Contribution of lakes to global greenhouse gas emissions: Mechanisms, quantification and mitigation strategies

Lakes cover only 1.8 % of Earth's land yet emit 0.35-0.55 Pg C yr^-1 as CO₂, 60-120 Tg CH₄, and 60-150 Gg N₂O, about 5 % of global fossil-fuel emissions. This review synthesizes recent advances in lake GHG mechanisms, measurement, and mitigation, and outlines key research directions. Net respiration generally exceeds primary production, maintaining CO₂ supersaturation, while anaerobic methanogenesis dominates CH₄ release; oxic pathways linked to methyl-phosphonate cleavage and cyanobacterial leakage add up to 28 % of CH₄ in warm, P-limited, dissolved organic carbon (DOC)-rich waters. Roughly 60 % of N₂O originates from nitrifier-denitrification. Multi-scale monitoring now combines satellite retrievals, eddy covariance, and buoy sensors, yet global budgets still vary ten-fold because small ponds, littoral "hot spots", and winter ice-outs are under-sampled and gas-transfer coefficients are inconsistent. A range of mitigation measures offers substantial climate-related benefits: (i) enhanced wastewater treatment, urine-diverting sanitation, and vegetated buffers cut CH₄ + N₂O by 15-25 %, while generating climate and water quality co-benefits can value at billions of USD globally; (ii) biomass harvesting and floating macrophytes lower CH₄ + CO₂ by up to 57 %; (iii) micro-bubble destratification or moderate sulfate dosing trim residual CH₄ by 25-60 %. Together, these measures can abate 0.01-0.08 Mt CO₂-eq yr^-1 per 100 ha of intensively managed urban lake, enough to achieve 6-10 % of the Global Methane Pledge. Future priorities are resolving the oxic-methane paradox, standardising monitoring, and applying AI-driven up-scaling to embed lake mitigation within SDGs, turning lakes from overlooked emitters into actionable components of climate and water-quality policy.