Influence of Thermal Stratification on Seasonal Net Ecosystem Production and Dissolved Inorganic Carbon in a Shallow Subtropical Lake

Abstract

Thermal stratification is a critical physical process controlling carbon (C) flux from lakes into the atmosphere. In general, vertical water temperature profiles in shallow subtropical lakes can vary significantly because typhoons frequently induce vertical mixing across the entire lake due to strong winds and rapid flushing from river inputs. Since C fluxes are driven by dissolved inorganic C (DIC), it is necessary to understand stratification's influence on DIC dynamics in shallow subtropical lakes. Therefore, we aimed to clarify the impact of stratification on DIC in Yuan-Yang Lake, a typical shallow subtropical mountain lake, by developing a net ecosystem production (NEP) model. We measured the vertical profile of water temperature and DIC once or twice a month from July 2004 to December 2017. We applied a three-dimensional hydrological model to estimate residence time and NEP, which revealed that large amounts of DIC are stored in the lower layer from spring to summer due to the suppression of vertical mixing by stratification. In autumn and winter, the lake was well mixed, and DIC was evenly distributed in the water column due to vertical mixing. This was confirmed by vertical DIC profiles.