Total arsenic concentrations and arsenic species present in naturally decomposing Ecklonia radiata tissues collected from various marine habitats

To investigate the release and degradation of arsenoribosides associated with the brown alga Ecklonia radiata, tissues were collected in various marine micro-habitats (water column, sand intertidal, and rock platform intertidal) to establish the importance of decomposition stage and the micro-habitat in which decomposition occurs on arsenoriboside degradation. Total arsenic concentrations in E. radiata tissues varied in a similar pattern across all three sampling locations (Lake Tabourie, Burrill Lake, and Ulladulla Harbour) with concentrations in live tissues (53–124 μg As g^?1 (dry mass)) greater than concentrations in tissues decomposing in the water column (28–90 μg As g^?1 (dry mass)), which were in turn higher than concentrations in tissues decomposing in intertidal environments (16–21 μg As g^?1 (dry mass)). Arsenoribosides, specifically sulfonate (SO₃-), phosphate (PO₄-), and glycerol (Gly-) accounted for all of the arsenic extracted from live E. radiata tissues. Arsenoribosides also accounted for 100 % of the extractable arsenic species in E. radiata tissues decomposing in the water column. The proportions of arsenic species in decomposing E. radiata tissue from intertidal environments varied with sampling location and therefore micro-habitat. In rock platform-based intertidal zones (Burrill Lake and Ulladulla harbour), considerable concentrations of unextractable arsenic (10–60 %) were present plus known arsenoriboside degradation products such as dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA), and arsenate (As(V)). In sand/beach-based intertidal zones, however, the vast majority of arsenic (≈95 %) was unextractable with only small concentrations of arsenoribosides and As(V) present. This study demonstrates that the release and further degradation of arsenoribosides from E. radiata tissues occurs in a two-step process with arsenoribosides released via leaching, whilst E. radiata remains suspended within the water column. Arsenoribosides are then degraded to various intermediate arsenic species once E. radiata tissues settle on intertidal environments; however, the degree of degradation varies relative to whether decomposition occurs on rock platform or sand-based environments. These results illustrate the key role of marine micro-habitats in the degradation of arsenoribosides contained within marine macro-algae.     

Concentration,Distribution, Source,and Risk Assessment of PAHs and Heavy Metals in Surface Water from the Three Gorges Reservoir,China

Fifteen polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cr, Ni, As, Cd, Pb, and Hg) were quantified in 19 surface water sites of the Three Gorges Reservoir, China. The total concentrations of 15 PAHs and six heavy metals in the 19 sample sites ranged from 130.8 ng L^?1 to 227.5 ng L^?1 and 3.2 μg L^?1 to 6.0 μg L^?1, respectively. The mean concentration of As was the highest among the six heavy metals (2.1 ± 0.3 μg L^?1), followed by Cr (0.5 ± 0.3 μg L^?1), Ni (1.3 ± 0.1 μg L^?1), Cd (0.2 ± 0.01 μg L^?1), Pb (0.07 ± 0.08 μ g L^?1) and Hg (0.05 ± 0.08 μg L^?1). The isomer ratio results suggest that PAHs at most sites were mainly from petroleum combustion, while coal and biomass combustion was the main source at sites 1, 2, 6, 7, 9, 14, and 17. Based on principal component analysis, the main source of heavy metals was anthropogenic activities and weathering of bedrocks. Depending on characteristic of RQ_(NCs) ≥ 1 and RQ_(MPCs) < 1, BaA showed higher potential ecological risk than other PAHs, therefore, all sampling site needed to be paid much more attention, included some remedial actions. Meanwhile, after assessing human health risk of heavy metal, it was unlikely to experience adverse health effects, even exposing through more pathways and six kinds of heavy metals simultaneously.     

