentrations within the ranges of 0.2–2.1 μg g⁻¹ and 10–67 μg g⁻¹, respectively; whereas in Ohuira lagoon, Cd concentrations were lower (0.1–0.5 μg g⁻¹) and Pb concentrations were higher (115–180 μg g⁻¹) than in the other lagoons. The metal fluxes (μg cm⁻² y⁻¹) for the three lagoons fell within the ranges of 0.02–0.15 for Cd, 0.7–6.0 for Cu, 0.001–0.045 for Hg, and 0.7–20 for Pb. The Hg pollution in Estero de Urías was attributed to the exhausts of the thermoelectric plant of Mazatlan and the metal enrichment in Chiricahueto and Ohuira was related to the agrochemical wastes from the croplands surrounding these lagoons.     

Assessment of organic pollutants in the offshore sediments of Dubai, United Arab Emirates

Fifteen stations (st) were selected along Dubai coastal region to delineate the distribution and the source of total petroleum hydrocarbon (TPH), total organic carbon (TOC), total Kjeldhal nitrogen (TKN), polycyclic aromatic hydrocarbon (PAHs) and polychlorinated biphenyls. The concentrations of TPH fluctuated between 2 μg g ⁻¹ and 48018 μg g ⁻¹ and the values of TOC were in the range of 0.16–5.9 wt%, while TPAHs ranged from 0.09 μg g ⁻¹ to 161.72 μg g ⁻¹. On the other hand, TPCBs showed values between 0.8 μg kg⁻¹ and 93.3 μg kg⁻¹ and TKN values varied from 218 μg g⁻¹ to 2457 μg g ⁻¹. Distribution of oil and organic compounds in Dubai sediments are safe compared with previous studies except for limited areas at the northeastern offshore. These readings are probably due to: (1) presence of commercial or industrial ports, dry docks and fishing harbours and (2) population centers mainly concentrated at the northern part of the study area. Results indicate that TOC can be used as indicator of oil pollution only in heavily oiled sediments. The highest values of TOC, TPH, TPAHs and TPCBs corresponded to the stations covered with fine sand, due to adsorption properties and larger surface area. The evaporation of low boiling point compounds from surface layers led to enrichment of sediments with the thick residual. Al-Hamriya St 3 exhibited the highest values of TPH, TOC, TPAHs and TPCBs and the second highest value of TKN.