Variations in total organic carbon and grain size distribution in ephemeral river sediments in western India

Total organic carbon (TOC) and grain size distribution (sand, silt, and clay) in the ephemeral Mahi River (western India) sediments were measured to look at their effectiveness in understanding the late Quaternary monsoon conditions. Four sites spread across the alluvial zone and three sites from the estuarine zone were sampled. TOC concentration in the sediments of the alluvial and estuarine zone sites ranged between 0.04 and 0.39% and 0.04 and 0.23%, respectively. It was observed that grain size differed significantly at the alluvial zone sites, whereas an uniform trend was found in the estuarine zone sites. The study indicated that low concentration of TOC and coarse size fractions (sand) in sediments were well correlated with available records of arid/weaker palaeomonsoon periods, whereas higher concentration of TOC and fine grain size fractions (silt + clay) in sediments were well correlated with available records of enhanced palaeomonsoon periods of the ephemeral Mahi River. Uniform concentrations of TOC and fine grain size particles in sediments at the estuarine zone sites are attributed to the backwater in the system, deeper sedimentation, and/or greater decomposition processes. It is concluded that, TOC and grain size distributions in the ephemeral river sediments are simple and effective parameters to develop an understanding about late Quaternary monsoon conditions in ephemeral rivers.