Economic Critical Resources for the Industrial Exploitation of Natural Gas Hydrate

Since the implementation of several pilot production tests were in natural gas hydrate(NGH) reservoirs in terrestrial and marine settings, the study of NGH has entered a new stage of technological development for industrial exploitation. Prior to the industrial exploitation of any given NGH reservoir, the economic feasibility should be examined. The first step of economic evaluation of a NGH reservoir is to know whether its resource amount meets the requirement for industrial exploitation. Unfortunately, few relevant studies have been conducted in this regard. In this study, the net present value(NPV) method is employed to estimate the economic critical resources required for the industrial exploitation of NGHs under different production scenarios. Sensitivity analysis is also performed in order to specify the effects of key factors, such as the number of production wells, gas price, technological improvement and tax incentive, on the economic critical resources. The results indicate that China requires the lowest economic critical resource for a NGH reservoir to be industrially exploited, ranging from 3.62 to 24.02 billion m3 methane. Changes in gas price and tax incentives also play significant roles in affecting the threshold and timeline for the industrial exploitation of NGH.

南海东沙海域末次冰期最盛期以来的沉积特征

对采自南海东北部东沙海域不同海区的14个大型重力活塞样进行肉眼观察描述、沉积物涂片分析和粒度分析，并利用浮游有孔虫氧碳同位素、AMS^14C测年和碳酸盐地层学等方法对上述柱状样进行地层年代划分。有关沉积特征结果表明，末次冰期最盛期以来其沉积物组分、沉积特征、沉积速率存在较明显的时空差异，从区域上可划分成3个沉积区：Ⅰ区沉积物类型较单一，沉积连续，未见底栖生物扰动和非正常搬运沉积，钙质组分相对贫乏，CaCO3含量偏低，一般不超过10％，自生黄铁矿特别丰富。沉积速率偏离，全新世沉积速率最高达41．7cm／ka；Ⅱ区水深最大，超过3000m，位于深海盆区。该区以沉积搬运作用明显，岩性复杂多变、浊流沉积较发育为特征。沉积物粒度明显变粗，砂含量在3个海区中最高，陆源物质石英、长石和钙质生物群（主要是有孔虫）明显增加，其中石英、长石含量最高达83％，CaCO3含量最高达57％。全新世沉积速率最高达31.6cm／ka；Ⅲ区以正常深海沉积为主，为青灰色含硅质钙质生物黏土质粉砂，富含生物化石，CaCO3含量一般介于10％～30％之间，石英、长石含量偏低，全新世沉积速率最高达20cm／ka。造成上述差异的主要因素有水深、地理位置、陆源物质的稀释作用、沉积搬运和碳酸盐溶解作用等。

Influence of Gas Hydrate on the Acoustic Properties of Sediment: A Comprehensive Review with a Focus on Experimental Measurements

In recent years, natural gas hydrate has attracted increasing attention worldwide as a potential alternative energy source due to its attributes of wide distribution, large reserves, and low carbon. Since the acoustic characteristics of hydratebearing reservoirs clearly differ from those of adjacent formations, an acoustic approach, using seismic and acoustic logging, is one of the most direct, effective and widely used methods among the identification and characterization techniques for hydrate reservoir exploration. This review of research on the influence of hydrate(content and distribution) on the acoustic properties(velocity and attenuation) of sediments in the past two decades includes experimental studies based on different hydrate formation methods and measurements, as well as rock physics models. The main problems in current research are also pointed out and future prospects discussed.

Extraction of Carotenoids and Fatty Acids from Microalgae Using Supercritical Technology

The work described here is based on a comparative study of carotenoids and fatty acids extracted from Synechococcus sp. with (1) pure supercritical CO2, (2) CO2 with 5% (v/v) ethanol as cosolvent and (3) ultrasound-assisted extraction using N, N-dimethylformamide (DMF). The effects of extraction conditions on supercritical CO2 extraction with and within cosolvent were analyzed at different temperatures (40℃, 50℃ and 60℃) and pressures (200, 300 and 400 bars). SFE with CO2 proved to be the most selective method for the extraction of β-carotene, but under these conditions the contents of zeaxanthin and fatty acids were only comparable to or lower than those obtained with techniques that use SFE cosolvent. The SFE technique with CO2 and ethanol simultaneously extracted β-carotene and zeaxanthin and not only increased the concentrations of fatty acids obtained, but also helped to remove fatty acids (palmitoleic and linolenic acid) that were not obtained with pure CO2. Comparison of the supercritical technology with the ultrasound-assisted extraction (UAE) shows that the former technique is the most appropriate due to the fact that ethanol is generally regarded as a safe solvent in comparison to DMF.

