Ion content and ion excretion of Spartina anglica in relation to salinity and redox potential of salt marsh soil

Concentrations of Na, K, Ca, Mg, Fe, Mn, and Zn were determined in polluted estuarine (Western Scheldt) and non-polluted (Eastern Scheldt) salt marsh soil, in the shoot tissue of plants of Spartina anglica and in the excretion of the salt glands of Spartina anglica. Excretion of ions by the salt glands of Spartina anglica was analysed with increasing salinity (0, 300, and 500 mM NaCl) and with increasing values of the redox potential of the salt marsh soil (from ?300 mV to +600 mV). Salt glands of Spartina anglica, growing in containers filled with salt marsh soil in the greenhouse excreted Na-ions at a rate of 1.0–1.8 mmol Na⁺ g^?1 dry wt of the shoot tissue over a period of 18 days implying that about every 6–18 days the amount of Na⁺ present in the shoot tissue is being removed by the salt glands. The excretion rate of K-ions was 0.02–0.14 mmol g^?1 dry wt/18 days. Zinc ions are excreted by the salt glands to such a rate (0.03–0.11 μmol g^?1 dry wt/18 days) that every 36–900 days the amount of zinc present in the leaves is removed. There was no relation between excretion of Zn ions by the plants and the concentration of zinc in the soil. The excretion of Fe and Mn is reported and was found to be related to increasing values of the redox potential.     

Distribution of Trace Elements in Meromictic Pit Lake

Studies were conducted at the deepest location of the meromictic Piaseczno pit lake, southern Poland, which was created in abandoned sulphur opencast. Pearson correlation and PCA were used to established the relationship between the elements and physico-chemical parameters of the water, whereas discriminant test to study vertical and time differentiation of Cd, Pb, Sr, Cu, Zn, Mn, and Fe concentrations. The results indicated both vertical (except Cu and Zn) and time differentiations of studied elements in the lake water. The highest concentrations of Cd, Pb, and Sr were found in the monimolimnion, that of Mn and Fe in the anoxic water. Depth profiles of Cu and Zn did not show any pronounced trend. Pb and Sr distributions in the water were related to alkalinity, Cl^? and COD, Cd to alkalinity and Cl^?, Mn and Fe to the redox conditions, Mn to water pH, and Fe to the alkalinity. The upper (0–15 cm) layer of the sediment consisted mainly of S (24.2 Atom%), Fe (21.62%), Ca (18.4%), Si (14.3%), and (Al 6.3%) and reflected mainly processes proceeded in the anoxic water-sediment interface. Calculated accumulation coefficients (K _d) of the elements in the sediment are discussed.     

Nitrogen fixation (C2H2 reduction) in a salt marsh: Its relationship to temperature and an evaluation of an in situ chamber technique

A temperature controlled chamber for the in situ measurement of nitrogen fixation (acetylene reduction) in a vegetated salt marsh is described. Rates of acetylene reduction activity (ARA) were linear during a 9 h incubation. Measurements of acetylene penetration into the sediment indicate that the chamber technique measures ARA within the top 2–4 cm of the sediment column. This depth of penetration accounted for approx. 60% of the total ARA in the sediment column. Measurements of in situ ARA in three zones of a vegetated salt marsh (tall, medium and short height Spartina alterniflora) over a year were positively correlated with seasonal temperature variations. About 70–80% of the seasonal variation in ARA was explained by the Arrhenius relationship: ARA (μmol C₂H₄m⁻²h⁻¹)=α exp(−β/fT); where T is the ambient air temperature (°C) and α and β are constants. The constant α in this model increased from 20.1 to 40.5 while β increased from 17.5 to 20.7 along a transect from the tall to short height-form S. alterniflora communities. These differences suggest that there is spatial variability within the salt marsh among the variables that affect nitrogen fixation.     

