Potential P limitation leads to excess N in the pearl river estuarine coastal plume

There is excess nitrate (NO3) in the Pearl River coastal plume in the southern waters of Hong Kong in summer. We hypothesize that phosphorus (P) limitation controls the utilization of excess NO3 due to the high N:P ratio in the Pearl River. To test this hypothesis, we conducted two 1-day cruises on July 13 and 19, 2000 to examine the response of the phytoplankton to P additions with respect to changes in biomass, uptake of nutrients and nutrient uptake ratios using a batch incubation of natural water samples collected from the Pearl River estuary and adjacent coastal waters. At a station (E1, salinity =5) in the Pearl River estuary, the N/P ratio at the surface was 46:1, (64 muM DIN: 1.3 muM PO4) and decreased to 24:1 (12 muM DIN: 0.5 muM PO4) downstream at a station (Stn 26, salinity =26) in the coastal plume south of Hong Kong. Without a P addition, NO3 in the water samples collected at E1 could not be depleted during a 9 day incubation (similar to20 muM NO3 remaining). With a P addition, NO3 disappeared completely on day 6 with the depletion of the added PO4 (2-3 muM). This was also true for a station, E4 (salinity= 15) further downstream, but within the estuary. At Stn 26, in the coastal plume south of Hong Kong, NO3 (similar to11.5 muM) was eventually depleted without the addition of PO4, but it took 8 days instead of 5 days for Stn E4. The uptake ratio of dissolved inorganic nitrogen (DIN) to PO4, without a P addition was 51:1, 43:1 and 46:1 for Stns E1, E4 and 26, respectively. With a P addition, the DIN/PO4 uptake ratio decreased to 20:1, 14:1 and 12:1, respectively, for the 3 stations. These results clearly indicate potential P limitation to utilization of NO3 in the Pearl River estuary, resulting in excess NO3 in waters of the coastal plume downstream of the estuary, some of which would eventually be transported offshore. High uptake ratios of N:P without a P addition (43N:1P) suggest that phytoplankton have a nitrogen uptake capacity in excess of the Redfield ratio of 16N: 1P by 2.5-3 times. The value of 2.5-3 times was likely a maximum that should have contained a contribution of P released from desorption of P from sediments or from regeneration by zooplankton grazing and bacterial activity during the incubation of natural water samples. Without a P addition, however, phytoplankton biomass did not increase. This means that P turnover rates or regeneration may allow phytoplankton to take up additional N in excess of the Redfield ratio and store it, but without increasing the algal biomass. Therefore, high ambient N:P ratios in excess of the Redfield ratio do indicate potential P limitation to phytoplankton biomass in this estuarine coastal ecosystem. (C) 2004 Elsevier Ltd. All rights reserved.

Response of cyanobacterial carbon concentrating system to light intensity: a simulated analysis

Cyanobacteria possess a delicate system known as the carbon concentrating mechanism (CCM), which can efficiently elevate the intracellular inorganic carbon (Ci) concentration via active transportation. The system requires energy supplied by photosystems; therefore, the activity of the Ci transporter is closely related to light intensity. However, the relationship between CCM and light intensity has rarely been evaluated. Here, we present an improved quantitative model of CCM in which light is incorporated, and developed a CCM model that modified after Fridlyand et al. in 1996. Some equations used in this model were inducted to describe the relationship between transport capacity and light intensity, by which the response of the CCM to light change is simulated. Our results indicate that the efficiency of the carbon concentrating system is sensitive to light intensity. When the external Ci concentration was low, CO2 uptake dominated the total Ci uptake with increasing light intensity, while under high external Ci concentrations HCO3- uptake primarily contributed to the total Ci uptake. Variations in the ratio of energy allocated between the transport systems could markedly affect the operation of CCM. Indeed, our simulations suggest that various combinations of Ci fluxes can provide a possible approach to detect the way by which the cell distributes energy produced by the photosystems to the two active Ci transport processes. The proportion of the energy consumed on CCM to the total energy expenditure for the fixation of one CO2 molecule was determined at 18%-40%.