Expected adult lifespan in tropical trees: Long-term matrix demography in a large plot

Background: Documenting the entire lifetime of long-lived organisms requires splicing together short-term observations. Matrix demography provides a tool to calculate lifetime statistics, but large samples from juvenile to adult are needed, and few such studies have been done in tropical trees because high species diversity limits sample sizes. The 50-ha plot at Barro Colorado in Panama was designed to provide large samples, and with 30years of censuses, accurate population matrices can be constructed.Methods: In 31 abundant species, I divided all individuals≥1 cm dbh into 4 or 5 size class in each of seven censuses. Movements of stems between size classes over two censuses are termed transitions, and I constructed complete transition matrices for each species. From the matrices, I derived analytic solutions for lifetime demographic statistics. Expected adult lifespan from the sapling stage was the key statistic.Results: Expected adult lifespan from the sapling stage varied 100-fold over the 31 species, from 0.5 to 50 years,and maturation time varied from 19 to nearly 200 years. Species with the highest growth rates also had high death rates, and theoretical calculations of reproductive lifespan show that the fast-growing pioneer species have short expected adult lifespans relative to the average slow-growing, shade-tolerant species. Within the slowgrowth category, however, there was high variation in expected adult lifespan, and several shade-tolerant species under-performed the pioneers in terms of adult lifespan.Conclusions: Analytical solutions from population matrices allow theoretical analyses that integrate short-term growth records into lifespans of tropical trees. The analyses suggest that pioneer species must reproduce more successfully than shade-tolerant species to persist in the Barro Colorado forest. My next goal is to incorporate seed production and germination into lifetime matrix demography to test this hypothesis.

Basal repertoire of toxin-related transcripts in the zoanthid Protopalythoa variabilis(Cnidaria,Anthozoa)

OBJECTIVE To analyze the whole transcriptome of zoanthid Protopalythoa variabilis(P.variabilis),a cnidarian,and discover the potential toxic substances in P.variabilis.METHODS The P.variabilis RNA deep sequencing was performed using the HiSeq 2500 automatic sequencing platform.All the unigenes generated from the assembly process were functionally annotated based on the similarity with databases.The multiple alignments of translated toxin-related sequences were performed with Clustalw2,and amino acid identity and similarity highlighted by using BoxShade tool.Three different methods including ITASSER,PEP-FOLD and MODELLER were applied to predict tri-dimensional models of toxin-related polypeptides from translated transcript sequences of P.variabilis.The toxicity of one of the putative toxins,namely ShK/Aurelin-like peptide,was evaluated using zebrafish model.RESULTS A total of 67,549,914 pairs of quality-filtered,90-base-pair Illumina reads from an mRNA sample were obtained.The de novo assemblies yielded 276,526 contigs.The sequence comparison of 130,121 unigenes with entries in Toxin database showed that 1542 unigenes were potential peptide toxins at which 11 unigenes were related to Stichodactyla toxin(ShK)domain(Pfam ID:PF01549).ShK is a 35 residues peptide sequence that was firstly discovered from the sea anemone Stichodactyla helianthus.Here,we found out one ShK-like peptide that processed a relatively higher sequence similarity with known ShK(Uniprot ID:P29186)of Bunodosoma granuliferum(red warty sea anemone).The Protopalythoa Shk-like peptide was submitted to Probis server to detect probable binding site and found to match with a protein AURELIN(PDB id:2lg4,UniProt id:Q0MWV8)which possesses structural homology with previously identified antimicrobial peptides and K+-channel-blocking toxins.Our results showed that the ShK/Aurelin-like peptide was lethal to zebrafish embryos at concentrations above 30-μmol·L1,and could induce zebrafish locomotor deficit at 10μmol·L-1.CONCLUSION This study,for the first time,presented the whole transcriptome profile and a potential toxic peptide of P.variabilis.

