Progradation of the Changjiang River delta since the mid-Holocene

Subaqueous deltaic deposits with approximately 30 radiocarbon ages show that the Changjiang River delta was strongly affected by tides and that the delta progradation rate after 2 kaBP was almost double the rate before 2 kaBP. This change in the progradation rate correlates well with the active extension of the subaerial delta plain shown by previous work. Widespread human activities, such as farming, deforestation, and dike construction, probably resulted in an increase in sediment discharge to the river-mouth area.     

Use of chemometric and geostatistical methods to evaluate pesticide pollution in the irrigation and drainage channels of the Ebro river delta during the rice-growing season

Data sets obtained from quantitative analysis of seventeen pesticides in water samples from a network of irrigation and drainage channels in the Ebro river delta (Catalonia, NE Spain) have been analysed by chemometric and geostatistical methods. Samples were taken at fourteen locations during the main rice-growing season, from May to August 2005. Principal-component analysis enabled investigation of the spatial and temporal distribution of the main pollution patterns caused by application of pesticides in the region under study. A first pesticide-contamination pattern from the Ebro river was differentiated from a second more specific pattern from the water-drainage channels of the delta, collected from the rice fields. The seasonal peak in this more specific rice pesticide source was observed in July. Coupling the results from chemometric data analysis with use of geostatistical methods was shown to be a useful procedure for discovery of the most significant spatial and monthly variations of the main pesticide-contamination patterns, taking into account the particular geographical structure of the area under study.     

Progradation of the Changjiang River delta since the mid-Holocene

Subaqueous deltaic deposits with approximately 30 radiocarbon ages show that the Changjiang River delta was strongly affected by tides and that the delta progradation rate after 2 kaBP was almost double the rate before 2 kaBP. This change in the progradation rate correlates well with the active extension of the subaerial delta plain shown by previous work. Widespread human activities, such as farming, deforestation, and dike construction, probably resulted in an increase in sediment discharge to the river-mouth area.     

Contamination by Organochlorine Pesticides in the Estuaries of Southeast China* 06 A

Persistent organic pollutants(POPs) such as organochlorine pesticides are of global concern due to their widespread occurrence and persistence. This paper reports recent research studying the distribution and fate of organochlorine pesticides in the Jiulong River, the Minjiang River and the Pearl River estuaries in Southeast China. Eighteen organochlorine pesticides were extracted from water, pore water and sediment samples, followed by analysis by GC-ECD. The results showed that the contamination levels were similar in these three estuaries.The levels of the total organochlorine pesticides in porewater were significantly higher than those in surface water, due to the high affinity of these hydrophobic compounds for sediment phase. Among the hexachlorocyclohexane (HCH) compounds, β-HCH was found to be the most important isomer. The analysis of 1, 1,1-trichloro-2,2-bis-chlorophenyl-ethane(DDT) and its metabolites showed that 1, 1-dichloro-2[o-chlorophenyl]-2[p-chlorophenyl]-ethylene (DDE) was dominant in the group.Koywords Organochlorine insecticides, DDT, Lindane, Jiulong River Estuary, Minjiang River Estuary, Pearl River Estuary, Water, Sediment     

SEDIMENTO-DYNAMIC CHARACTERISTICS OF THE HUANGHE (YELLOW) RIVER SUBAQUEOUS DELTA

The runoff of the Huanghe contains a great amount of suspended load and forms the high-density underflows (hyperpycnal currents) at the river mouth. The sediments over the subaqneous delta are mainly transported by the underflow. The sediment texture gradually get fining seawards, which relates to the attenuation of the hyperpycnal currents and hypopycnal plumes. Being hydraulically equivalent to the medlum-silt-sized quartz, which is the dominant component in the sediments, the clastic mica concentrates on the delta. The maximum thickness of the subaqueous delta is about 16m and the period of accumulation lasted from 12 to 16 years, therefore its sedimentary rate ranges from 110 to 130 cm/a.     

