Effect and microbial mechanism of suspended sediments particle size on nitrous oxide emission in eutrophic lakes

摘要

Suspended sediment (SPS) is an important environmental factor in eutrophic lakes, where they may play a significant role in the microbial nitrogen cycle and thus affect the N2O source and sink function. This study investigated the correlation and corresponding microbial mechanisms between N2O emission fluxes and SPS particle sizes. N2O emission characteristics were investigated in four parallel operated lab-scale microcosmic systems, in which different sizes of SPS particles were inoculated (i.e., <75, 75-150, 150-300, and >300 & mu;m). The results show that, N2O emission fluxes in the eutrophic lakes were exponentially correlated with the lake trophic level index (TLI) (R2 = 0.94, p < 0.01) and the specific surface area of the SPS (R2 = 0.38, p < 0.05). In the microcosmic systems, SPS with 75-150 & mu;m particles had the highest N2O emission rate of 5.94 & PLUSMN; 0.007 & mu;g N/ L/d, which was 2.6 times that of the <75 & mu;m particle size system. The microcosmic system with particle size >300 & mu;m had the highest N2O reduction rate (Vmax) of 6.776 & mu;mol/L/h, which was 16-50 times that of the other three groups. Larger particle size SPS have a smaller specific surface area, which could affect the microenvironment on SPS surface and thus affect the microbe functions. The microbial community structure results indicated that the dominant microorganisms on the SPS surface were denitrifying bacteria. The maximum (nirS + nirK)/nosZ ratio was 30.2 for the 75-150 & mu;m system, which was nearly 2 times higher than the other systems. The >300 & mu;m system had the highest nosZ abundance, indicating a strong ability to reduce N2O. The cooccurrence networks analysis indicated that the cooperation and competition among nitrifiers and denitrifiers determined N2O emissions. These results provide fundamental insights into the influence of SPS size on N2O emissions in eutrophic lakes.

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