Soil quality around a solid waste dumpsite in Port Harcourt, Nigeria

The levels of soil parameters and selected heavy metals around a solid waste dumpsite receiving untreated wastes from all sources and a control site within Port Harcourt, Nigeria have been examined. Top soil (0–15 cm) and sediment samples were collected and analysed for pH value, particle size, total nitrogen, potassium, available phosphorus, organic matter, effective cation exchange capacity, cadmium, nickel and lead using standard methods. The results showed that the waste dump contributed to the high levels of nutrients and heavy metals. The dry season mean concentrations were: organic matter (5.28 ± 1.34% or 132,422.4 kg ha^?1), K (1.60 ± 0.52 meq per 100 g), N (0.09 ± 0.06% or 2257.2 kg ha^?1), Av.P (15.11 ± 7.57 μg g^?1), Cd (1.34 ± 0.72 μg g^?1), Ni (4.10 ± 1.63 μg g^?1) and Pb (38.85 ± 22.18 μg g^?1) while the wet season mean concentrations were organic matter (5.46 ± 1.39% or 136,936.8 kg ha^?1), K (2.79 ± 0.81 meq per 100 g), N (0.10 ± 0.05% or 2508 kg ha^?1), Av.P (9.22 ± 2.69 μg g^?1), Cd (1.72 ± 1.22 μg g^?1), Ni (14.95 ± 14.94 μg g^?1) and Pb (53.50 ± 40.09 μg g^?1). There was efficient mineralization process in the area. The texture of soil on the main dumpsite was loamy sand, which suggests that the ground water in the area is susceptible to contamination by surface pollutants. The texture of soil at the control site is sandy loam while sediment has the textural class of sand. Decomposed organic materials and agricultural activities influenced the texture of soils. The soils from the main dump and sediment were slightly alkaline while the control soil was moderately acidic. In both seasons, a significant variation exists (P < 0.05) between the metal concentrations in soil at the main dump and those in the sediments with a positive correlation (r = 0.572149) in the wet season and (r = 0.956647) in the dry season. The presence of liming materials and activities of microorganisms on the waste dump increased the pH of the soils. The accumulation of nutrients results in the luxuriant growth of plants/crops on the waste dump.     

Discontinuous ammonia excretion and glutamine storage in littoral Oniscidea (Crustacea: Isopoda): testing tidal and circadian models

A key evolutionary development facilitating land colonization in terrestrial isopods (Isopoda: Oniscidea) is the intermittent liberation of waste nitrogen as volatile ammonia. Intermittent ammonia release exploits glutamine (Gln) as an intermediary nitrogen store. Here, we explore the relationship between temporal patterns of ammonia release and Gln accumulation in three littoral oniscideans from Southern California. Results are interpreted in terms of water availability, habitat, activity patterns, and ancestry. A two-way experimental design was used to test whether ammonia excretion and Gln accumulation follow a tidal or diel periodicity. Ammonia excretion was studied in the laboratory using chambers with or without available seawater and using an acid trap to collect volatile ammonia. Ligia occidentalis releases ammonia directly into seawater and accumulates Gln during low tide (48.9 ± 6.5 μmol g^?1 at low tide, 24.1 ± 3.0 μmol g^?1 at high tide), indicating that excretion is tidally constrained. Alloniscus perconvexus and Tylos punctatus can excrete ammonia directly into seawater or utilize volatilization. Both species burrow in sand by day and show a diel excretory pattern, accumulating Gln nocturnally (31.8 ± 2.7 μmol g^?1 at dawn and 21.8 ± 2.3 μmol g^?1 at dusk for A. perconvexus; 85.7 ± 15.1 μmol g^?1 at dawn and 25.4 ± 2.9 μmol g^?1 at dusk for T. punctatus) and liberating ammonia diurnally. Glutaminase shows higher activity in terrestrial (0.54–0.86 U g^?1) compared to intertidal (0.25–0.31 U g^?1) species, consistent with the need to generate high PNH₃ for volatilization. The predominant isoform in Armadillidium vulgare is phosphate dependent and maleate independent; phosphate is a plausible regulator in vivo.     

