Variation in carbon and nitrogen stable isotopes in POM and zooplankton in a deep reservoir and relationship to hydrological characteristics

Abstract

We investigated the carbon and nitrogen stable isotope composition of particulate organic matter (POM) and zooplankton to understand the effects of highly variable hydrologic inputs with the onset of the summer monsoon season in Lake Soyang, Korea. The main characteristic separating pre-monsoon and post-monsoon seasons in Lake Soyang is the dramatic difference in hydrologic inflow. Pre-monsoon δ¹³C-POM (range −32.4 to −21.8‰) was lower than post-monsoon δ¹³C-POM (range −25.5 to −19.9‰). Epilimnetic δ¹³C-POM was higher post-monsoon compared to pre-monsoon, except in 2007. In the metalimnion, pre-monsoon δ¹³C-POM varied among years, while the variation in δ¹³C-POM post-monsoon was small and was related to the inflow of organic matter during summer monsoon storms. δ¹³C-zooplankton was lower post-monsoon (range −31.9 to −24.4‰) compared to pre-monsoon (range −19.4 to −17.7 ‰), while δ¹⁵N-zooplankton showed the opposite pattern (pre- and post-monsoon average 6.6 ± 2.0‰ and 4.3 ± 1.5‰, respectively). In Lake Soyang, the seasonal variation in δ¹³C-zooplankton was closely related to annual succession in the phytoplankton community and δ¹³C-phytoplankton. Thus, the results of this study provide some insights into the use of δ¹³C and δ¹⁵N measurements for understanding linkages between varying hydrologic characteristics and seasonal variation in the stable isotope composition of zooplankton. The dramatic seasonal change in hydrologic inputs in the monsoonal climate and consequent changes in turbid surface water inflow is linked with changes in the phytoplankton and zooplankton communities in Lake Soyang.

Keywords:

• carbon
• nitrogen
• stable isotope
• POM
• zooplankton

Acknowledgements

We thank the students in the Environmental Research Laboratory for assisting with fieldwork. We appreciate the suggestions from three anonymous reviewers, which improved the paper. This study was supported by the CAER (Center for Aquatic Ecosystem Restoration) of Eco-STAR project (EW 42-08-10) from MOE (Ministry of Environment, Republic of Korea). This research was conducted for the Survey on the Environment and Ecosystem of Lakes in the Han River System in Fundamental Investigation on the Environment of the Han River project funded by the Han River Watershed Management Fund. Jae-Yong Lee was supported by Brain Korea 21 Program.