Large old trees influence patterns of delta13C and delta15N in forests

Large old trees are the dominant primary producers of native pine forest, but their influence on spatial patterns of soil properties and potential feedback to tree regeneration in their neighbourhood is poorly understood. We measured stable isotopes of carbon (delta(13)C) and nitrogen (delta(15)N) in soil and litter taken from three zones of influence (inner, middle and outer zone) around the trunk of freestanding old Scots pine (Pinus sylvestris L.) trees, to determine the trees' influence on below-ground properties. We also measured delta(15)N and delta(13)C in wood cores extracted from the old trees and from regenerating trees growing within their three zones of influence. We found a significant and positive gradient in soil delta(15)N from the inner zone, nearest to the tree centre, to the outer zone beyond the tree crown. This was probably caused by the higher input of (15)N-depleted litter below the tree crown. In contrast, the soil delta(13)C did not change along the gradient of tree influence. Distance-related trends, although weak, were visible in the wood delta(15)N and delta(13)C of regenerating trees. Moreover, the wood delta(15)N of small trees showed a weak negative relationship with soil N content in the relevant zone of influence. Our results indicate that large old trees control below-ground conditions in their immediate surroundings, and that stable isotopes might act as markers for the spatial and temporal extent of these below-ground effects.     

A statistical approach to delta layer depth profiling

We present a simple statistical model describing the removal and relocation of material during a sputter depth profiling experiment. All input parameters are determined from low‐fluence molecular dynamics simulations, making the model de facto parameter free. The model can be used to extrapolate data from the molecular dynamics simulations to projectile fluences relevant to sputter depth profiling experiments. As a result, the erosion of the surface is calculated in terms of fluence‐dependent filling factors of different sample layers. Using input data determined for the 20‐keV C₆₀ cluster bombardment of silicon, it is found that a steady‐state erosion profile is reached after removal of approximately 20 monolayer equivalents of material. Plotting the contribution of particles from a specific layer to the instantaneous sputtered flux, one can directly determine the delta layer response function predicted from such a model. It is shown that this function can be parameterized by the semiempirical Dowsett response function, and the resulting fitting parameters are compared with published depth profile data. The model is then used to study the role of different processes influencing the observed depth resolution. We find that the statistical nature of the sputtering process suffices to explain many features of experimentally measured delta layer depth profiles. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of flooding on delta15N, delta18O, 1delta15N and 2delta15N signatures of N2O released from estuarine soils--a laboratory experiment using tidal flooding chambers

The influence of flooding on N2O fluxes, denitrification rates, dual isotope (delta18O and delta15N) and isotopomer (1delta15N and 2delta15N) ratios of emitted N2O from estuarine intertidal zones was examined in a laboratory study using tidal flooding incubation chambers. Five replicate soil cores were collected from two differently managed intertidal zones in the estuary of the River Torridge (North Devon, UK): (1) a natural salt marsh fringing the estuary, and 2 a managed retreat site, previous agricultural land to which flooding was restored in summer 2001. Gas samples from the incubated soil cores were collected from the tidal chamber headspaces over a range of flooding conditions, and analysed for the delta18O, delta15N, 1delta15N and 2delta15N values of the emitted N2O. Isotope signals did not differ between the two sites, and nitrate addition to the flooding water did not change the isotopic content of emitted N2O. Under non-flooded conditions, the isotopic composition of the emitted N2O displayed a moderate variability in delta18O and 2delta15N delta values that was expected for microbial activity associated with denitrification. However, under flooded conditions, half of the samples showed strong and simultaneous depletions in 1delta15N and delta18O values, but not in 2delta15N. Such an isotope signal has not been reported in the literature, and it could point towards an unidentified N2O production pathway. Its signature differed from denitrification, which was generally the N2O production pathway in the salt marsh and the managed retreat site.     

