Effects of pH on ferri-cyanide uptake and assimilation by several plants

This paper presents an investigation of the capacity of four different plants to remove and assimilate ferri-cyanide at different pH conditions. Detached roots of weeping willows (Salix babylonica L.), rice (Oryza sativa L. cv. JY 98), soybean (Glycine max L. cv. WH) and maize (Zea mays L. var. HK) were hydroponically exposed to ferri-cyanide in a closed system at 25?±?0.5°C for 24?h kept under darkness. Almost all applied ferri-cyanide was in the complex form in the hydroponic solution at pH????7.0 in the absence of light, while dissociation of ferri-cyanide to free cyanide and iron in solution was detected at pH????6.5. All plant species used were found to be able to remove and assimilate ferri-cyanide efficiently. The uptake and assimilation rates appeared to be inversely related to the pH, in which positive effects were observed at pH 6.0 and 6.5. Remarkable decreases in the assimilation rates were found at pH 8.0. Results presented here suggest that changes in solution pH have a substantial influence on not only the speciation of ferri-cyanide in the plant growth media, but also the uptake and assimilation mechanisms of ferri-cyanide by plants.     

Estimates of potential nitrate reductase activity in sediments: comparisons of two incubation methods and four inhibitors

Sediment samples, collected from a large shallow lake, Taihu, China, were incubated in two conditions (with and without air extraction) with regard to four soil enzyme’s inhibitors (dry and moist heat sterilizations, chloramphenicol and toluene) to estimate the potential nitrate reductase (Nar) activities. The objectives of paper were to define (1) whether to exclude air from the mixture of sediment and substrate solution prior to incubation was necessary, and (2) the efficacy of four inhibitors when assaying the enzyme. No significant difference between two incubation methods was found (P < 0.05), indicating that it is not necessary for estimating the potential Nar activity in the sediment to construct an initial anaerobic condition by air extractions prior to incubation. Toluene (1.0 mL/g sediment) and dry heat sterilization effectively and persistently inhibit the reduction of nitrate to nitrite during the incubation of 42 h. The authors concluded that both should be used as preferred inhibitors. In contrast, chloramphenicol (30 μg/g sediment) and moist heat sterilization inhibitors restrained nitrate reduction for <24 h only. In addition, it was found that no nitrite produced was substantially reduced in 24 h. Therefore, it should be needless for potential Nar activity estimation in the sediment to add 2,4-dinitrophenol to inhibit nitrite reductase.     

Chromium uptake by giant reed under rhizobacterial inhibition

The role of rhizospheric microbes of giant reed (Arundo donax L.) in Cr uptake from hydroponic culture was investigated. The control group was exposed to Cr in range of 25–100 mg L^?1 containing a control itself (with no metal addition). The experimental group received same Cr treatments, but in addition was exposed to antibiotic treatment in order to inhibit rhizospheric bacteria. The range of Cr accumulated in the roots was 3–7.65 mg L^?1; in stem it ranged 2.15–42.4 mg kg^?1; while in leaves, the range of Cr content was 13.7–15 mg kg^?1. Overall, Cr uptake in A. donax (without rhizobacterial inhibition) was root < leaf < stem. However, the amount of Cr uptake in plants with rhizobacterial inhibition was significantly less (~4.6-folds in 100 mg L^?1 Cr treatment) than those without such inhibition clearly highlighting that rhizobacterial inhibition decreased the Cr uptake. The experimental results clearly demonstrated that the inhibition of the rhizobacterial populations had great influence on the Cr uptake. However, Cr uptake could not be completely inhibited as some metal uptake was observed after the rhizobacterial inhibition although it was significantly less than the Cr uptake of plants without such inhibition.     

