Simulation Study On The Alkalinized-salinized Grasslands In The Songnen Plain, China

The vast alkalinized-salinized grasslands in the Songnen Plain, Northeastern China, are suffering from degradation resulting from soil alkalization and salinization. The topographical features and climatic conditions of the area result in a very slow primary soil alkalization and salinization process. Human抯 over-utilization of the grasslands, e.g. overgrazing and mowing, results in a secondary soil alkalization and salinization process, which is much faster than the primary one. It is a process of serious degradation of the grassland, and leads quick regressive successions of the meadow steppe ecosystem. A general regressive succession process under overgrazing can be separated into some phases in terms of their dominant species, 1) Aneurolepidium chinense, 2) Aneurolepidium chinense and Chioris 憊irgata, 3) Chloris virgata, and 4) Suaeda glauca. In this paper, we attempted to build a process-based model, to describe the ecological processes in the grassland ecosystems, and to estimate the potential impacts of different grazing intensity on the grassland. This model was constituted with five submodels, which described the 1) climatic valuables for grassland ecosystems, 2) the hydrological pro~esses in the soil, 3) the alkalizationlde- alkalization and salinizationlde-salinization processes in the soil, 4) the growth processes of the herbaceous communities and 5) the potential impacts of different grazing intensities on the grasslands. Some important climatic variables for grassland ecosystems were described in the submodel of climatic valuables, including temperature, precipitation, radiation, relative humidity, sunshine fraction and wind velocity. Analytical equations were used to calculate the radiation at any topographical situation, which includes the possible iii - lv - duration of sunshine, exoatmospheric solar radiation, and total solar radiation. Amended Penman抯 equation was used to evaluate the potential evapotranspiration of China. The simulation results were verified to be effective with the observed pan evaporation data from 900 meteorological observation stations. After combining a numerical integration model and a water balance model, a physically-based modelling of hydrological processes in soil was built with the Object-oriented design. This model is run at daily-time step, and it can be used for different soil texture classes. It was used for simulating dynamics of soil water with great vertical spatial heterogeneous. The hydrological processes of four different soils in Songnen grasslands were simulated and the results and the results were verified with the experimental data from four dots in Songnen Plain in 1997. A dynamical model was built on the basis of salt and water balanced modelling and mechanism modelling. This model is a daily-time step, and suit for the simulation the movements of salts in heterogeneous soil. As a case study of the model, the dynamics of salt concentration, exchangeable sodium percentage (ESP) and pH were simulated on two plots in 1997, with A. chinense and S. corniculata growing on it respectively. Comparing with the experimental data, the simulation results can express the dynamics of saline and alkaline in different seasons. Climatic valuables, soil moisture, salt concentration, ESP and pH were regarded as the most importan...