Statistical Properties of Distribution of Solid Particles at the Bottom Setting in Turbulent Shear Flow

In this paper the behaviors of settling particles in turbulent shear flow are investigated and the statistical properties of distribution of the particles at the bottom are obtained experimentally and theoretically. For the properties of distribution of the particles, the mean settling length of the particle, that is, the mean value of the streamwisely transporte length of the particle, and the standard deviation of the settling length are considered. These statistical properties are obtained by experiment and the trajectories of the settling particles are photographed by storoboscopic light. Then, on the basis of these experimental results, the stochastic models for the behaviors of the settling particles are developed. These models can explain well the actual phenomena, and it is found that these stochastic models are to be pertinent. Problems to be solved in the future are discussed

30-year changes in the nitrogen inputs to the Yangtze River Basin

To understand both spatial and temporal changes in nitrogen inputs to the Yangtze River Basin (YRB), we collected decadal statistical data for 1980, 1990, 2000 and 2010 at the county level and the annual statistical data for the period 1980–2010 at the provincial level of China. Based on these datasets, we estimated the nitrogen inputs, including the atmospheric deposition, synthetic N fertilizer, biological N fixation and recycling reactive N inputs, such as N from human waste and animal excrement, crop residue recycled as manure, and N emission from burning crop residue. The results showed that, geographically, the variation of the total amount of N input during the last 30 years ( δN  =  N _2010  –  N _1980 ) has increased about 0–50 kg ha ^−1 over most of the area of the YRB. Moreover, it has increased dramatically by about 50–300 kg ha ^−1 in the Sichuan Basin, the Han River Basin, the Poyang and Dongting lake basins, and the Yangtze Delta as well. Temporally, the total amount of N inputs to the whole YRB was approximately 16.4 Tg N in 2010, which was a 2.0-fold increase over 1980. It increased dramatically in the 1990s and then stabilized at a high level in the 2000s. The major N inputs were human and animal wastes as well as synthetic fertilizers, but they varied regionally. Animal waste was the major input to the water source regions, and its contribution percentage gradually decreased from upper to lower reaches. In contrast, the contribution of N fertilizer increased from upper to lower reaches, and became the major input to the middle and lower reaches. The total N inputs changed slightly in the upper reaches, but increased largely in the middle reaches in the last 30 years. However, in the lower reaches, it had increased remarkably before 2000, and then tended to decrease in the last decade. Finally, the atmospheric N deposition over the basin increased continuously in the last 30 years