Greenhouse gas emissions from rice based cropping systems: Economic and technologic challenges and opportunities

Recent market slump in rice, less rainfall during monsoon, high temperature and scarcity of water during dry season leads to lower grain yield and less profit from rice cultivation in India. Farmers’ grow upland crops like chickpea (Cicer arietinum), greengram (Vigna radiate), mustard (Brassica nigra), corn (Zea maize), pigeonpea (Cajanus cajan), potato (Solanum tuberosum), sunflower (Helianthus annuus) etc. along with rice (Oryza sativa) during the dry season. However, knowledge of greenhouse gas (GHG) emission from these rice based cropping systems is very limited. In the present study four rice based cropping systems was studied along with rice-rice rotation system as control in respect of GHG emission, yield potential and economic feasibility. Conventional plantation and fertilizer application methodology was followed for each crop. Methane (CH₄) and nitrous oxide (N₂O) flux from field plots were studied with conventional closed chamber method using gas chromatograph. CH₄ flux was recorded highest from rice-rice rotation plots (304.25 kg ha⁻¹). N₂O flux was recorded 1.02 kg ha⁻¹ from rice-rice rotation system during wet season. However, during wet season, higher N₂O flux (1.93 kg ha⁻¹) was recorded from rice-potato-sesame rotation plots. Annual N₂O flux was also recorded significantly low (3.42 kg ha⁻¹) from rice-rice rotation plots and high (6.19 kg ha⁻¹) from rice-chickpea-greengram rotation plots. Significantly lower annual grain yield was recorded from rice-rice rotation plots (9.25 Mg ha⁻¹) whereas it was 18.84 Mg rice eq ha⁻¹ from rice-potato-sesame rotation system. The global warming potential (GWP) of rice-rice rotation system was recorded significantly high (8.62 Mg CO₂ ha⁻¹) compare to plots with different rice based cropping systems. Computing all C-emission from cradle-to-grave, highest total C-cost was recorded from the rice-rice rotation system ($62.00 ha⁻¹). We have made an attempt to calculate the C-credit of different rice based cropping systems by considering the difference of C-cost with control. The study suggests that the rice-potato-sesame is most sustainable among different cropping system studied in terms of economic profit ($62.00 ha⁻¹). We have made an attempt to calculate the C-credit of different rice based cropping systems by considering the difference of C-cost with control. The study suggests that the rice-potato-sesame is most sustainable among different cropping system studied in terms of economic profit (1248.21 ha⁻¹) and C-credit ($38.60 ha⁻¹). The result of the study may be limited to the study region; however, the study has potential use in respect to the development of agriculture practice for adaptation to climate change.     

High-field 1H T1 and T2 NMR relaxation time measurements of H2O in homeopathic preparations of quartz, sulfur, and copper sulfate

Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure. To investigate the latter, we measured for the first time high-field (600/500 MHz) ¹H T₁ and T₂ nuclear magnetic resonance relaxation times of H₂O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS). Homeopathic preparations of quartz (10c–30c, n = 21, corresponding to iterative dilutions of 100⁻¹⁰–100⁻³⁰), sulfur (13x–30x, n = 18, 10⁻¹³–10⁻³⁰), and copper sulfate (11c–30c, n = 20, 100⁻¹¹–100⁻³⁰) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there was a significant increase in T₁ for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls. In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T₁ relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations thus may exhibit specific physicochemical properties that need to be determined in detail in future investigations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Adsorption of fluoride on clay minerals and their mechanisms using X-ray photoelectron spectroscopy