Long-term observations of the vertical distributions of mineral elements and phosphorus dynamics in sediments in a shallow eutrophic lake in Japan

Purpose

To explore the mechanisms in the deposition and release of phosphorus (P) in the sediment of a shallow eutrophic lake using preserved samples, we investigated the vertical and temporal changes in P, manganese (Mn), sulfur (S), iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) in the sediment samples and the phosphate in the sediment pore water samples over a period of 6 years.

Materials and methods

The upper 15 cm of sediment from Lake Kasumigaura in Japan was collected monthly from 2003 to 2008 from the center of the lake. Sediment cores were divided into seven depth segments and were acid-digested for an elemental analysis via inductively coupled plasma atomic emission spectroscopy. Phosphate concentrations of the sediment pore water were determined using the molybdenum blue method. A multiple regression analysis was conducted by setting the P content as the response variable and Mn, S, Fe, Al, Ca, and Mg as explanatory variables.

Results and discussion

The results of the multiple regression analysis demonstrated that P co-precipitates with Fe and Al oxides and accumulates on the sediment surface. The vertical distributions of Mn and S suggest that Mn reduction occurs within the 0–1-cm-depth layer of the sediment and that iron sulfide is actively formed in the 6–10-cm-depth layer of the sediment. These findings imply that the layer in which ferric oxides are reduced to ferrous ions is present near the 1–6-cm-depth layer of the sediment. This layer corresponds to the layer in which the maximum phosphate concentration of the sediment pore water often occurred (the 2–6-cm-depth layer). These results indicate that vertical distributions of mineral elements are useful for assessing P dynamics in sediments.

Conclusions

The lake sediments record the dynamics of P in the sediment. Our analytical approach using long-term observation data demonstrated that the accumulation and release of P associated with a change in the redox state can be assessed based on the vertical distributions of mineral elements in the lake sediments.

     

Trace Element Concentrations in Saltmarsh Soils Strongly Affected by Wastes from Metal Sulphide Mining Areas

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L^?1 and maximum Zn 0.553 mg L^?1) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg^?1 of Mn, 62,280 mg kg^?1 of Zn, 16,845 mg kg^?1 of Pb, 77 mg kg^?1 of Cd, 418 mg kg^?1 of Cu and 725 mg kg^?1 of As), and soluble metals in the pore water reached 38.7 mg L^?1 for Zn, 3.15 mg L^?1 for Pb, 48.0 mg L^?1 for Mn, 0.61 mg L^?1 for Cd and 0.29 mg L^?1 for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility.     

Behavior of Metals Under Different Seasonal Conditions: Effects on the Quality of a Mexico–USA Border River

Spatial and seasonal mobilization trends of metals in surface water were evaluated in the US–Mexico San Pedro River (SPR). Water samples were collected at five sampling stations for the analysis of dissolved oxygen, pH, electric conductivity, sulfates, and metals (Cd, Cu, Fe, Mn, Pb, and Zn). Quality of the water was characterized through Ecological Criteria of Water Quality (ECWQ) established in Mexico and Water Quality Criteria (Environmental Protection Agency (EPA)). High total metal concentrations were detected as follows: Fe?>?Cu?>?Mn?>?Zn?>?Pb?>?Cd. Metal concentrations were slightly higher in dry season than in rainy season: Cd (below detection limit (BDL)–0.21 mg L^?1), Cu (BDL–13 mg L^?1), Fe (0.16–345 mg L^?1), Mn (0.12–52 mg L^?1), Pb (BDL–0.48 mg L^?1), and Zn (0.03–17.8 mg L^?1). Low pH and dissolved oxygen values as well as high sulfate content were detected in both seasons. High values of metals (Cd, Cu, Fe, Mn, Pb, Zn) were detected at station E1 representing pollution source, as well as at stations E2 (Cd, Cu, Fe, Mn), E3 (Fe, Mn, Pb), and E4 and E5 (Fe, Mn). Detected concentrations exceeded maximum permissible established in ECWQ and Water Quality Criteria (EPA). Efflorescence salts on sediments in the dry season could increase levels of metals in water column. This study provides valuable information on the potential mobility of metals in surface water of SPR located in an arid environment where transport processes are strongly linked to climate. The information derived from this study should help the regional and national authorities to address present environmental regulations.     

