The N: P: Si Stoichiometry and Relative Abundance of Diatoms in Ganga River

Abstract

In order to assess the changing pattern of N: P: Si stoichiometry and associated shift in the abundance of diatoms, we analysed DO, BOD, NO3-, PO43-, DOC and DSi in a 37 km long stretch of Ganga River. The N: P stoichiometry declined (from 13.6 to 5.3) at downstream sites receiving urban influence. Similar was the trend for Si: P ratio indicating relatively higher input of P in comparison to N and Si. The chlorophyll a biomass and gross primary productivity (GPP) showed positive correlation with BSi (P < 0.001) and P enrichment at downstream favoured the abundance of Amphipleura, Aulacoseira, Craticula, Cymbella, Fallacia and Fragilaria. Since the excessive growth of exploitative species may replace less adapted diatoms, the skewed elemental stoichiometry in the study river may alter the diatom assemblages with increased abundance of P favoured species at urban sites. The study has relevance addressing diatom community level cause-effect relationships and provides important cues for designing action plan towards restoration of this major river system.