Significant diurnal variation of CO2 flux from a shallow eutrophic lake: effects of submerged aquatic vegetation and algae bloom
Zhuangzhuang Zhang, Ruihong Yu, Xinghui Xia, Jin Li, Heyang Sun, Zhengxu Cao, Zhen Qi, Changwei Lü, Xixi Lu
Abstract
Shallow eutrophic lake with submerged aquatic vegetation (SAV) has high primary productivity, but its diurnal variation of CO 2 flux remains unclear. Moreover, algae bloom has become a serious environmental problem; however, its effects are still unclear. Thus, monthly measurement in Lake Ulansuhai, a shallow eutrophic lake in China, was conducted throughout the ice-free period (April–October, 2019), to study monthly and diurnal variation of CO 2 flux and the effects of algae bloom, SAV, and trophic state. Results show that the area with SAV (Site 1) acts as a CO 2 sink during both daytime and nighttime in most months (spanning 5 months), and CO 2 absorption during nighttime accounts for 25–45% of the total daily absorption. In contrast, the area with both SAV and algae (from May to September; Site 2) during whole ice-free period acts as a CO 2 source during nighttime all the time, accounting for 30–100% (average of 80%) of the total daily emissions. Site 1 (without algae) during whole ice-free period acts as a net CO 2 sink with CO 2 flux of −7.3 ± 4.73 mmol m −2 d −1 , whereas Site 2 (with algae) plays as CO 2 source with CO 2 flux of 5.54 ± 3.15 mmol m −2 d −1 . Furthermore, monthly variation during 7 months suggests that total daily CO 2 emission flux in April (after ice-melt period) at Site 1 (without algae) and Site 2 (with algae) reached 17.78 and 34.75 mmol m −2 d −1 , respectively, indicating that the period plays an important role for CO 2 emission budget during the whole ice-free period. Results show that the effects of algae bloom and SAV need to be paid more attention in further works.