Early Diagenesis in Sediments of the Venice Lagoon (Italy) and Its Relationship to Hypoxia

This work focuses on sediments of a shallow water lagoon, located in densely populated area undergoing multiple stressors, with the goal increasing understanding links between diagenetic processes occurring sediments, dynamics dissolved oxygen (DO) column, and potential consequences hypoxia. Sediment data were collected over three consecutive years, from 2015 to 2017, during spring–summer, at five stations. Measured variables included: sediment porosity, grain size organic carbon content, porewater microprofiles O 2 , pH H S, profiles inorganic (DIC), total alkalinity (TA), NH 4 + NO 3 – Fe, SO 2– . In addition, long-term time series saturations column (years 2005–2017) utilized order identify occurrence duration hypoxic periods. The results show that median DO saturation value summer months was below 50% (around 110 μmol L –1 ), values 25% (below threshold) can persist for more than 1 week. stations be divided two groups based their intensity: intense moderate. At these stations, average DIC net production rates, estimated trough steady-state model (Profile) were, respectively, 2.8 1.0 mmol m –2 d consumption rates respectively 1.6 0.4 while diffusive uptake fluxes, calculated microprofile data, 28.5 17.5 characterized by diagenesis, sulfide accumulated porewaters close sediment-water interface, reaching 0.7 mM 10 cm. Considering typical physico-chemical conditions, theoretical required consume down level demand ranges 5 18 days, absence mixing re-oxygenation. estimation highlights diagenesis may play crucial role triggering maintaining hypoxia lagoon waters season specific high intensity zones. could enhanced changes regional climate such as increase frequency heat waves.