The aqueous reduction of divalent mercury by sulfite

Divalent Hg is reduced by sulfite in aqueous solutions. The proposed mechanism involves the formation of an instable intermediate, HgSO₃, which decomposes to produce Hg⁺ which in turn is rapidly reduced to Hg⁰. The overall rate of the reaction is inversely dependent on the concentration of sulfite. This reaction may influence the concentration of Hg in cloud- and rain-water by reducing water soluble Hg²⁺ to volatile Hg⁰. At low concentrations of SO₂(g) (5 μg m⁻³, 25 °C), the rate of the conversion of Hg(SO₃)₂ ²⁻ to Hg⁰ becomes significant (> 1 % h⁻¹) at pH < 5.5. At higher S02 concentrations (500 pg m⁻³), the same rate is expected at pH < 4.5.     

Translocation of 203Hg labelled HgCl2 and CH3HgCl in an iron-humus podzol studied by radio-analytical techniques

Since increased Hg-concentrations in fish in lakes and rivers in northern Europe, northern parts of the U.S.A. and Canada were found, environmental Hg research has focused intensively on the factors determining leaching of mercury from soil into water systems. This article presents the results of a leaching experiment with undisturbed soil columns treated with HgCI₂ and CH₃HgCl using radio-analytical techniques. The columns were irrigated with rain of different acidity, rain volumes and irrigation intensities. The leaching of mercury was traced by detecting the vertical distribution of ²⁰³Hg in the soil profiles. Advantages and disadvantages of radioanalytical scanning techniques are discussed. The results of Hg leaching in the soil columns indicate a considerably stronger leaching of monomethyl mercury compared to inorganic mercury. Leaching of the two Hg-species is ruled by competition of H⁺ induced soil-Hg desorption with DOM-Hg complex formation; both being affected by rain acidity. Rain intensity had no visible effect on leaching of Hg²⁺ and CH₃Hg⁺. An extended rain duration increased the leaching of CH₃Hg⁺.     

Mercury Methylation Capacity and Removal of Hg Species from Aqueous Medium by Cyanobacteria

Most technologies used for decontamination presents good results for high concentrations, but limitations for lower ones. The desirable Hg concentration in the water is extremely low because of its toxicity. The aims of this study were to evaluate inorganic mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) toxicity in Nostoc paludosum, to assess the potential of this cyanobacteria strain to remove these Hg species from aqueous medium and also to investigate Hg methylation by the cyanobacteria. CH₃Hg⁺ determination was performed by gas chromatography-pyrolysis-atomic fluorescence spectrometry in cultures exposed to a concentration of 20 μg L^?1 for 30 days. Both Hg species were removed from the supernatant, ranging from 73 to 96% of Hg²⁺ and from 73 to 95% of CH₃Hg⁺. Ultrastructural Hg²⁺ effects in the cyanobacteria cells investigated by transmission electron microscopy revealed higher production of glycogen, cyanophycin, and intrathylacoidal spaces than the control group. When Hg was added to the culture in the form of CH₃Hg⁺, a decrease corresponding to approximately 60% of the initial concentration due to Hg volatilization was observed. The production of CH₃Hg⁺ by the cyanobacteria was detected in concentrations near the limit of detection (0.0025%) of the bioaccumulated THg. This is an advantage for biotechnological decontamination applications, as CH₃Hg⁺ is a very toxic specie and can be bioaccumulated and biomagnified. The results demonstrated that cyanobacteria cells are an efficient alternative to retain and/or remove Hg at low concentrations and they constitute a potential tool for a “final cleaning” of contaminated waste water.     

Potassium application reduces methane emission from a flooded field planted to rice

In a field study, potassium (K) applied as muriate of potash (MOP) significantly reduced methane (CH₄) emission from a flooded alluvial soil planted to rice. Cumulative emission was highest in control plots (125.34 kg CH₄ ha⁻¹), while the lowest emission was recorded in field plots receiving 30 kg K ha⁻¹ (63.81 kg CH₄ ha⁻¹), with a 49% reduction in CH₄ emission. Potassium application prevented a drop in the redox potential and reduced the contents of active reducing substances and Fe²⁺ content in the rhizosphere soil. Potassium amendment also inhibited methanogenic bacteria and stimulated methanotrophic bacterial population. Results suggest that, apart form producing higher plant biomass (both above- and underground) and grain yield, K amendment can effectively reduce CH₄ emission from flooded soil and could be developed into an effective mitigation option, especially in K-deficient soils.     

