Investigation of Soil Magnetic Characteristics Efficiency for Sediment Sources Differentiation



Designing effective strategies for sediment management and control is closely related to identification of sediment sources in a drainage basin. One of the methods for investigating sediment sources is using magnetic tracers for erosion and sediment yield studies. Sediment source identification using magnetic characteristics is a simple, inexpensive, quick and non-destructive method having applicability in different environments. One of the parameters which is used in most sediment tracing studies is susceptibility magnetization parameter which is measured in low frequency (XLf) and high frequency (XHf). Another magnetic parameter which is used in sediment tracing is frequency depended susceptibility magnetization (xFD). The objective of this study is investigating the applicability of magnetic characteristics of soil and sediment samples as tracers in identification and differentiation of sediment sources in five small drainage basins in Semnan Province: Amrovan, Atari, Ebrahim-Abad, Ali-Abad and Royan. Land use of all drainage basins is rangeland as they have cool, semi-arid climate and variable lithological units.
By field work, different lithological units (as surface sources units) and gully walls (as sub-surface sources) were identified as sediment sources. Sampling of surface sources was preformed from 0-2 centimeter depth and sampling of sub-surface sources was performed on gully walls. Sediments deposited behind dam reservoirs of the basin outlet were also sampled. The total of 250 samples was collected. The samples were air-dried sieved and particles less than 63 microns were separated for further analysis.
In this study, two parameters of XLf and XFD which are easily measured using a magnetic susceptibility meter were used as sediment tracers. These parameters were measured using the BartingtonMS2 susceptibility meter of the Geophysics Institute of University of Tehran.
The potential of magnetic parameters as sediment sources in the studied drainage basin was determined using the Kruskal-Wallis and Discrimination Function Analysis (DFA) statistical tests. Using Kruskall-Wallis test, the amount of P for all characteristics was lower than the critical value and therefore they were entered in DFA Analysis. The percentages of the samples which were correctly classified by DFA Analysis were between 39.9% to 57.5% in different drainage basins. The highest percentage using combined XLf and XFD parameters was 65 % in Ali-Abad drainage basin and the lowest percentage was 48% in Amrovan drainage basin. No single characteristics could differentiate sediment sources completely in different drainage basins. XLf had lower differentiation potential relative to XFD in all drainage basins for example the differentiation potential of XLf varies from 39.9% in Ebrahim-Abad to 52.5% in Ali-Abad drainage basin. Whereas the differentiation potential of XFD is from 43.3% (in Ebrahim Abad drainage basin) to 57.5% (in Ali-Abad drainage basin).The results show that using composite tracers will increase the differentiation potential relative to using single tracers.