Microbial decomposition of leached or extracted dissolved organic carbon and nitrogen from pasture soils

Microbial decomposition of extracted and leached dissolved organic carbon (DOC) and nitrogen (DON) was demonstrated from three pasture soils in laboratory incubation studies. DOC concentration in water extracts ranged between 29 and 148 mg C L^?1 and DON concentration ranged between 2 and 63 mg N L^?1. Between 17 and 61 % of the DOC in the water extracts were respired as CO₂ by microbes by day 36. DON concentrations in the extracts declined more rapidly than DOC. Within the first 21 days of incubation, the concentration of DON was near zero without any significant change in the concentration of NO₃ ^? or NH₄ ⁺, indicating that microbes had utilized the organic pool of N preferentially. Decomposition of leached DOC (ranged between 7 and 66 mg C L^?1) and DON (ranged between 6 and 11 mg N L^?1) collected from large lysimeters (with perennial pasture; 50 cm diameter?×?80 cm deep) followed a similar pattern to that observed with soil extracts. Approximately 28 to 61 % of the DOC in leachates were respired as CO₂ by day 49. The concentration of DON in the leachates declined to below 1 mg N L^?1 within 7–14 days of the incubation, consistent with the observations made with extractable DON. Our results clearly show that DOC and DON components of the dissolved organic matter in pasture soils, whether extracted or leached, are highly decomposable and bioavailable and will influence local ecosystem functions and nutrient balances in grazed pasture systems and receiving water bodies.     

Effect of plant-mediated oxygen supply and drainage on greenhouse gas emission from a tropical peatland in Central Kalimantan,Indonesia

Abstract

To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH₄) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH₄, carbon dioxide (CO₂) and nitrous oxide (N₂O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH₄ fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m^?2 h^?1) followed by the flooded forest sites (1.37 ± 2.03 mg C m^?2 h^?1), the drained burnt site (0.220 ± 0.143 mg C m^?2 h^?1), and the drained forest site (0.0084 ± 0.0321 mg C m^?2 h^?1). Dissolved CH₄ concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L^?1) followed by the drained burnt site (45.2 ± 29.8 μmol L^?1), the flooded forest sites (1.15 ± 1.38 μmol L^?1) and the drained forest site (0.860 ± 0.819 μmol L^?1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L^?1) compared to the burnt sites (4.0 ± 2.9 μmol L^?1). These results suggest that CH₄ produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO₂ fluxes were significantly higher in the drained forest site (340 ± 250 mg C m^?2 h^?1 with a water table level of ?20 to ?60 cm) than in the drained burnt site (108 ± 115 mg C m^?2 h^?1 with a water table level of ?15 to +10 cm). Dissolved CO₂ concentrations were 0.6–3.5 mmol L^?1, also highest in the drained forest site. These results suggested enhanced CO₂ emission by aerobic peat decomposition and plant respiration in the drained forest site. N₂O fluxes ranged from ?2.4 to ?8.7 μg N m^?2 h^?1 in the flooded sites and from 3.4 to 8.1 μg N m^?2 h^?1 in the drained sites. The negative N₂O fluxes might be caused by N₂O consumption by denitrification under flooded conditions. Dissolved N₂O concentrations were 0.005–0.22 μmol L^?1 but occurred at < 0.01 μmol L^?1 in most cases. GWP was mainly determined by CO₂ flux, with the highest levels in the drained forest site. Despite having almost the same CO₂ flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH₄ emission (not significant). N₂O fluxes made little contribution to GWP.     

Variations in concentrations of N and P forms in leachates from dried soils rewetted at different rates

