Spectroscopy of Salts Common in Saline Soils

Rapid identification and large-scale mapping of salt-affected lands can help improve environmental resource management. Spectroscopy is a potentially effective tool for assessing the distribution of salt crusts and salt-affected soils in barren landscapes of arid regions. This chapter examines high resolution spectral data of the hand-held spectrometer for characterizing properties of various salts commonly present in saline soils. The materials examined include: i) evaporites commonly formed on the soils of arid and semi-arid regions; halite (NaCl), thenardite (Na₂SO₄); nahcolite (NaHCO₃), gypsum (CaSO₄.2H₂O), and their mixtures; ii) salt crusts formed on the surface of two torrifluvents. Spectral reflectance was measured with a GER 3700 spectroradiometer in the visible and near infrared region (400–2500 nm); and the positions of the dominant absorption features of the tested samples were documented. Crystal size and salt concentrations affected reflectivity, but did not affect the positions of the absorption bands of the salt crusts significantly. Dominant absorption features of spectra of salt crusts and evaporites were slightly different in their positions. Spectroscopy can be used under certain conditions to identify the presence of primary diagnostic spectral features of gypsum, nahcolite, thenardite and halite crusts. Additional research is needed if spectral data are to be used for identifying the types and quantities of salt crusts present on salt-affected lands.