Osamu Nagata

Falling atmospheric pressure as a trigger for methane ebullition from peatland

[1]xa0Peatlands are widely regarded as a significant source of atmospheric CH4, a potent greenhouse gas. At present, most of the information on environmental emissions of CH4 comes from infrequent, temporally discontinuous ground-based flux measurements. Enormous efforts have been made to extrapolate measured emission rates to establish seasonal or annual averages using relevant biogeochemical factors, such as water table positions or peat temperatures, by assuming that the flux was stationary during a substantial nonsampling period. However, this assumption has not been explicitly verified, and little is known about the continuous variation of the CH4 flux in a timescale of individual flux measurement. In this study, we show an abrupt change in the CH4 emission rate associated with falling atmospheric pressure. We found that the CH4 flux can change by 2 orders of magnitude within a matter of tens of minutes owing to the release of free-phase CH4 triggered by a drop in air pressure. The contribution of the ebullition to the total CH4 flux during the measurements was significant (50–64%). These results clearly indicated that field campaigns must be designed to cover this rapid temporal variability caused by ebullition, which may be especially important in intemperate weather. Process-based CH4 emission models should also be modified to include air pressure as a key factor for the control of ebullient CH4 release from peatland.

Methane emissions from five paddy fields with different amounts of rice straw application in central Hokkaido, Japan

Abstract Rice paddy fields are a major source of methane (CH4) emissions, a potent greenhouse gas. We assessed CH4 emissions from five existing paddy fields farmed in a snowy temperate region in central Hokkaido, Japan. All fields had continuous flooding and a paddy–fallow–paddy (rice) crop rotation system, but with different amounts of rice straw application. The rice straw application rate in the fields ranged from 0 to 219 g dry matter m−2. CH4 emission increased with increasing amounts of rice straw. A peak in CH4 emission at the end of the reproductive stage was observed in all fields receiving rice straw. When continuous flooding was interrupted by drainage for harvesting, emissions from all fields also dropped quickly. Total CH4 emissions ranged from 4.04 to 40.8 g CH4-C m−2 per growing season. We found that CH4 emissions (g CH4-C m−2 per g dry matter) as per unit (dry matter) of rice straw applied in this study were significantly (P < 0.05) higher than those of calculated reported values, presumably because of the retardation of straw decomposition rates during the winter fallow. There was a significant correlation between rice straw carbon application (SCA) rate and total CH4 emission in continuously flooded fields (CH4 emission [g C m−2 per growing period] = 0.486 × SCA [g C m−2] − 1.644, r 2 = 0.884, P < 0.05), and emissions were 2–10-fold greater than from fields with no rice straw. The results indicate that the presence of rice straw has a significant influence on CH4 emissions from paddy fields.