The rate at which dried soils are rewetted can affect the quantities and forms of nutrients in leachates. Both dried and moist replicated (n?=?3) samples of two contrasting grassland soil types (clayey vs brown earth) were irrigated during laboratory experiments with identical total amounts of water, but at different rates, ranging from 0 h, increasing by 30-min increments up to 4 h, and additionally a 24-h rewetting rate. Total P concentrations in leachates from dried samples of both soils generally decreased as rewetting rate increased, ranging from 2,923?±?589 μg P L^?1 (0.5 h rewetting rate) to 731?±?46.0 μg P L^?1 (24 h, clayey soil) and 1,588?±?45.1 μg P L^?1 (0.5 h) to 439?±?25.5 μg P L^?1 (24 h brown earth). Similar patterns in concentrations occurred for molybdate reactive P (MRP), although concentrations were generally an order of magnitude lower, indicating that the majority of the leached P was probably organic. The moist brown earth leached relatively high concentrations of MRP (maximum 232?±?10.6 μg P L^?1, 0.5 h), unlike the moist clayey soil (maximum 20.4?±?10.0 μg P L^?1, 0 h). The total oxidised N concentrations in leachates were less affected by rewetting rate, although longer rewetting rates resulted in decreased concentrations in leachates from the dried samples of both soils. The difference in responses to rewetting rates of the two soils is probably due to differences in the fate of the microbial biomass and adsorption properties in the soils. Results show that soil moisture could be an important factor in regulating nutrient losses and availability, especially under changing patterns of rainfall predicted by future climate change scenarios.     

Dynamics and Characteristics of Fluorescent Dissolved Organic Matter in the Groundwater, River and Lake Water

Fluorescent dissolved organic matters (FDOM) in the groundwater-river-lake environments were investigated using three-dimensional excitation-emission matrix (EEM) and measuring the dissolved organic carbon (DOC), inorganic anions and electric conductivity (EC) in shallow groundwater, river and lake waters. DOC concentrations were high and largely varied in groundwater, 16–328 μM C (mean 109?±?88 μM C), and in river waters, 43–271 μM C (mean 158?±?62 μM C) and were very low in the lake Biwa waters, 89–97 μM C (mean 93?±?2 μM C). The fluorescence properties of EEM showed that the fulvic-like components (peak C, peak A and peak M) were dominated in groundwater and river waters, but protein-like components (peak T) was in lake waters. The peak C was observed at $ {{\text{Ex}}} \mathord{\left/ {\vphantom {{{\text{Ex}}} {{\text{Em}}}}} \right. \kern-0em} {{\text{Em}}} = {320 \pm 9} \mathord{\left/ {\vphantom {{320 \pm 9} {424 \pm 5}}} \right. \kern-0em} {424 \pm 5}\;{\text{nm}} $ in groundwater, and 340?±?5/432?±?4 nm in river waters, but the lake waters detected the two peaks, 347?±?7/441?±?11 nm (peak C) as a minor peak and 304?±?2/421?±?8 nm (peak M) as a major peak. Emission wavelength of peak T was observed to shorten in wavelengths from groundwater to river and then lake waters. Peak T in lake waters showed at shorter in wavelengths (279?±?2/338?±?11 nm) at the middle point of Lake Biwa compared to those of lake shore site (283?±?3/350?±?7 nm). Photo-irradiation experiment on upstream waters suggested the changes in the fluorescence peaks of fulvic acid-like substances in lake waters, which might be caused by photo-degradation. DOC concentration was significantly correlated with inorganic anions and EC in river waters. However, such correlations were not observed in groundwater. Anion concentrations in lake waters were low with respect to DOC concentration. These results showed that the optical and chemical properties of FDOM are characteristically varied among groundwater, river and lake waters, indicating the impacts of environments to various FDOM at the same watershed level.     

Hg, Cu, Pb, Cd, and Zn Accumulation in Macrophytes Growing in Tropical Wetlands

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g^?1 Hg, 6.5?C250.3 mg g^?1 Cu, 0.059?C0.245 mg g^?1 Pb, 0.004?C0.066 mg g^?1 Cd, and 31.8?363.1 mg g^?1 Zn in roots and 0.033?C0.888 mg g^?1 Hg, 2.2?C70.7 mg g^?1 Cu, 0.005?C0.086 mg g^?1 Pb, 0.001?C0.03 mg g^?1 Cd, and 12.6?C140.4 mg g^?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.     

