Exploring the Dynamics of Dissolved Oxygen and Vertical Density Structure of Water Column in the Youngsan Lake

Abstract

The Youngsan Lake was constructed to supply agricultural water to the extensive rice fields in the basin of the lake in 1981. Hypoxia has often developed in the bottom water of the lake during the warm season although the water depth is relatively shallow (< 16 m). We investigated the spatial and temporal variations of dissolved oxygen (DO) and physical properties such as water temperature, salinity and turbidity to elucidate the effects of change in physical properties on DO dynamics in the lake. Vertical profiles of DO, temperature, salinity, and water density were also explored to verify the development of stratification in relation to DO variation in the water column. Hypoxia (DO < 2 mg L-1) was not observed in the upper regions whereas hypoxia was detected in the lower regions during the warm season. Thermocline generally developed in the lower regions during the warm season unlike the previous studies in which no thermocline was observed. However, water column was well mixed when freshwater water was discharged from the reservoir through the sluice gate of the dike. DO concentrations also decreased when halocline or pycnocline developed during the dry season suggesting that the vertical stratification of water column affects DO dynamics although the water depth is shallow in the Youngsan lake. 1) 1. 서론 용존산소(dissolved oxygen, DO)는 호기성 호흡에 의존하는 수중 생물들에게는 생태적 그리고 진화적으로 매우 중요한 환경인자이다. 산소는 수중 생물들의 대사 활동의 공급원으로 산소 부족시에는 성장률, 공간적 분 포, 거동, 생식, 생존 등에 부정적 영향을 미친다(Diaz 와 Rosenberg, 1995; Breitburg 등, 2003; Breitburg 등, 2009; Conley 등, 2009). 일반적으로 용존산소의 농도 가 2 mg L-1 일 경우 빈산소(hypoxia)라고 정의하는데