Effect of nitrogen deposition on CH4 uptake in forest soils in Hokkaido, Japan

Abstract It has been well documented by short-term artificial experiments that the CH4 uptake is inhibited by N input, especially NH4 p+-N input. To investigate the effect of the natural N input by throughfall and other factors on the CH4 uptake in forest soils, we measured the CH4 uptake rates for 6 months during the snow-free period of the year and N input by throughfall throughout the year at 10 sites in Hokkaido, Japan, from 1997 to 2002. Water filled pore space (WFPS) and pH values in the soils varied widely among the sites (38-93% and 3.9-6.2, respectively). The rates of NH4 p+-N and NH3 p--N inputs ranged from 1.3 to 6.9 kg N hap-1 yearp-1 and from 0.8 to 2.9 kg N hap-1 yearp-1, respectively. The NH4 p+-N input was generally higher than the NH3 p--N input. Total N input by throughfall amounted to 2.3-9.4 kg N hap-1 yearp-1. The highest CH4 uptake rate occurred within the period from July to September (41-215 μg CH4 mp-2 hp-1) each year at most sites. CH4 uptake rate was relatively low (~50 μg CH4 M-2 hp-1) at northern sites, while a high CH4 uptake rate was observed throughout the year 100 (≽ CH4 mp-2 hp-1) at southern sites. The mean CH4 uptake rates were significantly different among the sites. Cumulative CH4 uptake ranged from 1.4 to 6.6 kg CH4 hap-1 [184 d]p-1 with a mean values of 3.22 ± 1.36 kg CH4 hap-1 [184 d]p-1. Cumulative CH4 uptake increased with increasing temperature and decreased with an increase in precipitation (Rain), NH4 p+-N input (TFNH4) WFPS, soil total C (TC), and total N (TN). There was a quadratic relationship between the CH4 uptake and NH3 p--N input (TFNO3), soil pH, and C / N ratio in soil. A regression equation was obtained as follows to predict the CH4 uptake in forest soils: Cumulative CH4 uptake = 0.47 / Rain + 0.38 / TFNH4 + 0.34 / TC - 0.30 / TFN03 (R p2 = 0.74, p = 0.0001). This equation indicates that atmospheric N input into forest soils is one of the main factors that control cumulative CH4 uptake with precipitation, total carbon content in soil in Hokkaido, Japan.

Importance of Internal Proton Production for the Proton Budget in Japanese Forested Ecosystems

Annual biogeochemical fluxes (bulk precipitation, throughfall, stem flow, soil solution and vegetation uptake) of inorganic elements were observed in eight cool temperature forested ecosystems in Hokkaido, northern Japan, in order to determine the mechanisms of acid neutralization in Japanese forest ecosystems. We compared our results with the other biogeochemical studies in Japan, north Europe and US from the literature. In many Japanese forests, the internal proton production (IPS) by base cation accumulation into the vegetation was a major proton source, rather than external acidic deposition, and the IPS also affected the base cation fluxes from the mineral. IPS in Japanese forest tended to be larger than that in north Europe and US. Our results suggested that the high acid neutralizing ability of Japanese forests could be attributed to the strong relationship between the base cation buffering of the soil and the larger contribution of IPS as a proton source. acidic deposition|biogeochemical cycling|forest ecosystem|Japan|proton budget

Varietal difference in radiocesium uptake and transfer from radiocesium deposited soils in the genusAmaranthus

Abstract Within Amaranthaceae, 33 different varieties, including local varieties from Japan, were grown in 2012 in a field in the town of Iino in the Fukushima prefecture, which is located approximately 51 km north of Tokyo Electric Power Company, Fukushima Daiichi Nuclear Power Plant (FDNPP). The contamination level of the soil was 2770 ± 140 Bq kg−1 dry weight (134Cesium (Cs) + 137Cs, average ± SE), and the field was also cultivated in 2011. There was a significant varietal difference in the dry weight production, radiocesium accumulation and transfer factor (TF) of radiocesium from the soil to the plant. The ratio of the lowest TF to the highest TF was approximately 3. Because the ratio of 137Cs to 133Cs was significantly positive, radiocesium seems to be absorbed in a manner similar to that of 133Cs. It is suggested that the varietal difference in the behavior of radiocesium uptake mainly depends on its genetic background rather than on environmental factors.

Snow cover manipulation in agricultural fields: as an option for mitigating greenhouse gas emissions

Short-term N2O emission occurs in relation to snowmelt within seasonally frozen soil. To understand the effects of changing winter climates on the N2O flux, snow cover manipulation experiments are useful. In Japan, snow cover manipulation is practiced by farmers to improve agricultural yield and is executed either by applying a broadcast of blackish agent onto the snow cover, which leads to faster snow-melting thereby extending the crop-growing season, or by snow cover removal/re-accumulation, leading to an enhanced soil frost depth for weed management. Implementation of these practices involves using an amount of fossil fuel, in addition to influencing soil-derived N2O emissions, therefore, the load factors of snow cover management practices per unit area of agricultural field were estimated in this study. Field data including micrometeorological conditions, ground surface flux of N2O, and amount of fossil fuel consumed during machinery operation for management practices, were obtained at two sites in Hokkaido over 2xa0years (2008–2010). Fuel consumption for the field spreading was found to be unexpectedly small (0.017xa0Mg CO2 eqxa0ha−1). It was therefore suggested that acceleration of snowmelt may have the potential to reduce net greenhouse gas emissions if the agent used is a low-degradable C-rich material, such as charcoal. For soil frost control, the fossil fuel consumption during a set of snow cover removal/re-accumulation (estimated as 0.052xa0Mg CO2 eqxa0ha−1) is discussed, together with the relationship between possible mechanisms causing stimulation of N2O production in frozen soil and inherent large differences in N2O flux among sites.