Simultaneous Determination of Multi-Organotin Compounds in Seawater by Liquid-Liquid Extraction-High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

The hyphenated technique of high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was applied to the simultaneous determination of five organotin compounds (trimethyltin, dibutyltin, tributyltin, diphenyltin and triphenyltin) in seawater samples. Agilent TC-C18 column was used for the separation, the mobile phase of HPLC was CH3CN : H2O: CH3COOH=65 : 23 : 12 (phi), 0.05% TEA, and pH value was adjusted to 3.0 by diluent ammonia. The flow rate was 0.6 mL . min(-1). Five mixed organotin compounds in a mix standard solution from 100 to 0.5 mu g . L-1 were applied for the method assessment. The experimental results indicate that the correlation coefficient of calibration curves (R-2) for each organotin compound was over 0.998 and the detection limits of the five organotin compounds were lower than 3 ng . L-1. Different mixed organic solvents including dichloromethane or toluene were used for extraction of organotin and the extraction condition of organotin from seawater was optimized. The 100 mL seawater acidized by hydrochloric acid was extracted by 10 mL carbon dichloride (CH2Cl2) with 2% tropolone for 10 min twice. Extracted organic solvents were mixed And blown to one drop by nitrogen with the rate of 1.7 mL . min(-1), then 1 mL acetonitrile was added to the drop for redissolving the organotin compounds. Finally, the mixed redissolution was filtered by 0.22 mu m organic filter membrane before analysis. it was found that the only organotin compound in seawater was triphenyltin (TPHT) and the content was 53.2 ng . L-1. The recoveries test from the standard addition for diphenyltin (DPHT), dibutyltin (DBT), tributyltin (TBT) and triphenyltin (TPHT) were over 80%. However, the recovery for trimethyltin (TMT) was relatively low and the value was 50%. The reason might be attributed to the decomposition or adsorption of those compounds during the extraction procedure. Further study on this subject is in progress.

Stress corrosion cracking of AISI 321 stainless steel in acidic chloride solution

The stress corrosion cracking (SCC) of LambdaISI 321 stainless steel in acidic chloride solution was studied by slow strain rate (SSR) technique and fracture mechanics method. The fractured surface was characterized by cleavage fracture. In order to clarify the SCC mechanism, the effects of inhibitor KI on SCC behaviour were also included in this paper. A study showed that the inhibition effects of KI on SCC were mainly attributed to the anodic reaction of the corrosion process. The results of strain distribution in front of the crack tip of the fatigue pre-cracked plate specimens in air, in the blank solution (acidic chloride solution without inhibitor KI) and in the solution added with KI measured by speckle interferometry (SPI) support the unified mechanism of SCC and corrosion fatigue cracking (CFC).

Speciation Analysis of Organotin Compounds in Shellfish by Hyphenated Technique of High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

The hyphenated technique of high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry(HPLC-ICP-MS) was applied to the simultaneous determination of five organotin compounds in the shellfish samples. Agilent TC-C-18 column was selected, mobile phase of the HPLC was CH3CN:H2O: CH3COOH = 65:23:12 (V/V), 0. 05% TEA, pH = 3.0 at flow rate 0.4 mL/min. Five mixed organotin standards from 100 mu g/L to 0. 5 mu g/L was used for the method evaluation. The experimental results indicate that the linearity (R-2) for each compound was over 0.998. The shellfish samples were treated by supersonic extraction with mobile phase for 30min. Four organotin compounds including dibutyltin (DBT), tributyltin (TBT), diphenyltin (DphT) and triphenyltin (TPhT) in shellfish samples were detected with method mentioned above. It was found that the domain compounds in the samples were tributyltin (TBT) and triphenyltin (TPhT). The recoveries test from the standard addition for trimethyltin (TMT tributyltin (TBT), and triphenyltin (TPhT) were, over 80%. However, the recoveries for diphenyltin (DPhT) and dibutyltin (DBT) were relatively low, 37.3% and 75.2% respectively. The reason might be attributed to the decomposition of those compounds during the extraction procedure. The further study on this subject is under the progress.

Growing season ecosystem respirations and associated component fluxes in two alpine meadows on the Tibetan Plateau

From 30 June to 24 September in 2003 ecosystem respiration (Re) in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- (GC) based techniques. Simultaneously, plant removal treatments were set to partition Re into plant autotrophic respiration (Ra) and microbial heterotrophic respiration (Rh). Results indicated that Re had clear diurnal and seasonal variation patterns in both of the meadows. The seasonal variability of Re at both meadow sites was caused mainly by changes in Ra, rather than Rh. Moreover, at the Kobresia humilis meadow site (K_site), Ra and Rh accounted for 54% and 46% of Re, respectively. While at the Potentilla fruticosa scrub meadow (P_site), the counterparts accounted for 61% and 39%, respectively. T test showed that there was significant difference in Re rates between the two meadows (t = 2.387, P = 0.022). However, no significant difference was found in Rh rates, whereas a significant difference was observed in Ra rates between the two meadows. Thus, the difference in Re rate between the two meadows was mainly attributed to plant autotrophic respirations. During the growing season, the two meadows showed relatively low Q(10) values, suggesting that Re, especially Rh was not sensitive to temperature variation in the growing season. Additionally, Re and Rh at the K_site, as well as Rh at the P_site was negatively correlated with soil moisture, indicating that soil moisture would also play an important role in respirations.

