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Good practice Imported

Mashike Steel-Slag Seagrass Beds — Japan's First Fisheries-Cooperative/Private-Company Joint Blue Carbon Credit

Japan · Mashike · See the Japan profile

Evidence: Observational / pre–post Top 40% 47/100 · Ask Evidence Copilot about this practice

In Mashike, Hokkaido, Nippon Steel and the local fisheries cooperative turned steelmaking slag into a growth substrate for seaweed beds, generating Japan's first blue-carbon credit jointly certified to a private company and a fishing community.

49.5 t-CO2
Certified CO2 absorption (2018-2022)
33.3 t-CO2
Certified CO2 absorption (2023)
21
Sites where the technique has been trialled nationwide
Mashike Steel-Slag Seagrass Beds — Japan's First Fisheries-Cooperative/Private-Company Joint Blue Carbon Credit

Details

Maturity
Scaling
Promoter
Nippon Steel Corporation / Mashike Fisheries Cooperative Association
Period
2004-present (J Blue Credit certified 2022)
Keywords
steel industry, fisheries, marine ecosystem restoration

Context

Since 2004, Nippon Steel and the Mashike Fisheries Cooperative Association have applied an iron-rich mixture of steelmaking slag and fermented wood-chip humus to the seabed off Mashike, Hokkaido, to help regrow seaweed 'sea forests' that had suffered isoyake die-off.

Objectives

The partnership aimed to turn a steel-industry byproduct into a restoration input and, eventually, a certified blue-carbon credit.

Activities

Monitoring covering 2018-2022 measured seaweed-bed carbon absorption resulting from the slag/humus treatment.

Results

In 2022, this monitoring recorded 49.5 t-CO2 of absorption, certified under Japan's national J Blue Credit registry as the country's first credit issued jointly to a private company and a fisheries cooperative; a further 33.3 t-CO2 was certified for 2023, and the technique has since been trialled at 21 sites nationwide.

Conclusions

Japan's education/science ministry commended the method for supporting biodiverse seaweed ecosystems, but certified volumes remain small relative to industrial-scale emissions, and the approach's long-term footprint depends on continued steel production for its slag input.

Implementation
Indicative cost
Low (< €50k) — No cost figures are reported; the input is a repurposed industrial byproduct (steelmaking slag).
Time to results
Long (> 3 years) — Applied since 2004; first J Blue Credit certified in 2022 (covering 2018-2022), a further credit for 2023; trialled at 21 sites nationwide.
Staffing & skills
Nippon Steel Corporation (slag/humus material, private co-certificate holder), Mashike Fisheries Cooperative Association (site management, co-certificate holder)

Conditions for success

  • A reliable local supply of steelmaking slag and fermented wood-chip humus
  • Long-run joint monitoring (18 years) before pursuing formal carbon certification
  • A national blue-carbon credit registry (J Blue Credit) to formalise and monetise outcomes

Common failure modes

  • Long-term reliance on continued steel production as the slag input source is a sustainability trade-off

Where it fits

Governance type
private company-fisheries cooperative joint venture
Scale
local (single bay, replicated at 21 sites nationally)
Income level
high-income

Commonly funded by

Own resources / municipal budget

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Data sources

Where this practice's information was retrieved from, and when.

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