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Abstract:

Flooding leads to many problems which are the major concerns of environment and society in north of Iran. Therefore, our knowledge increasing about flooding and identification of its source could be useful to decline devastating effects of floods. This study was conducted to investigate the micromorphological aspects of flooded soils in Masoule Rudkhan watershed, north of Iran. Four soil pedons were selected in representative (non-flooded) soil (P1) and flooded soil (P2) in the upstream with shale parent rock and representative soil (P3) and flooded soil (P4) in downstream with greenschist parent rock, respectively. Soil profile description and sampling were carried out based on soil survey manual and after analyzing of samples, soils were classified as Typic Udifluvents in the flooded soils, Typic Dystrudepts and Typic Hapludualfs in representative soil developed on shale and greenschist parent rocks, respectively. Based on obtained results there are lithologic discontinuities in flooded soils that can be confirmed by micromorphology observations. This soils microstructure ranges from a massive to weakly developed granular and weak developed sub-angular blocky and vughs were prominent. Although chitonic c/f-related distribution was the most common in the representative soils, but the prominent one was porphyric. The fine fraction mainly had stipple and mosaic speckled b-fabric, while stipple speckled and crystallitic b-fabrics observed in flooded soils. No signs of clay illuviation were observed in flooded soils, while flood coating and lignin-rich plant residues, rock fragments, charcoal, artefacts and so different mineral fragments were most widespread. Presence of calcite features as nodule and coatings, as well as pyroxene and olivine minerals were remarkable in flooded soils that have been derived by calcareous rocks, local bedrocks (gabbro and peridotite), the reworking of deposits and aggregates. The calculated micromorphological index of soil evolution (MISECA) revealed weakly developed Udifluvents in the flooded soils. Generally, soils and susceptibility of parent rock could be as key factors for source routing of flooding, that some micromorphological aspects and mineral identification could be powerful tools for this target.