library_construction_protocol: Sediment microbial DNA was extracted by using the FastDNA SPIN Kit. The hypervariable V4 region of the eukaryotic 18S rRNA gene was amplified using the primer pairs 528F and 706R. The PCR products of each sample were pooled in triplicate reactions and gel-purified. All libraries were sequenced on the Illumina Hiseq platform using a paired-end strategy