Mercury and Methylmercury in Upland and Wetland Acid Forest Soils of a Watershed in NE-Bavaria,Germany

Mercury (Hg) and methylmercury (CH₃Hg⁺) are global pollutants, but little information is available on their distribution and mobility in soils and catchments of Central Europe. The objective of this study was to investigate the pools and mobility of Hg and CH₃Hg⁺ in different forest soils. Upland and wetland forest soils, soil solutions and runoff were sampled. In upland soils the highest contents of total-Hg were found in the Oh layer of the forest floor (>400 ng g^-1) and the storage of non geogenic total-Hg (calculated for 60 cm depth) was about 120 mg/m². The storage of total-Hg was one order of magnitude lower in wetland soils as compared to the upland soils. By far the largest proportion of total-Hg in soils was bound in immobile fractions. The depth gradients of CH₃Hg⁺ did not correspond to those of total-Hg and the highest contents of CH₃Hg⁺ in upland soils were observed in the litter layer of the forest floor and in the Bsv horizon. The CH₃Hg⁺ content of the wetland soils was generally much higher in comparison with upland soils. CH₃Hg⁺ in solution was found in the forest floor percolates of upland soils and in wetland soils, but not in soil solutions from mineral soil horizons. Gaseous losses of Hg as well as methylation of Hg are likely in wetland soils. The latter might be highly relevant for CH₃Hg⁺ levels in runoff.     

Alkalinity of virgin solonetzes in northern Kalmykia (the Arshan-Zel’men Experimental Station)

The alkalinity of virgin solonetzes of the Ergeni Upland, Ergeni Plain, and Sarpinsk Lowland has been studied. These soils are characterized by the neutral salinization and the high alkalinity of the solonetzic and subsolonetzic horizons. The analysis of the soil water extracts demonstrated that the highest alkalinity is typical of the subsolonetzic horizons containing calcium carbonates (the B2 and BCca horizons). In the solonetzic horizons without CaCO₃, the alkalinity is lower despite the high exchangeable sodium percentage (up to 42%). The alkalinity of the solonetzic and subsolonetzic horizons may be conditioned by two processes: (a) the hydrolysis of the exchange complex (EC) containing sodium (EC-Na + H₂O ↔ EC-H + Na⁺ + OH⁻) and (b) the reaction of the ion exchange with the substitution of calcium for sodium in the exchange complex (EC-2Na + CaCO₃ ↔ EC-Ca + 2Na⁺ + CO₃²⁻). Calculations performed on the basis of the thermodynamic equations of the physicochemical equilibria according to the LIBRA program indicate that soda is absent in the solonetzic horizons, whose alkalinity is related to the carbonatecalcium equilibria. The high alkalinity of the calcareous subsolonetzic horizons is related to the presence of soda in combination with CaCO₃. The formation of soda in these horizons is due to the reaction of ion exchange described by Gedroits.     

Effects of option mitigating ammonia volatilization on CH4 and N2O emissions from a paddy field fertilized with anaerobically digested cattle slurry

A lysimeter experiment was carried out to evaluate the effects of the NH₃ volatilization mitigation by adding anaerobically digested cattle slurry (ADCS) alone, with wood vinegar (WV) or with a higher level of floodwater (HFW), on emissions of CH₄ and N₂O from a paddy soil planted with fodder rice. We have carried out the following treatments: (1) chemical fertilizer, (2) ADCS, (3) ADCS + WV, and (4) ADCS + HFW; the height of floodwater was 10 cm in the latter treatment, and it was 3 to 4 cm in the other treatments just before fertilizer applications. Nitrogen fertilizer rate added to soil in each treatment was 30 g NH₄⁺–N m⁻² (split in one basal and two top-dressing additions). Ammonia volatilization in the ADCS treatment was 2.7 g NH₃–N m⁻² throughout the growing season, and it was significantly reduced by 79% and 55% in the ADCS + WV and ADCS + HFW treatments, respectively. The total amount of CH₄ emitted in the ADCS treatment in the growing season was not significantly enhanced by the mitigation of NH₃ volatilization either by adding wood vinegar or by increasing the height of the floodwater. Negligible N₂O emissions were observed in all treatments during the growing period.     