Variation of cadmium uptake, translocation among rice lines and detecting for potential cadmium-safe cultivars

Cadmium (Cd) pollution highly threats to rice consumption for humans. This study aims to investigate the variation of Cd uptake and translocation among rice lines and to screen cadmium-safe cultivars (CSCs). Total of 146 rice lines were grown in artificially Cd pollution hydroponics within 30 day followed by a pot culture in which 17 rice lines were planted and treated with different Cd levels until maturity. The results showed that Cd tolerance and Cd accumulation significantly (p < 0.05) varied among 146 rice lines in the hydroponics experiment as well as among the 17 rice lines in the followed pot culture. Cd contents of brown rice significantly correlated with Cd accumulations in plant and their translocation from vegetative organs to edible parts, implying that extremely attention should paid to Cd translocation and its influence factors for CSCs selection. IRBN95-90 and D26B of maintainer lines and Lu5278-I332, Lu17-T21712, Lu17-I2R60 of restorer lines were detected to be potential CSCs under 2 and 10 mg kg^?1 Cd level, which confirmed the feasibility of selection of CSCs from rice lines. Therefore, the study confirmed the variations of Cd uptake and translocation among rice lines and a combinatorial and recursive selection process is feasible and affordable to screen CSCs to reduce Cd risk for rice consumption.     

Quantification of photosynthetic inorganic carbon utilisation via a bidirectional stable carbon isotope tracer

The amount of bicarbonate utilised by plants is usually ignored because of limited measurement methods. Accordingly, this study quantified the photosynthetic assimilation of inorganic carbon (CO₂ and HCO₃ ^?) by plants. The net photosynthetic CO₂ assimilation (P _N), the photosynthetic assimilation of CO₂ and bicarbonate (P _N’), the proportion of increased leaf area (f _LA) and the stable carbon isotope composition (δ¹³C) of Orychophragmus violaceus (Ov) and Brassica juncea (Bj) under three bicarbonate levels (5, 10 and 15 mm NaHCO₃) were examined to determine the relationship among P _N, P _N’ and f _LA. P _N’, not P _N, changed synchronously with f _LA. Moreover, the proportions of exogenous bicarbonate and total bicarbonate (including exogenous bicarbonate and dissolved CO₂-generated bicarbonate) utilised by Ov were 2.27 % and 5.28 % at 5 mm bicarbonate, 7.06 % and 13.28 % at 10 mm bicarbonate, and 8.55 % and 17.31 % at 15 mm bicarbonate, respectively. Meanwhile, the proportions of exogenous bicarbonate and total bicarbonate utilised by Bj were 1.77 % and 3.28 % at 5 mm bicarbonate, 2.11 % and 3.10 % at 10 mm bicarbonate, and 2.36 % and 3.09 % at 15 mm bicarbonate, respectively. Therefore, the dissolved CO₂-generated bicarbonate and exogenous bicarbonate are important sources of inorganic carbon for plants.     

Salix acmophylla,Tamarix smyrnensis and Phragmites australis as biogeochemical indicators for copper deposits in Elazıǧ, Turkey

The flora of Maden Çayı valley grows in a soil medium which is heavily contaminated with Cu, Fe, Mn, Zn and other metals derived from waste discharges to the Maden Çayı (stream) from the Maden Cu Mining works. Soil, water and plant samples were collected from 47 sites (mostly along the Maden Çayı valley) and analysed for copper. In all the plant species, Cu was concentrated more in the twigs of the plants than in their leaves and flowers. Correlation coefficients (r) were calculated for the correlation between the concentrations of Cu in the twigs of plants and those of the corresponding soil. Statistics of correlation were as follows: Salix acmophylla r=0.93 (n=19, P<0.01), Tamarix smyrnensis r=0.93 (n=20, P<0.01) and Phragmites australis r=0.72 (n=18, P<0.01). Salix acmophylla, Tamarix smyrnensis and Phragmites australis are therefore good indicators of the copper concentrations in the soil and these species could be successfully used for biogeochemical prospecting. These species are typical and common species of the semi-arid Anatolian climate.     

