Impacts of the Yellow River diversion on sediment microbial community compositions and biogeochemical iron processes from the estuary to the Bohai Sea

Mengxuan Yang^{1, 2}, Chao Tang^{1, 2}, Yuchen Li^{1, 2}, Quanchao Cui^{1, 2}, Siqi Zhao³, Xiaowen Liu², Xiaole Sun^{1, 2*}
1 Key Laboratory of Ocean Observation and Forecasting, Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China
2 University of Chinese Academy of Sciences, Beijing 100049, PR China
3 University of Helsinki

The diversion of the river channel in the Yellow River Delta has greatly changed the water flow path, not only leading to a drastic regime shift of land-sea mass fluxes, but also reshaping ecosystem in the estuary. However, how the biogeochemical Fe processes respond to such changes and couple to microbial community remains under studied. We collected over 1m-long sediment cores and pore water samples from the old and present Yellow River estuary as well as the central Bohai Sea. Our results show that porewater Fe (II) concentrations from the present Yellow River estuary can reach up to 10mg/l at a depth of 15cm , much higher than that at a depth of 15 cm in central Bohai Sea (<5mg/l), which agrees well with more Fe oxides observed in sediments. Analysis of 16S rRNA gene amplicon sequencing and metagenomic data provides information of the structure and functional potential of iron-related microbial communities. Iron reducer Deltaproteobacteria bacterium are widely present in all layers, acting as the second most abundant group of 4-6% after nitrogen metabolism microorganisms in the upper 55cm. They are the most abundant species (7-9%) in 75-120cm . Sulfate reducer Desulfobacterales bacterium (1-2%) are found in a depth of 75cm; Possible methane producer Candidatus Bathyarchaeota archaeon (2-3%) were also discovered in a depth of 160cm. Furthermore, microbial alpha diversity increases between 1– 120cm and then decrease down in deeper sediments. Beta diversity shows that microorganisms in present and old Yellow River estuary sediments are mainly clustered into three types, which directly correlated with depth. Above 120cm, microbial assemblages are primarily governed by dispersal, controlled by the input of Yellow River. Below 120cm, local adaptation becomes more important. Functional analysis also supports this, the distribution of iron metabolism related pathways K02014 and K03738 is similar to that of species. Our findings demonstrate that the change of mass delivery to the sea may have profound impacts on biogeochemical Fe processes in association with microbial community shifts.



 

Yellow River diversion, iron cycling, metagenome sequencing analysis, microbial community