Photosynthesis of Saussurea superba and Gentiana straminea is not reduced after long-term enhancement of UV-B radiation

Experiments were conducted in an alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37degrees29'-37degrees45'N, 101degrees12'-101degrees33'E; altitude 3200 m). Effects of enhanced ultraviolet-B (UV-B) radiation on photosynthesis of the alpine plants of Saussurea superba and Gentiana straminea were investigated. Both species were exposed to a UV-B-BE density at 15.80 kJ m(-2) per day, simulating nearly 14% ozone (O-3) reduction during the plant growing season. Neither photosynthetic CO2 uptake rate nor photosynthetic O-2 evolution rate were decreased after a long period of enhanced UV-B radiation treatment. On the contrary, there was a tendency to increase of both parameters in both species. The photosynthetic pigments were also increased, when expressed on a leaf area basis. UV-B absorbing compounds, detected by the absorbance values at 300 mm, had a tendency to increase in both species after enhanced UV-B radiation. After long-term exposure of plants to enhanced UV-B radiation, leaf morphology was also affected. Leaf thickness in both S. superba and G. straminea were increased significantly (P < 0.001). This supports our hypothesis that the increase of leaf thickness in both species after long-term exposure of enhanced UV-B radiation could compensate for the photodestruction of photosynthetic pigments when light passes through the leaf. Therefore, photosynthesis is not reduced in either species when expressed on leaf area basis. (C) 2003 Elsevier B.V. All rights reserved.