Seasonal Variations in Vertical Redox Stratification and Potential Influence on Trace Metal Speciation in Minerotrophic Peat Sediments

Seasonal variations in pore water and solid phase geochemistry were investigated in urbanized minerotrophic peat sediments located in southwestern Michigan, USA. Sediment pore waters were collected anaerobically, using pore water equilibrators with dialysis membranes (“peepers”) and analyzed for pH, alkalinity, dissolved ΣPO₄ ^?3, ΣNH₄ ⁺, ΣS^?2, SO₄ ^?2, Fe⁺³, Fe⁺², and Mn⁺² at 1-2 cm intervals to a depth of 50 cm. Cores collected adjacent to the peepers during all four seasons were analyzed for reactive solid phase Fe according to extraction methods proposed by Kostka and Luther (1994). The association of Fe and trace metals (Mn, Pb, Zn, Cu, Cr, Co, Cd, U) with operationally defined solid phase fractions (carbonates, iron and manganese oxides, sulfides/organics and residual) was assessed for cores extracted during winter and spring using extraction methods proposed by Tessier et al. (1979, 1982). Pore water Fe and S data demonstrate a clear seasonal variation in redox stratification of these sediments. The redox stratification becomes more compressed in spring and summer, with relatively more reducing conditions closer to the sediment water interface (SWI), and less reducing conditions near the SWI in fall and winter. In the upper 10–15 cm of sediment, the pool of ascorbate extractable Fe, thought to be indicative of reactive Fe(III) oxides, diminishes during spring and summer, in agreement with seasonal changes in redox stratification indicated by the pore water data. Tessier extractions indicate that the total extractable quantity of all metals analyzed in this study decrease with depth, and that the majority of the non-residual Fe, Pb, Zn, Cu, Cr, Co, Cd, and U is typically associated with the sulfide/organic fraction of the sediments at all depths. Non-residual Mn, in contrast, is significantly associated with carbonates in the upper 15–25 cm of the sediment, and predominantly associated with the sulfide/organic fraction only in deeper sediments.     

Responses of nitrogen cycling and related microorganisms to brackish wetlands formed by evapotranspiration

Elevated evapotranspiration due to warmer air temperature could raise salinity and nutrient levels of some inland wetlands, potentially impacting nitrogen cycling. To characterize the impact of high evapotranspiration on soil microbial nitrogen cycling in inland wetlands, we compared freshwater and brackish marsh(or non-marsh) wetlands in terms of sediment ammonia-oxidizing rate(AOR), denitrifying rate(DR), and related microbial communities in a typical inland basin, the Hulun Lake basin, in Chi...     

Controlled experimental acidification of lake sediments and resulting trace metal behavior

Severe stream water acidification occurs at higher altitudes (> 600 m a.s.l.) in the Western Harz mountains in Northern Germany. Since 1986 an interdisciplinary research team has followed the fate of pollutants in the 50 km² catchment of an important drinking water reservoir (Lake Söse). An acidification experiment has estimated the role of the remobilization of selected elements from the lake sediments via acidification. Aquaria were used to monitor the effects of a stepwise acidification (from the natural pH of 6.5 to 5.0, 4.0 and 3.0) of the water column over a reconstituted sediment layer. The sediment chemistry has been analyzed before and after the acidification by XRF. The water chemistry was sampled at time intervals and analyzed by ICP-MS. With a pH drop from 6.5 to 3.0, many elements increase in concentration in the water of the acidified basins. Enrichment factors were: Al (5000), Ba (10), Cd (220), Co (800), Cu (170), Ni (90), Pb (5000), and Zn (400). This corresponds fairly well with the field data. Al, Cd, Fe, Mn, and Pb exceed German drinking water limits at pH 4.0. The combined high concentrations (μg L^?1) of Al (1000–2600), Cd (2–4), Cu (4–7), Pb (30–60), and Zn (100–300) in the water column of the acidified streams are not only toxic for fish but also for many other aquatic organisms. Chemical changes in the sediment are not significant within the experimental setup.     