Microbial CO<Subscript>2</Subscript> assimilation is not limited by the decrease in autotrophic bacterial abundance and diversity in eroded watershed

The impacts of soil erosion on soil structure, nutrient, and microflora have been extensively studied but little is known about the responses of autotrophic bacterial community and associated carbon (C)-fixing potential to soil erosion. In this study, three abandoned croplands (ES1, ES2, and ES3) and three check dams (DS1, DS2, and DS3) in the Qiaozi watershed of Chinese Loess Plateau were selected as eroding sites and depositional sites, respectively, to evaluate the impacts of soil erosion on autotrophic bacterial community and associated C-fixing potential. Lower abundance and diversity of autotrophic bacteria were observed in nutrient-poor depositional sites compared with nutrient-rich eroding sites. However, the relative abundances of obligate autotrophic bacteria, such as Thiobacillus and Synechococcus, were significantly enhanced in depositional sites. Deposition of nutrient-poor soil contributed to the growth of obligate autotrophic bacteria. The maximum microbial C-fixing rate was observed in DS1 site (5.568?±?1.503 Mg C km^?2 year^?1), followed by DS3 site (5.306?±?2.130 Mg C km^?2 year^?1), and the minimum was observed in ES2 site (0.839?±?0.558 Mg C km^?2 year^?1). Soil deposition significantly enhanced microbial C-fixing rate. Assuming a total erosion area of 1.09?×?10⁷ km², microbial C-fixing potential in eroded landscape can range from 0.01 to 0.06 Pg C year^?1. But its effect on the C pool recovery of degraded soil is limited. Dissolved organic C (DOC) was the main explanatory factor for the variation in soil microbial C-fixing rate (72.0%, P?=?0.000).     

Heavy Metal Content of Plant Species along Nilüfer Stream in Industrialized Bursa City, Turkey

The Paraíba do Sul river is located in one of the most developed part of Brazil and receives many organic and industrial effluents directly affecting the ichthyofauna. Concentration of four heavy metals (Cu, Cr, Zn and Pb) were determined in two tissues (muscle and gonads) of three abundant fish species from different trophic levels (Oligosarcus hepsetus—carnivore, Geophagus brasiliensis—omnivore and Hypostomus luetkeni—detritivore) between November 2002 and April 2003. The aim was to test the hypothesis that the trophic level and the proximity from impacted areas influence levels of contamination and to assess if these species are indicators of large-scale habitat quality. Levels of heavy metals were detected by Total Reflection X-ray Fluorescence with Synchrotron Radiation (SR-TXRF) at the Brazilian National Synchrotron Radiation Laboratory (LNLS). Generally, gonads showed higher metal concentration than muscles, except for Cr. All examined metals, but Cu, exceeded the maximum permitted concentration (mpc) by the Brazilian legislation for human consumption in at least one tissue. O. hepsetus (carnivore) showed the highest contamination levels, followed by G. brasiliensis (omnivore) and H. luetkeni (detritivore). The middle-upper segment, which encompasses large urban areas, showed the highest levels of metal contamination in most cases. O. hepsetus showed the highest levels of contamination in muscles for Pb in the middle-upper river segment (7.98?±?3.73; mpc?=?2.0 μg g^?1) and for Cr in the upper (5.53?±?0.05; mpc?=?0.10 μg g^?1) and middle-upper (4.20?±?0.85; mpc?=?0.10 μg g^?1) segments, which indicates that human population should avoid to consume these fishes species from these segments of the Paraíba do Sul river.     

Effects of Changed Soil Conditions on the Mobility of Trace Metals in Moderately Contaminated Urban Soils

Changes in the soil chemical environment can be expected to increase the leaching of trace metals bound in soils. In this study the mobility of trace metals was monitored in a column experiment for two contaminated urban soils. Four different treatments were used (i.e. rain, acid rain, salt and bark). Leachates were analysed for pH, dissolved organic carbon (DOC) and for seven trace metals (cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn)). The salt treatment produced the lowest pH values (between 5 and 6) in the effluent whereas the DOC concentration was largest in the bark treatment (40–140 mg L^?1) and smallest in the salt and acid treatments (7–40 mg L^?1). Cadmium, Ni and Zn were mainly mobilised in the salt treatment, whereas the bark treatments produced the highest concentrations of Cu and Pb. The concentrations of Cu, Cr, and Hg were strongly correlated with DOC (r ²?=?0.90, 0.91 and 0.96, respectively). A multi-surface geochemical model (SHM-DLM) produced values for metal dissolution that were usually of the correct magnitude. For Pb, however, the model was not successful indicating that the retention of this metal was stronger than assumed in the model. For all metals, the SHM-DLM model predicted that soil organic matter was the most important sorbent, although for Pb and Cr(III) ferrihydrite was also important and accounted for between 15 and 50% of the binding. The results confirm the central role of DOC for the mobilization of Cu, Cr, Hg and Pb in contaminated soils.     