This research investigates the adsorption mechanisms of fluoride (F) on four clay minerals (kaolinite, montmorillonite, chlorite, and illite) under different F⁻ concentrations and reaction times by probing their fluoride superficial layer binding energies and element compositions using X-ray photoelectron spectroscopy (XPS). At high F⁻ concentrations (C ₀ = 5–1000 mg·L⁻¹), the amount of F⁻ adsorbed (Q _F), amount of hydroxide released by clay minerals, solution F⁻ concentration, and the pH increase with increasing C ₀. The increases are remarkable at C ₀>50 mg·L⁻¹. The QF increases significantly by continuously modifying the pH level. At C ₀<5–100 mg·L⁻¹, clay minerals adsorb H⁺ to protonate aluminum-bound surface-active hydroxyl sites in the superficial layers and induce F⁻ binding. As the C ₀ increases, F⁻, along with other cations, is adsorbed to form a quasi-cryolite structure. At C ₀>100 mg·L⁻¹, new minerals precipitate and the product depends on the critical Al³⁺ concentration. At [Al³⁺]>10^−11.94 mol·L⁻¹, cryolite forms, while at [Al³⁺]<10^−11.94 mol·L⁻¹, AlF₃ is formed. At low C ₀ (0.3–1.5 mg·L⁻¹), proton transfer occurs, and the F⁻ adsorption capabilities of the clay minerals increase with time.     

Carbon storage versus fossil fuel substitution: a climate change mitigation option for two different land use categories based on short and long rotation forestry in India

Short rotation bioenergy crops for energy production are considered an effective means to mitigate the greenhouse effect, mainly due to their ability to substitute fossil fuels. Alternatively, carbon can be sequestered and stored in the living biomass. This paper compares the two land use categories (forest land and non-forest land) for two management practices (short rotation vs. long rotation) to study mitigation potential of afforestation and fossil fuel substitution as compared to carbon storage. Significant carbon benefit can be obtained in the long run from using lands for growing short rotation energy crops and substituting fossil fuels by the biomass thus produced, as opposed to sequestering carbon in the biomass of the trees. When growth rates are high and harvest is used in a sustainable manner (i.e., replanting after every harvest), the opportunities for net carbon reductions appear to be fossil fuel substitution, rather than storage in ecosystem biomass. Our results suggest that at year 100 a total of 216 Mg C ha⁻¹ is sequestered for afforestation/reforestation using long rotation sal (Shorea robusta Gaertn.f) species, as opposed to offset of 412 Mg C ha⁻¹ for carbon storage and fossil fuel substitution for short rotation poplar (Populus Deltoides Marsh) plantations. The bioenergy option results in a continuous stream of about 3 Mg C ha⁻¹ yr⁻¹ of carbon benefits per year on forest land and 4 Mg C ha⁻¹ yr⁻¹ on non-forest land. Earlier studies have shown that in India waste land availability for establishing energy plantations is in the range of 9.6 to 36.5 Mha. Thus, using the 758 Tg biomass per year generated from 9.6 Mha waste land gives a mitigation potential in the range of 227 to 303 Tg C per year for carbon storage and fossil fuel substitution from poplar plantation for substituting coal based power generation. Depending upon the land availability for plantation, the potential for energy generation is in the range of 11,370 PJ, possibly amounting to a bioenergy supply of 43% of the total projected energy consumption in 2015. Further studies are needed to estimate the mitigation potential of other species with different productivities for overall estimation of the economic feasibility and social acceptability in a tropical country like India.     

Global warming potential of emissions from rice paddies in Northeastern China

In this study, paddy fields in Jilin province which are flooded parcel of arable lands used for growing rice (Oryza sativa Linn.) were selected as the object. Long-term exploitation of paddy fields led to variations of soil organic carbon (SOC) and green house gases (GHGs) emissions which might contribute to global warming. In order to calculate the amount of global warming potentials (GWPs) of emissions from ricepaddies and find the correlations among rice yield, SOC storage and GWP, DeNitrification-DeComposition (DNDC) model was used to simulate SOC densities and fluxes of main GHGs emitted from paddy fields. After verification, simulation results were used to calculate SOC storages and 100-year GWPs from 1949 to 2009. Results indicated that SOC densities in depths of 0–10 cm, 10–20 cm and 20–30 cm all kept increasing. Average methane (CH₄) and nitrous oxide (N₂O) fluxes were 278.55 kg carbon (kgC) ha⁻¹ a⁻¹ and 2.22 kg nitrogen (kgN) ha⁻¹ a⁻¹. The SOC storage (0–30 cm) had increased from 3.96 × 10⁹kgC in 1949 to 47.85 × 10⁹kgC in 2009. In addition, GWP emission was increasing exponentially in the past 61 years, from 0.16 × 10⁶ Mg carbon dioxide equivalents (CO₂-equivalents) to 66.36 × 10⁶ Mg CO₂-equivalents. Both SOC storage and GWP presented obviously linear relation to rice yields. Overall, the research suggested that long-term rice yields could be used to estimate the SOC storage and GWP variations.     