Improved compound-specific delta13C analysis of n-alkanes for application in palaeoenvironmental studies

We present an optimized method for compound-specific stable carbon isotope (delta(13)C) analysis of n-alkanes. For sample preparation, the traditionally used Soxhlet extraction was replaced by accelerated solvent extraction (ASE). delta(13)C values of individual n-alkanes--measured using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS)--were first drift-corrected with regularly discharged pure CO(2) pulses as reference gas and, secondly, corrected for the amount dependence of the delta(13)C values by co-analyzing standards with varying analyte concentrations. Finally, the delta(13)C values were calibrated against two internal standards. The improved method was applied to selected sediment samples from a palaeoenvironmental study in subtropical NE Argentina. The measured delta(13)C values of all long-chain n-alkanes (nC(27), nC(29), nC(31) and nC(33)), representing biomarkers for terrestrial plants, correlate significantly with the delta(13)C of bulk organic matter (delta(13)C(TOC)). The latter is hence corroborated as a proxy for C3-C4 vegetation changes. Furthermore, the delta(13)C variations reveal higher amplitudes for nC(31) and nC(33) than for nC(27) and nC(29), indicating that the former n-alkanes mainly derive from C3 and/or C4 grasses, whereas the latter homologues mainly derive from C3 plants (trees and shrubs). Except for the lowermost part of the sediment core, the delta(13)C values of the mid-chain alkanes nC(23) and nC(25) do not reflect the terrestrial delta(13)C pattern, thus indicating that they are probably mainly of lacustrine origin.     

Use of carbon isotope analysis to understand semi-arid erosion dynamics and long-term semi-arid land degradation

Many semi-arid areas worldwide are becoming degraded, in the form of C(4) grasslands being replaced by C(3) shrublands, which causes an increase in surface runoff and erosion, and altered nutrient cycling, which may affect global biogeochemical cycling. The prevention or control of vegetation transitions is hindered by a lack of understanding of their temporal and spatial dynamics, particularly in terms of interactions between biotic and abiotic processes. This research investigates (1) the effects of soil erosion on the delta(13)C values of soil organic matter (SOM) throughout the soil profile and its implications for reconstructing vegetation change using carbon-isotope analysis and (2) the spatial properties of erosion over a grass-shrub transition to increase understanding of biotic-abiotic interactions by using delta(13)C signals of eroded material as a sediment tracer. Results demonstrate that the soils over grass-shrub transitions are not in steady state. A complex interplay of factors determines the input of SOM to the surface horizon of the soil and its subsequent retention and turnover through the soil profile. A positive correlation between event runoff and delta(13)C signatures of eroded sediment was found in all plots. This indicates that the delta(13)C signatures of eroded sediment may provide a means of distinguishing between changes in erosion dynamics over runoff events of different magnitudes and over different vegetation types. The development of this technique using delta(13)C signatures of eroded sediment provides a new means of furthering existing understanding of erosion dynamics over vegetation transitions. This is critical in terms of understanding biotic-abiotic feedbacks and the evolution of areas subject to vegetation change in semi-arid environments.     

Long-term morpho-dynamics in special type of estuary

Thousands of rocky hills and islands scattered in the Pearl River delta plain and the adjacent coastal waters in South China have been or will be acted as deposition nucleus during the evolution process of the delta. The Huangmaohai estuarine complex consists of two of the eight major outlets of the Pearl River estuarine system. Since sea level reached the present level approximately 6000 years ago, especially in the last 250 years, the Huangmaohai estuarine complex has progressed to the sea by filling up the sea inlets formed between these rocky islands and between mainland and islands. This 'filling up' process left deep imprints on the long-term mor-pho-dynamic equilibrium in the estuaries. The present paper reveals that the long-term mor-pho-dynamic relation originating from this 'filling up' process in the Huangmaohai estuarine complex is different from that in many coastal plain estuaries in several aspects: (1) longitudinal variation of estuary width, (2) longitudinal variation of tidal range, (3)     