Tillage system affects fertilizer-induced nitrous oxide emissions

Since the development of effective N₂O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N₂O emissions and the abundance of microbial communities involved in N₂O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N₂O and CO₂ fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N₂O emissions decreased in the order CAN and SL (CAN?=?748.8?±?206.3, SL?=?489.4?±?107.2 μg kg^?1) followed by MC (284.2?±?67.3 μg kg^?1) and ZERO (29.1?±?5.9 μg kg^?1). Highest cumulative N₂O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N₂O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N₂O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N₂O emissions within the soil profile according to N and C species added during fertilization.     

Mercury volatilization from a floodplain soil during a simulated flooding event

Purpose

Middle-European floodplain soils are often contaminated with mercury (Hg) and periodically flooded. In this study, the influence of a flooding event and subsequent dewatering on the volatilization of elemental Hg and methylated species was investigated in a laboratory experiment.

Material and methods

Undisturbed soil cores were taken from a topsoil (12.1?±?0.75 mg kg^?1 Hg) at the Elbe River in Lower Saxony, Germany. Soil columns were incubated at 20 °C with varying soil moisture (water-saturated for 2 weeks, 95 and 90 % water content for 1 week each), and the redox potential (E_H) was recorded. The gaseous Hg that accumulated in the headspace of the flux chamber of the columns was pumped over cooled traps filled with adsorber material and analyzed by gas chromatography/inductively coupled plasma mass spectrometry for the various Hg species.

Results and discussion

The watering of the soil resulted in a rapid decrease in the E_H and the achievement of strongly reducing conditions (E_H??1 Hg at the beginning to 5.78 μg L^?1 Hg at the end of the experiment. Species analyses revealed that exclusively elemental Hg volatilized. The volatilization rate was between 1.73 and 824 ng m^?2 h^?1 Hg, which is consistent with other studies at the Elbe River.

Conclusions

Even when flooded for a longer period of time, floodplain soils should show neither emission of methylated Hg nor exceptionally high volatilization of elemental Hg.     

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.     

Pilot-scale counter-current acid leaching process for Cu,Pb, Sb,and Zn from small-arms shooting range soil

Purpose

The main objective of this study was to evaluate the potential of a counter-current leaching process (CCLP) on 14 cycles with leachate treatment at the pilot scale for Pb, Cu, Sb, and Zn removal from the soil of a Canadian small-arms shooting range.

Materials and methods

The metal concentrations in the contaminated soil were 904?±?112 mg Cu kg^–1, 8,550?±?940 mg Pb kg^–1, 370?±?26 mg Sb kg^–1, and 169?±?14 mg Zn kg^–1. The CCLP includes three acid leaching steps (0.125 M H₂SO₄?+?4 M NaCl, pulp density (PD)?=?10 %, t?=?1 h, T?=?20 °C, total volume?=?20 L). The leachate treatment was performed using metal precipitation with a 5-M NaOH solution. The treated effluent was reused for the next metal leaching steps.

Results and discussion

The average metal removal yields were 80.9?±?2.3 % of Cu, 94.5?±?0.7 % of Pb, 51.1?±?4.8 % of Sb, and 43.9?±?3.9 % of Zn. Compared to a conventional leaching process, the CCLP allows a significant economy of water (24,500 L water per ton of soil), sulfuric acid (133 L H₂SO₄ t^–1), NaCl (6,310 kg NaCl t^–1), and NaOH (225 kg NaOH t^–1). This corresponds to 82 %, 65 %, 90 %, and 75 % of reduction, respectively. The Toxicity Characteristic Leaching Procedure test, which was applied on the remediated soil, demonstrated a large decrease of the lead availability (0.8 mg Pb L^–1) in comparison to the untreated soil (142 mg Pb L^–1). The estimated total cost of this soil remediation process is 267 US$ t^–1.

Conclusions

The CCLP process allows high removal yields for Pb and Cu and a significant reduction in water and chemical consumption. Further work should examine the extraction of Sb from small-arms shooting range.     