Binding of methylmercury compounds by humic and fulvic acids

Humic and fulvic acids were isolated from Fawn Lake in Ontario and investigated by membrane dialysis for their ability to bind CH₃Hg⁺. By measuring the distribution of methylmercury compounds in and outside of the dialysis membrane, for the first time, binding capacities and conditional stability constants for CH₃Hg⁺ and humic acids could be calculated. Equilibrium between inner and outer dialysis solution was reached within 24 hours without losses of CH₃Hg⁺ in humic solution. The ratio of bound to unbound CH₃Hg⁺ increased with decreasing total CH₃Hg⁺ levels in the system. The percentage of free methylmercury compounds increased with decreasing pH. Fawn Lake humic acid showed two different binding sites. The conditional stability constant of the stronger site was calculated as 1.3 × 10¹². This site was able to bind 0.2 ng CH₃Hg⁺ per mg of humic acid.     

Reduced net atmospheric CH4 consumption is a sustained response to elevated CO2 in a temperate forest

We compared, from 2004 through 2006, rates of soil–atmosphere CH₄ exchange at permanently established sampling sites in a temperate forest exposed to ambient (control plots; ∼380 μL L⁻¹) or elevated (ambient + 200 μL L⁻¹) CO₂ since August 1996. A total of 880 observations showed net atmospheric CH₄ consumption (flux from the atmosphere to the soil) from all static chambers most of the time at rates varying from 0.02 mg m⁻² day⁻¹ to 4.5 mg m⁻² day⁻¹. However, we infrequently found net CH₄ production (flux from the soil to the atmosphere) at lower rates, 0.01 mg m⁻² day⁻¹ to 0.08 mg m⁻² day⁻¹. For the entire study, the mean (±SEM) rate of net CH₄ consumption in control plots was higher than the mean for CO₂-enriched plots, 0.55 (0.03) versus 0.51 (0.03) mg m⁻² day⁻¹. Annual rates of 184, 196, and 197 mg m⁻² for net CH₄ consumption at control plots during the three calendar years of this study were 19, 10, and 8% higher than comparable values for CO₂ enriched plots. Differences between treatments were significant in 2004 and 2005 and nearly significant in 2006. Volumetric soil water content was consistently higher at CO₂-enriched sites and a mixed-effects model identified a significant soil moisture x CO₂ interaction on net atmospheric CH₄ consumption. Increased soil moisture at CO₂-enriched sites likely increases diffusional resistance of surface soils and the frequency of anaerobic microsites supporting methanogenesis, resulting in reduced rates of net atmospheric CH₄ consumption. Our study extends our observations of reduced net atmospheric CH₄ consumption at CO₂-enriched plots to nearly five continuous years, suggesting that this is likely a sustained negative feedback to increasing atmospheric CO₂ at this site.     

Secondary salinity effects on soil microbial biomass

Secondary soil salinilization is a big problem in irrigated agriculture. We have studied the effects of irrigation-induced salinity on microbial biomass of soil under traditional cotton (Gossypium hirsutum L.) monoculture in Sayhunobod district of the Syr-Darya province of northwest Uzbekistan. Composite samples were randomly collected at 0–30 cm depth from weakly saline (2.3 ± 0.3 dS m⁻¹), moderately saline (5.6 ± 0.6 dS m⁻¹), and strongly saline (7.1 ± 0.6 dS m⁻¹) replicated fields, 2-mm sieved, and analyzed for pH, electrical conductivity, total C, organic C (C_Org), and extractable C, total N and P, and exchangeable ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻, and CO₃²⁻), microbial biomass (C_mic). The Na⁺ and Cl⁻ concentrations were 36-80% higher in strongly saline compared to weakly saline soil. The C_Org concentration was decreased by 10% and C_Ext by 40% by increasing soil salinity, whereas decrease in C_mic ranged from 18-42% and the percentage of C_Org present as C_mic from 8% to 26%. We conclude that irrigation-induced secondary salinity significantly affects soil chemical properties and the size of soil microflora.     

Effects of climatic factors and soil management on the methane flux in soils from annual and perennial energy crops

Methane flux rates were measured on a loamy sand soil within perennial and annual energy crops in northeast Germany. The study was performed in closed chambers between 2003 and 2005 with four measurements per week. A mixed linear model including the fixed effects of year, rotation period, crop and fertilisation was applied to determine the influence of climatic factors and soil management on the CH₄ flux. Soil water content and air temperature were added as co-variables. With the exception of air temperature, all fixed effects and the co-variable soil water content influenced the CH₄ flux. The soil of annual crops consumed 6.1 μg CH₄ m⁻² h⁻¹, significantly more than the soil of perennial crops with 4.3 μg CH₄ m⁻² h⁻¹. It is suggested that soil water content plays the key role in CH₄ flux between pedosphere and atmosphere. In the range of water contents between 5% and 15%, our model describes that a soil water content increase of 1% induces a net emission of 0.375 μg CH₄ m⁻² h⁻¹. As the soil of the experimental field was well-drained and aerobic, it represented a net sink for CH₄ throughout the study period.     

