The N:P:Si stoichiometry as a predictor of ecosystem health: a watershed scale study with Ganga River, India

ABSTRACT

The present study was conducted from March 2016 to February 2017 to investigate human-driven shifts in N:P:Si stoichiometry along a 2320 km stretch of the Ganga River. Concentrations of nutrients (${\text{NO}}_3^{-}$ , ${\text{NH}}_4^{+}$ and ${\text{PO}}_4^{3-}$), dissolved organic carbon (DOC) and dissolved silica (DSi) were measured in river water and in surface runoff to explore possible role of lateral flow and evaluate if there was a shift in the elemental stoichiometry of N, P and Si. Our study revealed that catchment runoff is an important factor, in addition to urban-industrial flushing, enhancing nutrient enrichment causing a shift in N:P:Si ratios leading to N limitation over P (N:P < 16:1) and Si limitation over N (N:Si > 1). Among the seven dominant diatom genera considered here, diatom abundance changed with concurrent changes in water chemistry. Sites with overall low N:P ratios favoured P-loving species such as Diatoma vulgaris, Fragilaria intermedia and Gomphonema parvulum. The study shows that the N:P:Si stoichiometry if coupled with changes in diatom abundance may be a useful predictor of anthropogenic environmental effects in the Ganga River. This watershed scale study invite attention towards significance of N:P:Si stoichiometry for properly addressing the eutrophy and efforts to rejuvenate the river.

KEYWORDS:

• Diatom
• elemental stoichiometry
• Ganga River
• nutrient limitation

Acknowledgements

We thank the Coordinators, Center of Advanced Study in Botany and DST-FIST for laboratory facilities.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research was funded by the Council of Scientific and Industrial Research, New Delhi, India [09/013(0611)/2015-EMR-I] in the form of fellowship to ES.