Gypsum and water management interactions for revegetation and productivity improvement of brackish marsh in Louisiana

Abstract

A field study evaluating the effects of gypsum and water management on the survival, yield, and protein content of selected species of marsh vegetation was conducted on an open area inundated by brackish water near Hackberry, Cameron Parish, Louisiana. The overall growth and yield response of four species of marsh vegetation: joint grass (Paspalum vaginatum SW.), marsh hay cordgrass (Spartina patens Muh L.), salt grass (Distichlis spicata L.), and American three square (Scirpus americanus Pers.) to gypsum addition (0 versus 7 Mg/ha) and water management (flooded versus non‐flooded plots) were statistically evaluated.

Soil drying was detrimental to the overall growth and yield of all marsh vegetation. There was zero plant survival in the non‐flooded plots except the marsh hay cordgrass with a survival rate of 32.8 %.

Plots receiving 7 Mg gypsum/ha had significantly higher dry matter production than the control. Gypsum application increased dry yield of joint grass (5.44 to 8.08 Mg/ha), marsh hay cordgrass (1.90 to 6.91 Mg/ha), salt grass (0.97 to 2.79 Mg/ha) and three‐square (1.55 to 2.84 Mg/ha) in flooded plots. The yield of marsh hay cordgrass, the only surviving species in the non‐flooded plots, produced a yield increase of 0.40 Mg/ha in response to gypsum. Significantly higher survival rates were observed in flooded plots treated with gypsum than in the non‐flooded plots receiving no gypsum. The mean survival rate for the gypsum‐ treated plots was 68.2%, as opposed to 21.9% for the untreated plots.     

Pollutants in drainage channels following long‐term application of Mancozeb to banana plantations in southeastern Mexico

The aim of this study was to investigate how long‐term Mancozeb application to banana plantations affects the occurrence of pollutants in drainage‐channel sediment and water under tropical conditions. We estimated the possible accumulation of Mancozeb's principal metabolite ethylenethiourea (ETU), as well as manganese (Mn) and zinc (Zn) as components in channel sediment and water. We took samples during the tropical‐rainfall season and the low‐rainfall season. For sediment samples, we determined the contents of ETU, Mn, and Zn. For water samples, we determined the concentration of ETU. Additionally, we took water samples from a runnel that is the receiving body of hydraulic flow from the system. In both seasons, ETU in the sediment was near the detection limit (0.01 mg kg^–1) and did not show any accumulation. However, Mn in sediment at all sampling sites exceeded the threshold values for aquatic life of 630 mg kg^–1 with values between 635 and 7256 mg kg^–1. The Zn concentrations in sediment varied from 87 to 190 mg kg^–1 and exceeded the threshold values for aquatic life of 98 mg kg^–1 at several sites. Furthermore, we determined an accumulation of these heavy metals in the sediments of the banana‐planted zone in comparison with sediments in pasture reference sites. In contrast to the low concentration of ETU in sediment, its concentration in drainage and runnel water (5.9–13.8 μg L^–1) exceeded the EU threshold value for drinking water (0.1 μg L^–1) by up to nearly 140 times. However, the threshold value for aquatic life was not exceeded. We conclude that long‐term Mancozeb application does lead to a severe accumulation of Mn in sediments and of ETU in surface water. New strategies should be used to control black Sigatoka, including integrated methods of pest control so that long‐term negative effects on the environment can be avoided.     