Accumulation of arsenic in soil and rice under wetland condition in Bangladesh

Shallow tube well (STW) water, often contaminated with arsenic (As), is used extensively in Bangladesh for irrigating rice fields in the dry season, leading to potential As accumulation in soils. In the current study the consequences of arsenic from irrigation water and direct surface (0–15 cm) soil application were studied under field conditions with wetland rice culture over 2 years. Twenty PVC cylinders (30-cm length and 30-cm diameter) were installed in field plots to evaluate the mobility and vertical distribution of soil As, As mass balance, and the resulting influences on rice yield and plant-As concentration in Boro (dry season) and transplanted (T.) Aman (wet season) rice over the 2-year growth cycle. Treatments included irrigation-water As concentrations of 0, 1 and 2 mg L^?1 (Boro season only) and soil-As concentrations of 10 and 20 mg kg^?1. Following the 2-year cropping sequence the major portion (39.3–47.6%) of the applied arsenic was retained within the rooting zone at 0–15 cm depth, with 14.7–19.5% of the total applied As at the 5–10 cm and 10–15 cm soil depths compared to 1.3–3.6% at the 35–40 cm soil depth. These results indicate the relatively low mobility of applied As and the likely continued detrimental accumulation of As within the rooting zone. Arsenic addition in either irrigation water or as soil-applied As resulted in yield reductions from 21 to 74 % in Boro rice and 8 to 80 % in T. Aman rice, the latter indicating the strong residual effect of As on subsequent crops. The As concentrations in rice grain (0.22 to 0.81 µg g^?1), straw (2.64 to 12.52 µg g^?1) and husk (1.20 to 2.48 µg g^?1) increased with increasing addition of As. These results indicate the detrimental impacts of continued long-term irrigation with As-contaminated water on agricultural sustainability, food security and food quality in Bangladesh. A critical need exists for the development of crop and water management strategies to minimize potential As hazard in wetland rice production.     

Role of Organic Carbon Sources and Sulfate in Controlling Net Methylmercury Production in Riverbank Sediments of the South River,VA (USA)

Mercury (Hg) transport and methylmercury (MeHg) production in riverbank sediments are complex processes influenced by site-specific physical and biogeochemical conditions. The South River watershed in VA, USA, contains elevated concentrations of Hg in riverbank and floodplain sediments, which has the potential to methylate. The role of specific organic carbon sources in promoting methylation reactions in natural sediments under dynamic flow conditions is not well understood. Four saturated column experiments were conducted, including a control column, which received South River water as an influent solution, and three columns that received South River water amended with: acetate (5.8 mM); lactate (5.7 mM); and lactate (5.7 mM) with SO₄^2? (10.1 mM). The amendments were selected to promote growth of different microorganisms to gain an understanding of the microbial processes, controlling rates of methylation. The column receiving lactate and SO₄^2? had the highest MeHg concentrations in the effluent and in the pore water near the effluent at 1.8 and 4.9 μg L^?1, respectively. At the cessation of the column experiments, the lactate–sulfate column sediments contained the highest populations of enumerable sulfur-reducing bacteria and the highest solid-phase MeHg at 530 ± 100 ng g^?1 dry wt. from the interval closest to the influent. The results suggest that the form and availability of electron donors and acceptors are primary factors controlling rates of methylation in the South River sediment.     

Evaluation of Garden Crop Mercury Uptake and Potential Exposure from Consumption of Garden Crops Grown on Floodplain Soils

ABSTRACT

This study investigated Hg uptake from soil into garden crops to help assess the significance of human consumption of crops as a potential route of exposure to Hg. Locations for both a floodplain and a control garden were identified within the Augusta Forestry Center near Crimora, VA, USA, which is about 16 river-km downstream from the city of Waynesboro, along the South River. The floodplain garden had measured soil Hg concentrations ranging from 4.2 to 78 mg Hg kg^?1 dry weight basis in the surface to 15-cm deep layer. A total of 139 samples from the floodplain garden from 17 different crops were analyzed for Hg. All crop samples (except for nine) had less than 0.1 μg Hg g^?1 wet weight basis (ww). Many samples were less than the method detection limit (MDL) of 0.003 μg Hg g^?1 ww. Based on the measured Hg concentrations and several conservative assumptions (e.g., Hg assumed present when less than MDL; 100% consumption from the geographical area in which study was conducted; and 100% bioavailable Hg as methyl Hg), consumption of crops with these Hg levels is not expected to be a significant route of Hg exposure.     

