Mingyuan Du

Quantitative model of soil erosion rates using 137Cs for uncultivated soil

By using the mass balances model and by introducing an erosion constant (mean annual relative loss of 137 Cs) and depth distribution function of 137 Cs in soil, a quantitative model of soil erosion rate using 137 Cs loss was developed for uncultivated soils. Depth distribution patterns of 137 Cs in the soil profile, sampling years, and the amount of 137 Cs fallout each year were considered.The model shows that the estimated rate of soil erosion is controlled mainly by the distribution pattern of 137 Cs in the soil profile. By inputting different depth distribution functions of 137 Cs, the year of sampling and the different input fraction of total fallout value each year, several simulation results of soil loss were given.The results of numerical simulation proved that the relationship between the rate of soil loss and 137 Cs depletion is neither linear nor logarithmic. They are dependent on the distribution patterns of 137 Cs in the soil profile, sampling year, and input fraction of total fallout value.

A quantitative model for estimating mean annual soil loss in cultivated land using 137Cs measurements.

Abstract The radioisotope 137Cs has been widely used to determine rates of cultivated soil loss, Many calibration relationships (including both empirical relationships and theoretical models) have been employed to estimate erosion rates from the amount of 137Cs lost from the cultivated soil profile. However, there are important limitations which restrict the reliability of these models, which consider only the uniform distribution of 137Cs in the plough layer and the depth. As a result, erosion rates they may be overestimated or underestimated. This article presents a quantitative model for the relation the amount of 137Cs lost from the cultivated soil profile and the rate of soil erosion. According to a mass balance model, during the construction of this model we considered the following parameters: the remaining fraction of the surface enrichment layer (F R), the thickness of the surface enrichment layer (H s), the depth of the plough layer (H p), input fraction of the total 137Cs fallout deposition during a given year t (F t ), radioactive decay of 137Cs (k), sampling year (t). The simulation results showed that the amounts of erosion rates estimated using this model were very sensitive to changes in the values of the parameters F R, H s, H p. We also observed that the relationship between the rate of soil loss and 137Cs depletion is neither linear nor logarithmic, is very complex. Although the model is an improvement over existing approaches to derive calibration relationships for cultivated soil, it requires empirical information on local soil properties and the behavior of 137Cs in the soil profile. There is clearly still a need for more precise information on the latter aspect and, in particular, on the retention of 137Cs fallout in the top few millimeters of the soil profile and on the enrichment and depletion effects associated with soil redistribution (i.e. for determining accurate values of F R and H s).

137Cs depth distribution in haplic-udic ferrosols of southern China and its implication for soil erosion

The depth distribution of 137Cs (cesium-137) and its relationship with organic carbon and different particle size fractions in Haplic-Udic Ferrosols in Yujiang, Southern China, are described in this paper. Compared with other sites, the lower 137Cs inventories associated with uncultivated soils on or close to the crests indicate the relatively low 137Cs in situ retention ability of the soil. Therefore, the use of 137Cs techniques in erosion studies on uncultivated Haplic-Udic Ferrosols may create some significant difficulties and limitations, including identifying the suitable 137Cs reference site and its validity on and near the crests. The impact of the soil erosion process to a depth of more than 4 to 6 cm on the sloping dry farmland and dry terrace farmland indicates that the widely accepted assumption of uniform 137Cs depth distribution within the plough layer may not apply in these soils, although it does basically hold true for the paddy terrace field, in the area dominated by Haplic-Udic Ferrosols. For uncultivated Haplic-Udic Ferrosols, the organic matter may not control the downward migration of 137Cs because no significant relationship was found between the depth distribution of 137Cs and that of organic matter. It was also demonstrated that the 137Cs fallout is associated mainly with the clay fraction, whereas the organic matter is associated mainly with the silt fraction. For Haplic-Udic Ferrosols, the waterinduced erosion removes preferentially the clay associated with the relatively high concentration of 137Cs and low content of organic matter.

DISTRIBUTION OF 137CS AND ORGANIC CARBON IN PARTICLE SIZE FRACTIONS IN AN ALUMI-HAPLIC ACRISOL OF SOUTHERN CHINA

The distributions of 137Cs and organic carbon and their relationships in various particle size fractions of an Alumi-Haplic Acrisol in Southern China were studied. 137Cs was enriched primarily in the clay fraction (<2 μm), indicating that 137Cs was preferentially adsorbed by finer soil particles. Organic carbon content in the clay fraction was no higher than in the very fine silt fraction (2–5 μm) for most soil samples. For different particle size fractions of the Alumi-Haplic Acrisol, the relationship between 137Cs and organic carbon could be described by a power function for the clay fraction (<2 μm) and by a linear function for the other fractions. The significant correlation (r = 0.85, P = 0.05) between 137Cs and organic carbon in the clay fraction (<2 μm) demonstrated that organic carbon contributed to 137Cs sorption in the clay of the soil samples. A particle size correction factor was determined based on the distribution of 137Cs in different particle size fractions. The value of 1.3–1.5 for the particle size correction factor indicated that selective removal of soil particles during soil erosion had an important effect on the accuracy of the estimate of the soil erosion rate for the Alumi-Haplic Acrisol of Southern China Therefore, it is necessary to consider the particle size correction factor in the quantitative models of soil erosion in the Alumi-Haplic Acrisol of Southern China characterized by a high clay content.

