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Murakami T.,Nagoya University | Murakami T.,Kanazawa University | Takamatsu T.,Japan National Institute of Environmental Studies | Katsuta N.,Gifu University | And 5 more authors.
Quaternary Science Reviews | Year: 2012

We observed timescale-dependent changes in the correlations between biogenic silica (bioSi) and uranium concentrations of bulk sediment from the Buguldeika Saddle, Lake Baikal. There was a positive correlation for the glacial-interglacial (100 kyr) scales over the 180 kyr, with inverse correlations for centennial- to-millennial scales during the last three interglacial states (MIS 5, 3, and 1). The distinction of these correlations between the time scales suggests that the sedimentation processes of bioSi and U differ from each other. The Baikal bioSi concentration record is generally regarded as a paleotemperature proxy, reflecting the diatom production of the lake. On the other hand, we concluded that the temporal variation of the U concentration in the sediment reflected the weathering intensity in the south of Lake Baikal watershed associated with changes in the rainfall/moisture levels.Based on the paleoclimate proxies from Lake Baikal, climates in continental interior Asia are identified as having dry and wet conditions during the glacial and interglacial periods, respectively. This accounts for the rhythms in growth and retreat of ice sheets in Eurasia on glacial-interglacial scales. In the interglacial periods (MIS 5, 3, and 1), the continental interior is, contrary to the glacial-interglacial climate changes, characterized by alternating warm-dry and cool-wet climates with periods in tens of thousands years. In particular, such shifts in the climate stand out prominently at the beginning of MIS 5d. The detrended U record for the last 5.2 kyr shows wet events at 4.3-3.7, 3.2-2.3, 1.8-1.2, and 0.8-0.3 kyr. These events coincide with the timing of the North Atlantic ice-rafted debris events, which were possibly related to solar activity. All this evidence suggests that climate in the continental interior followed significantly different fluctuation patterns in the glacial-interglacial and shorter time scales. © 2012 Elsevier Ltd.


Shichi K.,Japan Forestry and Forest Products Research Institute | Takahara H.,Kyoto Prefectural University | Hase Y.,Goshoura Cretaceous Museum | Watanabe T.,Tohoku University | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

We reconstructed vegetation changes and fire events in the southern Lake Baikal region over the past 33. cal. kyr using a sediment core from the Buguldeika Saddle, southern Lake Baikal, to examine vegetation response to past short-term climate variations. Herbs, such as Artemisia and Asteraceae, were dominant just before the Last Glacial Maximum (LGM). Low pollen accumulation rates (PARs) with little herb pollen indicate sparse herbaceous vegetation cover during the LGM. Picea expanded after the Bølling interval, suggesting expansion of riparian areas, and shrub Alnus rapidly increased during the following Allerød interval. Abies and Pinus subgen. Haploxylon began to increase at the beginning of the Holocene and Pinus subgen. Diploxylon has been highly dominant since the middle Holocene. The vegetation change after the LGM is similar to that from other sites in the Lake Baikal region, but the responses to short-term climate events are pronounced. Fluctuations in herb elements and vegetation cover as indicated by the PAR correspond to the Younger Dryas (YD) cooling event. The decline in the PAR and increase in herb taxa were remarkable at the beginning of the YD, but Larix and Picea trees were distributed in river valleys near Lake Baikal in the latter half. The rapid expansion of Betula and Artemisia following frequent fires in the early Holocene may have been in response to the 8.2. cal. ka. BP cooling event. From these findings, the southern Lake Baikal region, including the Selenga River basin, may possibly have been more sensitive than other parts of the region to abrupt climate changes. © 2013 Elsevier B.V.