Optimizing carbon sequestration in commercial forests by integrating carbon management objectives in wood supply modeling

This paper provides a methodology for generating forest management plans, which explicitly maximize carbon (C) sequestration at the forest-landscape level. This paper takes advantage of concepts first presented in a paper by Meng et al. (2003; Mitigation Adaptation Strategies Global Change 8:371–403) by integrating C-sequestration objective functions in existing wood supply models. Carbon-stock calculations performed in Woodstock^TM (RemSoft Inc.) are based on C yields generated from volume table data obtained from local Forest Development Survey plots and a series of wood volume-to-C content conversion factors specified in von Mirbach (2000). The approach is used to investigate the impact of three demonstration forest-management scenarios on the C budget in a 110,000 ha forest in south-central New Brunswick, Canada. Explicit demonstration scenarios addressed include (1) maximizing timber extraction either by clearcut or selection harvesting for greatest revenue generation, (2) maximizing total C storage in the forest landscape and in wood products generated from harvesting, and (3) maximizing C storage together with revenue generation. The level of clearcut harvesting was greatest for scenario 1 (≥15 × 10⁴ m³ of wood and ≥943 ha of land per harvesting period), and least for scenario 2 (=0 m³ per harvesting period) where selection harvesting dominated. Because softwood saw logs were worth more than pulpwood ($60 m⁻³ vs. $40 m⁻³) and were strategic to the long-term storage of C, the production of softwood saw logs exceeded the production of pulpwood in all scenarios. Selection harvesting was generally the preferred harvesting method across scenarios. Only in scenario 1 did levels of clearcut harvesting occasionally exceed those of selection harvesting, mainly in the removal of old, dilapidated stands early in the simulation (i.e., during periods 1 through 3). Scenario 2 provided the greatest total C-storage increase over 80 years (i.e., 14 × 10⁶ Mg C, or roughly 264 Mg ha⁻¹) at a cost of $111 per Mg C due to lost revenues. Scenarios 3 and 1 produced reduced storage rates of roughly 9 × 10⁶ Mg C and 3 × 10⁶ Mg C, respectively; about 64% and 22% of the total, 80-year C storage calculated in scenario 2. The bulk of the C in scenario 2 was stored in the forest, amounting to about 76% of the total C sequestered.     

Construction of l-Isoleucine Overproducing Strains of Corynebacterium glutamicum

Corynebacterium glutamicum   is used for the industrial production of the amino acids l-glutamate (1×10⁶ tons/year) and l-lysine (300×10³ tons/year). The classical approach to obtain amino acid overproducing strains of C. glutamicum was mutagenesis and then a selection of mutants. In the past 10 years the genetic engineering and amplification of genes have become fascinating methods for studying metabolic pathways in greater detail and for constructing microbial strains with desired genotypes. To obtain l-isoleucine overproducing strains of C. glutamicum we therefore studied the l-isoleucine biosynthesis by overexpression of the various corresponding genes. To enable a flux increase in recombinant strains all genes specific for l-threonine and l-isoleucine biosynthesis were cloned from this bacterium. We demonstratet that amplification of the feedback inhibition insensitive homoserine dehydrogenase and homoserine kinase in a high l-lysine overproducing strain enable the channeling of the carbon flow from the intermediate l-aspartate semialdehyde towards homoserine, resulting in an accumulation of l-threonine. To obtain effective l-isoleucine overproduction a deregulated threonine dehydratase was overexpressed in l-threonine producing strains of C. glutamicum. In this way the l-threonine was converted to l-isoleucine, which was secreted up to 30 g/l into the culture medium. Received: 7 April 1998 / Accepted in revised form: 27 August 1998     

