Eutrophic Lake Taihu as a significant CO2 source during 2000-2015

Inland lakes receive growing attentions on eutrophication and their roles in global carbon cycle. However, understanding how inland lakes contribute to global carbon cycle is seriously hampered due to a shortage of long-term records. This study investigated the carbon dioxide (CO2) flux from the lake Taihu, a large (2400 km(2)) and shallow (mean depth 1.9 m) eutrophic lake in subtropical region, based on a long term (2000-2015) measurement of the partial pressure of carbon dioxide (pCO(2)) at high spatiotemporal resolution, We found that the Lake Taihu was a significant source of atmospheric CO2 with an average CO2 emission flux at 18.2 +/- 8.4 mmol m(-2) d(-1) (mean +/- 1standard deviation) and a mean annual pCO(2) value of 778 +/- 169 mu atm. The highest pCO(2) and CO2 flux were observed in eutrophic zone with a high external input of carbon and nutrient, and the lowest in non-eutrophic zones with no direct external input of nutrient and carbon. A substantial seasonal pattern in pCO(2) was observed, particularly in eutrophic pelagic area, and was significantly negatively correlated with chlorophyll a. Long-term measurement showed the interannual variation in annual lake CO2 dynamics, which was highly sensitive to human-induced nutrient input. Watershed input of carbon and nutrient leads to the high CO2 level, counterbalancing the in-lake primary production. All lines of evidence suggest that human activities may have predominate contribution to CO2 source in the lake Taihu, and this mechanism might be widespread in global freshwater lakes. (C) 2019 Elsevier Ltd. All rights reserved.