Minghong Chen

Agricultural phosphorus flow and its environmental impacts in China

The transfer of nutrients from agricultural land to waters attracts the attention of policy makers as well as scientists as it plays an increasingly significant role in affecting the water environment. It is therefore essential to first understand the nutrient flow in agricultural systems and then correspondingly formulate a series of cost-effective policies and best management practices (BMPs). On the basis of an emission inventory analysis (EIA) and a nutrient full balance (NFB) calculation, this paper presents a partial substance flow analysis (SFA) method, as well as an Agricultural Phosphorus Flow Analysis (AgiPhosFA) model, to describe the phosphorus (P) flow in the agricultural systems in China and assess the impact of human activities on waters driven by agriculture and rural life. It is estimated that average P input and output were 28.9 kg ha(-1) a(-1) and 14.2 kg ha(-1) a(-1) respectively in China in 2004, while the total P utilization efficiency (Plant uptake P/P input) in agriculture was 45.7% leading to an average P surplus of 14.7 kg ha(-1) a(-1). Excessive P application through mineral fertilizer in the arable farming system has led to the accumulation of soil P and constituted a risk to the recipient water quality, whereas the grassland grazing system is confronted with a severe P deficit problem which has resulted in widespread grass degradation. Therefore it may be an efficient way to mitigate the problems simultaneously by regulating and balancing the P flows between the two systems. Uncertainties of the method and model are also discussed in terms of model conceptualization, data and parameters, and spatial and temporal variability.

Estimating nutrient releases from agriculture in China: An extended substance flow analysis framework and a modeling tool

Agriculture related pollution has attracted the attention of policy makers as well as scientists in China as its contribution to water impairment has increased, and quantitative information at the national and regional levels is being sought to support decision making. However, traditional approaches are either time-consuming, expensive (e.g. national surveys) or oversimplified and crude (e.g. coefficient methods). Therefore, this study proposed an extended substance flow analysis (SFA) framework to estimate nutrient releases from agricultural and rural activities in China by depicting the nutrient flows in Chinese agro-ecosystems. The six-step process proposed herein includes: (a) system definition; (b) model development; (c) database development; (d) model validation; (e) results interpretation; and (f) uncertainty analysis. The developed Eubolism (Elementary Unit based nutrient Balance mOdeLIng in agro-ecoSysteM) model combined a nutrient balance module with an emission inventory module to quantify the nutrient flows in the agro-ecosystem. The model was validated and then applied to estimate the total agricultural nutrient loads, identify the contribution of different agricultural and rural activities and different land use types to the total loads, and analyze the spatial pattern of agricultural nutrient emissions in China. These results could provide an entire picture of agricultural pollution at the national level and be used to support policy making. Furthermore, uncertainties associated with the structure of the elementary units, spatial resolution, and inputs/parameters were also analyzed to evaluate the robustness of the model results.

One-dimensional numerical simulation of non-uniform sediment transport under unsteady flows

One-dimensional numerical models are popularly used in sediment transport research because they can be easily programmed and cost less time compared with two- and three-dimensional numerical models. In particular, they possess greater capacity to be applied in large river basins with many tributaries. This paper presents a one-dimensional numerical model capable of calculating total-load sediment transport. The cross-section-averaged sediment transport capacity and recovery coefficient are addressed in the suspended load model. This one-dimensional model, therefore, can be applied to fine suspended loads and to hyperconcentrated flows in the Yellow River. Moreover, a new discretization scheme for the equation of unsteady non-uniform suspended sediment transport is proposed. The model is calibrated using data measured from the Yantan Reservoir on the Hongshui River and the Sanmenxia Reservoir on the Yellow River. A comparison of the calculated water level and river bed deformation with field measurements shows that the improved numerical model is capable of predicting flow, sediment transport, bed changes, and bed-material sorting in various situations, with reasonable accuracy and reliability.

Effects of sediment particle morphology on adsorption of phosphorus elements

Abstract Sediment particle surface morphology affects phosphorus adsorption. This paper studied the phosphorus adsorption on sediment particle by using a Scanning Electron Microscope (SEM) and an Energy Dispersive X-ray Spectroscopy (EDS). Sediment samples from the Yangtze, Yellow and Yongding rivers in China were chosen to measure the particle surface morphology, surface gray scale and element distribution maps. These samples were firstly cleaned and put into phosphate solution for adsorption. Both the Langmuir equation and Freundlich equation were used for descriptions of adsorption-desorption isotherms for sediments. Particles were then dried and scanned. The results show that the adsorption of phosphorus depends on the surface morphology of particles. Phosphorus exists mostly in the ridges and channels, while a few exist in the slopes, and casually in the peaks, passes and pits.

Effect of biofilm on the rheological properties of cohesive sediment

Biofilm, a product of metabolic activity, has an important effect on the physico-chemical properties of cohesive sediment. However, little effort has been made to determine the substantial effects of biofilm growth on specific sediment properties, for example rheological properties. Understanding the changes associated with biofilm growth and quantifying the time scales over which these changes occur are important for understanding how biofilms mediate sediment properties and processes and the development of sediment transport mechanics. The effect of biofilm on the rheological properties of cohesive sediment was investigated experimentally. The rheological properties of sediment slurries with and without biofilm at different growth phases were measured and compared. Measurement showed biofilm growth has a significant effect on the rheological properties of cohesive sediment. Rheological equations for biofilm sediment and expressions for rheological properties which change over time are proposed. These equations, and information on biofilm sediment, are important for inclusion of biosedimentological processes in models of sediment dynamics.

