Appendix 1: Experimental site
The three experimental plots established at the Sapporo and Memuro sites (CO, SM and
SR), measure 10 m × 15 m and 10 m × 10 m, respectively. No field replications were made
of the experimental plots due to the lack of available space. All plots were kept bare during
the two-year observation period (November 2008 to October 2010) to enable precise
observations of the atmosphere-snow-soil interactions. Air temperature and precipitation
were measured at each site, and snow cover height, albedo of the ground or snow cover
surface, and soil temperatures at depths of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.7 m were
measured in each plot. Measurements were conducted as follows: snow cover height was
measured using a ruler 2 to 3 times weekly; the albedo was determined as the ratio of
individually-measured daily mean reflection to incoming short wave radiation using an
albedo meter (PCR-02, Kipp and Zonen B.V.); soil temperature was measured using T-type
thermocouples inserted to soil depths as specified above; and soil frost depth was recorded
as the 0˚C fringe estimated by the interpolation.
During the two-year observation period the annual mean air temperature was lower at the
Memuro site (6.0˚C and 6.2˚C for the first and second study years, respectively) than at the
Sapporo site (7.9˚C and 8.0˚C, respectively). Similarly, the mean early-to-midwinter air
temperature (December–February) was lower at the Memuro site (-6.3˚C and -7.9˚C for the
first and second study years, respectively) than at the Sapporo site (-2.5˚C and -3.7˚C,
respectively). Annual precipitation was roughly 10% higher at the Memuro site (1003 mm
and 1183 mm for the first and second study years, respectively) than at the Sapporo site
(910 mm and 1043 mm, respectively), whereas cumulative early-to-midwinter precipitation
was lower at the Memuro site (152 mm and 132 mm for the first and second study year,
respectively) than at the Sapporo site (269 mm and 190 mm, respectively).
The maximum snow cover height at the CO and SM plots was 0.86 and 0.79 m at the
Sapporo site, and 0.72 and 0.69 m at the Memuro site in the first and second study years,
respectively (Fig. 2). The application of charcoal onto the snow cover as an ASA in the SM
plots caused a decline in the albedo of the snow cover surface from 0.7-1.0 to 0.2-0.4, and
enhanced the process of snowmelt, particularly at the Memuro site. Snowmelt was
completed 14 and 10 days earlier in the SM plot (in comparison with the respective CO
plot) at the Memuro site in the first and second study year, respectively, but 6 and 3 days
earlier at the Sapporo site in the respective years. Except for the Memuro site in the first
study year, several snowfall events occurred after the ASA application and negated the
decrease in albedo (data not shown). Despite the unexpected snowfall, the albedo decreased
again immediately after the snow covering the ASA had melted, and finally snowmelt was
stimulated to a maximum extent. In the SR plots snow cover height was occasionally below
0.2 m, and thus reduced successfully by the operations (Fig. 2). At both sites, the annual
maximum soil frost depth at the CO and the SM plots ranged from 0.0 m to 0.15 m.
However, the results were not the same for the SR plot where depths exceeded 0.2 m: at the
Memoru site depths of 0.42 m and 0.53 m were recorded in the first and second study year,
respectively; and at the Sapporo site depths of 0.21 m and 0.27 m were recorded. The
maximum soil frost depth was observed in February at both sites.
