Saturday, 15 July 2006

Soil Moisture Temporal Patterns in a Forested Catchment.

Qing Zhu, Dept of Crop and Soil Science, The Pennsylvania State Univ, 116 ASI Bldg, State College, PA 16802, Henry Lin, Penn State Univ, 415 Agricultural Sciences and Industries Bldg, University Park, PA 16802, and Xiaobo Zhou, Pennsylvania State Univ, 116 ASI Bld., University Park, PA 16802.

Soil moisture is a key parameters governing interactions between the atmosphere, the land surface, and the ground water. It is highly variable in both space and time and the knowledge of such variability is important for understanding and predicting many environmental processes. This study investigates different patterns of in situ observed soil moisture changes in a forested catchment with the alteration of the overall catchment wetness, and explores the relationships of such patterns to spatial variables including terrain attributes, soil types, and vegetation. Based on the analysis of 77 monitoring sites distributed throughout the catchment, we found that the majority of the monitoring sites located in the Ernest, Blairton and Rushtown soil series had an exponential relationship between the observed soil moisture contents at multiple depths and the whole catchment mean wetness, while most of the monitoring sites located in the Berks and Weikert soil series showed a linear relationship. There were only few monitoring sites located in the Berks and Weikert soil series that had a logarithmic relationship between the observed soil moisture contents and the whole catchment mean wetness. The reason for such varying temporal responses is explained by the varying soil moisture holding capacities and different landscape positions these soil series occupied in the catchment. We grouped the monitoring sites having the linear relationship into three categories: the first shows a faster rate of increase in soil moisture contents than the overall mean of the whole catchment; the second shows a slower rate of increase compared to the catchment overall mean; and the third group has approximately equal rate of change as the catchment overall mean. Such varying groups of monitoring sites are related to the differences in the terrain attributes, soil types and their properties, and the vegetation type in the catchment. Nearly all of the monitoring sites located at the ridge of the catchment belong to the third category. The monitoring sites located in or near the valley floor, with thick Ernest and Blairton soil series and evergreen vegetation, belong to the first category. We are further examining the other factors (such as various terrain attributes including the topographic wetness index) in relation to the observed temporal patterns of in situ soil moisture changes in this catchment.

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