Role of sedimentary processes and environmental factors in determining the distribution pattern of diatoms and marine/terrestrial palynomorphs in a tropical coastal wetland.

Abstract

Factors controlling the distribution of marine and terrestrial palynomorphs in a coastal ecosystem were studied from surface sediments of 17 stations of Vembanad wetland, Kerala. Marine and terrestrial organic matter, mangrove and terrestrial pollen, dino agellate cysts, diatoms, Total organic carbon, percentage of sand, silt and clay, total dissolved solids and salinity were recorded in the sediment samples from each station. Based on the study, three depositional zones were identi ed in the Vembanad wetland i)  ood tidal basin, ii) Central tidal basin, and iii)  uvial basin. The constant composition of terrestrial and mangrove pollen in the 8 stations of the northern Vembanad ecosystem from Munambaom-Barmouth points to tidal in uence. Low percentage of dinocysts and pollen but high percentage of diatoms in Munambaom, Cherai beach, and Midway to Cherai stations of the central part of Vembanad is probably due to prevalence of high energy and an oxidizing environment of deposition. Abundance of terrestrial pollen as well as fresh water diatoms, but extremely low representatives of marine dinocyst in the southern stations Kochi Shipyard-Kumarakaom indicate high  uvial supply and proximal setting with respect to the terrestrial source. This study helped to elucidate the role of different factors, i.e. proximal-distal trend, tidal  ushing, hydrodynamic conditions, climate and redox state of the depositional environment in determining the distribution of marine and terrestrial palynomorphs in a coastal environment.