Alteration of Carbon Balance Induced by Changes of Water Level in a Typical Saline-alkali Wetland, Momoge Wetland, China

Northeastern wetlands are important carbon sinks in China, yet increasing water-level fluctuations driven by climate change and human activities may substantially alter their carbon balance. However, the hydrological controls on carbon source–sink dynamics in saline-alkali wetlands remain poorly understood. In this study, field measurements and the DeNitrification-DeComposition (DNDC) model were integrated to investigate carbon emissions and carbon balance across water-depth zones in the Momoge Wetland, a typical saline-alkali wetland in Northeast China, and to identify potential carbon-sink hotspots. Results showed that the shallow-water area was the high-value area for carbon emission in the growing season of Momoge Wetland, with the highest mean CO₂ emission flux from Schoenoplectus nipponicus (919.50 mg/(m²·h)) and the highest mean CH₄ emission flux from Phragmites australis (28.80 mg/(m²·h)). The shallow-water areas exhibited high carbon fluxes but also showed the strongest carbon sequestration capacity due to high vegetation productivity (net ecosystem exchange = −11.25 × 10³ kg C/(ha·yr)), while the deep-water area showed a slight carbon source (0.38 × 10³ kg C/(ha·yr)). As Phragmites australis occupies a leading position in the net carbon sink capacity of Momoge Wetland, water level was the main factor affecting the wetland carbon sink, but climatic drought reduces the wetland carbon-sink capacity. By integrating water-level change, vegetation succession, and wetland carbon sinks into the overall research framework, this study proposes a new solution to carbon sink accounting that can help explore the alkaline wetland carbon cycle more deeply.