Phosphorus sorption characteristics of sediment in the Simiyu and Kagera River basins: implications for phosphorus loading into Lake Victoria

As part of a larger study to assess the influence of land use on riverine and atmospheric phosphorus (P) loading to Lake Victoria, P sorption characteristics of eight composite bottom sediment samples from the Simiyu and Kagera rivers were determined using the Langmuir equation. The samples had low to medium Langmuir adsorption maxima (Γ_m), ranging from 107 to 201μg g^?1. Langmuir binding energy co-efficient (K) ranged from 60 to 181μg l^?1 and the equilibrium P concentration at zero sorption (EPC₀) from 0.1 to 2.75μg g^?1. By using Langmuir co-efficients derived from P sorption experiments and soluble reactive phosphorus (SRP) concentrations measured in rivers as well as the in-shore waters of Lake Victoria, it was possible to determine the potential release of SRP into the lake by sediment from the two catchments. For the 2000 water-year, it was estimated that about 28.65 ± 0.89 (mean ± SD) and 66 ± 6.76 tons of SRP were released into Lake Victoria by sediment deposited by the Simiyu and Kagera rivers, respectively. The implications of these results to future management of cultural eutrophication in Lake Victoria are also discussed.     

Swainsonine,a novel fungal metabolite: optimization of fermentative production and bioreactor operations using evolutionary programming

The optimization of bioreactor operations towards swainsonine production was performed using an artificial neural network coupled evolutionary program (EP)-based optimization algorithm fitted with experimental one-factor-at-a-time (OFAT) results. The effects of varying agitation (300–500 rpm) and aeration (0.5–2.0 vvm) rates for different incubation hours (72–108 h) were evaluated in bench top bioreactor. Prominent scale-up parameters, gassed power per unit volume (P _g/V _L, W/m³) and volumetric oxygen mass transfer coefficient (K _L a, s^?1) were correlated with optimized conditions. A maximum of 6.59 ± 0.10 μg/mL of swainsonine production was observed at 400 rpm-1.5 vvm at 84 h in OFAT experiments with corresponding P _g/V_L and K _L a values of 91.66 W/m³ and 341.48 × 10^?4 s^?1, respectively. The EP optimization algorithm predicted a maximum of 10.08 μg/mL of swainsonine at 325.47 rpm, 1.99 vvm and 80.75 h against the experimental production of 7.93 ± 0.52 μg/mL at constant K _L a (349.25 × 10^?4 s^?1) and significantly reduced P _g/V _L (33.33 W/m³) drawn by the impellers.     

A Study on Cadmium Phytoremediation Potential of Indian Mustard,Brassica juncea

The objective of this study was to investigate Cd phytoremediation ability of Indian mustard, Brassica juncea. The study was conducted with 25, 50, 100, 200 and 400 mg Kg^?1 CdCl₂ in laboratory for 21 days and Cd concentrations in the root, shoot and leaf tissues were estimated by atomic absorption spectroscopy. The plant showed high Cd tolerance of up to 400 mg Kg^?1 but there was a general trend of decline in the root and shoot length, tissue biomass, leaf chlorophyll and carotenoid contents. The tolerance index (TI) of plants were calculated taking both root and shoot lengths as variables. The maximum tolerance (TI _shoot = 87.4 % and TI _root = 89.6 %) to Cd toxicity was observed at 25 mg Kg^?1, which progressively decreased with increase in dose. The highest shoot (10791 μg g^?1 dry wt) and root (9602 μg g^?1 dry wt) Cd accumulation was achieved at 200 mg kg^?1 Cd treatment and the maximum leaf Cd accumulation was 10071.6 μg g^?1 dry wt achieved at 100 mg Kg^?1 Cd, after 21 days of treatment. The enrichment coefficient and root to shoot translocation factor were calculated, which, pointed towards the suitability of Indian mustard for removing Cd from soil.     

