Diurnal and seasonal variations of pCO and fluorescent dissolved organic matter (FDOM) in different polluted lakes.

This study aimed to assess pollution and daily-to-seasonal dynamics of the partial pressure of CO (pCO) and CO degassing flux concerning the fluorescent dissolved organic matter (FDOM) from tropical lakes. A membrane-enclosed pCO sensor and water quality multimeter analyzer was deployed to continuously record daily and seasonal variations in pCO and CO degassing flux in three lakes in Savar, Dhaka. During both wet and dry seasons, all lake water was supersaturated with CO in contrast to the atmospheric equilibrium (~400 μatm). The pCO values in the lake water during the dry season were relatively low in comparison, and the pCO levels in the wet season were much higher due to external inputs of organic matter from watersheds and direct inputs of CO from soils or wetlands. The estimated water-to-air CO degassing flux in the different levels of polluted lakes varies with the pollution context. Study areas calculated the carbon flux and three lakes released respectively 86.75×10g CO year, 13.8×10g CO year, and 9.17×10g CO year. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy combined with parallel factor (PARAFAC) analysis was used to investigate the distributions of fluorescent components in DOM. EEM-PARAFAC analysis identified humic-like, fulvic-like, protein-like, and more tyrosine-like FDOM components and their environmental dynamics. Terrestrial DOM may provide inputs to the terrestrial humic-like component in the lake water. In contrast, the biological activity of plankton-derived FDOM is the most likely source for the autochthonous humic-like component. FDOM and DO concentrations have negative correlations with pCO, indicating that when the FDOM and DO level is decreased, the amount of pCO values increases.