Denitrifying anaerobic methane-oxidizing bacteria in river networks of the Taihu Basin: Community dynamics and assembly process

Spatio-temporal patterns and drivers of CH4 and CO2 fluxes from rivers and lakes in highly urbanized areas

Gaseous carbon exchange at the water-air interface of rivers and lakes is an essential process for regional and global carbon cycle assessments. Many studies have shown that rivers surrounding urban landscapes can be hotspots for greenhouse gas (GHG) emissions. Here we investigated the variability of diffusive GHG (methane [CH4] and carbon dioxide [CO2]) emissions from rivers in different landscapes (i.e., urban, agricultural and mixed) and from lakes in Suzhou, a highly urbanized region in eastern China. GHG emissions in the Suzhou metropolitan water network followed a typical seasonal pattern, with the highest fluxes in summer, and were primarily influenced by temperature and dissolved oxygen concentration. Surprisingly, lakes were emission hotspots, with mean CH4 and CO2 fluxes of 2.80 and 128.89 mg m-2 h-1, respectively, translating to a total CO2-equivalent flux of 0.21 g CO2-eq m-2 d-1. The global warming potential of urban and mixed rivers (0.19 g CO2-eq m-2 d-1) was comparable to that for lakes, but about twice the value for agricultural rivers (0.10 g CO2-eq m-2 d-1). Factors related to the high GHG emissions in lakes included hypoxic water conditions and an adequate nutrient supply. Riverine CH4 emissions were primarily associated with the concentrations of total dissolved solids (TDS), ammonia‑nitrogen and chlorophyll a. CO2 emissions in rivers were mainly closely related to TDS, with suitable conditions allowing rapid organic matter decomposition. Compared with other types of rivers, urban rivers had more available organic matter and therefore higher CO2 emissions. Overall, this study emphasizes the need for a deeper understanding of the impact of GHG emissions from different water types on global warming in rapidly urbanizing regions. Flexible management measures are urgently needed to mitigate CO2 and CH4 emissions more effectively in the context of the shrinking gap between urban and rural areas with growing socio-economic development.

Dynamics of the sedimentary bacterial communities in a plain river network: similar coalescence patterns with bacterioplankton communities driven by distinct assembly processes

IMPORTANCE

Microorganisms play important roles in driving the biogeochemical cycles within river ecosystems. It has been suggested that hydrologic conditions could influence microbial communities in rivers, but their specific effects on the behaviours of microbial coalescence have not been thoroughly investigated. In this study, the dynamics of sedimentary bacterial communities within a plain river network were analyzed by amplicon sequencing followed by several ecological models to uncover the underlying assembly processes. Additionally, a comparative analysis between bacterioplankton communities and sedimentary bacterial communities was performed to unveil their coalescence patterns. The results suggested that similar coalescence patterns between sedimentary bacterial and bacterioplankton communities were driven by distinct assembly processes under dynamic hydrological conditions. These findings enhanced our understanding of microbial diversity features within river ecosystems.