Spatial variability of soil available phosphorus in a typical watershed in the source area of the middle Dan River,China

Phosphorus is an essential and common limiting element for plants. Phosphorus losses from agricultural production systems are known to contribute to accelerated eutrophication of natural waters. In this study, soil available phosphorus (SAP) content and SAP density were estimated based on a soil survey of a small watershed in the Dan River, China, and the spatial heterogeneity of SAP distribution and the impacts of land-use types, elevation, slope and aspect on SAP were assessed. Field sampling was carried out based on a 100 m × 100 m grid system overlaid on the topographic map of the study area, and samples were collected in three soil layers to a depth of 40 cm. A total of 190 sites were sampled, and 539 soil samples were collected. The results showed that classical kriging could successfully interpolate SAP content in the watershed. SAP content showed a downward trend with the increase in soil depth and the extent of SAP variability in the three soil layer is moderate. There were significant differences among the three soil layers (P < 0.01). The land use had a great impact on the SAP content. ANOVA indicated that the spatial variation of SAP contents under different land-use types was significant (P < 0.01). The SAP density of different land-use types followed the order of cropland > forestland > grassland. The mean SAP density of cropland, forestland and grassland at a depth of 0–40 cm was 4.28, 3.74 and 2.81 g/m², respectively. SAP and topographic factors showed that SAP content increased with decreasing altitude and slope gradient. The soil bulk density played a very important role in the assessment of SAP density. In conclusion, the soils in the source area of the middle Dan River would reduce SAP with conversions from cropland to forest or grassland.     

The Influence of Coastal Nutrients on Phytoplankton Productivity in a Shallow Low Inflow Estuary,Drakes Estero,California (USA)

Seasonal wind-driven upwelling along the U.S. West Coast supplies large concentrations of nitrogen to surface waters that drives high primary production. However, the influence of coastal upwelled nutrients on phytoplankton productivity in adjacent small estuaries and bays is poorly understood. This study was conducted in Drakes Estero, California, a low inflow estuary located in the Point Reyes National Seashore and the site of an oyster mariculture facility that produces 40 % of the oysters harvested in California. Measurements of nutrients, chlorophyll a, phytoplankton functional groups, and phytoplankton carbon and nitrogen uptake were made between May 2010 and June 2011. A sea-to-land gradient in nutrient concentrations was observed with elevated nitrate at the coast and higher ammonium at the landward region. Larger phytoplankton cells (>5 μm diameter) were dominant within the outer and middle Estero where phytoplankton primary productivity was fueled by nitrate and f-ratios were >0.5; the greatest primary production rates were in the middle Estero. Primary production was lowest within the inner Estero, where smaller phytoplankton cells (<5 μm) were dominant, and nitrogen uptake was dominated by ammonium. Phytoplankton blooms occurred at the outer and middle Estero and were dominated by diatoms during the spring and dry-upwelling seasons but dinoflagellates during the fall. Small flagellated algae (>2 μm) were dominant at the inner Estero where no blooms occurred. These results indicate that coastal nitrate and phytoplankton are imported into Drakes Estero and lead to periods of high new production that can support the oyster mariculture; a likely scenario also for other small estuaries and bays.     

Phytotoxicity assessment of γ-Fe2O3 nanoparticles on root elongation and growth of rice plant

