Life-Cycle Environmental Burdens of Cultivated Seaweed as Blue Food: The Case Study of Wakame and Kelp in Dalian, China

Abstract

Cultivated seaweed, known as blue food, benefits environmental sustainability, such as mitigating climate change when replacing land-based food with carbon-intensive fertilizer input. However, seaweed cultivation still generates environmental burdens that remain unclear, especially in China, where approximately 60% of global seaweed is cultured. Here, we developed life cycle assessment (LCA) models to quantitatively compare the environmental performance of two seaweed species of wakame (Undaria pinnatifida) and kelp (Saccharina japonica) cultivated by floating rafts. The cultivation system covers five processes. We developed scenarios to examine the environmental performance by controlling the seedling density and cultivation line inputs. Results show that the environmental loads of wakame are 20-40% higher than those of kelp, with carbon footprints ranging from 21-36 kgCO2e and 14-35 kgCO2e per ton of wet weight, respectively. Seaweed cultivation at sea produces the most environmental burdens. The polyethylene cultivation lines were identified as the crucial input influencing environmental performance. Extending the service time of cultivation lines by 10% reduces the environmental load by ~5% on average. Reducing seedling density with fewer cultivation line inputs can slightly decrease the environmental burden, but with less seaweed yield. Nitrogen and phosphorus removal by seaweed from marine areas is two orders of magnitude lower than fertilizer applied in land cropping systems in typical provinces but is four orders higher than the life-cycle emissions of seaweed cultivation. Our study adds new knowledge for policymakers to quantitatively understand the environmental burdens of cultured seaweed (especially for wakame Undaria pinnatifida) as a blue food alternative to land-based foods.

Keywords: Seaweed, blue food, Life cycle assessment, environmental burdens, Climate change, nutrient removal