太阳活动变化对中低纬电离层的影响

With the variations of solar activity, solar EUV and X-ray radiations change over different timescales (e.g., from solar cycle variation to solar flare burst). Since solar EUV and X-ray radiations are the primary energy sources for the ionosphere, theirs variations undoubtedly produce significant and complicated effects on the ionosphere. So the variations of solar activity significantly affect the ionosphere. It is essential for both ionospheric theory and applications to study solar activity effects on the ionosphere. The study about solar activity variations of the ionosphere is an important part of the ionospheric climatology. It can enhance the understanding for the basic processes in the ionosphere, ionospheric structure and its change, ionosphere/thermosphere coupling, and so on. As for applications, people need sufficient knowledges about solar activity variations of the ionosphere in order to improve ionospheric models so that more accurate forecast for the ionospheric environments can be made. Presently, the whole image about the modalities of ionospheric solar activity variations is still unknown, and related mechanisms still cannot be well understood. This paper is about the effects of the 11-year change in solar activity to the low- and mid-latitude ionosphere. We use multi-type ionospheric observations and model to investigate solar activity effects on the electron density and ionospheric spatial structure, and we focus on discussing some related mechanisms. The main works are as follows: Firstly, solar activity variations of ionospheric peak electron density (NmF2) around 1400 LT were investigated using ionosonde observations in the 120°E sector. The result shows that the variation trend of NmF2 with F107 depends on latitudes and seasons. There is obvious saturation trend in low latitudes in all seasons; while in middle latitudes, NmF2 increases linearly with F107 in winter but saturates with F107 at higher solar activity levels in the other seasons. We calculated the photochemical equilibrium electron density to discuss the effects induced by the changes of neutral atmosphere and dynamics processes on the solar activity variations of NmF2. We found that: (1) Seasonal variation of neutral atmosphere plays an important role in the seasonal difference of the solar activity variations of NmF2 in middle latitudes. (2) Less [O]/[N2] and higher neutral temperature are important for the saturation effect in summer, and the increase of vibrational excited N2 is also important for the saturation effect. (3) Dynamics processes can significantly weaken the increase of NmF2 when solar activity enhances, which is also a necessary factor for the saturation effect. Secondly, solar activity variations of nighttime NmF2 were investigated using ionosonde observations in the 120°E sector. The result shows that the variation trends of NmF2 with F107 in nighttime are different from that in daytime in some cases, and the nighttime variation trends depend on seasons. There is linear increase trend in equinox nighttime, and saturation trend in summer nighttime, while the increase rate of NmF2 with F107 increases when solar activity enhances in winter nighttime (we term it with “amplification trend”). We discussed the possible mechanisms which affect the solar activity variations of nighttime NmF2. The primary conclusions are as follows: (1) In the equatorial ionization anomaly (EIA) crest region, the plasma influx induced by the pre-reversal enhancement (PRE) results in the change of the variation trend between NmF2 and F107 from “saturation” to “linear” after sunset in equinoxes and winter; while the recombination process at the F2-peak is the primary factor that affects the variation trend of NmF2 with F107 in middle latitudes. (2) The recombination coefficient at the F2-peak height reaches its maximum at moderate solar activity level in winter nighttime, which induces NmF2 attenuates more quickly at moderate solar activity level. This is the main reason for the amplification trend. (3) The change of the recombination process at the F2-peak with solar activity depends on the increases of neutral parameters (temperature, density et al.) and the F2-peak height (hmF2). The seasonal differences in the changes of neutral atmosphere and hmF2 with solar activity are the primary reasons for the seasonal difference in the variation trend of nighttime NmF2 with F107. Finally, we investigated the solar activity dependence of the topside ionosphere in low latitudes using ROCSAT-1 satellite (at 600 km altitude) observations. The primary results and conclusions are as follows: (1) Latitudinal distribution of the plasma density is local time, seasonal, and solar activity dependent. In daytime, there is a plasma density peak at the dip equator. The peak is obviously enhanced at high solar activity level, and the strength of the peak strongly depends on seasons. While at sunset, two profound plasma density peaks (double-peak structure) are found in solar maximum equinox months. (2) Local time dependence of the latitudinal distribution is due to the local time variation of the equatorial dynamics processes. Double-peak structure is attributed to the fountain effect induced by strong PRE. Daytime peak enhances with solar activity since the plasma density increases with solar activity more strongly at the dip equator due to the equatorial vertical drift, and its seasonal dependence is mainly due to the seasonal variations of neutral density and the equatorial vertical drift. In the sunset sector, seasonal and solar activity dependences of the latitudinal distribution are related to the seasonal and solar activity variations of PRE. (3) The variation trend of the plasma density with solar activity shows local time, seasonal, and latitudinal differences. That is different from the changeless amplification trend at the DMSP altitude (840 km). Profound saturation effect is found in the dip equator region at equinox sunset. This saturation effect in the topside ionosphere is realated to the increase of PRE with solar activity. Solar activity variation trend of the topside plasma density was discussed quantitatively by Chapman-α function. The result shows that the effect induced by the change of the scale height is dominant at high altitudes; while the variation trend of ROCSAT-1 plasma density with solar activity is suggested to be related to the changes of the peak height, the scale height, and the peak electron density with solar activity.

渤海湾地区末次冰期古环境

The loess-paleosol sequence in China is one of the best archives for studying paleoenvironmental and paleoclimatic processes. The loess deposits in the coast of the Bohai Sea are suitable for the study of aridification in the northern China during glacial periods (fig.2-1). In this paper, stratigraphy was correlated by using magnetic susceptibility, grain size, and thermoluminence (TL) and accelerater mass spectrometer (AMS) ~(14)C ages. Based on the loess records, an interpretation has been made for paleoenvironmental changes on the coast of the Bohai Sea during the last glacials. The results of magnetic susceptibility, grain size, biostratigraphy, TL and ~(14)C dating, suggest that the loess-paleosol sequence in the coast of the Bohai Sea is discontinuous. The loess deposits correlated with the marine δ~(18)O stage 2 are usually absent in some profiles. Also, the thickness of the loess deposits in the same period varied significantly in different sections. In the coast of the Bohai Sea, the higher magnetic susceptibility corresponds to the finer grain size, consistent with the results of the Loess Plateau. It is indicated that the changes in magnetic susceptibility and grain size may record the paleoclimatic fluctuations of the last glacial. Although the loess deposits during the last glacial have been slightly altered by slope runoff, they have still remained main characters as the representative loess deposits of the Loess Plateau. During the last glacial, the less accumulation rate in the coast of the Bohai Sea is similar to that of the desert-loess transition zone in the northwestern Loess Plateau, and the all section contain high concentrations of sand (>60μm), indicate that the aridification in the Bohai Sea occurred during the glacial. But the changes in sand content of loess deposits along a north-south transect of the Bohai Sea and the changes of magnetic susceptibility implicate that desertification might not occur in the shelf of the Bohai Sea during the last glacial. The frequent fluctuations of summer monsoon during the marine δ~(18)O stage 4 are demonstrated by magnetic susceptibility, frequency-dependent susceptibility and the abundance of foraminifera. 46 genera, 71 species of foraminifera were identified from 138 loess samples. Almost all of the foraminifera are present in the last glacial loess, but the distribution patterns of foraminifera show significant temporal changes. The results of magnetic susceptibility, grain size and XRD indicate that not only sea-level changes had influences on foraminifera abundance, but also variations in sediment flux by rivers when sea-level drops might control the abundance of foraminifera. In addition, the diversity and exquitability of the foraminifera suggest that the frequent fluctuations of foraminifera fossil abundance during the marine δ~(18)O stages could be partly attributed to leaching. In summary, the changes in foraminifera of abundance related to the paleoclimatic variations, and the aridification extends to the coast of the eastern China during the last glacial.

