Linkage of Microbial Parameters with Sediment Physicochemical Properties in Subsurface Fluvial Sediment Deposits of the Mahi River Basin, Western India.

The linkage between sediment physicochemical and microbial parameters within river terrace sedimentary ecosystems of semiarid regions is still in infancy. Here, we investigated microbial enzyme activities involved in C, N, P, and S cycling, and quantitative PCR (qPCR) based gene abundance of two laterally deposited sediment cores (28 and 25 m deep) comprising the Late Quaternary sediments of the Mahi River (Gujarat, India). Gene abundance indicates the presence of a sustainable bacterial population throughout both cores. The stratified subsurface sediments had notable microbial enzyme activities indicating an important role of both cores in biogeochemical cycling. Correlation between microbial and geological parameters revealed that various trace elements, rare earth elements, K2O, P2O5, EC, TDS, and salinity link significantly with microbial parameters. However, the direction and magnitude of the correlation differ in both cores under study. These results emphasize that sediment physicochemical properties influence microbial parameters differently in the laterally deposited subsurface sediments. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-021-00998-4.

Tracing the Vedic Saraswati River in the Great Rann of Kachchh.

The lost Saraswati River mentioned in the ancient Indian tradition is postulated to have flown independently of the Indus River into the Arabian Sea, perhaps along courses of now defunct rivers such as Ghaggar, Hakra and Nara. The persistence of such a river during the Harappan Bronze Age and the Iron Age Vedic period is strongly debated. We drilled in the Great Rann of Kachchh (Kutch), an infilled gulf of the Arabian Sea, which must have received input from the Saraswati, if active. Nd and Sr isotopic measurements suggest that a distinct source may have been present before 10 ka. Later in Holocene, under a drying climate, sediments from the Thar Desert probably choked the signature of an independent Saraswati-like river. Alternatively, without excluding a Saraswati-like secondary source, the Indus and the Thar were the dominant sources throughout the post-glacial history of the GRK. Indus-derived sediment accelerated the infilling of GRK after ~6 ka when the Indus delta started to grow. Until its complete infilling few centuries ago, freshwater input from the Indus, and perhaps from the Ghaggar-Hakra-Nara, probably sustained a productive marine environment as well as navigability toward old coastal Harappan and historic towns in the region.