Metal fluxes at the sediment–water interface in rivers in the Turvo/Grande drainage basin, S?o Paulo State, Brazil

Purpose

The Turvo/Grande drainage basin (TGDB), located in the northwestern region of S?o Paulo state, covers an area of 15,983?km². The region is typically regarded as agricultural by the S?o Paulo State Environmental Agency, but the industrial area is expanding, and some studies have shown that metal concentrations in water can be higher than the values regulated by Brazilian law. Therefore, the aim of this study was to assess the role of sediments as a source or a sink of metals for drainage basin management.

Materials and methods

Interstitial water from different sediment depths (0?C42?cm) and the sediment?Cwater interface and sediment core samples were collected in February and July 2010 from the Preto, Turvo, and Grande rivers. Quantification of Cr, Cu, Fe, Mn, Ni, and Pb in these samples was performed by graphite furnace or flame atomic absorption spectrometry. Metal diffusive flux estimation from sediment into the overlying water was calculated by Fick??s First Law of Diffusion.

Results and discussion

The fluxes of all metals for the three rivers were positive, indicating diffusion into the overlying water. Ni and Pb showed the lowest diffusive fluxes, which ranged from 2.4 to 3,978???g?m^?2?day^?1 for Ni and from ?0.1 to 1,597???g?m^?2?day^?1 for Pb. In turn, Cu and Cr were subject to the largest transfer to water, especially in the dry season (Cr, 4.5?C7,673???g?m^?2?day^?1; Cu, 1.3?C14,145???g?m^?2?day^?1). The Preto River (urban area) showed smaller fluxes than the Grande River (agricultural area), and the values of the latter were higher than those found in other impacted areas of the world.

Conclusions

The diffusive fluxes indicate that sediments from the TGDB act as a source of metals for the water column, with increased export of metals, particularly Cr and Ni, from the sediment into the overlying water during the dry season.     

Biogeochemical Cycle of Mercury and Methylmercury in Two Highly Contaminated Areas of Tagus Estuary (Portugal)

Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g^?1 and 0.76–201 ng g^?1, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L^?1, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year^?1 and an MMHg deposition of up to ca. 6000 mg year^?1. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.     

Initiale Marschbodenentwicklung aus brackigen Sedimenten des Dollarts an der südwestlichen Nordseeküste

Initial marsh soil development from brackish sediments The initial marsh soil development from brackish sediments was investigated in a transect from the tidal flat to the dike in the southeast Dollart (Lower Saxony, Germany). Oxidized morphological features increased from the tidal flat to the dike. Simultaneously the bulk density increased from 0.57 g cm^—3 to 1.12 g cm^—3 and the water content decreased from 78.8 % to 54.9 %. The soils closest to the tidal flat were massive, those closest to the dike had a crumble structure. The clay/carbonate ratio increased slightly from 3.3 to 4.8 in the same succession as well as the C/N ratio from 13.9 to 15.6. Likewise the salinity decreased from 7.8 ‰ to 1.5 ‰ and the dominance of Na was replaced by Ca within the pool of exchangeable and soluble cations. The data indicate initial processes of marsh soil development: structure forming, settlement, aeration, salt and lime loss, decomposition and changing ratios of adsorbed cations. Similar to marine developments the soils will enter the terrestrial phase as carbonate containing soils not characterized by the brackish sedimentation conditions. For the initial development of today old marshland soils (”︁Kleimarshes”) from brackish sediments, in contrast, it is likely, that they were already free of carbonate when entering the terrestrial phase. This is explained by long‐term reduction and oxidation of sulfur and low sedimentation rates.     