Partial oxidation of ethane to syngas in an oxygen-permeable membrane reactor

A perovskite-type oxide of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) with mixed electronic and oxygen ionic conductivity at high temperatures was used as an oxygen-permeable membrane. A tubular membrane of BSCFO made by extrusion method has been used in the membrane reactor to exclusively transport oxygen for the partial oxidation of ethane (POE) to syngas with catalyst of LiLaNiO/gamma-Al2O3 at temperatures of 800-900 degreesC. After only 30 min POE reaction in the membrane reactor, the oxygen permeation flux reached at 8.2 ml cm(-2) min(-1). After that, the oxygen permeation flux increased slowly and it took 12 h to reach at 11.0 ml cm(-2) min(-1). SEM and EDS analysis showed that Sr and Ba segregations occurred on the used membrane surface exposed to air while Co slightly enriched on the membrane surface exposed to ethane. The oxygen permeation flux increased with increasing of concentration of C2H6, which was attributed to increasing of the driving force resulting from the more reducing conditions produced with an increase of concentration of C2H6 in the feed gas. The tubular membrane reactor was successfully operated for POE reaction at 875 degreesC for more than 100 h without failure, with ethane conversion of similar to 100%, CO selectivity of >91% and oxygen permeation fluxes of 10-11 ml cm(-2) min(-1). (C) 2002 Elsevier Science B.V. All rights reserved.

Coke formation during the methanol conversion to olefins in zeolites studied by UV Raman spectroscopy

Coke formation on/in ZSM-5, USY and SAPO-34 zeolites was investigated during the methanol conversion to olefins at temperatures from 298 to 773 K using ultraviolet (UV) Raman spectroscopy. The fluorescence interference that usually obscures the Raman spectra of zeolites in the conventional Raman spectroscopy, particularly for coked catalysts, can be successfully avoided in the UV Raman spectroscopy. Raman spectra are almost the same for adsorbed methanol on the three zeolites at room temperature. However, the Raman spectra of the surface species formed at elevated temperatures are quite different for the three zeolites. Coke species formed in/on SAPO-34 are mainly polyolefinic species, and in/on ZSM-5 are some aromatic species, but polyaromatic or substituted aromatic species are predominant in USY at high temperatures. Most of the coke species can be removed after a treatment with O-2 at 773 K, while some small amount of coke species always remains in these zeolites, particularly for USY. The main reason for the different behavior of coke formation in the three zeolites could be attributed to the different pore structures of the zeolites. (C) 2000 Elsevier Science B.V. All rights reserved.

Catalytic cracking of 1-butene to propene and ethene on MCM-22 zeolite

Catalytic cracking of butene to propene and ethene was investigated over HMCM-22 zeolite. The performance of HMCM-22 zeolite was markedly influenced by time-on-stream (TOS) and reaction conditions. A rapid deactivation during the first I h reaction, followed by a quasi-plateau in activity, was observed in the process along with significant changes in product distributions, which can be attributed to the fast coking process occurring in the large supercages of MCM-22.

Combined single-pass conversion of methane via oxidative coupling and dehydro-aromatization

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO-La2O3/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate constant of the overall process revealed about 1.5 x 10(-6) s(-1). Up to 72 h on stream, the yield of aromatics was still maintained at 5.0% with a methane conversion of 9.6%, which is obviously higher than that reported for the conventional MDA process with single catalyst. Upon the TPR results, this wonderful enhancement would be attributed to an in-situ formation of CO2 and H2O through the OCM reaction, which serves as a scavenger for actively removing the coke formed during the MDA reaction via a reverse Boudouard reaction and the water gas reaction as well.