UV-B as a Photoacclimatory Enhancer of the Hermatypic Coral <i>Stylophora pistillata</i>

Photoacclimation processes are crucial for the survival of all photosynthetic organisms in the photic zone. Changes in photosynthetic active radiation (PAR) are however simultaneous to changes in UV-B radiation. The influence of UV-B levels on bio-optical and physiological parameters of deep (30 m) corals from the species Stylophora pistillata and their symbiotic algae, zooxanthellae, was examined during their gradual, stepwise acclimation to a shallow depth (3 m). Drastic exposure of deeper corals to higher UV-B levels in shallower depths is usually fatal. Hence, the acclimation process lasted 118 days and included 10 intermediate stations with an addition of similar amount of PAR at each depth transfer. Concomitantly, in an on-shore experiment, fragments from the same colonies were acclimated by changing shading nets corresponding in PAR levels to each in situ station. Since UV-B is attenuated more efficiently than PAR in seawater, the PAR: UV-B ratio changes in the depth experiment while remaining constant under the neutral density nets. This provided the opportunity to evaluate the importance of UV-B to photoacclimation. In both experiments all fragments survived, in spite of a four-fold difference in levels of PAR and a 140-fold difference in UV-B flux between the initial and final conditions. Both experimental designs resulted in reduction of zooxanthellae density, photosynthesis rates, and quantum yields of PSII, while cellular chlorophyll content remained unaffected. Zooxanthellae density and maximal photosynthetic rate was found decreased in correlation with UV-B radiation, whether it was elevated logarithmically with reducing depths or linearly with reducing shades. Conversely, quantum yields of PSII were adjusted according to the enhancement of PAR rather than UV-B. We conclude that UV-B enhances the magnitude of photoacclimation to higher PAR. This novel aspect of photoacclimation can provide the basis for our understanding of the underlying mechanisms that result in UV-related bleaching.

the National Natural Science Foundation of China(41877029,41961130383);Royal SocietyNewton Advanced Fellowship(NAF\R1\191017);Wuhan Science and Technology Bureau(2019020701011469).

Due to the tremendous diversity of microbial organisms in topsoil,the estimation of saturated richness in a belowground ecosystem is still challenging.Here,we intensively surveyed the 16S rRNA gene in four 1 m2 sampling quadrats in a typical grassland,with 141 biological or technical replicates generating over 11 million sequences per quadrat.Through these massive data sets and using both non-asymptotic extrapolation and non-parametric asymptotic approaches,results revealed that roughly 15919±193,27193±1076 and 56985±2347 prokaryotic species inhabited in 1 m2 topsoil,classifying by DADA2,UPARSE(97%cutoff)and Deblur,respectively,and suggested a huge difference among these clustering tools.Nearly 500000 sequences were required to catch 50%species in 1 m2,while any estimator based on 500000 sequences would still lose about a third of total richness.Insufficient sequencing depth will greatly underestimate both observed and estimated richness.At least~911000,~3461000,and~1878000 sequences were needed for DADA2,UPARSE,and Deblur,respectively,to catch 80%species in 1 m2 topsoil,and the numbers of sequences would be nearly twice to three times on this basis to cover 90%richness.In contrast,α-diversity indexes characterized by higher order of Hill numbers,including Shannon entropy and inverse Simpson index,reached saturation with fewer than 100000 sequences,suggesting sequencing depth could be varied greatly when focusing on exploring differentα-diversity characteristics of a microbial community.Our findings were fundamental for microbial studies that provided benchmarks for the extending surveys in large scales of terrestrial ecosystems.

Evaporation and CO_(2)fluxes in a coastal reef:an eddy covariance approach

Introduction:We conducted season-long observations of evaporation and carbon flux at the Gulf of Aqaba coast,northern Red Sea.We used the eddy-covariance method with a two-tower setup to measure evaporation rates over land and sea and the advection between them.Using a three-dimensional mass balance approach,we calculated total evaporation as the sum of two main components in our site:horizontal advection and turbulent vertical flux,with half-hourly change of water vapor storage and horizontal flux divergence found to be negligible.Outcomes:Average evaporation rates were 11.4[mm/day]from April through May(early summer)and 10.5[mm/day]from June through August(summer).The coastal reef was a CO_(2)sink over the period of measurements,significantly higher in June through August than in April through May.The main environmental drivers of CO_(2)flux were humidity,water temperature,sensible heat flux,and wind speed.Discussion:The rates of evaporation near the shore were considerably higher than values reported in other studies typically used to represent the mean for the whole Gulf area.We found that evaporation rates computed by common bulk models approximate the mean values of evaporation but have poor representativeness of the intra-daily temporal variation of evaporation.There was a significant correlation between CO_(2)flux and evaporation attributed to common environmental drivers of gas diffusion,turbulent fluxes,and horizontal transport.Conclusion:We conclude that observations of fluxes in coastal waters need to use at least a two-tower system to account for the effect of horizontal advection on the total flux.