Biosorption of Cr(III) from aqueous solution by freeze-dried activated sludge: Equilibrium, kinetic and thermodynamic studies

Batch biosorption experiments were conducted to remove Cr(III) from aqueous solutions using activated sludge from a sewage treatment plant. An investigation was conducted on the effects of the initial pH, contact time, temperature, and initial Cr(III) concentration in the biosorption process. The results revealed that the activated sludge exhibited the highest Cr(III) uptake capacity (120 mg·g⁻¹) at 45°C, initial pH of 4, and initial Cr(III) concentration of 100 mg·L⁻¹. The biosorption results obtained at various temperatures showed that the biosorption pattern accurately followed the Langmuir model. The calculated thermodynamic parameters, ΔGo° ( − 0.8–4.58 kJ·mol⁻¹), ΔH° (15.6–44.4 kJ·mol⁻¹), and ΔS° (0.06–0.15 kJ·mol⁻¹·K⁻¹) clearly indicated that the biosorption process was feasible, spontaneous, endothermic, and physical. The pseudo first-order and second-order kinetic models were adopted to describe the experimental data, which revealed that the Cr(III) biosorption process conformed to the second-order rate expression and the biosorption rate constants decreased with increasing Cr (III) concentration. The analysis of the values of biosorption activation energy (E _a = −7 kJ·mol⁻¹) and the intraparticle diffusion model demonstrated that Cr(III) biosorption was film-diffusion-controlled.     

Decay of cacti and carbon cycling

Cacti contain large quantities of Ca-oxalate biominerals, with C derived from atmospheric CO₂. Their death releases these biominerals into the environment, which subsequently transform to calcite via a monohydrocalcite intermediate. Here, the fate of Ca-oxalates released by plants in arid environments is investigated. This novel and widespread form of biomineralization has unexpected consequences on C cycling and calcite accumulation in areas with large numbers of cacti. The magnitude of this mineralization is revealed by studying the large columnar cactus Carnegiea gigantea (Engelm.) Britton and Rose in southwestern Arizona (locally called the saguaro). A large C. gigantea contains on the order of 1×10⁵ g of the Ca-oxalate weddellite—CaC₂O₄·2H₂O. In areas with high C. gigantea density, there is an estimated 40 g C_atm m⁻² sequestered in Ca-oxalates. Following the death of the plant, the weddellite transforms to calcite on the order to 10–20 years. In areas with high saguaro density, there is an estimated release of up to 2.4 g calcite m⁻² year⁻¹ onto the desert soil. Similar transformation mechanisms occur with the Ca-oxalates that are abundant in the majority of cacti. Thus, the total atmospheric C returned to the soil of areas with a high number density of cacti is large, suggesting that there may be a significant long-term accumulation of atmospheric C in these soils derived from Ca-oxalate biominerals. These findings demonstrate that plant decay in arid environments may have locally significant impacts on the Ca and inorganic C cycles.     