Three dimensional numerical simulation of the flow over complex terrain with windbreak hedge

Abstract In order to clarify the effects of windbreaks on flow and to determine where to set windbreaks for the optimum prevention of wind erosion in a complex terrain, a three-dimensional numerical model for simulating wind distribution over a real complex terrain with a variation of relative height less than 100 m is used. The three-dimensional, time-dependent Navier–Stokes equation written with generalized coordinates and the Smagorinsky-type scheme for turbulent parameterization are use in the model. Numerical simulations of windbreak effect on wind speed distribution over a sand dune are carried out by erecting windbreak hedges at different places. The influence of topography and windbreaks on wind distribution, for example the location of the maximum wind speed reduction, are well simulated. Thus, the best setting place of windbreaks for the prevention of wind erosion may be decided by simulating the wind distribution over real terrain using the model. An example, using a 2 m high windbreak hedge for preventing sand shifting around a barchan sand dune, which is 5 m high, 64 m wide and 96 m long, is given and the effect of the windbreak hedge is discussed. The simulation results show that the best place should be at 18–22 m in front of the top of the sand dune.

Soil erosion study on hillside in Southern Jiangsu Province using the cesium-137 tracer technique

Abstract Up to now, there had been little concern about soil erosion in the low mountainous and hilly area of the southern Jiangsu Province. In order to analyze the erosion impacts on the eutrophication of Taihu Lake and on the local soil degradation, the 137Cs tracer technique was used to investigate the process of soil redistribution (soil erosion and soil deposition) in the study area. In our study, various landforms and different land uses were selected and the local 137CS reference inventory of 2,200 Bq m−2 was determined. Based on the principle of the 137Cs tracer technique, mass balance models with a definite physical significance for estimating the degree of erosion of cultivated and uncultivated soils were constructed. In contrast to most of the other models, especially the quantitative model of cultivated soil, 137Cs penetration to the depth below the cultivated layer was taken into account, which might enable to avoid overestimating the erosion rate. The results showed that soil erosion occurred in the southern Jiangsu Province and that the erosion rate of cultivated soil was much higher than that of uncultivated soil. The soil erosion rate in a tea plantation even reached a value of 3,913 Mg km−2 year−1. Besides, the results indicated that human activities can accelerate but also mitigate soil erosion.

Inflammatory and degranulation effect of yellow sand on RBL-2H3 cells in relation to chemical and biological constituents

Recent studie pointed out that allergic diseases have increased during the Asian dust storm event (ADSE) in Japan. Daily observations and the atmospheric concentrations of yellow sand (YS) aerosol have been increasing. In this study, YS samples collected from three sites of Japan during ADSE in 2009-2010 were used. The particles were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence-energy dispersive spectrometer (XRF-EDS). We investigate ability of YS extract on enhancing the chemical mediator release and cytokine production from rat basophilic leukemia (RBL-2H3) cells. The dust particles at Fukuoka and Tsukuba were abundant in aluminum (Al), iron (Fe), potassium (K) and titan (Ti) than those at Naha. Concentration of the trace endotoxin and Cryptomeria japonica pollen allergen (Cry j 1) were measured in YS extract. After exposure of RBL-2H3 cells to YS extract, the β-hexosaminidase (β-hex) release, tumor necrosis factor-alpha (TNF-α) production were enhanced in RBL-2H3 cells. This process depends on endotoxin, Cry j 1 and other allergen present in the YS extract. YS water extract also show a strong cytotoxic effect on the cells. This data suggest that low levels of endotoxin and Cry j 1 in YS may cause allergy during the ADSE.

Soil Redistribution investigations by combined use of soil 137Cs and selected chemical properties

Abstract The 137Cs spatial redistribution data have been widely used to estimate soil redistribution rates over the past 45 years approximately. However, the frequent changes in land use in China have limited the general application of the 137Cs tracer technique to soil erosion or deposition budget on the mid- / long-term. In this paper, soil 137Cs measurements and some chemical properties, such as the soil organic carbon and available phosphorus contents, were simultaneously used to identify sediment sources and to reveal the spatial characteristics of soil redistribution. The deposition rates after and before the changes in local land use could be estimated using the approach proposed in this study. The reclamation of formerly uncultivated slopes was found to lead not only to striking accelerated soil erosion but also to considerable changes in the slope form. A typical footslope site on 5-year-old reclaimed sloping land which appeared to have experienced net erosion before 1997, has become a site with deposition reaching a rate of 3.0 cm year−1 since 1997. Besides the soil 137Cs activity, the soil organic carbon content was found to be a very meaningful indicator of the extent of soil erosion or deposition, and the significant difference in the soil available phosphorus content between uncultivated and cultivated land could become a very sensitive and suitable criterion for identifying sediment sources under different land uses.

Three-dimensional prediction of maize pollen dispersal and cross-pollination, and the effects of windbreaks

With the extensive adoption of transgenic crops, an understanding of transgene flow is essential to manage gene flow to non-GM crops. Thus, a flexible and accurate numerical model is required to assess gene flow through pollen dispersal. A three-dimensional atmospheric model combined with a diffusion transport model would be a useful tool for predicting pollen dispersal since it would be flexible enough to incorporate the effects of factors such as the spatial arrangement of crop combinations, land use, topography, windbreaks, and buildings. We applied such a model to field measurements of gene flow between two adjacent maize (Zea mays) cultivars, with suppression effects due to windbreaks, in an experimental cornfield in Japan. This combined model reproduced the measured cross-pollination distribution quite well in the case of maize plots with plant windbreaks slightly taller than the maize and without windbreaks, but the model underestimated the effect of a 6-m-tall windbreak net beyond 25 m from the donor pollen source on cross-pollination. The underestimation was most probably due to the problem of assimilated wind data. The model showed that the 6-m-tall windbreak and the plant wind break suppressed average cross-pollination rate by about 60% and 30%, respectively. Half-tall and coarser mesh windbreak net suppressed cross-pollination rates by 40% by reducing the swirl of donor pollen by reduced wind speed.