Response of CH<Subscript>4</Subscript> oxidation and methanotrophic diversity to NH<Subscript>4</Subscript><Superscript>+</Superscript> and CH<Subscript>4</Subscript> mixing ratios

Methane oxidising activity and community structure of 11, specifically targeted, methanotrophic species have been examined in an arable soil. Soils were sampled from three different field plots, receiving no fertilisation (C), compost (G) and mineral fertiliser (M), respectively. Incubation experiments were carried out with and without pre-incubation at elevated CH₄ mixing ratios (100 ml CH₄ l⁻¹) and with and without ammonium (100 mg N kg⁻¹) pre-incubation. Four months after fertilisation, plots C, G and M did not show significant differences in physicochemical properties and CH₄ oxidising activity. The total number of methanotrophs (determined as the sum the 11 specifically targeted methanotrophs) in the fresh soils was 17.0×10⁶, 13.7×10⁶ and 15.5×10⁶ cells g⁻¹ for treatment C, G and M, respectively. This corresponded to 0.11 to 0.32% of the total bacterial number. The CH₄ oxidising activity increased 10⁵-fold (20–26 mg CH₄ g⁻¹ h⁻¹), the total number of methanotrophs doubled (28–76×10⁶ cells g⁻¹) and the methanotrophic diversity markedly increased in treatments with a pre-incubation at elevated CH₄ concentrations. In all soils and treatments, type II methanotrophs (62–91%) outnumbered type I methanotrophs (9–38%). Methylocystis and Methylosinus species were always most abundant. After pre-incubation with ammonium, CH₄ oxidation was completely inhibited; however, no change in the methanotrophic community structure could be detected.     

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH₄⁺-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH₄⁺ concentration, an excess of NH₄⁺-N does not further increase NO₃⁻ formation rate in the soil, but only supports accumulation of NO₂⁻-N and gaseous losses of N as N₂O. Soils were amended with 10 to 500 μg NH₄⁺-N g⁻¹ soil. In both soils, addition of NH₄⁺-N increased production of NO₃⁻-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N₂O increased in the whole range of amendments in both soils. At the highest level of NH₄⁺-N addition, NO₂⁻-N accumulated in cattle-affected soil while NO₃⁻-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH₄⁺-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N₂O.     

Crop residues and fertilizer nitrogen influence residue decomposition and nitrous oxide emission from a Vertisol

Crop residues with high C/N ratio immobilize N released during decomposition in soil, thus reducing N losses through leaching, denitrification, and nitrous oxide (N₂O) emission. A laboratory incubation experiment was conducted for 84 days under controlled conditions (24°C and moisture content 55% of water-holding capacity) to study the influence of sugarcane, maize, sorghum, cotton and lucerne residues, and mineral N addition, on N mineralization–immobilization and N₂O emission. Residues were added at the rate of 3 t C ha⁻¹ to soil with, and without, 150 kg urea N ha⁻¹. The addition of sugarcane, maize, and sorghum residues without N fertilizer resulted in a significant immobilization of soil N. Amended soil had significantly (P < 0.05) lower NO₃⁻–N, which reached minimum values of 2.8 mg N kg⁻¹ for sugarcane (at day 28), 10.3 mg N kg⁻¹ for maize (day 7), and 5.9 mg N kg⁻¹ for sorghum (day 7), compared to 22.7 mg N kg⁻¹ for the unamended soil (day 7). During 84 days of incubation, the total mineral N in the residues + N treatments were decreased by 45 mg N kg⁻¹ in sugarcane, 34 mg kg⁻¹ in maize, 29 mg kg⁻¹ in sorghum, and 16 mg kg⁻¹ in cotton amended soil compared to soil + N fertilizer, although soil NO₃⁻–N increased by 7 mg kg⁻¹ in lucerne amended soil. The addition of residues also significantly increased amended soil microbial biomass C and N. Maximum emissions of N₂O from crop residue amended soils occurred in the first 4–5 days of incubation. Overall, after 84 days of incubation, the cumulative N₂O emission was 25% lower with cotton + N fertilizer, compared to soil + N fertilizer. The cumulative N₂O emission was significantly and positively correlated with NO₃⁻–N (r = 0.92, P < 0.01) and total mineral N (r = 0.93, P < 0.01) after 84 days of incubation, and had a weak but significant positive correlation with cumulative CO₂ in the first 3 and 5 days of incubation (r = 0.59, P < 0.05).     

