Abstract: Against the backdrop of China's dual carbon targets, proper disposal of high-moisture invasive aquatic plants has become essential for watershed ecological restoration and biomass circularity. Pistia stratiotes L., a typical floating invasive macrophyte characterized by rapid propagation and massive biomass accumulation, releases nitrogen, phosphorus, and greenhouse gases upon random stockpiling or direct incineration, causing secondary water pollution while squandering inherent carbon sequestration capacity. This study followed ISO 14040 and ISO 14044 standards, adopting 1 kg functionalized hydrochar as the functional unit within a cradle-to-gate boundary spanning harvesting, transportation, pretreatment, hydrothermal carbonization, solid-liquid separation, drying, and functionalization. The life cycle inventory integrated laboratory measurements, market survey data, and the Ecoinvent 3 database. Two disposal routes, hydrothermal carbonization-based resource recovery and direct incineration, were evaluated across four power supply scenarios: coal-fired power, regional mixed grid, solar power, and wind power.coal-fired power, regional mixed grid, solar power, and wind power. Six CML-IA baseline midpoint indicators were assessed: fossil depletion potential (FDP), global warming potential (GWP), human toxicity potential (HTP), photochemical ozone creation potential (POCP), acidification potential (AP), and eutrophication potential (EP). Uncertainty arising from electricity consumption, ethanol dosage, and transport distance was quantified through single-factor sensitivity analysis and 10 000-iteration Monte Carlo simulation. Hydrothermal carbonization achieved substantial emission reductions relative to incineration, with eutrophication potential and photochemical ozone creation potential decreasing by 95.30% and 93.32%, respectively. Stage-resolved GWP values were 3.33×10^-2 kg CO₂ eq for harvesting, 0.58 kg CO₂ eq for transportation, 3.29 kg CO₂ eq for pretreatment, 15.40 kg CO₂ eq for hydrothermal carbonization, 6.31 kg CO₂ eq for solid-liquid separation, 9.21 kg CO₂ eq for drying, and 18.90 kg CO₂ eq for functionalization, with corresponding FDP contributions of 0.38, 6.67, 29.10, 136, 54.91, 81.40, and 173 MJ. Normalized results identified FDP (1.53×10^-11) and GWP (1.07×10^-11) as the dominant impact categories, primarily attributable to coal-reliant electricity consumption. Functionalization and hydrothermal carbonization accounted for 39.91% and 25.61% of the total environmental burden, respectively. Sensitivity analysis revealed that the coal-power baseline yielded 537 MJ FDP and 60.6 kg CO₂ eq GWP, whereas solar substitution reduced these to 92.7 MJ and 3.2 kg CO₂ eq, corresponding to reductions of 82.70% and 94.72%; wind power delivered comparatively modest mitigation. Clean energy substitution therefore represents a pivotal intervention for achieving synergistic pollutant abatement and decarbonization. Monte Carlo simulations indicated POCP exhibited the highest uncertainty, mainly ascribed to ethanol volatilization losses and regional incompatibility of background databases, while HTP and EP remained robust with negligible variability. Complementary life cycle costing estimated unit production costs at 33.78 CNY/kg, partially offset by revenues from co-produced bio-oil and hydrothermal liquid. Scale-up of production capacity and optimization of ethanol recovery efficiency emerged as the most effective leverage points for enhancing cost competitiveness against commercial activated carbon. This functionalized hydrochar route based on Pistia stratiotes L. converts invasive biomass into high-performance adsorbents while enabling long-term carbon sequestration, consistent with national dual carbon objectives. The approach integrates pollution remediation, biomass resource recovery, and carbon storage benefits, circumventing the excessive energy demand and pollutant emissions characteristic of conventional incineration. This study establishes quantitative benchmarks and a standardized LCA framework for the low-carbon valorization of high-moisture aquatic biomasses, providing a methodological reference for the engineering application of invasive plant-based functional materials.