Appendix 2: Measurement of CO2 and N2O fluxes of soil
A circular stainless steel collar (275 mm OD) with a water groove (20 mm in height) was
embedded at the center of the subplot (2 m × 2 m), and potassium nitrate was supplied
therein at a rate of 50 kg N ha-1 during late October 2008 and 2009 to mimic the excess
residual mineral N level in local farmlands after harvest. Chambers made of colored
polyvinylchloride measuring 0.25-m in diameter, 0.40 m in height, and 19.6-L in volume
were used to observe the net N2O and CO2 emission rates. Air samples drawn from the
chamber headspace at 1, 11, 21 and 31 min after the onset of measurements, were
individually injected into a pre-evacuated 20-mL vial capped with a butyl rubber septum or
a pre-evacuated 150-mL Tedlar® bag. The N2O concentration was determined using a gas
chromatograph (Shimadzu 14B, Shimadzu Co. Ltd, Japan) equipped with an electron
capture detector, whereas the CO2 concentration was determined using an infrared analyzer,
(ZFP9, Fuji Electric), or gas chromatograph (GC-14B, Shimadzu) equipped with a thermal
conductivity detector. Emission rates (μg N m-2 h-1 and mg C m-2 h-1) were derived as the
slope of a linear regression computed for measured N2O and CO2 concentration data in the
chamber versus time (ppm h-1). To keep the area between the chamber and the ground
surface airtight, the groove on the collar was filled with liquid water as a seal. However,
during the period when the collar was under the snow cover, the chamber was placed
directly onto the snowpack surface to minimize any disturbance of the snow cover height.
At that time, the quality of the air-tightness between the chamber and the snowpack surface
was uncertain; therefore, the slope values were statistically tested as shown in Yanai et al.
(2011). Any slope that did not differ significantly from 0 (Student’s t-test, α = 0.20, thus p ≥
0.10) was regarded as 0 ppm h-1, i.e., no net gas emissions occurred. The gas sampling was
carried out at two- to three-day intervals during the snowmelt period (March–early April)
and weekly for the remainder of the time. Cumulative emissions over the monitoring period
(kg N ha-1 and Mg C ha-1) were calculated by linear interpolation of the observed emission
rates.
In addition, the CH4 flux was not measured because of its negligibly small contribution
to the total greenhouse gas balance in an arable upland field (Koga et al. 2004; Koga et al.
2006), and it was not known whether the CH4 flux responded significantly to the seasonal
freeze-thaw conditions of soil (see Flessa et al. 1995; Maljanen et al. 2007).
ESM Table 1 Local snow cover manipulation techniques conducted in agricultural fields in
Hokkaido, northern Japan.
Main obj ective
Means
Timing to do
snow cover height
air temperature
Acceleration of snowmelt
*extention of the growing
season for crop plants
*alleviation of the damage
from snow mold
application of blackish
powders onto snow cover
surface
early spring
over 0.5 m
over 0 ˚C; daily mean
Soil frost control
*frost-kill of unharvested
potato tubers in soil
removal and re-accumulation
of snow cover
early to mid winter
over 0.2 m
below 0 ˚C; daily maximum
ESM Table 2 Physico-chemical properties of wood-based waste charcoal† used as an
agricultural snowmelt agent.
Moisture
Total Carbon
Total Nitrogen
P2O5
CaO
MgO
K 2O
Fe
Mn
Zn
Cu
pH (1:2.5)
EC (1:5)
SSA ‡
Values shown are on an oven-dry basis
†
: dark 4 mm-granular, pyrolysis at 800°C
‡
: Specific surface area, N2 as sorbent
g kg -1
g kg -1
g kg -1
g kg -1
g kg -1
g kg -1
g kg -1
g kg -1
mg kg -1
mg kg -1
mg kg -1
dS m -1
m 2 g -1
250
922
8.5
1.16
15.0
2.86
7.01
1.47
258
29.3
50.9
9.5
2.11
54
ESM Fig. 1 Schematic diagram of N2O flux in early spring affected by seasonal
soil-freezing and insulation of soil from cold air during the snow-melting period. Modified
from Yanai et al. (2012)
References
Flessa H, Dörsch P, Beese F (1995) Seasonal variation of nitrous oxide and methane fluxes
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Koga N, Sawamoto T, Tsuruta H (2006) Life cycle inventory-based analysis of arable land
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Koga N, Tsuruta H, Sawamoto T, Nishimura S, Yagi K (2004) N2O emission and CH4
uptake in arable fields managed under conventional and reduce tillage cropping
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Maljanen M, Kohonen AR, Virkajärvi P, Martikainen PJ (2007) Fluxes and production of
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