This study was conducted to determine the phytotoxicity of 6 nm γ-Fe₂O₃ nanoparticles (IONPs) in terms of root elongation and the physiological performance of rice plants. Rice seeds (Oryza sativa L. var. Koshihikari) exposed to IONPs at 500, 1,000 and 2,000 mg/L, had a significantly higher root elongation than the control and its bulk counterparts (IOBKs), indicating that the effect can be nanospecific. In a 14-week greenhouse pot experiment, the CO₂ assimilation rate in IOBK and IONP-treated pots (500 and 1,000 mg/pot) decreased over time, with the decline (maximum 42.5 %) being less pronounced for IONPs, indicating that the effect cannot be inferred from the toxicity of nanoscale size iron oxide. Excessive adsorption of IONPs onto soil colloids with subsequent low water extractable iron was responsible for the unremarkable phytotoxic nature of IONPs in the rice plants. Amendment of IONPs coated with 20 mmol citric acid (IONPs-Cit) significantly diminished the CO₂ assimilation rate and the decrease was similar to its bulk counterpart (IOBKs-Cit). However, maximum shoot growth inhibition (37 %) was associated with the application of IOBKs-Cit. It was concluded that massive accumulations of Fe plaque on the root surfaces of IOBKs-Cit treatments due to a decline in the pH of rhizoplane soils compared to the IONPs-Cit treatments were responsible for the remarkable shoot growth reduction. This study provided evidence of the phytotoxicity of γ-Fe₂O₃ nanoparticles, demonstrating the lower toxicity of nanosized iron oxide compared to a microsized preparation under reductive conditions.     

Copper desorption kinetics in wheat (Triticum aestivum L.) rhizosphere in some sewage sludge amended soils

Rhizosphere has different chemical and biological properties from bulk soils. Information about copper (Cu) desorption characteristics in the rhizosphere soils is limited. The objectives of this study were to determine Cu desorption characteristics and the correlation of its parameters with Cu extracted by DTPA-TEA, AB-DTPA and Mehlich 3 in bulk and rhizosphere amended soils with sewage sludge (10 g of sewage sludge was added to 1 kg soil) under greenhouse conditions in a rhizobox. The kinetics of Cu desorption in the rhizosphere and bulk was determined by successive extraction with DTPA-TEA in a period of 1 to 504 h at 25 ± 1 °C. The results showed that Cu extracted using several chemical extractants in the rhizosphere were significantly (P < 0.05) lower than in the bulk amended soils. In addition, Cu extracted using successive extraction in the rhizosphere were significantly (P < 0.01) lower than in the bulk soils. The best model for describing extraction data for the bulk and rhizosphere soils was the parabolic diffusion equation. Desorption kinetics of Cu conformed fairly well to first order and power function models. The results indicated that Cu diffusion rate in the wheat rhizosphere soils lower than in the bulk soils. Cu desorption rate in parabolic diffusion ranged from 0.326 to 0.580 mg kg^?1 h^?1/2 in the bulk soils, while it ranged from 0.282 to 0.490 mg kg^?1 h^?1/2 in the rhizosphere soils. Significant correlation (P < 0.05) between determine R values of parabolic diffusion and Cu desorption during 504 h with extracted Cu using DTPA-TEA, AB-DTPA and Mehlich 3 were found in the bulk and the rhizosphere soils. The results of this research revealed that Cu desorption characteristics in the wheat rhizosphere soils are quite different from bulk soils amended with sewage sludge.     

Fate and transport of ethanol-blended dissolved BTEX hydrocarbons: a quantitative tracing study of a sand tank experiment

To estimate the behavior of ethanol-blended dissolved BTEX hydrocarbons in groundwater, a quantitative tracing study instead of qualitative analysis was carried out by using a large sand tank, into which 2-L solution including bromide, ethanol and dissolved BTEX was injected under a controlled hydraulic condition. Mean residence time (MRT), pore volume swept by solute (V _p), retardation coefficient (R) and biodegradation rate constant (k) of injected solutes were estimated. Compared with bromide that was used as a conservative tracer, ethanol and BTEX had shorter MRT and smaller V _p with the sequence of EtOH < T < E < m/p-X < o-X < B < Br. Biodegradation was confirmed as evidenced by the consumptions of dissolved oxygen (DO), nitrate and sulfate, and the production of acetate. The sequence of k as EtOH > T > E > m/p-X > o-X > B was just opposite to the sequences of MRT and V _p. The relationship among above sequences implies that MRT and V _p can be used as indicators to assess in situ biodegradability of a solute. Biodegradation of a reactive solute can make its MRT shortened and V _p shrunk. In addition, the sorption of ethanol could be neglected (R = 1.0), whereas BTEX compounds were adsorbed (R = 1.04–1.15). It should be noted that biodegradation of a solute can affect the estimation of its retardation coefficient. To our knowledge, this paper provides an available route to quantitatively estimate biodegradability of a solute in groundwater.     