Paleoenvironmental conditions in the Spanish Miocene–Pliocene boundary: isotopic analyses of Hipparion dental enamel

Expansion of C₄ grasses during Late Miocene and Early Pliocene constitutes one of the most remarkable biotic events of the Cenozoic era. The Teruel–Alfambra region (northeastern Spain) contains one of the most complete Miocene–Pliocene sequences of mammalian fossil sites in the world. In this study, stable isotope (δ ¹³C and δ ¹⁸O) analyses have been performed on the tooth enamel from the equid Hipparion from 19 localities spanning a time interval from approximately 10.9 to 2.7 Ma. This time range starts with the first appearance of this genus in Spain and ends at its extinction. An increase in δ ¹³C at about 4.2 Ma has been observed, indicative of a shift toward a more open habitat. This shift may be related to a large scale vegetation change which occurred across the Miocene–Pliocene boundary when C₄ grasses expanded. This expansion might in turn be linked to global tectonic events such as the uplift of the Himalaya and/or the closure of the Panama Isthmus. However, other more regional factors may have ultimately enhanced the trend toward more open habitats in the Western Mediterranean Basin. The Messinian Salinity Crisis was a major environmental event that may have been responsible for the isotopic changes seen in the equid Hipparion from the Iberian Peninsula along with an increase in the aridity detected ~4.6 Ma ago in the Sahara. Even though the exact factor triggering the isotopic change observed in the Hipparion enamel remains mostly unknown, this study demonstrates that the global environmental changes detected across the Miocene–Pliocene boundary are also recorded in the realm of the Iberian Peninsula. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Adsorptive behaviors of humic acid onto freshly prepared hydrous manganese dioxides

This study focused on the adsorptive behaviors of humic acid onto freshly prepared hydrous MnO₂(s) (δMnO₂), and investigated the feasibility of employing δMnO₂ for humic acid removal from drinking water. Effects of such parameters as molecular mass of humic acid, kinds of divalent cations on adsorptive behaviors and possible mechanisms involved were investigated. This study indicated that humic acid with higher molecular mass exhibited more tendency of adsorbing onto δMnO₂ than that with lower molecular mass. Ca²⁺ facilitated more humic acid adsorption than Mg²⁺; UV-Vis spectra analysis indicated higher capabilities of Ca²⁺ coordinating with acidic functional groups of humic acid than that of Mg²⁺. Additionally, ζ potential characterization indicated that Ca²⁺ showed higher potential of increasing gz potential of δMnO₂ than Mg²⁺. Ca²⁺ of 1.0 mmol/L increased ζ potential of δMnO₂ from −37 mV (pH 7.9) to +7 mV (pH 7.2), while 1.0 mmol/L Mg²⁺ increased to lower value as −9 mV (pH 6.5), correspondingly. Fourier transform infrared (FTIR) spectra demonstrated the adsorption of humic acid onto δMnO₂, showing the important roles of-COO⁻ functional groups and surface Mn-OH in the adsorption of humic acid onto δMnO₂. Translated from Acta Scientiae Circumstantiae, 2005, 25(3): 351–355 [译自: 环境科学学报]     

高铵条件下绿狐尾藻的生理与氮磷吸收特征

为了探讨水生植物绿狐尾藻(Myriophyllum aquaticum)在生态湿地系统对高铵态氮(NH_4~+-N)的耐受及氮(N)、磷(P)吸收能力,试验设置3个高NH_4~+水平(70、210、420 mg·L~(-1))的营养液,对绿狐尾藻培养21 d,研究高浓度NH_4~+对绿狐尾藻生理及N、P吸收特征的影响.结果表明,70 mg·L~(-1)高NH_4~+处理,绿狐尾藻生长健壮,培养21 d后,茎高和生物量分别达到40.56 cm和17.82 g·穴-1;与70 mg·L~(-1)高NH_4~+对照相比,210 mg·L~(-1)高NH_4~+处理下,绿狐尾藻丙二醛含量显著增加,但叶绿素和可溶性糖含量仍较高,说明其受到一定NH_4~+的胁迫,但不影响其正常生长,茎和生物量的生长速率与对照无显著差异.当NH_4~+水平达到420 mg·L~(-1)时,丙二醛含量增加了2倍,茎高和生物量生长速率仅为对照的27.4%和17.9%,植物受到严重胁迫,生长受阻甚至死亡.3种高NH_4~+处理下,绿狐尾藻总N和总P含量的变化范围为30.7~53.4 mg·g~(-1)和3.8~7.7mg·g~(-1),表现出对N、P超高的吸收能力.鉴于绿狐尾藻在高浓度NH_4~+-N中的高耐受性,及很强的N、P吸收能力,绿狐尾藻可作为高铵/氨废水生物处理中理想的湿地生物,将具有良好的应用前景.     