Crop Residue Effects on Total and Dissolved Losses of Fe,Mn, Cu,and Zn by Runoff

Runoff may cause losses of micronutrients from soils. This can result in environmental problems such as contaminant transfers to water or a decrease in soil fertility. Appropriate soil management may reduce these micronutrient losses. This study examined the effect of applying crop residues to the soil surface on iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) losses by runoff. Runoff and sediment yield were measured on 1-m² plots using a rainfall simulator with constant 65 mm h^?1 intensity. Eight successive rainfall applications were performed at 65 mm each. Corn (Zea mays L.) straw was applied to plots at rates ranging from 0 to 8 t ha^?1. Both total and dissolved concentrations of the micronutrients studied were decreased by corn straw applications. After 520 mm cumulative rainfall, total soil losses ranged from 150 to 15354 kg ha^?1 depending on the amount of corn straw applied. Total micronutrient concentrations in runoff were as follows: Fe from 14.98 to 611.12 mg L^?1, Mn from 0.03 to 0.61 mg L^?1, Cu from 0.10 to 1.43 mg L^?1, and Zn from 0.21 to 5.45 mg L^?1. The relative contribution of the dissolved fraction to the total micronutrient content loss was low, but varied depending on the nutrient, being less than 1 percent for Fe and Mn and almost 10 percent for Zn. Total and dissolved concentrations in runoff of the studied elements decreased exponentially as the rate of applied corn straw increased. In conclusion, the addition of corn straw to soil reduced micronutrient losses.     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Production of gaseous mercury in tropical hydromorphic soils in the presence of ferrous iron: a laboratory study

In this paper, we demonstrate that reduction of Hg(II) to Hg⁰ under anaerobic conditions, followed by volatilization of Hg⁰ to the atmosphere, might be responsible for the removal of Hg from tropical hydromorphic soils. We conducted a series of kinetic batch experiments in which we added Hg(II) to anoxic suspensions of a soil clay fraction and haematite nanoparticles. The clay fraction came from three depths in a hydromorphic soil by the Leblond River in French Guiana, South America: close to the upper and lower boundaries (30–40 cm and 90–100 cm) and within the central part (60–70 cm) of the frequently water‐saturated clay horizon. We prepared a second set of soil clay fraction suspensions with Fe(III) citrate, whose reduction acted as a source of dissolved Fe(II) to investigate the influence of Fe(II) on the production of Hg⁰. Reduction of Hg(II) to Hg⁰ occurred with all samples amended with Fe(III) citrate. Laboratory experiments with haematite suspensions demonstrated that adsorption of Fe(II) to the haematite surface created very reactive sites for the reduction of Hg(II), while in the absence of haematite particles, no production of Hg⁰ occurred. The greatest production of Hg⁰ was found for the depth intervals 30–40 cm and 90–100 cm, where the total mercury concentration exhibits a local minimum. The observed pseudo‐first order rate constants for the 90–100 cm depth sample were close to rate constants reported for abiotic reduction of Hg(II) by Fe(II) adsorbed on mineral surfaces. Significant production of Hg⁰ was found for the 90–100 cm depth interval sample, both with and without Fe(III) citrate. A biotic pathway as well as abiotic reduction by Fe(II) might be involved in the reduction of Hg(II) to Hg⁰.     

Response of bean micronutrient nutrition to arsenic and salinity

The effects of different levels of arsenic (As) and salinity on bean plant (Phaseolus vulgaris L., cv. Buenos Aires) nutrition were investigated. We studied the processes of absorption and accumulation of chloride (Cl) and micronutrient elements: boron (B), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn). The experiment was performed in soilless culture at two levels of As: 2 and 5 mg As L^‐1 [added as sodium arsenite (NaAsO₂)], and three saline levels [only sodium chloride (NaCl) was added]: 1, 2, and 4 dSm^‐1. Sodium arsenite and NaCl significantly affected micronutrients allocation within the bean plant at levels used in this study. Arsenite depressed Mn and Cl concentrations in the root, whereas root B, Cu, and Zn levels were increased. Boron, Cu, Fe, and Cl concentrations were significantly higher in As‐stressed plants compared with controls. The addition of NaCl increased the Cl and Mn concentrations in roots and Cl, Fe, and Mn in leaves.     

