Carbon sequestration in reclaimed soils
Andrew Trlica, Sally Brown
U. of Washington, College of Forest Resources
INTRODUCTION: World soils contain more than three times as much carbon as both the
atmosphere and in Earth’s biomass (Lal, 2004). Management of soils and land-use practices to
enhance soil organic carbon content could remove up to one million tonnes of carbon per year from
the atmosphere, a significant move to slow the rise in atmospheric carbon dioxide levels (Pacala
and Socolow, 2004). Similarly, reclamation of degraded soils worldwide could potentially capture 3
million tonnes of carbon per year during the 20-50 years of initial soil recovery (Lal, 1997). Using
organic residuals in reclamation encourages greater carbon accrual on degraded lands (Tian et al.
2009), and the use of such residuals in surface mine reclamation could carry additional greenhouse
gas avoidance benefits (Brown and Subler, 2007).
The current study was initiated to compare carbon storage on mine soils reclaimed with biosolids to
similar soils reclaimed conventionally. By quantifying carbon storage and accrual on degraded soils
amended with biosolids, a protocol for generating carbon credits for adopting this approach to
reclamation. It is hoped that carbon credits from reclaimed soils could help defray the cost of
reclamation and lead to better long-term outcomes.
METHODS: Soils were collected from several areas disturbed by surface mining and subsequently
reclaimed with biosolids amendment. Site history and reclamation details were collected from
knowledgeable sources. Samples were collected from random locations at each site, at depths of
0-15cm and 15-30cm. Bulk density samples were also taken.
Total carbon (percent by weight) was measured using an automated dry combustion analyzer. In
cases where warranted, soils were treated with HCl to remove carbonate carbon, and a thermal
approach was used to quantify coal-C contamination where it was suspected.
Site-wide C storage was calculated by the following equation:
%C * Bulk density (Mg/m3) * .15m = C storage (Mg/ha)
Mine
Washington
Biosolids
Conventional
Pennsylvania
Biosolids
Conventional
Massachusetts
Biosolids
Conventional
BC Copper
Biosolids
Conventional
BC Sand
Biosolids
Unrecl'd topsoil
C storage
(Mg/ha)
C gain:input
(Mg/Mg)
54.09 (13.74)
42.71 (8.75)
0.10
68.06 (22.66)
44.81 (14.81)
0.33
104.42 (43.54)
16.96 (15.15)
0.18
42.98 (1.48)
4.60 (1.56)
0.32
39.99 (15.75)
32.02 (2.90)
0.16
RESULTS: Sites reclaimed with biosolids
amendment stored significantly more carbon,
mostly in the top 15cm than conventionally
reclaimed soils (See Table). Below 15cm there
were typically no differences apparent. For
every tonne of biosolids applied, between 0.10
and 0.33 tonnes of carbon were stored in soil
CONCLUSIONS: Biosolids amendment
enhanced carbon storage on reclaimed mine
soils. The higher carbon storage is probably
a combination of the additional carbon added
with the amendment and the generally higher
plant biomass inputs to the soil organic
carbon pool that follow biosolids reclamation.
The effect of biosolids is remarkably
persistent, with sites up to ~30 years old still
showing marked net carbon storage over
conventional. Biosolids could be a useful tool
for establishing carbon credit for mine
reclamation, but the response of a soil to
biosolids input is very sensitive to local
conditions.
REFERENCES:
Brown, S. and Subler, S. 2007. In: Mine Closure 2007, pp.
459.
Lal, R. 2004. Science 304:1623
Lal, R. 1997. Soil Till. Res. 43:91
Pacala S. and Socolow, R. 2004. Science 305:968
Tian, G et al. 2009. JEQ 38:61