Formation of a Groundwater Table by Trench Irrigation and Evapotranspiration in a Drained Peatland

To evaluate the coexistence of agricultural managements and wetland ecosystem conservation, the Bibai mire, an ombrotrophic mire in Hokkaido, Japan, was selected as an experimental site that had been affected by neighboring agricultural managements. Since the lowering of the level of the groundwater table in the peripheral area of the mire had threatened indigenous vegetations, keeping the groundwater table shallow by trench irrigation seemed to be an effective measure to recover the original vegetation. The objective of the present study was to quantify the amount of water and the effective area of trench irrigation required in a bamboo-invading area in a pristine mire. We constructed a trench 28 m long and irrigated at the rate of 2.22 m3 d−1 in a bamboo-invading area in the mire. And to analyze the hydro-meteorological conditions under the trench irrigation, we measured the saturated hydraulic conductivity of the peat layer (3.8 × 10−3 cm s−1), the evapotranspiration rate (2.80 mm d−1), the depth of the non-irrigated groundwater table (0.15 m) and the surface gradient (0.00493). In addition, using the mass conservation equation and Darcys law, we derived a steady state model of the level of the groundwater table formed by trench irrigation, which required the five parameters mentioned above. The irrigated water spread over a distance of only about 15 m to both sides of the trench. The model also estimated that the distance for the irrigated area was 14.6 m and we concluded that the irrigated area was limited within a distance of 20 m distances to both sides of the trench and that the irrigation rate per unit trench length did not exceed 0.12 m2 d−1 for realistic values of the evapotranspiration rate and the saturated hydraulic conductivity in peatland.

Seasonal Dynamics of Biogeochemical Proton and Base Cation Fluxes in a White Birch Forest in Hokkaido, Japan

Biogeochemical proton and base cation fluxes in a 30-year old white birch forest composed of Dystric Cambisols in northern Hokkaido, Japan were estimated using data on atmospheric deposition (AD), throughfall (TF), stemflow (SF), and discharge from soils (DS) and plant uptake (UP) from early June to November 1999. In the monitoring period, proton flux was 0.20kmolcha−1 for AD, 0.07 for TF+SF, and 0.03 for DS, indicating that atmospheric acid input was neutralized through plant and soil. Base cation flux was 1.29 for AD, 1.23 for TF+SF, and 0.99 for DS and plant base cation uptake was 2.14, indicating that the soil was the major source of base cation for plant. However, these seasonal fluxes showed various trends. Cumulative base cation flux in TF+SF showed constant increase trend during the whole period, which was similar to AD. Proton flux in AD jumped once just after a heavy rain of 255mm for 8 days at the end of July. Trends for the proton and base cation fluxes in TF plus SF were similar to that of AD. Although proton and base cation fluxes of DS were not found until middle July because of vegetation uptake and no flow, both fluxes increased suddenly after the heavy rain in July. After August, the base cation and proton fluxes in the DS increased continuously, due to the lack of plant uptake and intermittent rainfall. In this study, it is clear that plant activity and water flow are very important driving force for seasonal dynamics of biogeochemical cycling.

