Wastewater discharge intensity drives coastal microbial community assembly and pollution history determines their...

Microbial communities in coastal sediments are vital for ecosystem stability and biogeochemical cycles. Disposal of wastewater treatment plant effluents into coastal environments might change the microbial community, further affecting ecosystem functioning. However, an important knowledge gap is how the different types and intensities of wastewater influence the microbial community assembly. Here, we constructed a series of microcosms using coastal sediments with (SY) and without (HB) a history of wastewater discharge in the Hangzhou Bay, to analyze the effects of different types (domestic, industrial) and intensities (0 %, 50 %, 100 %) of wastewater on the microbial communities. The results showed the species diversity of SY was higher than that of HB, and significant differences in community composition were also observed. The wastewater intensity had a more significant impact on the microbial community than the type of wastewater. As the wastewater intensity increased, both species and functional diversity in sediments significantly decreased. The HB microbial community showed a stronger response to increased pollution levels, and the assembly mechanism of microbial community changed from a stochastic process to a deterministic process (the ratio of stochasticity changed from 52.23 % to 28.63 %); wastewater shock reduced the complexity and stability of the HB microbial network, and reduced the number of keystone taxa. Conversely, the SY microbial community exhibited greater stability and resistance to wastewater shock, with stochastic processes consistently dominating microbial community assembly (the ratio of stochasticity ranged from 50.99 % to 57.40 %). Our results provide new insights on the impacts of human activities on coastal environment, which are crucial for environmental assessment and pollution control.