The relationship between water temperature and dissolved organic carbon concentration in Lake Shinji

To clarify the temperature dependence of dissolved organic carbon (DOC) concentration, we sampled water once per week at the center of Lake Shinji from July 1, 2010 to June 27, 2011. Maximum, minimum, average, and median total organic carbon (TOC) concentrations were 4.7, 1.9, 2.8, and 2.6 mg L-1, respectively. DOC concentrations of these concentrations were 2.7, 1.3, 1.9, and 1.8 mg L-1, respectively. By dividing the DOC by the TOC of these sample we found ratios of 0.86, 0.47, 0.70, and 0.72, respectively. A positive correlation was found between water temperature and DOC, and there was a time lag between temperature increase/ decrease and DOC increase/ decrease. The correlation coefficient for the simple regression between temperature and DOC improved when we delayed temperature data. The highest coefficient of correlation was gained when we added 8.6 weeks (60 days) to temperature data.