Effect of water-level fluctuations on methane and carbon dioxide dynamics in a shallow lake of Northern China: Implications for wetland restoration

Shallow lakes are characterized by strong hydrological fluctuations, affecting their biochemistry and carbon (C) balance. This study explored carbon dioxide (CO2) and methane (CH4) flux under strong water-level fluctuations in a shallow lake while also addressing its implications regarding wetland restoration. The DeNitrification-DeComposition (DNDC) model, a process-based biogeochemical model, was used to simulate CO2 and CH4 flux under intensive water-level fluctuations in Lake Baiyangdian (BYD), Northern China. Results showed that: (i) the DNDC model was able to reasonably capture CO2 and CH4 dynamics, which were determined to be extremely sensitive to water-depth fluctuations at a −10 cm to 10 cm range; (ii) the lowest CO2 flux was observed at a 40-day duration, while the trend in annual CH4 flux was to increase as inundation time increased, changing from −2.27 kg C/ha/y to 1.57 kg C/ha/y; and (iii) CO2 and CH4 flux increased under higher fluctuation frequencies, wherein CO2 flux was lowest in January and February and CH4 flux increased from December to March under certain frequencies. Our results indicate that water-level fluctuations (e.g., water depth, duration, frequency, and timing) affected both CO2 and CH4 flux. As it pertains to water diversion projects used for shallow lake restoration initiatives, the optimum approach, pertinent to water yields, diversion time, and duration, should first be considered carefully. Results from this study provide useful information for assisting policymakers with respect to reducing gaseous C emissions during ecological water transfer project regulations in shallow lakes.