Using Clay Mineralogy to Infer Sources of Suspended Clay and Silt in a Watershed: Quantitative Approach1
- Y. P. Hsieh2
A functional procedure for using clay mineralogy to infer sources of suspended clay and silt in a watershed is presented. The information could lead to estimation of soil loss from various parts of a watershed, if the dispersion factor of the source soils can be evaluated. The suspended clay and silt carried by the Gallatin River and its tributaries were used to illustrate the methodology. Clay mineralogy of the clay and silt is expressed as the relative percent peak heights of minerals from the x-ray diffractogram. The percent peak heights of these minerals are found reproducible (CV = 6%), and additive in nature. Analysis of variance reveals that clay mineralogy is significantly different among the tributaries of the Gallatin River. The results of discriminant analysis substantiated that clay mineralogy can be a signature of the suspended clay and silt carried by the Gallatin River and its tributaries. The Q-mode factor analysis technique was applied to “demix” the suspended clay and silt of the main stream into its source components. The results of Q-mode factor analysis indicate that clay and silt carried by the Gallatin River was mainly from Taylor Fork (92%) on 7 May 1971. The source of clay and silt in Taylor Fork was further traced back to its upper-stream above Wapiti Creek (90%). The source of suspended solids in West Fork varied according to the sampling dates. On 27 May 1971, the north and south branches contributed almost equal parts of that to West Fork, while on 8 June 1971, the south branch contributed the majority (84%) of clay and silt to West Fork. The proposed method of sediment tracing by clay mineralogy is relatively simple and economical compared to the conventional stream monitoring methods. More important, it provides an independent alternative to the conventional methods of soil erosion assessment in a watershed.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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