Net sediment N2 fluxes in a southern New England estuary: variations in space and time

Over the past three decades, Narragansett Bay has undergone various ecological changes, including significant decreases in water column chlorophyll a concentrations, benthic oxygen uptake, and benthic nutrient regeneration rates. To add to this portrait of change, we measured the net flux of N₂ across the sediment–water interface over an annual cycle using the N₂/Ar technique at seven sites in the bay for comparison with measurements made decades ago. Net denitrification rates ranged from about 10–90 μmol N₂–N m^?2 h^?1 over the year. Denitrification rates were not significantly different among sites and had no clear correlation with temperature. Net nitrogen fixation (?5 to ?650 μmol N₂–N m^?2 h^?1) was measured at three sites and only observed in summer (June–August). Neither denitrification nor nitrogen fixation exhibited a consistent relationship with sediment oxygen demand or with fluxes of nitrite, nitrate, ammonium, total dissolved inorganic nitrogen, or dissolved inorganic phosphate across all stations. In contrast to the mid-bay historical site where denitrification rates have declined, denitrification rates in the Providence River Estuary have not changed significantly over the past 30 years.     

MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay,France)

Hg cycling in biologically productive coastal areas is of special importance given the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. Field experiments were performed during three different seasons in Arcachon Bay, a mesotidal lagoon (SW France), to assess the variability of the water column concentrations, sediment–water exchanges and potential formation and degradation of MMHg. The objectives were to evaluate the contribution of intertidal mudflats to MMHg production and the various pathways of Hg species export. Dissolved and bulk concentrations of Hg species in the water column downstream of tidal flats were measured throughout several tidal cycles. The Hg benthic fluxes at the sediment–water interface were determined by means of benthic chambers for three different stations. Hg methylation and demethylation potentials were determined in surficial sediments and the water column using isotopic tracers. The tidal surveys demonstrated that benthic remobilization of Hg occurs primarily in association with sediment erosion and advection during ebb tide. However, elevated dissolved Hg concentrations observed at low tide were found to be caused by a combination of pore-waters seeping, benthic fluxes and methylation in the water column. Benthic fluxes were more intense during late winter conditions (median MMHg and inorganic Hg (IHg) fluxes: 64 and 179 pmol m^?2 h^?1, respectively) and subsequently decreased in spring (median 0.7 and ?5 pmol m^?2 h^?1, respectively) and fall (median ?0.4 and ?1.3 pmol m^?2 h^?1, respectively). The trends in methylation and demethylation potentials were at the opposite of the fluxes, two times lower during winter than for spring or fall conditions. In this tidal environment, MMHg production in surface sediments and its subsequent release is estimated to be the major source of MMHg to the water column during winter and spring time. However, during the more productive summer period, the Hg methylation extent in the water column may be very significant and equivalent to the sediment contribution.     

Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient

The photosynthetic characteristics through P-E curves and the effect of UV radiation on photosynthesis (measured as rapid adjustment of photochemistry, F _v/F _m) and DNA damage (as formation of CPDs) were studied in field specimens of green, red and brown algae collected from the eulittoral and sublittoral zone of Fildes Peninsula (King George Island, Antarctic). The content of phenolic compounds (phlorotannins) and the antioxidant activity were also studied in seven brown algae from 0 to 40 m depth. The results indicated that photosynthetic efficiency (α) was high and did not vary between different species and depths, while irradiances for saturation (E _k) averaged 55 μmol m^?2 s^?1 in subtidal and 120 μmol m^?2 s^?1 in eulittoral species. The studied species exhibited notable short-term UV tolerance along the vertical zonation. In intertidal and shallow water species, decreases in F _v/F _m by UV radiation were between 0 and 18 %, while in sublittoral algae, decreases in F _v/F _m varied between 3 and 35 % relative to PAR treatment. In all species, recovery was high averaging 84–100 %. The formation of CPDs increased (15–150 %) under UV exposure, with the highest DNA damage found in some subtidal species. Phlorotannin content varied between 29 mg g^?1 DW in Ascoseira mirabilis from 8 m depth and 156 mg g^?1 DW in Desmarestia menziesii from 17 m depth. In general, phlorotannin concentrations were constitutively high in deeper sublittoral brown algae, which were correlated with higher antioxidant activities of algal extracts and low decreases in photosynthesis. UV radiation caused a strong decrease in phlorotannin content in the deep-water Himantothallus grandifolius, whereas in D. menziesii and Desmarestia anceps, induction of the synthesis of phlorotannins by UV radiation was observed. The antioxidant activity was in general less affected by UV radiation.     