Soil Degradation Due to Vicinal Intensive Hog Farming Operation Located in East Mediterranean

One of the main environmental impacts of concentrated animal feeding operations is the soil degradation in vicinity with the livestock breeding facilities due to substances such as ammonia emitted from the various stages of the process. Owing to the high temperatures of the Mediterranean ecosystems, the evolution of gasses is more extensive and the soil degradation is consequently more severe than those obtained in northern Europe. In this research, the soil degradation effects of a large meat-producing, processing, and packaging unit have been investigated. The investigated intensive hog farming operation (IHFO) is located at a limestone soil coastal area with sea to the north and hills to the south. Soil samples of the upper mineral soil were taken in various distances and directions from the IHFO boundaries. Thirteen experimental cycles were carried out in the duration of 1.5 years starting in March 2009 until October 2010. The soil samples were analyzed on pH and electrical conductivity (EC) values as well as NH₄ ⁺ and NO₃ ⁻ concentrations. Significantly higher concentrations of the two nitrogen forms were observed on samples at increasing proximity downwind from the farm (south). Southern soil average NH₄ ⁺ and NO₃ ⁻ concentrations ranged between 0.4–118 μg NH₄ ⁺-N g⁻¹ soil and 6.1–88.4 μg NO₃ ⁻-N g⁻¹ soil, respectively. The variation of emitted gasses depositions was clearly reflected in the average pH and EC values. Average pH and EC values downwind from IHFO boundaries varied between 7.1–8.2 and 140–268 μS/cm, respectively.     

Heterotrophic nitrification is the predominant NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> production mechanism in coniferous but not broad-leaf acid forest soil in subtropical China

A study was carried out to investigate the potential gross nitrogen (N) transformations in natural secondary coniferous and evergreen broad-leaf forest soils in subtropical China. The simultaneously occurring gross N transformations in soil were quantified by a ¹⁵N tracing study. The results showed that N dynamics were dominated by NH₄⁺ turnover in both soils. The total mineralization (from labile and recalcitrant organic N) in the broad-leaf forest was more than twice the rate in the coniferous forest soil. The total rate of mineral N production (NH₄⁺ + NO₃⁻) from the large recalcitrant organic N pool was similar in the two forest soils. However, appreciable NO₃⁻ production was only observed in the coniferous forest soil due to heterotrophic nitrification (i.e. direct oxidation of organic N to NO₃⁻), whereas nitrification in broad-leaf forest was little (or negligible). Thus, a distinct shift occurred from predominantly NH₄⁺ production in the broad-leaf forest soil to a balanced production of NH₄⁺ and NO₃⁻ in the coniferous forest soil. This may be a mechanism to ensure an adequate supply of available mineral N in the coniferous forest soil and most likely reflects differences in microbial community patterns (possibly saprophytic, fungal, activities in coniferous soils). We show for the first time that the high nitrification rate in these soils may be of heterotrophic rather than autotrophic nature. Furthermore, high NO₃⁻ production was only apparent in the coniferous but not in broad-leaf forest soil. This highlights the association of vegetation type with the size and the activity of the SOM pools that ultimately determines whether only NH₄⁺ or also a high NO₃⁻ turnover is present.     

Increased moisture and methanogenesis contribute to reduced methane oxidation in elevated CO2 soils

