Spatiotemporal Dynamics of Sediment Extracellular Enzyme Activities and Greenhouse Gas Fluxes in the Yangtze River Estuary Wetlands

Biological extracellular enzymes play a pivotal role in regulating biogeochemical cycling rates in wetland ecosystems. This study investigated the spatiotemporal variability, environmental factors, and potential associations of four key extracellular enzymes — β-glucosidase (BG), N-acetylglucosaminidase (NAG), urease (UE), and polyphenol oxidase (PPO) — with greenhouse gas (GHG) emissions including methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) in sediments of typical intertidal wetlands in the Yangtze River Estuary. Among the three gases measured, only CH₄ showed significant correlations with enzyme activities (p < 0.05), while CO₂ and N₂O exhibited no significant relationships. Seasonal field sampling, environmental monitoring, and laboratory incubation experiments were conducted across multiple sites. The results showed that the activities of all enzymes followed the seasonal pattern of autumn > summer > winter. Significant seasonal differences were observed for BG, NAG, and UE (p < 0.05), whereas PPO showed no significant seasonal variation. Enzyme activities also varied markedly among sites, reflecting spatial heterogeneity driven by local environmental conditions. Among the measured factors, redundancy and correlation analyses identified pH, total organic carbon (TOC), and extractable sediment sulfate (SSO₄²⁻) as the primary physicochemical drivers significantly regulating sediment extracellular enzyme activities. Due to combined environmental and biogeochemical controls, a significant positive correlation (p < 0.05) occurred only between BG activity and CH₄ flux under non-flooded condition. Overall, this study provides new insights into the spatiotemporal patterns of extracellular enzyme activities in estuarine wetlands, and highlighting their role in regulating GHG production and emission.