Inorganic nitrogen uptake kinetics of sugarcane (Saccharum spp.) varieties under in vitro conditions with varying N supply

An in vitro system was established for the characterisation of inorganic nitrogen uptake by sugarcane plantlets of variety NCo376. After multiplication and rooting, plantlets (0.27–0.3 g fresh mass) were placed on N-free medium for 4 days, and then supplied with 2–20 mM N as NO₃ ^?-N only, NH₄ ⁺-N only or NO₃ ^?-N + NH₄ ⁺-N (as 1:1). With few exceptions, on all the tested N media, the in vitro plants always had a higher V_max for NH₄ ⁺-N (28.69–66.51 μmol g^?1 h^?1) than for NO₃ ^?-N uptake (10.24–30.19 μmol g^?1 h^?1) and the K_m indicated a higher affinity for NO₃ ^?-N (0.02–7.38 mM) than for NH₄ ⁺-N (0.06–9.15 mM). When N was applied as 4 and 20 mM to varieties N12, N19 and N36, the interaction between variety, N form and concentration resulted in differences in the V_max and K_m. The high N-use efficient varieties (N12 and N19), as determined in previous pot and field trials, behaved similarly under all tested conditions and displayed a lower V_max and K_m than the low N-use efficient ones (NCo376 and N36). Based on this finding, it was suggested that the N-use efficient designation (from pot and field trials) may not be ascribed solely to N uptake. Assessment of the relative preference index (RPI) for NO₃ ^?-N and NH₄ ⁺-N uptake revealed that, at present, the RPI has no application in sugarcane due to its preferential uptake of NH₄ ⁺-N.     

Indirect N2O emissions from shallow groundwater in an agricultural catchment (Seine Basin, France)

Production and accumulation of nitrous oxide (N₂O), a major greenhouse gas, in shallow groundwater might contribute to indirect N₂O emissions to the atmosphere (e.g., when groundwater flows into a stream or a river). The Intergovernmental Panel on Climate Change (IPCC) has attributed an emission factor (EF_5g) for N₂O, associated with nitrate leaching in groundwater and drainage ditches—0.0025 (corresponding to 0.25% of N leached which is emitted as N₂O)—although this is the subject of considerable uncertainty. We investigated and quantified the transport and fate of nitrate (NO₃ ^?) and dissolved nitrous oxide from crop fields to groundwater and surface water over a 2-year period (monitoring from April 2008 to April 2010) in a transect from a plateau to the river with three piezometers. In groundwater, nitrate concentrations ranged from 1.0 to 22.7 mg NO₃ ^?–N l^?1 (from 2.8 to 37.5 mg NO₃ ^?–N l^?1 in the river) and dissolved N₂O from 0.2 to 101.0 μg N₂O–N l^?1 (and from 0.2 to 2.9 μg N₂O–N l^?1 in the river). From these measurements, we estimated an emission factor of EF_5g = 0.0026 (similar to the value currently used by the IPCC) and an annual indirect N₂O flux from groundwater of 0.035 kg N₂O–N ha^?1 year^?1, i.e., 1.8% of the previously measured direct N₂O flux from agricultural soils.     

