Spatial reversal of organic matter decomposition potential associated with inter-basin water diversion in a large regulated lake

Inter-basin water diversion (IBWD) alters hydrological connectivity, but its associations with organic matter (OM) decomposition across heterogeneous lake habitats remain poorly understood. This project examines OM decomposition potential and the taxonomic and functional profiles of cotton strip-colonizing microbiomes in Weishan Lake, a regulated lake along the Eastern Route of the South-to-North Water Diversion Project in China. Standardized cotton strip assays, water chemistry measurements, and shotgun metagenomic sequencing were combined across nine sites representing tributary rivers, lake centers, and stagnant zones. Two 30-day deployments began on 5 September and 7 October 2025, corresponding to the non-diversion and diversion periods, respectively. Daily tensile strength loss of cotton strips was used as a standardized proxy for OM decomposition potential. For metagenomic sequencing, eight strips from each site and deployment were pooled and divided into three aliquots, yielding 54 sequencing libraries from 18 site-period pools. These aliquots were subsamples of shared pools rather than independent biological replicates. Metagenomic analyses characterized microbial taxonomic composition and the relative genomic representation of carbon cycling genes, complemented by community assembly and co-occurrence network analyses. Decomposition potential exhibited contrasting habitat patterns between deployments, with the highest habitat mean shifting from stagnant zones to lake centers. The project examines how these patterns relate to water physicochemical conditions, microbial community organization, and genomic functional potential. Because the deployments coincided with seasonal cooling, the observed differences cannot be attributed uniquely to IBWD. The dataset supports investigation of microbial associations with substrate decomposition in regulated freshwater ecosystems without equating gene abundance with transcription or enzyme activity.