Surface charge distribution and its impact on interactions between sediment particles

Surface charge distribution has great impact on interactions between sediment particles, which is essential for flocculation studies. In this paper, the micro-morphology and surface charge distribution of quartz sand are measured using the electrical force microscope. Then, the statistical relationship between micro-morphology and surface charge distribution is obtained. Results show that quartz sand possesses a complex surface morphology, which has great impact on the charge distribution. Positive and negative charges mostly concentrate in the saddle, convex, and concave parts of the surface, while their distribution is less in the groove, ridge, and flat parts. A fitting equation between surface charge and non-spherical curvature is also obtained. The surface charge distribution on a mathematical sediment particle is then reproduced according to these relations, and the effect of charge heterogeneity on interactions between different particles is quantified and analyzed, indicating that surface charge distribution has a dramatic effect on interactions between sediment particles, and local surface potential is more important than the average surface potential. This study provides a new method for understanding the processes of flocculation in coastal and estuarine zones.

Phosphorus adsorption on natural sediments with different pH incorporating surface morphology characterization

Sediment samples from University Lake (U.L.) and Anacostia River (A.R.) were collected to study the phosphorus (P) adsorption with pH at 3.65, 4.75, and 5.65. The surface micro-morphology and pore structures of sediment particles were obtained using a scanning electron microscopy and gas adsorption method, respectively. Fourier analysis was then applied to approximate the surface morphology, which was incorporated into the Langmuir isotherm to directly derive the model parameters for P adsorption simulation. Meanwhile, an empirical function of pH was introduced to represent the pH effect on P adsorption. A stronger P adsorption was observed for the A.R. sediment due to the more clay minerals, smaller median diameter, and a greater percentage of large pores, and the increasing pH resulted in a decrease of adsorption equilibrium constant as well as the P adsorption capacity, which was well reproduced by the adsorption isotherms. This study would benefit the mechanism study of the interactions between sediment particles and pollutants, providing references for understanding the pollutants’ transport in aqueous systems.

Phosphorus adsorption onto clay minerals and iron oxide with consideration of heterogeneous particle morphology

Particle morphology plays an important role in solid-water interface adsorption, which affects the fate and behavior of phosphorus (P) in rivers and lakes and the resulting eutrophication. In this paper, three minerals including kaolinite, montmorillonite and hematite were considered to investigate the contributions of particle morphology to P adsorption using adsorption experiments and microscopic examinations. The Taylor expansion method is applied to quantitatively characterize the heterogeneity of surface morphology. The results reveal that local concave or convex micro-morphology characterized by the second order term of Taylor expansion F2, can affect the local adsorption capacity due to its effect on the distribution of surface charge and reactive sites. Moreover, the adsorbed P at different F2 here fits to a Weibull distribution, which can further define the representative average adsorption onto individual particles. A weighted average morphology factor F2a is derived to characterize the surface heterogeneity, and correlated with average P adsorption of particular mineral particles. In addition, the Sips model can successfully fit the experimental data of different minerals, and the heterogeneity parameters γ and adsorption capacity Qm in the model are proved to be functions with the basic mineral properties, including particle size, surface site density and morphology characterization as well. It is concluded that the complex surface morphology plays a significant role in particle adsorption and the morphological role need to be considered in the adsorption model in order to better describe the adsorption in system with heterogeneous solid surface.

3D Numerical Investigation of Distorted Scale in Hydraulic Physical Model Experiments

Abstract In some physical model experiments, it is necessary to use distorted models. It is difficult, however, to build in an optimal degree of distortion into the models to ensure a closer degree of similarity between the model and the prototype. Three-dimensional (3D) numerical simulation is used in this paper to model experiments with a straight channel under different distorted scales. The calculated results of stream-wise, lateral and vertical velocities and sediment concentration along the vertical direction are shown by comparing the deviations of the velocities and sediment concentration between the distorted model and a normal one. Generally the discrepancy between the distorted model and the normal in stream-wise velocity is acceptable, while in vertical and transverse directions, the velocity shows differences. Concerning sediment concentration and channel bed deformation, the effect of the distorted scale is mainly related to two different similarity criteria. The similarity ratio between the turbulence diffusion velocity and gravity settling velocity can reproduce better results of sediment concentration along the vertical direction. The better bed deformation results come, however, from the similarity ratio between the averaged flow velocity and gravity settling velocity.

Integrated Management of Source Water Quantity and Quality for Human Health in a Changing World

Water is an essential life-sustaining element of daily life for each and every one. However, water crisis in both quantity and quality seemingly becomes inevitable in such a changing world in terms of the variation of global environment, the ever-growing population, and the serious environmental pollution. Both water quantity and quality are influenced by the natural conditions such as climate, geography, topography, and geology, and human activities such as water withdrawal, excreta and sanitation, agriculture, industry, mining, traffic and transportation, and waste disposal and landfill. The adverse effects that the human race has exerted on water sources have in turn threatened human health either by limiting good hygiene or by impairing drinking water safety. To cope with the water crisis, innovative approaches to source water management have been proposed all around the world from a holistic perspective, based on integration of multidisciplinary work and within a collaborative framework. Fortunately enough, with the development of water and wastewater treatment technology, alternative water sources, including desalination, rainwater harvesting, and water reuse, have been exploited to satisfy the thirsty world.