Watanabe T.,Tohoku University | Minoura K.,Tohoku University | Nara F.W.,Tohoku University | Shichi K.,Japan Forestry and Forest Products Research Institute | And 3 more authors.
Global and Planetary Change | Year: 2012

Multi-proxy records (geochemistry, clay mineralogy and paleontology) from three sediment cores from Lake Hovsgol, northwest Mongolia, provide paleoenvironmental changes in continental Asia from the last glacial to the present (during the last 29calka BP). This paper presents the first continuous δ13C and δ18O dataset for ostracod shells (Cytherissa lacustris) from Lake Hovsgol sediments. A positive shift in ostracod δ13C values (from +0.5‰ to +3.2‰) began at ca. 21calka BP, and was associated with a decrease in δ13C values of total organic carbon (from -24.7‰ to -27.3‰) and an increase in the mass accumulation rate of total organic carbon (MAR-TOC). These results suggest that increased lake productivity led to the 13C-enrichment of dissolved inorganic carbon in Lake Hovsgol. In addition, decreases in clay content and the illite crystallinity index (full width at half maximum of the 10Å peak) began at ca. 21calka BP, indicating an increase in surface runoff and a change in sources of clastic materials in the watershed. The highest δ18Oostracod values (up to -4.8‰) at 16-15calka BP indicate the increases in precipitation from the East Asian monsoon. The total pollen amount increased, and Betula, Alnus, and Salix were dominant (up to 53%, 30%, and 6%, respectively) after 16-15calka BP. These findings indicate that broad-leaved trees expanded around Lake Hovsgol. In addition, fossil diatom valves appeared after 16-15calka BP, suggesting climate amelioration, and increased input of soil-derived nutrients and dissolved silica. Between 10 and 5calka BP (Holocene climate optimum), productivity was high in and around the lake (MAR-TOC, up to 47.3mg/cm2kyr; MAR-diatoms, up to 14.4×108 valves/cm2kyr; total pollen concentration, up to 9.0×105 grains/cm3). Environmental changes during the last 29kyr in and around Lake Hovsgol are clearly associated with fluctuations in summer insolation and East Asian monsoon intensity. © 2012 Elsevier B.V.


Hasegawa M.,Japan Forestry and Forest Products Research Institute | Okabe K.,Japan Forestry and Forest Products Research Institute | Fukuyama K.,Association of International Research Initiatives for Environmental Studies | Makino S.,Japan Forestry and Forest Products Research Institute | And 5 more authors.
Experimental and Applied Acarology | Year: 2013

The community structures of Mesostigmata, Prostigmata, and Oribatida in the soil of broad-leaved regeneration forests and conifer plantations of various ages were assessed alongside soil and plant environmental variables using three response metrics (density, species richness, and species-abundance distribution). The density and species richness of mites recovered swiftly after clear-cutting or replanting. Oribatid mites dominated the soil mite communities in terms of densities and species richness for both forest types. Soil mite communities in broad-leaved forests was related to forest age, the crown tree communities index, and forest-floor litter weight. In contrast, soil mite communities in the conifer plantation sites were related to various indices of understory plants. The development of the understory plants was synchronized with the silvicultural schedules, including a closed canopy and thinning. Such a conifer plantation management may affect indirectly the community of mites. © 2012 Springer Science+Business Media Dordrecht.


Yagihashi T.,Japan Forestry and Forest Products Research Institute | Nakamura K.,Japan Forestry and Forest Products Research Institute | Saitoh T.,Japan Forestry and Forest Products Research Institute | Matsumoto K.,Association of International Research Initiatives for Environmental Studies | And 4 more authors.
Nihon Ringakkai Shi/Journal of the Japanese Forestry Society | Year: 2015

A large number of Pinus thunbergii seedlings are required for establishment in coastal areas after the tsunami disaster. Therefore, a reduction in the duration of seedling nursing period and year-round planting to equalise the amount of work are required. We compared the stem growth of current-year containerised seedlings (CCS) and 2-year-old conventional bare-root seedlings (TBS), and planted the containerised seedlings every 2 months except during midwinter (January). There was no significant difference between the stem length of CCS and TBS after one growing season. For CCS planted during March, stem longitudinal growth was smaller than that of TBS; however, for those planted during November, no significant difference was noted. Stem radial growth of CCS was higher than that of TBS. Seedling percentage survival rates of CCS after one growing season was high (>98. 4%), regardless of the planted month. In conclusion, usage of current-year seedlings and year-round planting of containerised seedlings could be possible in the regions with environmental conditions similar to the study area.