Baseline Carbon Stocks Assessment and Projection of Future Carbon Benefits of a Carbon Sequestration Project in East Timor

Climate change is one of the most pressing environmental problems humanity is facing today. Forest ecosystems serve as a source or sink of greenhouse gases, primarily CO₂. With support from the Canadian Climate Change Fund, the Community-based Natural Resource Management for Carbon Sequestration project in East Timor (CBNRM-ET) was implemented to “maintain carbon (C) stocks and increase C sequestration through the development of community-based resource management systems that will simultaneously improve livelihood security”. Project sites were in the Laclubar and Remexio Sub-districts of the Laclo watershed. The objective of this study was to quantify baseline C stocks and sequestration benefits of project components (reforestation with fast-growing species, primarily Casuarina equisetifolia, and agroforestry involving integration of Paraserianthes falcataria). Field measurements show that mature stands (≥30 years) of P. falcataria and C. equisetifolia contain up to 200 Mg C ha⁻¹ in above ground biomass, indicating the vast potential of project sites to sequester carbon. Baseline C stocks in above ground biomass were very low in both Laclubar (6.2 Mg C ha⁻¹ for reforestation sites and 5.2 Mg C ha⁻¹ for agroforestry sites and Remexio (3.0 Mg C ha⁻¹ for reforestation and 2.5 Mg C ha⁻¹ for agroforestry). Baseline soil organic C levels were much higher reaching up to 160 Mg C ha⁻¹ in Laclubar and 70 Mg C ha⁻¹ in Remexio. For the next 25 years, it is projected that 137 671 Mg C and 84 621 Mg C will be sequestered under high- and low C stock scenarios, respectively.     

Technical feasibility study of an onshore ballast water treatment system

To fulfill the requirements of Guidelines for approval of ballast water management system (G8), a set of onshore ballast water treatment equipment utilizing micro-pore ceramic filtration (MPCF) and UV radiation (MPCF&UV) system was designed and set up with a maximum flow rate of 80 m³·h⁻¹. Technical feasibilities of MPCF&UV system were evaluated in three areas: removal efficiencies of indicator organism and oceanic bacteria, perdurability of a ceramic filter, and application on native seawater. The results showed that no indicator organism (Dunaliella) or oceanic bacteria was detected after treatment of 20 L MPCF and UV radiation at 1.3×10⁴ μW·s·cm⁻². A 20 L ceramic filter can run continuously for 5.3 h at the flow rate of 15 m³·h⁻¹ before its pressure drop up to 0.195 MPa. The removal percentage of total plankton amounts were 91.9% at a flow rate of 70 m³·h⁻¹ by 80 L MPCF and UV radiation at 1.3×10⁴ μW·s·cm⁻².     

Net Ecosystem Production of Boreal Larch Ecosystems on the Yenisei Transect

The study was carried out in the Turukhansk Research Station of Yenisei Transect (65^°46^′N, 89^°25^′E). Larch (Larix gmelinii (Rupr.) Rupr.) is the dominant overstory tree species. The research has been conducted on four permanent test plots in same-age mature (110-year old) and overmature (380-year old) post-fire larch stands of green moss and lichen groups of forest type. Carbon cycle parameters were assessed based on a biometric method. Quantitative analysis of carbon pools and fluxes shows that net ecosystem production of north taiga larch stands averages 32% of net primary production. Sink of atmospheric CO₂ makes 1.22 and 0.74 t C ha^{− 1} year^{− 1} for mature and overmature green moss larch stands, and 0.65 and 0.35 t C ha^{− 1} year^{− 1} for lichen type. Net carbon sink in the tree layer make up 9% of net primary production carbon, ground vegetation – 15%, and dead plant residues accumulation – 8% of atmospheric carbon uptake via photosynthesis.     

