鄱阳湖典型洲滩湿地土壤质地与水分特征参数研究

频繁干湿交替增强了鄱阳湖洲滩土壤水对湿地系统的动态调节作用。以鄱阳湖吴城国家自然保护区的一个典型洲滩湿地为研究区,调查分析了土壤质地沿高程梯度的分布特征,确定了不同土壤质地的水分特征参数,并阐述了土壤质地与其水分特征参数的空间异质性。结果发现:该洲滩湿地主要分布砂土、粉壤土和粘土三种类型。水平断面方向上,粒径较粗的砂土和粉壤土主要分布在高位滩地,而粒径相对较细的粘土主要分布在近湖区开阔水面的低位滩地;土壤剖面方向上,土壤质地呈现出固有分层特性。van Genuchten模型应用于鄱阳湖洲滩湿地土壤水分特征曲线拟合,证实了该模型在鄱阳湖洲滩湿地的适用性。模型结果表明土壤残余含水率θr变化约9%~19%,饱和含水率θs变化约42%~57%,土壤进气值的倒数α约0.01 cm~(–1),水分特征曲线形状参数n介于1.11~4.65之间。土壤含水率变化对van Genuchten模型中参数α和n较为敏感,而对θr和θs的敏感性相对较弱。研究成果可为后续该区域以及全湖区湿地生态水文模型的构建和发展提供背景信息和参数资料。

RESEARCH OF SOIL TEXTURES AND SOIL-WATER CHARACTERISTIC PARAMETERS IN A TYPICAL WETLAND OF POYANG LAKE

Frequent wetting and drying processes increase the dynamic regulation functions of soil water in the Poyang Lake wetlands. In this study, the soil textures and associated soil-water characteristic parameters were investigated using field sampling and laboratory testing in a typical wetland section at Wucheng, northern Poyang Lake. The main objectives of this paper are to analyze the spatial heterogeneity of the soil textures and water characteristic parameters in the wetland. Field investigations show that the wetland section has three different soil textures, including sand, silt sand and loam. The sand and silt sand primarily distribute at the high elevation of the wetland section, and the loam distributes at the low elevation area adjacent to the open lake water. This spatial pattern is likely to attribute to the highly dynamic water level variations due to the combined effects of local catchment rivers and the Yangtze River. The soil textures exhibit obviously spatial heterogeneity in this typical wetland section in both the horizontal and vertical directions. In addition, the van Genuchten model has the ability to capture the relationship between the soil water content and soil pressure head, and the correlation coefficient can reach up to 0.99. The saturated water content θ_s for different soil textures varies from 42% to 57%, and the residual water content θ_r varies between around 9% and 19%. The fitting values of α and n in van Genuchten model are around 0.01 cm^-1 and 3.2, respectively. These results demonstrate that soil textures play an important role in soil water storage and water transport processes. Sensitivity results further indicate that the variations of soil water content are more sensitive to the values of α and n than to those of the θ_r and θ_s. The outcomes of this study will not only provide background information relating to the soil water for the future model development of Poyang Lake wetland, but also make better understanding the ecological environment changes of the lake and its wetland and how these evolve along with the water regime changes. Our study produces a first step to bridge a major gap of soil investigation in the wetland, making it possible to better understand the soil physics, chemistry and nutrient transport within the lake wetland.