Greenhouse gas emissions from Daihai Lake, China: Should eutrophication and salinity promote carbon emission dynamics?

Greenhouse gases (GHGs) emitted or absorbed by lakes are an important component of the global carbon cycle. However, few studies have focused on the GHG dynamics of eutrophic saline lakes, thus preventing a comprehensive understanding of the carbon cycle. Here, we conducted four sampling analyses using a floating chamber in Daihai Lake, a eutrophication saline lake in Inner Mongolia Autonomous Region, China, to explore its carbon dioxide (CO) and methane (CH) emissions. The mean CO emission flux (FCO) and CH emission flux (FCH) were 17.54 ± 14.54 mmol/m/day and 0.50 ± 0.50 mmol/m/day, respectively. The results indicated that Daihai Lake was a source of CO and CH, and GHG emissions exhibited temporal variability. The mean CO partial pressure (pCO) and CH partial pressure (pCH) were 561.35 ± 109.59 µatm and 17.02 ± 13.45 µatm, which were supersaturated relative to the atmosphere. The regression and correlation analysis showed that the main influencing factors of pCO were wind speed, dissolved oxygen (DO), total nitrogen (TN) and Chlorophyll a (Chl.a), whereas the main influencing factors of pCH were water temperature (WT), Chl.a, nitrate nitrogen (NO-N), TN, dissolved organic carbon (DOC) and water depth. Salinity regulated carbon mineralization and organic matter decomposition, and it was an important influencing factor of pCO and pCH. Additionally, the trophic level index (TLI) significantly increased pCH. Our study elucidated that salinity and eutrophication play an important role in the dynamic changes of GHG emissions. However, research on eutrophic saline lakes needs to be strengthened.