Solid-Solution Metal Partitioning for the Upper Mero River Basin (NW Spain)

This study determines the seasonal variability of metal partition coefficients [aluminium (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] and analyses the importance of suspended sediments (SS), dissolved organic carbon (DOC) concentrations, pH, and discharge (Q) on the seasonal variability of metal partition coefficients (K_Ds) in the headwaters of the Mero River catchment, which drains an agroforestry area in northwestern Spain. Metal partition coefficients were used as an approach to relate dissolved and particulate fractions. Water samples were collected over 3 years (2005–2008) at the catchment outlet. The mean metal dissolved concentrations were: Fe (43.5 μg L^?1) > Al (23.3 μg L^?1) > Zn (1.8 μg L^?1) > Mn (1.2 μg L^?1) > Cu (0.3 μg L^?1). Partition coefficients followed the order Mn > Al > Fe > Zn > Cu, and their values exhibited low variability. Al, Cu, and Zn partition coefficients presented the greatest values in summer, except during 2007–2008, when the greatest K_Ds value was observed in autumn, whereas the K_Ds of Fe showed the greatest values in winter. The K_D of Mn has no seasonality. For Al, Cu, and Zn, the seasonal SS concentrations were closely related to Kd. For Fe, Kd was more closely related to DOC concentration than to SS concentration.     

Transfer of 137Cs and 40K from Agricultural Soils to Food Products in Terrestrial Environment of Tarapur, India

The ¹³⁷Cs and ⁴⁰K activities and transfer factors from soil to vegetables, grass, and milk from villages located around Tarapur Atomic Power Station (TAPS) were determined using high-resolution gamma spectrometry. A total of 32 soil, 21 vegetable, 23 dry paddy grass, and 23 milk samples were collected from 23 different agricultural farms from various villages around TAPS to determine transfer factors for natural environment. The mean concentration values for ¹³⁷Cs and ⁴⁰K in soil, grass, and milk were 2.39?±?0.86 Bq kg^?1, 0.31?±?0.23 Bq kg^?1, and 12.4?±?5.7 mBq L^?1 and 179?±?31 Bq kg^?1, 412?±?138 Bq kg^?1, and 37.6?±?9.3 Bq L^?1, respectively, for soil?Cgrass?Cmilk pathway. In the soil?Cvegetation pathway, the mean concentrations values for ¹³⁷Cs and ⁴⁰K were 2.15?±?1.04 Bq kg^?1, 16.5?±?7.5 mBq kg^?1, and 185?±?24, 89?±?50 Bq kg^?1, respectively. The evaluated mean transfer factors from soil?Cgrass, grass?Cmilk, and soil?Cvegetation for ¹³⁷Cs were 0.14, 0.0044, and 0.0073 and that of ⁴⁰K were 2.42, 0.0053, and 0.49, respectively. Only 15 out of total 44 milk and vegetable samples were detected positive for ¹³⁷Cs, indicating a very low level of bioavailability.     

Effect of Metals on Decolorization of Reactive Blue HERD by <Emphasis Type="Italic">Comamonas</Emphasis> sp. UVS

Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L^?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L^?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g^?1 cell h^?1 for maximum rate (V_max) and 112.35?±?0.34 mg L^?1 for the Michaelis constant (K_m). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg²⁺, Ca²⁺, Cd²⁺, and Zn²⁺, whereas decolorization was completely inhibited by Cu²⁺. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.     

Assessing daily egestion rates in earthworms: using fungal spores as a natural soil marker to estimate gut transit time

Earthworms have an important role in ‘bioturbation’—the mixing of soil due to biological processes. Quantification of earthworm bioturbation relies on estimating earthworm egestion rates which in turn depend on two parameters: the gut content of the worms and the gut transit time (GTT). Gut content can be determined relatively easily, but determining GTT is problematic. The present study aimed at estimating daily soil egestion rates of Aporrectodea caliginosa and Lumbricus terrestris, refining the most common approach for estimating GTT by using fungal spores as natural markers in ingested soil. This approach avoids the use of artificial markers that may adversely affect the earthworms. Gut transit time was estimated by tracking the passage of marked soil through the gut by the appearance of the spores in the egested faeces. Gut transit time was estimated to be 9.6?±?0.3 h for A. caliginosa and 11.6?±?0.5 h for L. terrestris. Gut content averaged 465?±?40(± standard error (SE))?mg dw g^?1 dw worm for A. caliginosa and 265?±?80 mg dw g^?1 dw worm for L. terrestris. From these values, daily egestion rates of 1.16 and 0.66 g dw faeces g^?1 dw worm d^?1 were calculated for A. caliginosa and L. terrestris, respectively. Both values compare well to literature values for each species. The presented method for GTT estimation is inexpensive, rapid and easy to evaluate, with spores being a good alternative to existing markers.     