Nara F.W.,Tohoku University | Watanabe T.,Tohoku University | Watanabe T.,University of Liège | Kakegawa T.,Tohoku University | And 6 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2010

Changes in sulfur cycles in Lake Hovsgol (northwest Mongolia) are discussed on the basis of total organic carbon (TOC), total sulfur (TS) concentrations and stable sulfur isotope ratios (δ34S) in two sediment cores (X104 and X106) covering the last glacial to the present. Correlation plots of TOC and TS (C-S plots) of the sediment cores indicate dissolved sulfate enrichment in sediment pore water and high sulfate reducing bacteria (SRB) activity during the climate transition from the last glacial to postglacial period (LG-PG transition, from ca. 21 to 11.6calka BP). In addition, positive shifts of δ34S values (from +3.7‰ to +32.6‰) were observed during the LG-PG transition. These results suggest a large influx of 34S-rich dissolved sulfate into the lake during this period. The 34S-rich dissolved sulfate may have accumulated on the shore (wetlands and marshes) of Lake Hovsgol during the last glacial period. Owing to the increase in atmospheric precipitation and lake level rise during the LG-PG transition, the 34S-rich dissolved sulfate may have been supplied from the shore to the lake. Increased sulfate influx during the LG-PG transition has also been observed in a Lake Baikal sediment core. Our new sulfur geochemical data shows past-environmental changes, particularly moisture changes, within continental Asia during the climate transition. © 2010 Elsevier B.V.


Honda Y.,University of Tsukuba | Ono M.,Association of International Research Initiatives for Environmental Studies
Environmental Health and Preventive Medicine | Year: 2011

Objectives: The objective of this study was to assess the relation between temperature and suicide mortality in Japan using time series analysis with a semiparametric approach. Methods: We analyzed the relation between daily fluctuations in suicide mortality and maximum temperatures for all regions in Japan over the period of time from 1972 to 1995 using a generalized additive model. The model controls for the time trend, season, selected meteorological parameters, day of the week, and holiday. Adjustment was based using penalized splines and the decision on the amount of smoothness was based on minimizing the unbiased risk estimation criterion. Results: The results show that suicide mortality in Japan has a seasonal character and it varies from year to year, with the highest occurrence in April, as well as in the first part of the week, especially on Mondays and Tuesdays. As for the day of the week, there were only few suicide cases on Saturdays and holidays. We found that for all regions in Japan when temperature increased the suicide mortality increased on the same day (lag = 0). Analysis by method of suicide showed that when temperature increased mortality significantly increased only for suicide by a violent method. The pattern of the relation for other methods remained unclear. Conclusions: This study suggests that an increase in temperature has a short-term effect on suicide mortality in Japan. © 2010 The Japanese Society for Hygiene.


Matsumoto K.,Japan Forestry and Forest Products Research Institute | Noerdjito W.A.,Indonesian Institute of Sciences | Fukuyama K.,Association of International Research Initiatives for Environmental Studies
Journal of Tropical Forest Science | Year: 2015

The biodiversity status of insects in plantations in the tropics is little known. To evaluate the biodiversity restoration function of the plantation, we compared the species richness and species composition of butterfly assemblages in three plantations of Acacia mangium, two ex-forest grasslands and a native forest in East Kalimantan based on repeated 45-min sampling sessions in December 2004, May 2005 and December 2005. Higher species richness was recorded in plantation than in grassland, indicating that the plantation could support more butterfly species. Even higher species richness was found in the native forest. The species accumulation trend indicated by a rarefaction curve suggested that there were many more undiscovered species in the native forest. The butterflies found in the native forest included many range-restricted species, which were not found in the plantation and grassland. These range-restricted species were thought to be specific to the interior of the native forest and unlikely to colonise the plantations. Artificial plantations established on degraded grasslands can enrich butterfly assemblage, but this enrichment is mainly due to the increase in species with moderate or wide distribution ranges, rather than the recovery of range-restricted native forest species. © Forest Research Institute Malaysia