Natural and man-made influences on suicides in northwestern Russia

Our main aim was to identify the impacts of natural (solar activity, geomagnetic disturbances) and man-made factors on suicides in northwestern Russia. Data on a total of 908 suicides in the town of Kirovsk (Murmansk oblast) were analyzed for the period from 1948 to 2010. The rates of suicides were analyzed with respect to seasons of the year. We have identified three maxima in the seasonal distribution of the number of suicides [March–May (P < 0.001), July (P = 0.006), October (P < 0.001)], which coincide with maxima in the distribution of the most intense (Ap > 150 nT) magnetic storms. Multi-taper method-spectrum analysis revealed periodicities (~9–10 and ~25 years) which may be related to the main cycles of solar activity. The periods of ~3.1–3.5 and ~2–2.3 years are probably the third and the fifth harmonics of 11-year solar cycle, respectively. These periods are correlating with similar periodic variations in geomagnetic aa-indexes and meteorological parameters. It was determined the statistically significant (r = 0.8; P = 0.005) relationship between suicide and Cu emissions from Cu–Ni smelters of Russian North for the period 1997–2009.     

Un « point chaud » sous le système du Rift syrien : données pétrologiques complémentaires sur les enclaves du volcanisme récent

Ultrabasic xenoliths (pyroxenites, lherzolites, harzburgites) in recent (Neogene–Quaternary) volcanoes have been studied in three localities within Syria: Jubates (North), Mhailbeh (Center), Tel Thannoun (South). P–T conditions of mineral equilibration have been estimated by pyroxene thermometry (temperature) and maximum CO₂ density in primary inclusions (minimum pressure). Pyroxenites equilibrate at significantly higher conditions (T about 1200 °C, P>15 kbar) than lherzolites and harzburgites (900<T<1100 °C, P between 10 and 15 kbar). All are within the spinel lherzolite field, whereas Cretaceous xenoliths originate within the garnet lherzolite field. To cite this article: A. Bilal, F. Sheleh, C. R. Geoscience 336 (2004).     

Effects of Tidal Flooding on Juvenile Willows

Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions.     

Particularités de la contamination crustale des phonolites : exemple du Velay oriental (Massif central)

Sr and Nd isotopic compositions of one trachyte, eight phonolites and five basalts have been measured. The isotopic characteristics of the trachyte can be explained by a combined assimilation–fractional crystallization process within an upper crustal magmatic chamber. Some phonolites display isotopic signatures identical to basalts, suggesting that they have been protected against any crustal assimilation during their formation. Some others have low Sr contents, whereas they are enriched in radiogenic Sr (0.70451<⁸⁷Sr/⁸⁶Sr_i<0.71192), and display basaltic ¹⁴³Nd/¹⁴⁴Nd ratios. Both observations could be explained by very strong alkali feldspar fractionation and by subsequent very low assimilation of surrounding rocks (between 0.3 and 4%) during intrusion. To cite this article: J.-M. Dautria et al., C. R. Geoscience 336 (2004).     

Zinc desorption kinetics in bean (Phaseolus vulgaris L.) rhizosphere in sewage sludge-amended calcareous soils