Distribution of surface soil mercury of Wuda old mining area,Inner Mongolia,China

In this study, mercury (Hg) concentrations in dustfall and topsoil were investigated. Three hundred forty-four samples were collected, including dustfall and topsoil samples, across an area of ～180 km² in Wuda, China. Dustfall Hg concentration in Wuda ranged from 10 to 6453 ng·g^?1_, with an average of 305 ng·g^?1, and topsoil Hg concentration ranged from 3 to 1537 ng·g^?1, with an average value of 135 ng·g^?1. The average dustfall Hg concentrations in the coalfield, industrial park, and urban areas were 289 ng·g^?1, 809 ng·g^?1, and 160 ng·g^?1, respectively, and the corresponding average topsoil Hg concentrations were 216 ng·g^?1, 242 ng·g^?1, and 91 ng·g^?1. Hg concentrations were significantly higher in the coalfield, industrial park, and urban areas compared with background values for Wuda and China tide soil. The coal Hg concentrations ranged from 273 to 346 ng·g^?1, with an average value of 317 ng·g^?1. Comparison of the Hg concentrations of Wuda coal with other regions and countries, indicated that Hg concentrations were significantly enriched in coal, highlighting that coal is the primary Hg source for Wuda District. While coal fires provided the primary source of Hg, some higher Hg values were caused by factors such as gangue hills and coalfield topography, the use of activated carbon with HgCl₂ as a catalyst in the industrial park, and several coal washeries in wasteland areas. In addition to atmospheric Hg, underground coal seam emissions served as another potential Hg source in the coalfield. The surface soil Hg in the coalfield and industrial park areas should be given closer attention in the future.     

Microdistribution of major to trace elements between roots of Halimione portulacoides and host sediments (Tagus estuary marsh,Portugal)

Aim

This study presents a micrometre-scale map of the elemental distribution within roots and surrounding sediment of Halimione portulacoides of a contaminated salt marsh in the Tagus estuary.

Methods

Microprobe particle induced X-ray emission analysis was performed in sediment slices containing roots with tubular rhizoconcretions attached to host sediments.

Results

Strong concentration gradients were found particularly in the inner part of rhizoconcretions adjacent to the root wall. Local enrichment was observed in sediment interstices with Fe precipitates and other associated elements. A maximum of 55 % of Fe was measured near the concretion–root interface, with a decrease to <5 % in the host sediment. Maximum concentrations of P (3 %), As (1,200 μg g^?1) and Zn (3,000 μg g^?1) were registered in concretions, one order of magnitude above the values of the host sediment. The elemental concentration profiles across roots showed that the epidermis was an efficient selective barrier to the entrance of elements. Fe and As were retained in the epidermis. The highest Cu and Zn concentrations were also observed in the epidermis. However, the concentrations of Mn, Cu and Zn increased in the inner root.

Conclusions

As and Fe were mostly retained in the concretion, whereas P, Mn, Cu and Zn were mobilised by the root.     

Nitrogen removal in coastal sediments of the German Wadden Sea

Although sediments of the German Wadden Sea are suspected to eliminate a considerable share of nitrate delivered to the SE North Sea, their denitrification rates have not been systematically assessed. We determined N₂ production rates over seasonal cycles (February 2009–April 2010) at two locations with two sediments types each, the first site (Meldorf Bight) receiving nitrate during all seasons from the Elbe river plume, and a second site on the island of Sylt, where nitrate is depleted during summer months. In sediments from the Sylt site, N₂ production ranged from 15 to 32 μmol N₂ m^?2 h^?1 in the fine sand station and from 7 to 13 μmol N₂ m^?2 h^?1 in the coarse sand station; N₂ production was not detected when nitrate was depleted in May and July of 2009. N₂ production in the Meldorf Bight sediments were consistently detected at higher rates (58–130 μmol N₂ m^?2 h^?1 in the very fine sand station and between 14 and 30 μmol N₂ m^?2 h^?1 in the medium sand station). Analysis of ancillary parameters suggests that major factors controlling N₂ production in coastal sediments of the German Wadden Sea are the nitrate concentrations in the overlying water, the ambient temperature, and the organic matter content of the sediment. Extrapolating our spot measurements to the zone of nitrate availability and sediment types, we estimate an annual nitrogen removal rate around 16 kt N year^?1 for the entire northern sector of the German Wadden Sea area. This corresponds to 14% of the annual Elbe river nitrogen load.