Evaluation of chemical amendments to control phosphorus losses from dairy slurry

Land application of dairy slurry can result in incidental losses of phosphorus (P) to runoff in addition to increased loss of P from soil as a result of a buildup in soil test P (STP). An agitator test was used to identify the most effective amendments to reduce dissolved reactive phosphorus (DRP) loss from the soil surface after land application of chemically amended dairy cattle slurry. This test involved adding slurry mixed with various amendments (mixed in a beaker using a jar test flocculator at 100 rpm), to intact soil samples at approximate field capacity. Slurry/amended slurry was applied with a spatula, submerged with overlying water and then mixed to simulate overland flow. In order of effectiveness, at optimum application rates, ferric chloride (FeCl₂) reduced the DRP in overlying water by 88%, aluminium chloride (AlCl₂) by 87%, alum (Al₂(SO₄)₃·nH₂O) by 83%, lime by 81%, aluminium water treatment residuals (Al‐WTR; sieved to <2 mm) by 77%, flyash by 72%, flue gas desulphurization by‐product by 72% and Al‐WTR sludge by 71%. Ferric chloride (€4.82/m³ treated slurry) was the most cost‐effective chemical amendment. However, Al compounds are preferred owing to stability of Al–P compared with Fe–P bonds. Alum is less expensive than AlCl₂ (€6.67/m³), but the risk of effervescence needs further investigation at field‐scale. Phosphorus sorbing materials (PSM) were not as efficient as chemicals in reducing DRP in overlying water. The amendments all reduced P loss from dairy slurry, but the feasibility of these amendments may be limited because of the cost of treatment.     

Geochemistry of Manganese in Neutral to Alkaline Soils of Punjab,Northwest India and Its Availability to Wheat and Rice Plants

Manganese (Mn) release in 18 soil–water suspensions after their equilibration for 24 and 240 h periods at 25°C was studied in a laboratory experiment. Total dissolved Mn released into the soil solution was observed to increase from a range of 0.03–0.41 mg L^?1 (mean = 0.13 mg L^?1) to a range of 0.45–44.44 mg L^?1 (mean = 22.40 mg L^?1) with the increase in incubation periods from 24 to 240 h, respectively. The increase in Mn released was observed to be related with the redox potential (pe) induced by incubation conditions. After 24 h of equilibration period, pe of soil–water suspension ranged from ?1.75 to 0.77 (mean = ?0.24). Increasing the incubation period to 240 h, pe of soil–water suspensions declined in the range of ?4.49 to ?2.74 (mean = ?3.29). Laboratory results of redox pe and corresponding dissolved manganese concentrations of some soil–water equilibrated systems were compared with the leaf Mn content in wheat and rice plants grown in the fields, from where soil samples were collected for laboratory experiment. These results demonstrated that decline in pe due to longer equilibration period (240 h) of soil–water systems in the laboratory experiment or keeping standing water for a couple of weeks in the fields for cultivation of rice crop results in higher release of Mn and eventually its higher uptake in rice than in wheat plants. Leaf manganese content in rice ranged from 94 to 185 mg kg^?1, which was markedly higher than its range from 25 to 62 mg kg^?1 found in the wheat grown at 10 different sites. Pourbaix diagrams were drawn for different soil–water systems containing carbonate, phosphate, or sulfate along with manganese. The presence of carbonate and phosphate anions along with manganese oxides minerals in the soil–water systems of all soils results in its precipitation as MnCO₃ and MnHPO₄, respectively, in both oxidized and reduced soil field environment. In Punjab, wheat and rice crops are generally cultivated on soils heavily fertilized with P fertilizers. The presence of phosphate anion with manganese oxides minerals in the soil–water systems of all soils results in the precipitation MnHPO₄ in both oxidized and reduced soil field environment. Thus, in P-fertilized soil, MnHPO₄ compound is even more predominant than aqueous Mn²⁺ and its solubility actually controlled the availability of Mn²⁺ to plants.