Long-term morpho-dyn amics in special type of estuary

Thousands of rocky hills and islands scattered in the Pearl River delta plain and the adjacent coastal waters in South China have been or will be acted as deposition nucleus during the evolution process of the delta. The Huangmaohai estuarine complex consists of two of the eight major outlets of the Pearl River estuarine system. Since sea level reached the present level approximately 6000 years ago, especially in the last 250 years, the Huangmaohai estuarine complex has progressed to the sea by filling up the sea inlets formed between these rocky islands and between mainland and islands. This ‘filling up’ process left deep imprints on the long-term morpho-dynamic equilibrium in the estuaries. The present paper reveals that the long-term morpho-dynamic relation originating from this ‘filling up’ process in the Huangmaohai estuarine complex is different from that in many coastal plain estuaries in several aspects: (1) longitudinal variation of estuary width, (2) longitudinal variation of tidal range, (3) unique combination of small-scale dynamic structures, (4) bidirectional jet systems, and (5) velocity field and turbidity maximum.     

Diffusion-reaction approach to electronic relaxation in solution. Exact solution for delta function sink models

We give a general method for finding the exact solution for the problem of electronic relaxation in solution, modelled by a particle undergoing diffusive motion in a potential in presence of a delta function sink. The diffusive motion is described by the Smoluchowski equation and the sink could be a delta function of arbitrary position and strength. The solution requires the knowledge of the Laplace transform of the Green’s function for the motion in the absence of the sink. We use the method to find the solution of the problem in the case where the diffusive motion is on a parabolic potential. This has been an unsolved problem for some time and is of considerable importance as a model for non-radiative electronic relaxation of a molecule in solution. The solution is analyzed to obtain the viscosity and temperature dependences of the rate constants.     

Minimization of carbon addition during derivatization of monosaccharides for compound-specific delta13C analysis in environmental research

Little is known about the delta13C composition of monosaccharides representing the largest carbon reservoir in the biosphere. The main reason for this might be that monosaccharides have to be derivatized prior to gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analyses and that a large isotopic correction is necessary for the carbon that has to be added to the original molecule during derivatization, resulting in large uncertainty of the calculated delta13C values of individual monosaccharides. The amount of added derivatization carbon is twice (alditol acetates) or even three times (trimethylsilyl (TMS) derivatives) as high as the amount of the original monosaccharide carbon. In addition, isotope fractionation occurs during acetylation. Therefore, the objectives of this study were (i) to minimize carbon addition during derivatization for GC/C/IRMS measurements of monosaccharides in soil and sediment samples and (ii) to quantify improvements in accuracy and precision of the final results. Minimization of carbon addition was accomplished by derivatization with methylboronic acid (MBA) and TMS thereafter (MBA method). Monosaccharides derivatized with the MBA method instead of TMS reduced the number of added carbon atoms from 2.2-2.7 to 0.3-0.8 per sugar carbon atom. Although the precision of GC/C/IRMS measurements with both methods is comparable (about 0.3 per thousand), delta13C values of an internal standard indicated that the newly developed MBA method is about 2 per thousand more accurate than the TMS method. delta13C comparison between soil samples that differed only slightly in their bulk carbon isotope signature showed that the MBA method is better in proving these small differences on a significant level. Total precision of the whole MBA method including all analytical and calculation steps is better by a factor of almost three than the TMS method.     

Evaluation of the sputtering rate variation in SIMS ultra‐shallow depth profiling using multiple short‐period delta layers

We have developed multiple short‐period delta layers as a reference material for SIMS ultra‐shallow depth profiling. Boron nitride delta layers and silicon spacer layers were sputter‐deposited alternately, with a silicon spacer thickness of 1–5 nm. These delta‐doped layers were used to measure the sputtering rate change in the initial stage of oxygen ion bombardment. A significant variation of sputtering rate was observed in the initial 3 nm or less. The sputtering rate in the initial 3 nm was estimated to be about four times larger than the steady‐state value for 1000 eV oxygen ions. Copyright © 2003 John Wiley & Sons, Ltd.     

Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.     

Methods to adjust for the interference of N2O on delta13C and delta18O measurements of CO2 from soil mineralization

In this paper we present an overview of the present knowledge relating to methods that avoid interference of N2O on delta13C and delta18O measurements of CO2. The main focus of research to date has been on atmospheric samples. However, N2O is predominantly generated by soil processes. Isotope analyses related to soil trace gas emissions are often performed with continuous flow isotope ratio mass spectrometers, which do not necessarily have the high precision needed for atmospheric research. However, it was shown by using laboratory and field samples that a correction to obtain reliable delta13C and delta18O values is also required for a commercial continuous flow isotope ratio mass spectrometer. The capillary gas chromatography column of the original equipment was changed to a packed Porapak Q column. This adaptation resulted in an improved accuracy and precision of delta13C (standard deviation(Ghent): from 0.2 to 0.08 per thousand; standard deviation(Lincoln): from 0.2 to 0.13 per thousand) of CO2 for N2O/CO2 ratios up to 0.1. For delta18O there was an improvement for the standard deviation measured at Ghent University (0.13 to 0.08 per thousand) but not for the measurements at Lincoln University (0.08 to 0.23 per thousand). The benefits of using the packed Porapak Q column compared with the theoretical correction method meant that samples were not limited to small N(2)O concentrations, they did not require an extra N2O concentration measurement, and measurements were independent of the variable isotopic composition of N2O from soil.     

Analysis of major and trace elements by INAA to predict the thousands year old sediment deposition environment in the Meghna river delta

Major, trace and rare earth elements have been measured in sediments of different layers to determine the controls of constituent minerals on the distribution of elements and sediment deposition environment in the Meghna river delta. The geochemical composition of sediments was enriched in SiO₂, Ca, Mg and Ba and depleted in Al, Fe, Ti, Mn, and Sr relative to PAAS (Post-Archaen Average Shale) value. The X-ray diffraction and elemental analyses demonstrate the dominant presence of quartz, micas, feldspar, chlorite, amphibole and clay minerals in sediments. The very low contents of trace elements suggest that the oxic condition was more prevalent during sediment deposition of Pleistocene-Holocene period and reflect the massive chemical weathering by biogeochemical reactions. The enrichment of light rare earth elements and La/Yb ratio reflect the intense silicate weathering of crustal materials and the high sediment depositional rate in the Meghna river delta.     

Seasonal changes in coastal dynamics and morphological behavior of the central and southern Changjiang River delta

Seasonal changes in sea level, tidal range, wind, riverine discharges, nearshore SSC (suspended sediment concentration) and bed-level of intertidal flat at 4 different sites were shown. In addition, the statistical relationships between the dynamics and the behavior of the sediment surface were examined. The average intertidal elevation seems negatively correlated to sea level while positively correlated to nearshore SSC. The effect of wind on seasonal cycle of average intertidal elevation is not evident although wind is an important factor governing short-term erosion/accretion events. The influence of riverine discharges on seasonal cycle of deltaic intertidal flats is masked by other factors. It is concluded that seasonality on mudflats is more complicated than on beaches.     

Probing residual interactions in unfolded protein states using NMR spin relaxation techniques: an application to delta131delta

Residual interactions in delta131delta, a large disordered fragment of staphylococcal nuclease, have been probed at two different pHs using backbone (15)N and side-chain methyl (2)H NMR spin relaxation techniques. The amplitudes of picosecond time-scale motions of both the backbone and side chains do not change considerably at either pH value, although they are significantly larger than those observed for folded proteins. In contrast, dramatic increases in the amplitudes of motions occurring on a nanosecond time scale are observed throughout delta131delta at pH 3 relative to pH 5. This is consistent with a picture in which residual hydrophobic contacts at pH 5 are disrupted by electrostatic repulsions that dominate at the lower pH.