Land use intensification is a major driver of biodiversity loss across ecosystems, yet itsconsequences for host-associated microbiomes in freshwater food webs remain poorlyunderstood. In this case study, we used the gut microbiome of mayfly larvae (Ephemeradanica) as a sensitive biological interface to assess how site-specific adjacent land use typesshape microbial community composition and functions in stream ecosystems. Larvae weresampled in summer and autumn from sites adjacent to forest, extensive grassland, andintensive agriculture along the Otterbach stream (Bavarian Forest, Germany). Combining 16SrRNA amplicon sequencing with long-read metagenomics, we show that site-specific land use,in interaction with seasonality, significantly restructures larval gut bacterial communitieswithout affecting alpha diversity. Rather than introducing distinct agriculturally derived taxa,agricultural land use acted as a selective environmental filter, enriching bacterial groups withspecific functional traits. Taxa enriched in the sites adjacent to agricultural sites harbouredgenes involved in complex carbon and xenobiotic degradation, short-chain fatty acidproduction, efflux pumps, and stress response. These functional signatures were furthersupported by 14 metagenome-assembled genomes linked to these enriched taxa. Together,our results reveal that site in combination with seasonality not only reshaped bacterialcommunity composition without affecting alpha diversity but also triggered shifts in theabundance of genes involved in microbial-host interactions and degradation pathways in E.danica larvae. This study also highlights the larval gut microbiome as a sensitive indicator ofenvironmental change, suggesting that environmental microbial shifts may have cascadingconsequences for freshwater trophic interactions and ecosystem functioning