PRIMARY RESEARCH PAPER Temporal and spatial variations of chemical oxygen demand in Lake Taihu, China, from 2005 to 2009 Yan Yin • Yunlin Zhang • Xiaohan Liu • Guangwei Zhu • Boqianq Qin • Zhiqiang Shi • Longqing Feng Received: 13 November 2010 / Revised: 17 January 2011 / Accepted: 18 January 2011 / Published online: 4 February 2011 Ó Springer Science+Business Media B.V. 2011 Abstract We undertook a study in Lake Taihu, China, from 2005 to 2009 including a total of 639 samples to determine: (i) the seasonal dynamics and spatial distribution of the chemical oxygen demand (COD) and (ii) the relationships between the COD concentration and the biochemical oxygen demand (BOD), phytoplankton pigment, total dissolved nitro- gen (TDN), and total dissolved phosphorus (TDP) concentrations, as well as the chromophoric dissolved organic matter (CDOM) absorption coefficient. There were significant spatial differences in the COD concentration, which gradually decreased from Zhu- shan Bay in the northwest, to the north, the lake center, and the southeast of the lake. The COD concentration was significantly higher at near-shore sites than that at open water sites. The mean COD concentrations were significantly higher in the spring and summer than in the winter and autumn. The lowest annual mean COD concentration appeared in 2009, which could be attributed to improvements in water quality management and high rainfall. The COD concentrations in all four seasons were strongly correlated with phytoplankton pigment, suggesting that extracellular release of COD from phytoplankton was an important COD source. The correlation coefficients between the COD and phytoplankton pigment concentrations were higher in the spring, summer, and autumn than in the winter, showing a more important contribution of phytoplankton degra- dation to COD in the algal bloom season than in the non-algal bloom season. These new data on the temporal and spatial characteristics of the COD in Lake Taihu will be crucial for developing future strategies for water quality management. Keywords Chemical oxygen demand Á Correlation analysis Á Lake Taihu Á Spatial and temporal variations Introduction In recent years, the shallow lakes in the middle and lower reaches of the Yangtze River in China have been seriously polluted because of the rapid eco- nomic development and intensified human activities in adjacent areas. Household and industrial wastes discharged into the estuaries and lakes in the region contribute significantly to this severe contamination Handling editor: Luigi Naselli-Flores Y. Yin Á Y. Zhang (&) Á X. Liu Á G. Zhu Á B. Qin Á Z. Shi Á L. Feng 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 210008, China e-mail: ylzhang@niglas.ac.cn Y. Yin Á X. Liu Graduate University of Chinese Academy of Sciences, Beijing 100049, China 123 Hydrobiologia (2011) 665:129–141 DOI 10.1007/s10750-011-0610-y