Elevated hydrostatic pressure promotes organic carbon mineralization in reservoir sediments

Sediment organic carbon mineralization is a key biogeochemical process regulating the balance between organic carbon decomposition and preservation in aquatic systems. Reservoir impoundment substantially alters the hydrostatic pressure regime experienced by sediments, yet its impacts on sediment organic carbon mineralization remain poorly understood. Here, using a custom-built hydrostatic pressure simulation system, we show that increasing hydrostatic pressure (0.1-2.1 MPa) significantly accelerates sediment organic carbon mineralization. In non-sterilized sediment-water incubations, the apparent organic carbon mineralization rate (CMR) at 2.1 MPa was 1.45-, 2.01-, and 1.72-fold higher than at 0.1 MPa on day 3, 6, and 9, respectively. In water-only incubations, the stimulatory effect was even stronger initially, with the CMR at 2.1 MPa reaching 4.59-fold higher than at 0.1 MPa on day 10, but declined rapidly over time. In sterilized sediment-water incubations, overlying-water DOC at 2.1 MPa was 1.26-fold higher than at 0.1 MPa, indicating that hydrostatic pressure can enhance DOC release even when microbial activity is suppressed. These findings reveal hydrostatic pressure as an overlooked control on sediment organic carbon mineralization and suggest that pressure-driven carbon transformation may be relevant to assessments of organic carbon burial efficiency and greenhouse-gas production potential in deep reservoirs.