Copper and zinc interaction on water clearance and tissue metal distribution in the freshwater mussel, Cristaria plicata, under laboratory conditions

Copper and zinc interaction on clearance from water and distribution in different tissues was investigated for the freshwater mussel, Cristaria plicata, under laboratory conditions. Clearance rate of Cu or Zn from water was highly dependent on exposure concentration. Interaction effect was most evident at 300 μg·L⁻¹ Cu exposure and depressed the Zn clearance rate significantly (p<0.05). However, the presence of 100 μg·L⁻¹ and 300 μg·L⁻¹ Zn hardly affected the Cu clearance rate. The 300 μg·L⁻¹ Cu presence enhanced Cu accumulation in each tissue most significantly (p<0.01), but caused Zn content to decrease in the gills by 62% (p<0.05), viscera by 49% (p<0.05) and foot by 31% (p<0.05), and increase in the mantle by 97% (p<0.05) and the muscles by 243% (p<0.05) for different Zn exposure treatments. The response of metal accumulation in various tissues of the test mussels indicated that Zn transferred from the gills, viscera and foot to the mantle and muscles might be one of the important characteristics of the Zn regulatory mechanism by leading to a narrow range of Zn concentration in the different tissues.     

Nitrifying population dynamics in a redox stratified membrane biofilm reactor (RSMBR) for treating ammonium-rich wastewater

Nitrogen removal performance and nitrifying population dynamics were investigated in a redox stratified membrane biofilm reactor (RSMBR) under oxygen limited condition to treat ammonium-rich wastewater. When the NHt₄⁺-N loading rate increased from 11.1±1.0 to 37:2 ± 3:2 gNHt₄⁺-N·m⁻²·d⁻¹, the nitrogen removal in the RSMBR system increased from 18.0±9.6 mgN·d⁻¹ to 128.9±61.7 mgN·d⁻¹. Shortcut nitrogen removal was achieved with nitrite accumulation of about 22:3 ± 5:3 mgNO₂⁻-N·L⁻¹. Confocal micrographs showed the stratified distributions of nitrifiers and denitrifiers in the membrane aerated biofilms (MABs) at day 120, i.e., ammonia and nitrite oxidizing bacteria (AOB and NOB) were dominant in the region adjacent to the membrane, while heterotrophic bacteria propagated at the top of the biofilm. Real-time qPCR results showed that the abundance of amoA gene was two orders of magnitude higher than the abundance of nxrA gene in the MABs. However, the nxrA gene was always detected during the operation time, which indicates the difficulty of complete washout of NOB in MABs. The growth of heterotrophic bacteria compromised the dominance of nitrifiers in biofilm communities, but it enhanced the denitrification performance of the RSMBR system. Applying a high ammonia loading together with oxygen limitation was found to be an effective way to start nitrite accumulation in MABs, but other approaches were needed to sustain or improve the extent of nitritation in nitrogen conversion in MABs.     

Process evaluation of an alternating aerobic-anoxic process applied in a sequencing batch reactor for nitrogen removal

