Freshwater bivalves, such as Diplodon chilensis (Hyriidae), play a key role in water quality and nutrient dynamics in aquatic ecosystems, influencing sediment properties and biological communities (Vaughn & Hakenkamp, 2001; McCasker & Humphries, 2021). This study evaluated the effect of D. chilensis on total organic matter (TOM), total phosphorus (Total-P), total nitrogen (Total-N), total chlorophyll (Total-Ch), and macro- and meiofaunal densities in the sediments of Laguna Chica de San Pedro (Chile; 36º 50´40”S; 73º 04´59”W). D. chilensis (Hyriidae) stands out as a megafiltering species due to its large size (7–8 cm), significantly impacting biogeochemical processes. A randomized complete block design (RCBD) was implemented using experimental mesocosms. Four plastic racks (50 × 50 cm) were placed at depths of 6–7 m for two months over a year, covered with nylon mesh to prevent bivalve escape and predation. Each rack contained nine aluminum trays (15 × 15 × 5 cm) with fine sand, previously washed and dried. These trays were assigned to three groups: Control 1 (sand, N=3), Control 2 (sand and sealed shells of four dead D. chilensis individuals, N=3), and Treatment (sand and five live D. chilensis individuals, N=3). Results showed a significant ~30% increase in TOM, meiofaunal abundance, and richness in the treatment with live bivalves compared to the controls, which did not differ significantly. Similar effects were observed for Total-N and Total-Ch but not for Total-P. These findings highlight the role of D. chilensis as an ecosystem engineer, influencing biogeochemical cycles, nutrient dynamics, and sediment biodiversity in freshwater ecosystems. Understanding these interactions is essential for managing and conserving aquatic environments, as bivalves contribute to habitat structuring and nutrient regulation. Further research should explore long-term effects and interactions with other biotic and abiotic factors. Funding: FONDECYT Regular N° 1231089.