Nara F.W.,Tohoku University | Nara F.W.,University of Liège | Watanabe T.,Tohoku University | Watanabe T.,University of Liège | And 7 more authors.
Quaternary Science Reviews | Year: 2014

Stable nitrogen isotope ratios (δ15N) in sediment cores recovered from two Siberian lakes (Baikal and Hovsgol) are determined in order to evaluate the biologically mediated nitrogen cycle from the Last Glacial period to the postglacial period. The ranges of δ15N values from the two lakes are similar, varying from+2.8‰ to+6.7‰. The high values of δ15N (around+6‰) during the Last Glacial Maximum (LGM, 26.5-19calkaBP) indicate that a larger fraction of the available nitrate in both lakes was utilised by phytoplankton. A cool and dry climate during the LGM may have limited the input of terrestrial nitrate, resulting in the use of a large fraction of the nitrate, and low productivity, in both lakes. The use of a smaller fraction of the nitrate by phytoplankton in both lakes after the LGM (19-12calkaBP) is reflected in the lower δ15N values (down to+3.0‰). The increase in summer insolation after the LGM caused increased vertical mixing of the lake water column, which transported nitrate upwards from the deeper waters and into the photic zone. The reduced rate of nitrogen consumption after the LGM indicates that nitrate was more readily available to phytoplankton at this time and did not limit their activities. This change suggests that other factors limited phytoplankton activity during this period. At the climatic transition between Oxygen Isotope Stages 2 and 1 (around 11.5calkaBP), the rapid increase in δ15N (from+3.0‰ to+6.0‰) reflected a rapid increase in nitrate utilization. At this transition, increases in precipitation and lake levels, which were associated with the increased intensity of the East Asian Monsoon, may have brought a large influx of nutrients required by the phytoplankton into the lakes from the watershed. This hydrological change led to increased phytoplankton activity in both lakes, resulting in increased nitrate consumption. The δ15N data obtained here from the sediments of lakes Baikal and Hovsgol suggest that the nitrogen cycle in the Siberian region is strongly linked to hydrological changes across the Asian continent, which are related to global climate change. © 2014 Elsevier Ltd.


Yonemura S.,Japan National Institute for Agro - Environmental Sciences | Nouchi I.,Japan National Institute for Agro - Environmental Sciences | Nouchi I.,Association of International Research Initiatives for Environmental Studies | Nishimura S.,Japan National Institute for Agro - Environmental Sciences | And 5 more authors.
Biology and Fertility of Soils | Year: 2014

No-tillage (NT) management is a promising method to sequester soil C and mitigate global warming caused by agricultural activities. Here, we report 4 years of continuous soil respiration rates and weekly nitrous oxide (N2O) and methane (CH4) emissions in NT and conventional-tillage (CT) plots in a typical Japanese volcanic soil. Overall, the soil respiration, N2O emission, and CH4 uptake decreased significantly in the NT plot. A difference in soil respiration and N2O emission between the two plots began after the tillage treatment and the incorporation of crop residues and fertilizers, whereas the CH4 uptake did not vary significantly during the fallow period after the treatments. The N2O emission was higher from the CT than from the NT plot during the fall. The overall lower CH4 uptake in the NT than in the CT plot likely resulted from a combination of decreased soil gas diffusivity and higher mineral N content at the soil surface. Higher soil respiration and N2O emission occurred in the NT plot in the summer of 2003 and were plausibly caused by an increase in the soil moisture content that resulted from lower temperatures during July and August; the higher soil moisture must have accelerated the decomposition of organic matter accumulated in the topsoil. These results indicate that NT management is generally effective for the mitigation of the total GWP by reducing soil respiration and N2O emission in temperate regions; however, NT management may increase rather than decrease these emissions when fields experience cool summers with frequent rainfall. © 2013 Springer-Verlag Berlin Heidelberg.

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