In order to improve the nitrogen removal efficiency and save operational cost, the feasibility of the alternating aerobic-anoxic process (AAA process) applied in a sequencing batch reactor (SBR) system for nitrogen removal was investigated. Under sufficient influent alkalinity, the AAA process did not have an advantage over one aerobicanoxic (OAA) cycle on treatment efficiency because microorganisms had an adaptive stage at the alternating aerobic-anoxic transition, which would prolong the total cycling time. On the contrary, the AAA process made the system control more complicated. Under deficient influent alkalinity, when compared to OAA, the AAA process improved treatment efficiency and effluent quality with NH₄ ⁺-N in the effluent below the detection limit. In the nitrification, the average stoichiometric ratio between alkalinity consumption and ammonia oxidation is calculated to be 7.07 mg CaCO₃/mg NH₄ ⁺-N. In the denitrification, the average stoichiometric ratio between alkalinity production and NO₃ ⁻-N reduction is about 3.57 mg CaCO₃/mg NO₃ ⁻-N. As a result, half of the alkalinity previously consumed during the aerobic nitrification was recovered during the subsequent anoxic denitrification period. That was why the higher treatment efficiency in the AAA process was achieved without the supplement of bicarbonate alkalinity. If the lack of alkalinity in the influent was less than 1/3 of that needed, there is no need for external alkalinity addition and treatment efficiency was the same as that under sufficient influent alkalinity. Even if the lack of alkalinity in the influent was more than 1/3 of that needed, the AAA process was an optimal strategy because it reduced the external alkalinity addition and saved on operational cost. Translated from Acta Scientiae Circumstantiae, 2004, 24(4): 576–580 [译自: 环境科学学报]     

Contrasting factors controlling microbial respiratory activity in the sediment of two adjacent Mediterranean wetlands

Electron transport system (ETS) activity of sediments as an indication of microbial metabolic activity was examined in two adjacent Mediterranean wetlands (southern Spain). We determined the spatio-temporal variation in ETS, and we explored the potential biological [organic matter (OM), chlorophyll a (Chl a), aerobic and anaerobic bacteria] drivers of sediment ETS activity. ETS activity was notably higher in the eutrophic Lake Nueva (34.91 μl O₂ g⁻¹ D.W. h⁻¹) than in the hypertrophic Lake Honda (24.99 μl O₂ g⁻¹ D.W. h⁻¹). Strong spatial differences were observed in ETS in both study sites. Highest ETS values were achieved at the surface sediment at the deepest sampling station in each lake and a notable reduction in ETS with sediment depth was observed. By using linear regression and multiple regression analysis, OM was identified as the best predictor of ETS in Lake Honda while Chl a was the best predictor in Lake Nueva. The strong influence of OM supply on ETS activity in sediment from Lake Honda was the consequence of the labile nature of sedimentary OM, while a more refractory OM (with a higher contribution of vascular plants) comprised most of the sedimentary OM from Lake Nueva. By contrast, a large contribution of phytobenthos (supported by a higher lake water transparency) to ETS has been recognized in sediments from Lake Nueva. In summary, the results of this study revealed that the relative importance of planktonic primary producers (phytoplankton), benthic algae and vascular plants in the study sites could explain the differences observed in the intensity of sediment ETS as well as in their drivers.     

An Experimental Burn to Restore a Moth-Killed Boreal Conifer Forest, Krasnoyarsk Region, Russia

Mechanical treatment and prescribed fire were used to restore a mixed conifer stand (Picea-Abies-Pinus) following mortality from an outbreak of Siberian moth (Dendrolimus superans sibiricus). Moth-killed stands often become dominated by Calamagrostis, a sod-forming grass. The large amount of woody debris and the sod hinder coniferous seedling establishment and development as well as creating conditions favorable to the establishment and propagation of wildfires. Fire has been demonstrated to be an effective method of reducing woody debris and eliminating sod, but the random nature and timing of wildfires often do not create conditions favorable for conifer regeneration. Our study was conducted in a mature fir dominated stand that died during an outbreak 6–8 years previously with most of the dead trees still standing. A bulldozer drove through the stand downing standing snags in late summer with 15–20 m between passes. Snags knocked down by the bulldozer and additional snag fall throughout the following winter increased downed dead wood 50–60% and large downed dead wood 80% compared to an adjacent untreated area. In June, a prescribed fire was set and fuel load consumption averaged 70%. Average soil temperatures during the burn ranged from 47 ^∘C at a depth of 2 cm to 10 ^∘C at 10 cm; hot enough to kill the grass. Following treatment, the potential for wildfire was reduced and the area was suitable for either natural conifer regeneration or planting without further mechanical site preparation.