Reclamation of Degraded Land with Biosolids Impacts of final land use, Impacts of reclamation method
GHG Consequences of Reclamation • Final land use post-reclamation • Reclamation improvements with biosolids • Land- and biosolids use interact
Reclamation to forest • High gains to Soil and Biomass C • Conventional and residuals reclamation
Partial Reclamation + Development • Some soil/biomass C • But large GHG costs for construction and use over life cycle
Field study – Soil C in Reclamation • Soil C benefits of biosolids reclamation • Compare similar conventional and biosolids sites up to 30 year post-reclamation
Results: Soil C sequestration
Results: Soil C sequestration • Soil C increases with biosolids § +15 Mg ha-1 (Centralia) § +38 Mg ha-1 (Highland Valley) • 0. 11– 1. 14 Mg CO 2 e per Mg biosolids
Results: Soil C sequestration • Increases and efficiency depend upon reclamation conditions and method Centralia, 0. 11 Mg CO 2 e per tonne: Old sites, 1 m topsoil, very high biosolids rate Pennsylvania, 0. 55 Mg CO 2 e per tonne: Old sites, relatively good topsoil, moderate biosolids addition Highland Valley, 1. 03 Mg CO 2 e per tonne: No topsoil, very poor conventional recl. , low biosolids rate Sechelt 1. 14 Mg CO 2 e per tonne: Good response, poor topsoil moderate biosolids addition
Study conclusions • 55– 139 Mg CO 2 e ha-1 Soil C increase for using residuals • Increase was present even after 30 years • Specific changes related to site conditions and reclamation history • What about other GHG shifts with reclamation?
Land use • House or forest? § § § Soil C Biomass C Construction/use/maintenance Operations: transport, soil N 2 O, fertilizer credit, etc. Competing biosolids uses
Life cycle assessment of reclamation • What is LCA? § Track all inputs/outputs/activi ties required § Assign environmental impact § Assess (relative) environmental consequences
Life cycle assessment of reclamation • Alternate post-reclamation land uses § Houses vs. forest § Reflects land-use pressures in Puget Sound
Life cycle assessment of reclamation • • 1 ha of degraded land Urban margin of Puget Sound region, WA 30 year timeline Houses or forest
Life cycle assessment of reclamation • “Choose your own adventure” • Natural cover (forest) § Biosolids reclamation § Conventional reclamation • Development
Reclamation – Soil Carbon • Conventional Reclamation: 110 Mg CO 2 e • Biosolids reclamation: 220 Mg CO 2 e • Based on C accumulation rate and Mg CO 2 e per tonne of biosolids
Reclamation – Biomass Carbon • PNW forests respond to biosolids (soil low in N) • Conventional: 183 Mg CO 2 e • Biosolids: 275 Mg CO 2 e
Conventional Reclamation • Reclamation to Doug Fir forest • 110 Mg CO 2 e soil C • 183 Mg CO 2 e biomass C • 393 Mg CO 2 e per ha total
Biosolids reclamation • • • Reclamation to D. Fir 220 Mg CO 2 e soil C 275 Mg CO 2 e biomass C 18 Mg CO 2 e N applied as N 2 O 477 Mg CO 2 e per ha total
Biosolids reclamation GHG emissions? • Need to consider emissions from biosolids management • Also alternate biosolids end-uses
Biosolids to Agriculture vs. -220 Mg CO 2 e soil C -275 Mg CO 2 e biomass C +18 Mg CO 2 e N 2 O +2 Mg CO 2 e transport (50 km) • Net: -475 Mg CO 2 e • • • -140 Mg CO 2 e soil C • -28 Mg CO 2 e fertilizer credit • +11 Mg CO 2 e transport (300 km) • Net: -157 Mg CO 2 e
Biosolids to Landfill vs. -220 Mg CO 2 e soil C -275 Mg CO 2 e biomass C +18 Mg CO 2 e N 2 O +2 Mg CO 2 e transport (50 km) • Net: -475 Mg CO 2 e • • • -29 Mg CO 2 e soil C • 346 Mg CO 2 e fugitive GHG • +14 Mg CO 2 e transport (350 km) • Net: +331 Mg CO 2 e
Net GHG balance of restoring vegetation • Biosolids reclamation § -475 Mg CO 2 e (30 years, 1 ha, 100 dt biosolids) • Conventional reclamation § -293 Mg CO 2 e • What if development is chosen instead?
Suburb development • Single-family houses • Asphalt roads • Built cover % according to USGS • Reclaim remaining land
Suburb development: Housing • US Census population density § 3. 9 houses/ha @ 243 m 2 (~2, 500 sq. ft) • LC GHG estimates: § Construction (incl. materials): 283 Mg CO 2 e § Maintenance/occupatio n: 989 Mg CO 2 e
Suburb development: Roads • USGS % impervious cover § 0. 44 ha ha-1 suburb • LC GHG estimates: § Construction (incl. materials): 93 Mg CO 2 e § Maintenance: 42 Mg CO 2 e
Net GHG balance of Suburb Development • • • +1, 272 Mg CO 2 e houses +135 Mg CO 2 e roads -52 Mg CO 2 e soil C -86 Mg CO 2 e biomass C Net: +1, 269 Mg CO 2 e • Extra commuter traffic GHG? § Excluded from LCA but. . . § ca. +1, 653 Mg CO 2 e over 30 yr
Development or Reclamation? vs. • Net: -293 to -475 Mg CO 2 e • Net: +1, 269 Mg CO 2 e • Modify and recombine scenarios to look for best and worst cases.
Worst Case + • • Low density suburb, and. . . Send biosolids to landfill, and. . . Conventional reclamation of partial land +1, 600 Mg CO 2 e – largest emissions, lowest offsets
Optimized Case + • Housing construction in urban core, and. . . • Biosolids for full reclamation • -5 to +141 Mg CO 2 e – minimized emissions, maximized offsets
Other ecosystem services • Improved with reclamation over development: § Water filtration; Biodiversity; Tourism value + + +
Conclusions • Land-use after reclamation has the biggest impact • Biosolids end-use is also has an impact § and is determined in part by land-use choices • Biosolids in Puget Sound may have best enduse in reclamation § but first need to not develop (degraded) land
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