Stable carbon isotope as a proxy for the change of phytoplankton community structure in cascade reservoirs from Wujiang River, China

Abstract

Phytoplankton community structure and δ13C of dissolved inorganic carbon (DIC), particulate organic carbon (POC), and phytoplanktonic carbon (PPC), and the related hydro-chemical parameters have been seasonally investigated in the cascade reservoirs from the Wujiang River Basin. Average values of δ13CDIC, δ13CPOC and δ13CPPC were −8.1±1.3‰, −29.6±2.8‰, and −30.9±4.5‰, respectively. Seasonal fluctuation of δ13CPPC was comparable to that of δ13CPOC and larger than that of δ13CDIC. The δ13CPPC values showed a significant linear correlation with δ13CPOC, indicating that endogenetic phytoplankton is the main source of POC in these cascade reservoirs. Compared to environmental factors such as temperature, taxonomic differences are the main factor influencing δ13CPPC in this study. As a result, the contribution of Bacillariophyta to the total phytoplankton showed a significant negative correlation with δ13CPPC and Δδ13C (δ13CPPC−δ13CDIC), respectively, suggesting that δ13CPPC can be used to discern the change of phytoplankton community structure although only two kinds of dominant algae (i.e. Bacillariophyta and Chlorophyta) facilitate achieving this relationship. This relationship will have an important significance in understanding evolvement of phytoplankton community structure with time using geochemical technique once it is confirmed at a larger scale in field study.