A systematic review of engineered oxygen supply (EOS) for remediating aquatic deoxygenation: Implications for marine ecosystem restoration

Driven by nutrient enrichment, climate warming, and altered hydrodynamics, deoxygenation is intensifying in coastal and marine waters, with escalating consequences for biodiversity, ecosystem function, and restoration efforts. Engineered oxygen supply (EOS) is increasingly proposed as a management response, yet existing syntheses are largely confined to freshwater systems, and marine applications have not been reviewed. To evaluate the suitability of available EOS technologies for marine settings, we conducted a systematic review of 205 EOS projects across aquatic systems, integrating freshwater and marine evidence to synthesise technique application, environmental context, monitoring design, and temporal and geographic trends. While several EOS techniques have been widely applied in freshwater systems since the 1960s, marine deployments have emerged primarily within the last two decades and remain substantially underrepresented. Existing marine applications are largely confined to stratified estuaries and semi-enclosed basins. Although many projects document sustained dissolved oxygen improvements, fewer extend monitoring consistently into geochemical and ecological domains at meaningful spatial and temporal scales, limiting inference regarding full ecosystem restoration. EOS techniques differ fundamentally in mechanism: mixing redistributes existing oxygen and facilitates natural mixing processes, whereas direct oxygen addition can directly augment the oxygen inventory, a distinction central to large-scale marine feasibility. Advancing marine EOS will require multi-domain monitoring and transparent economic assessment. Ongoing research increasingly centres on direct injection of pure oxygen at depth, particularly via line-diffuser systems, as a potential route for scaling EOS to larger coastal and open-ocean environments. • EOS applications synthesised across freshwater and marine systems. • Marine deployments remain limited to confined systems. • Technique suitability depends on hydrodynamics and stratification. • Nutrient loading shapes outcomes and management response. • Geochemical and ecological monitoring is required to assess restoration. • Line-diffuser pure oxygen injection is emerging for ocean-scale use.