Desorption of Zinc (Zn) in the rhizosphere soil is the primary factor that affects bioavailability of Zn. To improve predictions of Zn availability in amended soil, it is important that time-dependent desorption behavior of Zn in the rhizosphere soil should be understood. The greenhouse experiment was performed to determine Zn desorption characteristics in the bulk and the bean rhizosphere soils amended with municipal sewage sludge (1 % w/w) using rhizobox. The kinetics of Zn desorption was determined by successive extraction with 10-mM citric acid in a period of 1–504 h at 25 ± 1 °C in the bulk and the rhizosphere soils. Moreover, Zn was extracted using three extractants (DTPA-TEA, AB-DTPA, and Mehlich 3) in the bulk and the rhizosphere soils. The results showed that Zn extracted and Zn desorption rate in the bean rhizosphere soils were significantly (P < 0.01) lower than in the bulk soils. The mean of Zn desorption in the bulk and the rhizosphere soils were 16.47 and 15.50 mg kg^?1, respectively. Desorption kinetics of Zn conformed fairly well to first-order, parabolic diffusion, and power function equations. The results of kinetics study indicated that desorption rate coefficients decreased in the rhizosphere soils compared to the bulk soils. The correlation studies showed that the rate constants in the power function equation were significantly correlated (P < 0.05) with Zn extracted using DTPA-TEA, AB-DTPA and Mehlich 3 in the bean rhizosphere and the bulk soils. The results of this research showed that Zn desorption in citric acid in the bean rhizosphere of amended soils were lower than the bulk of amended soils.     

High Sulfide Intrusion in Five Temperate Seagrasses Growing Under Contrasting Sediment Conditions

Five temperate seagrasses (Amphibolis antartica, Halophila ovalis, Posidonia australis, Posidonia sinuosa and Zostera nigricaulis) were surveyed along the south-west coast of Western Australia. These morphological different seagrasses grow in contrasting sediments with large variations in sedimentary organic matter, carbonate and iron contents. We tested if sulfur composition in the plants responded to sulfur dynamics in the sediments and if plant morphology affected the sulfur composition of the plants. The sediments were characterized by low sulfate reduction rates (<9 mmol m^?2day^?1), low concentrations of dissolved sulfides in the pore waters (<74 μM) and low burial of sulfides (total reducible sulfur <0.8 mol m^?2) in the sediments. However, all seagrasses showed high intrusion in the below-ground parts with up to 84 % of the sulfur derived from sedimentary sulfides. There were no direct links between sulfur in the plants and sulfur dynamics in the sediments, probably due to low iron contents in the sediments limiting the buffering capacity of the sediments and exposing the plants to sulfides despite low rates of production and low pools of sulfides. The intrusion was linked between plant compartments (roots, rhizomes and leaves) for the two small species (H. ovalis and Z. nigricaulis), whereas the intrusion into the leaves was limited for the larger species (P. australis and P. sinuosa) and for A. antarctica, where extensive rhizomes and roots and the long stem for A. antarctica separate the leaves from the sediment compartment. Elevated intrusion was observed at two study locations, where natural deposition of organic matter or nutrient enrichment may be contributing factors to enhanced sulfide pressure.     

Location-based environmental factors contributing to rainfall-triggered debris flows in the Ba river catchment,northwest Viti Levu island,Fiji

Mass movements in tropical Pacific small island developing states (SIDS) can be devastating although studies are relatively few and contributing environmental factors are not often investigated in detail. On 25 January 2012, following 3 days of heavy monsoonal rainfall (c. 550 mm) during a La Niña episode, more than 150 debris flows were triggered in the western part of the Ba river catchment of northwest Viti Levu island, Fiji. Reconnaissance field survey and geographical information system (GIS) analyses using high-resolution satellite imagery were carried out to investigate factors that may have led to the occurrence of the debris flows in the catchment. We evaluated the correlation between the density of mass movements (number of mass movements/km²) and several continuous variables using data measured within the GIS. There was a weak but significant positive correlation between mass movement density and elevation (r = 0.38, p value < 0.01), cyclonic precipitation (r = 0.37, p value < 0.01) and stream density (r = 0.31, p value < 0.01). Ninety-three percent of the mass movements occur within a plantation of Pinus caribaea (Caribbean pine) on slopes oriented mainly to the northeast and east on (trade) windward slopes and may be significant factors for their development. Although forests generally have a stabilizing effect on slopes, the plantation at Ba was a mature stand on its second plantation cycle and is a species that has a shallow rooting system making it more susceptible to failure.     