Effects of bamboo biochar application on global warming in paddy fields in Ehime prefecture, Southern Japan

ABSTRACT Biochar application can reduce global warming via carbon (C) sequestration in soils. However, there are few studies investigating its effects on greenhouse gases in rice (Oryza sativa L.) paddy fields throughout the year. In this study, a year-round field experiment was performed in rice paddy fields to investigate the effects of biochar application on methane (CH4) and nitrous oxide (N2O) emissions and C budget. The study was conducted on three rice paddy fields in Ehime prefecture, Japan, for 2 years. Control (Co) and biochar (B) treatments, in which 2-cm size bamboo biochar (2 Mg ha−1) was applied, were set up in the first year. CH4 and N2O emissions and heterotrophic respiration (Rh) were measured using a closed-chamber method. In the fallow season, the mean N2O emission during the experimental period was significantly lower in B (67 g N ha−1) than Co (147 g N ha−1). However, the mean CH4 emission was slightly higher in B (2.3 kg C ha−1) than Co (1.2 kg C ha−1) in fallow season. The water-filled pore space increased more during the fallow season in B than Co. In B, soil was reduced more than in Co due to increasing soil moisture, which decreased N2O and increased CH4 emissions in the fallow season. In the rice-growing season, the mean N2O emission tended to be lower in B (−104 g N ha−1) than Co (−13 g N ha−1), while mean CH4 emission was similar between B (183 kg C ha−1) and Co (173 kg C ha−1). Due to the C release from applied biochar and soil organic C in the first year, Rh in B was higher than that in Co. The net greenhouse gas emission for 2 years considering biochar C, plant residue C, CH4 and N2O emissions, and Rh was lower in B (5.53 Mg CO2eq ha−1) than Co (11.1 Mg CO2eq ha−1). Biochar application worked for C accumulation, increasing plant residue C input, and mitigating N2O emission by improving soil environmental conditions. This suggests that bamboo biochar application in paddy fields could aid in mitigating global warming.

Estimating soil carbon stocks in an upland area of Tokachi District, Hokkaido, Japan, by satellite remote sensing

Soil carbon stocks (SCSs) in an upland area of Tokachi District, Hokkaido, Japan, were estimated by satellite remote sensing and a soil survey. The soil parent materials in the studied area were alluvial deposits, volcanic ash plus alluvial deposits, and volcanic ash. Surface soil carbon concentrations (SSCCs) were negatively correlated with satellite image data (green, red, and near-infrared reflectance) for each parent material. The highest correlations between reflectance and SSCCs were obtained from red wavelength reflectance for alluvial deposits (ru2009=u2009–0.82, pu2009<u20090.01) and volcanic ash plus alluvial deposits (ru2009=u2009–0.91, pu2009<u20090.01), and from near-infrared reflectance for volcanic ash (ru2009=u2009–0.90, pu2009<u20090.01). We generated an SSCC map of the study area using the regression equations and satellite reflectance data. The soil survey results showed that SSCCs were positively correlated with SCSs in the 0–30u2009cm depth interval for each parent material (best-fit regressions: alluvial deposits, ru2009=u20090.97; volcanic ash plus alluvial deposits, ru2009=u20090.97; volcanic ash, ru2009=u20090.97), and they were also positively correlated with SCSs in the 30–95u2009cm depth interval for volcanic ash (ru2009=u20090.94). We were therefore able to generate a map of estimated SCSs from the SSCC map and the regression equations developed between SSCCs and SCSs. The estimated and measured SCSs in both depth intervals showed an almost 1:1 relationship, with root-mean-square errors of 19.5 (0–30u2009cm) and 28.6u2009Mg carbon (C) ha–1 (30–95u2009cm). According to the SCS maps, SCSs at 0–30u2009cm depth in areas of alluvial deposits, volcanic ash plus alluvial deposits, and volcanic ash were mostly 50–150, 100–200, and 50–250u2009Mgu2009Cu2009ha–1, respectively, whereas at 30–95u2009cm depth in the volcanic ash area they were mostly less than 250u2009Mg C ha–1.