Awareness of global warming has stimulated research on environmental controls of soil methane (CH₄) consumption and the effects of increasing atmospheric carbon dioxide (CO₂) on the terrestrial CH₄ sink. In this study, factors impacting soil CH₄ consumption were investigated using laboratory incubations of soils collected at the Free Air Carbon Transfer and Storage I site in the Duke Forest, NC, where plots have been exposed to ambient (370 μL L⁻¹) or elevated (ambient + 200 μL L⁻¹) CO₂ since August 1996. Over 1 year, nearly 90% of the 360 incubations showed net CH₄ consumption, confirming that CH₄-oxidizing (methanotrophic) bacteria were active. Soil moisture was significantly (p < 0.01) higher in the 25–30 cm layer of elevated CO₂ soils over the length of the study, but soil moisture was equal between CO₂ treatments in shallower soils. The increased soil moisture corresponded to decreased net CH₄ oxidation, as elevated CO₂ soils also oxidized 70% less CH₄ at the 25–30 cm depth compared to ambient CO₂ soils, while CH₄ consumption was equal between treatments in shallower soils. Soil moisture content predicted (p < 0.05) CH₄ consumption in upper layers of ambient CO₂ soils, but this relationship was not significant in elevated CO₂ soils at any depth, suggesting that environmental factors in addition to moisture were influencing net CH₄ oxidation under elevated CO₂. More than 6% of the activity assays showed net CH₄ production, and of these, 80% contained soils from elevated CO₂ plots. In addition, more than 50% of the CH₄-producing flasks from elevated CO₂ sites contained deeper (25–30 cm) soils. These results indicate that subsurface (25 cm+) CH₄ production contributes to decreased net CH₄ consumption under elevated CO₂ in otherwise aerobic soils.     

Mercury speciation in contaminated soils by thermal release analysis

Thermal release analysis of mercury species in contaminated soils was performed by temperature controlled continuous heating of the samples in a furnace coupled to an Atomic Absorption Spectrophotometer (AAS). It was shown that this method allows the identification of different redox states of Hg-species through their characteristic releasing temperature ranges. The method was applied to Hg-contaminated samples from an inactive chlor-alkali production plant in former East Germany (GER), and from a gold mining area in Poconé, Mato Grosso, Brazil (BRA), as well as synthetic soil samples obtained by spiking pre-heated soil matrices (GER and BRA) with the following mercury species: Hg⁰, Hg₂Cl₂, HgCl₂, HgO and HgS. The samples GER, in general, frequently showed the presence of Hg²⁺ probably bound to humic substances, in the case of samples with higher total carbon content. Only in highly contaminated samples (>3000 ppm of mercury) was Hg⁰ the predominant species. The samples BRA more frequently showed the presence of mercury species in the lower oxidation states, i.e. Hg¹⁺ in combination with Hg⁰. The method allows observing changes in Hg-speciation in the samples with time, mainly changes among the oxidation states Hg⁰, Hg¹⁺ and Hg²⁺. The treated GER matrix showed a stronger tendency to oxidise Hf-species than the BRA treated matrix, in which only added Hg⁰ is partially oxidised to Hg²⁺ and Hg¹⁺. In contrast, the BRA matrix showed a pronounced tendency to reduce spiked Hg²⁺ to Hg¹⁺. This may be the reason for the presence of Hg¹⁺ in the majority of original BRA samples. The method appears to be very useful to study speciation of mercury and its dynamics. It can be used as a tool for monitoring mercury oxidation states and/or reactions of mercury in soils.     

Seasonal variability in the Mercury speciation of Onondaga Lake (New York)

Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with H_g. Species determined included total Hg (Hg_t), reactive (‘ionic’) Hg (Hg_i), monomethylmercury (CH₃HgX), elemental Hg (Hg°) and dimethylmercury (CH₃)₂Hg). Onondaga Lake was found to contain very high levels of Hg_t (2 to 25 ng L^?1 Hg), Hg_j (0.5 to 10 ng L^?1 Hg), and CH₃HgX (0.3 to 7 ng L^?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L^?1 and (CH₃)₂Hg was near the limits of detection (?0.001 ng) L^?1 in most samples. The greatest CH₃HgX concentrations in the hypolimnion, as well as the largest gradients of both CH₃HgX and (Hg_t), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H₂S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH₃)₂Hg in these MeHg and sulfide-rich waters calls into question the belief that CH₃HgX and H₂S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle.     

Methanotroph abundance not affected by applications of animal urine and a nitrification inhibitor,dicyandiamide, in six grazed grassland soils

Purpose  

Methanotrophs are an important group of methane (CH₄)-oxidizing bacteria in the soil, which act as a major sink for the greenhouse gas, CH₄. In grazed grassland, one of the ecologically most sensitive areas is the animal urine patch soil, which is a major source of both nitrate (NO₃ ⁻) leaching and nitrous oxide (N₂O) emissions. Nitrification inhibitors, such as dicyandiamide (DCD), have been used to mitigate NO₃ ⁻ leaching and N₂O emissions in grazed pastures. However, it is not clear if the high nitrogen loading rate in the animal urine patch soil and the use of nitrification inhibitors would have an impact on the abundance of methanotrophs in grazed grassland soils. The purpose of this study was to determine the effect of animal urine and DCD on methanotroph abundance in grazed grassland soils.