Nutrient-Replete Benthic Microalgae as a Source of Dissolved Organic Carbon to Coastal Waters

Dissolved organic carbon (DOC) flux dynamics were examined in the context of other biogeochemical cycles in intertidal sediments inhabited by benthic microalgae. In August 2003, gross oxygenic photosynthetic (GOP) rates, oxygen penetration depths, and benthic flux rates were quantified at seven sites along the Duplin River, GA, USA. Sediments contained abundant benthic microalgal (BMA) biomass with a maximum chlorophyll a concentration of 201 mg chl a m^?2. Oxygen microelectrodes were used to determine GOP rates and O₂ penetration depth, which were tightly correlated with light intensity. Baseline and ¹⁵N-nitrate amended benthic flux core incubations were employed to quantify benthic fluxes and to investigate the impact of BMA on sediment water exchange under nitrogen (N)-limited and N-replete conditions. Unamended sediments exhibited tight coupling between GOP and respiration and served as a sink for water column dissolved inorganic nitrogen (DIN) and a source of silicate and dissolved inorganic carbon (DIC). The BMA response to the N addition indicated sequential nutrient limitation, with N limitation followed by silicate limitation. In diel (light–dark) incubations, biological assimilation accounted for 83% to 150% of the nitrate uptake, while denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) accounted for <7%; in contrast, under dark conditions, DNF and DNRA accounted for >40% of the NO₃ ^? uptake. The N addition shifted the metabolic status of the sediments from a balance of autotrophy and heterotrophy to net autotrophy under diel conditions, and the sediments served as a sink for water column DIN, silicate, and DIC but became a source of DOC, suggesting that the increased BMA production was decoupled from sediment bacterial consumption of DOC.     

Geochemical and Sr–Nd–Pb isotopic insight into the low-Ti basalts from southern Paraná Igneous Province,Brazil: the role of crustal contamination

ABSTRACT

The south hinge of the Torres Syncline in southernmost Brazil hosts a volcanic succession of pahoehoe and rubbly Gramado-type lavas belonging to the ~132 Ma Paraná–Etendeka Igneous Province. We evaluate the geochemical and Sr–Nd–Pb isotopic variations using local-scale stratigraphy in order to discuss the petrogenesis of lava flows in a single magma type and to estimate the role of crustal contamination and the potential contaminants involved. The geochemical and isotopic variations along the lava pile are not systematic, implying that the magma chamber could have undergone successive replenishments of basaltic magma. The process of crustal assimilation explains the high and widespread initial Sr isotopic ratios at 0.707798–0.715751 and the very low ε_Nd at ?8.36 to ?5.41, with associated Pb isotopic variations (18.42 < ²⁰⁶Pb/²⁰⁴Pb < 18.86; 15.65 < ²⁰⁷Pb/²⁰⁴Pb < 15.71; 38.62 < ²⁰⁸Pb/²⁰⁴Pb < 39.37). The magmatic evolution of the SCSH and LJ lava flows begins with the storage of mafic liquids during a short period in the shallow-level magma chamber, which allowed the magma ascent with composition of olivine basalts. The continuous fractional crystallization within the magma chamber coupled with variable assimilation degrees of distinct contaminants with Palaeoproterozoic and Neoproterozoic ages, in addition to significant contribution of magma recharge, led to magma ascent with basaltic andesite composition that displays at surface a simple pahoehoe morphology. The continuous magma recharge in the magma chamber coupled with higher assimilation degree allowed the formation of basaltic andesite lavas with more contaminated isotopic signatures that exhibit rubbly morphology at the surface. Differentiation process of liquids coupled with the highest assimilation degrees of distinct contaminants during longer time in a shallow-level magma chamber, which is distinct from that where SCSH and LJ magmas have been stored, led to the formation of andesites of the Morro da Cruz section that exhibit the most contaminated isotopic signatures.