Fluoride Removal from Aqueous Solutions by a Carbonaceous Material from Pyrolysis of Sewage Sludge

Contact time, pH, fluoride concentration, and sorbent dose effects on the removal of fluoride ions by a carbonaceous material obtained from pyrolysis of sewage sludge (CM) were evaluated. Equilibrium was reached after 18?h of contact time and the maximum sorption was found at pH_eq?=?7.06?±?0.08, which corresponds to the zero charge point of the CM. The highest efficiency in the sorption system for fluoride removal (2.84?±?0.03?mg?F^?? $ g_{{CM}}^{{ - 1}} $ ) was found with 0.4?g_CM?L^?1 and with 20?g_CM?L^?1, 82.2?±?0.5% of fluoride was removed. The kinetic data of the process could be fitted to the pseudosecond order and the intraparticle mass transfer diffusion models, whereas isotherm to the Langmuir?CFreundlich equation. These results indicate that the mechanism is chemisorption on a heterogeneous material. Fluoride ions were best partially desorbed using a bicarbonate ions solution and the material was partially regenerated by using a solution of HCl (pH?=?1).     

Mercury Transport in a Low-Arctic River in Kobbefjord, West Greenland (64° N)

Mercury (Hg) transport was studied in a river in Kobbefjord, near Nuuk in West Greenland, during the 2009 and 2010 summer periods. The river drains an area of 32?km², and the Kobbefjord area is considered representative to low-Arctic West Greenland. The river water origins from both precipitation and melting of small glaciers and annual water discharges for 2009 and 2010 were estimated to be 29 and 26 million?m³, respectively. Mean Hg concentrations (±SD) were 0.46?±?0.17 and 0.26?±?0.17?ng?L^?1 for 2009 and 2010. The annual Hg transport was estimated to 14 and 6.4?g, corresponding to a transport rate of 0.45 and 0.20?g Hg km^?2?year^?1 from the river basin. The highest Hg concentrations (up to 1.0?ng?L^?1) and discharges were measured in spring 2009 along with melting of extensive amounts of snow deposited during the 2008?C2009 winter period. In contrast, the following 2009?C2010 winter period was relatively dry with less snowfall. This indicates that a major fraction of the Hg in this area is likely to come from Hg deposited along with winter precipitation (as wet deposition) released upon snowmelt. Also, the results show that while Hg concentrations were low in Kobbefjord River compared to other sub-Arctic/Arctic rivers, the annual Hg transport rates from the basin area were within the range reported for other sub-Arctic/Arctic areas.     

Litterfall Mercury in Two Forested Watersheds at Acadia National Park, Maine, USA

Litterfall can be an important flux of mercury (Hg) to soils in forested landscapes, yet typically the only available data to evaluate Hg deposition is from precipitation Hg monitoring. Litterfall was collected at 39 sampling sites in two small research watersheds, in 2003 and 2004, and analyzed for total Hg. Four vegetation classes were designated in this study as hardwoods, softwoods, mixed and scrub. The mean litter Hg concentration in softwoods (58.8 ± 3.3 ng Hg g^?1 was significantly greater than in mixed (41.7 ± 2.8 ng Hg g^?1 and scrub (40.6 ± 2.7 ng Hg g^?1, and significantly lower than in hardwoods (31.6 ± 2.6 ng Hg g^?1. In contrast, the mean weighted litter Hg flux was not significantly different among vegetation classes. The lack of a significant difference in litter Hg flux between hardwoods and softwoods was attributable to the large autumnal hardwood litter Hg flux being balanced by the higher softwood litter Hg concentrations, along with the higher chronic litterfall flux throughout the winter and spring in softwoods. The estimated annual deposition of Hg via litterfall in Hadlock Brook watershed (10.1 μg m^?2 and Cadillac Brook watershed (10.0 μg m^?2 was greater than precipitation Hg deposition and similar to or greater than the magnitude of Hg deposition via throughfall. These results demonstrate that litterfall Hg flux to forested landscapes can be at least as important as precipitation Hg inputs.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.