The Changing State of N: P: Si Stoichiometry in Ganga River: Possible Implications for Production and Fate of Phytoplankton Biomass
Pandey J* and Yadav A
Ganga Research Laboratory, Environmental Science Division, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi- 221005, India
*Correspondence E-mail: jiten_pandey@rediffmail.com
Key Words: Dissolved organic carbon, Ganga River, Nutrients, Phytoplankton, Stoichiometry
Received June 1st, 2014; Accepted Jan 11th, 2015; Published Jan 30th, 2015; Available online Feb 20th, 2015
Abstract
Nutrient loading to surface waters has increased over recent decades while silicon loading has remained relatively constant or declined. A shift in N: P: Si stoichiometric ratios due to anthropogenic influences may become a feature of changing biogeochemistry in surface waters. We studied the changing state of NO3–, NH4+, PO43-, Si4+, dissolved organic carbon (DOC), chlorophyll a (Chl a) biomass and gross primary productivity (GPP) along a 35 km long stretch of Ganga River at Varanasi (India). Concentrations of NO3–, NH4+, PO43 increased downstream characterized by anthropogenic influences, while silica showed an opposite trend. On a seasonal scale, unlike other nutrients, Si concentration was lowest in winter. The N: P stoichiometry showed a declining trend downstream indicating N limiting condition. The Si: N and Si: P ratios also showed deviation from classical Redfield ratios and indicated Si limitation as influenced by excessive N and P inputs. Chl a biomass and GPP followed a trend similar to nutrients. This relationship was also evident in DOC. Statistically significant differences in Chl a biomass and GPP as well as in N: P: Si and C: Chl a ratios indicated the changing state of stoichiometric coupling of essential elements with possible implication on ecological status of Ganga River.