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 -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 vs.
Biosolids to Landfill -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 vs.
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? Net: -293 to -475 Mg CO 2 e Net: +1,269 Mg CO 2 e vs. 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 end- use in reclamation but first need to not develop (degraded) land