| Soil moisture, which is absolutely required for the survival of plants, is an important connection point of Soil-Plant-Atmosphere Continuum (SPAC), and also a key humidity factor in characterizing habitat humidity. In this paper, we presented a case study conduted at the Honghe National Nature Reserve (HNNR), a typical inland marsh in Sanjiang Plain. According to the characteristics of eco-hydrology environment gradient, three typical types of vegetation/communities (island forests, shrubs and meadows) were chosen as the objects of soil moisture investigation. The investigation has been carried out for two consecutive years, in order to reveal the change rule of soil moisture under typical vegetation communities in marsh, and to find out their interaction relationships. By setting up HYDRUS model and quantitatively analyzing, the reslult would help provide some scientific and rational directions to district protection and management. Also, the case will help enrich the research on soil moisture dynamic of non-watershed areas.The major contents and conclusions could be divided into three parts as follows:(1) The analysis of precipitation and soil moisture dynamics measured under typical vegetation/communities. In this section, we mainly finished analyzing and discussing the changes of precipitation and the soil moisture dynamic from the viewpoints of time and space. Based on the meteorological data of historical statistics and experimental observations in recent33years in HNNR, interannual and seasonal variations of precipitaition were analyzed respectively. In the analysis of the soil moisture dynamic, the soil moisture had remarkable seasonal change. Basically, their dynamic changes were in accordance with the change of precipitation. Combined with precipitation, we used the method of statistical characteristics to analyze the variation of soil moisture under different types of vegetation/communities in2012and2013. It turned out that the soil moisture in the near surface had dramatic changes, where the variation coefficient value was up to0.317. In additon, the soil moisture content of all types of vegetation/communities was heavier in gennerl rainful period than in drought period. And among the different types of vegetation/communities, meadow got the heaviest soil moisture content, followed by forest and shrub.(2) The establishment and simulation of soil moisture model in HYDRUS3D softwre. Due to the limitation of research environment and other factors, the daily measured soil moisture data were not available and the relevant measurement parameters could not be gained. Therefore, we used mathematical model (HYDRUS3D) to solve the problem-simulating continuous daily soil moisture, and calculating the actual amount of evapotranspiration and deep seepage. This section revolves in model establishment, parameter settings, model simulation, parameter calibration and accuracy evaluation. As the values of simulation efficiency (0.52-0.84), root mean square (0.01-0.019cm3· cm-3), the average error (-0.007-0.002cm3· cm-3) and the relative mean absolute error (2%-17%) were showed, the simulated soil moisture content was in good agreement with the measured values. Thus, the daily evapotranspiration and deep seepage that calculated by the models would contribute to the next in-depth analysis.(3) The water balance analysis. This section was conducted on the basis of model simulation results-the actual amount of evapotranspiration and deep seepage. After the forms of water, entering (rainfall, water flowing backward) or outputting (evapo-transpiration, deepseepage) the system, were validated, a water balance equation could be built. The water balance equations established for inland forest, shrubs and meadow were used to quantitatively describe the flow of water in and out of their soil in depth of100cm. As the results showed, the soil water cycling of inland forest and meadow was a positive balance in the drought period, which meaned that the water was required and stored well. While in the general period, inland forest and shrubs got a negative balance. By comparising the daily change of each in and out parameters,it turned out that there was an increase in the amount of deep seapage when the rainfall was getting heavier, particularly evident in the non-marsh vegetation/communities (inland forest, shrubs). Thus the negative water balances refered that the water supply exceed the requirement of soil instead of water scarcity. By contrast, meadow community had a remarkable capacity of water conservation, and itsgrowth and distribution were conducive to maintain the marsh habitat characteristics. |
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