title: Dissolved oxygen stratification and response to thermal structure and long-term climate change in a large and deep subtropical reservoir (Lake Qiandaohu, China).
abstract: From January 2010 to March 2014, detailed depth profiles of water temperature, dissolved oxygen (DO), and chromophoric dissolved organic matter (CDOM) were collected at three sites in Lake Qiandaohu, a large, deep subtropical reservoir in China. Additionally, we assessed the changes in DO stratification over the past 61 years (1953-2013) based on our empirical models and long-term air temperature and transparency data. The DO concentration never fell below 2 mg/L, the critical value for anoxia, and the DO depth profiles were closely linked to the water temperature depth profiles. In the stable stratification period in summer and autumn, the significant increase in CDOM in the metalimnion explained the decrease in DO due to the oxygen consumed by CDOM. Well-developed oxygen stratification was detected at the three sites in spring, summer and autumn and was associated with thermal stratification. Oxycline depth was significantly negatively correlated with daily air temperature and thermocline thickness but significantly positively correlated with thermocline depth during the stratification weakness period (July-February). However, there were no significant correlations among these parameters during the stratification formation period (March-June). The increase of 1.67 °C in yearly average daily air temperature between 1980 and 2013 and the decrease of 0.78 m in Secchi disk depth caused a decrease of 1.65 m and 2.78 m in oxycline depth, respectively, facilitating oxygen stratification and decreasing water quality. Therefore, climate warming has had a substantial effect on water quality through changing the DO regime in Lake Qiandaohu.
authors.affiliation: Taihu Lake Laboratory Ecosystem Research Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China. Electronic address: ylzhang@niglas.ac.cn.
authors.forename: Yunlin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Chun'an Environmental Monitoring Station, Hangzhou, China.
authors.forename: Zhixu
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Institute of Environmental Protection Science, Hangzhou, China.
authors.forename: Mingliang
authors.initials: M
authors.lastname: Liu
authors.affiliation: Institute of Environmental Protection Science, Hangzhou, China.
authors.forename: Jianbo
authors.initials: J
authors.lastname: He
authors.affiliation: Taihu Lake Laboratory Ecosystem Research Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China.
authors.forename: Kun
authors.initials: K
authors.lastname: Shi
authors.affiliation: Taihu Lake Laboratory Ecosystem Research Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Yongqiang
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Taihu Lake Laboratory Ecosystem Research Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Mingzhu
authors.initials: M
authors.lastname: Wang
authors.affiliation: Taihu Lake Laboratory Ecosystem Research Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Xiaohan
authors.initials: X
authors.lastname: Liu
mesh_terms: D002681:China; D057231:Climate Change; D004784:Environmental Monitoring; D060106:Lakes / Q000032:analysis*; D010100:Oxygen / Q000032:analysis*; D012621:Seasons; D013696:Temperature; D060753:Water Quality
chemical_list: D010100:Oxygen
keywords: Climate change; Dissolved oxygen; Oxycline depth; Stratification; Thermocline depth