Time filter

Source Type

Ahn Y.-S.,Laboratory of Forest Ecosystem Management | Ahn Y.-S.,Chonnam National University | Kasahara T.,Laboratory of Forest Ecosystem Management | Otsuki K.,Laboratory of Forest Ecosystem Management | And 16 more authors.
Journal of the Faculty of Agriculture, Kyushu University | Year: 2015

The purpose of this study was to examine the long-term fluctuation in remains of Aegagropila linnaei associated with phytoplankton dynamics and sediment accumulation in Lake Takkobu, northern Japan. A. linnaei is a green alga requiring good light conditions (low phytoplankton production and a low density of fine sediment particles) for growth. Six lake sediment core samples were obtained, and lake sediment-core samples contained two tephra layers as Ko-c2 (1694) and Ta-a (1739). Fresh tephra deposition is the source of phosphorus in the lake, and induces an increase in phytoplankton. For the period 1694-1739, low sediment accumulations and low phytoplankton productions were observed, and A. linnaei remains were low, likely due to nutrient deficiency. Ko-c2 tephra deposition had no detectable influence on phytoplankton and A. linnaei dynamics, as insufficient tephra was deposited to induce a nutrient deficiency. However, phytoplankton productivity was attributed to Ta-a tephra deposition, which was at a higher influx than that of Ko-c2, in addition to human activities, such as deforestation and agricultural development. A. linnaei remains in 1739-1898 were increased despite the enhanced phytoplankton productivity caused by Ta-a tephra deposition. This evidence indicates that a phytoplankton impact on the transparency from 1739-1898 was probably insignificant, but the released nutrient from Ta-a tephra acted as a stimulus to make the A. linnaei grow. Therefore, A. linnaei existence depends on interaction between light conditions and sediment accumulation as well as nutrient conditions. Human activities after 1898 have directly influenced increased phytoplankton productivity and sediment accumulation, and result in A. linnaei degraded. Moreover, A. linnaei remains mainly were concentrated in sediment from northern zone close to lake outflow because their spherical form and free-floating filaments tend to be moved by water flow. In recent years, the distribution of A. linnaei in the lake was reduced due to the shading effect caused by the increase in phytoplankton production and the attenuation of sunlight by high sediment accumulation.

Fang Q.,Laboratory of Forest Ecosystem Management | Fang Q.,Beijing Normal University | Zhang L.,Laboratory of Forest Ecosystem Management | Zhang L.,Qingdao Agricultural University | And 7 more authors.
Journal of the Faculty of Agriculture, Kyushu University | Year: 2015

The relationship between soil erodibility and sediment-bound available nitrogen (AN) and available phosphorus (AP) losses were rarely mentioned in previous studies. The experiments were carried out using a soil flume and a rainfall simulator to evaluate the relationship. The impacts of rainfall intensity and slope on sediment-bound AN and AP losses and the relationship between soil erodibility and soil properties were also studied. Eight simulated rainfalls were applied on the flumes with different conditions (two rainfall intensities, two slopes) from two contrasting soil of China (Burozems and Cinnamon) with two replicates. The soil erodibility of Cinnamon is much higher than that of Burozems. The higher soil erodibility of the Cinnamon soil resulting in greater runoff, soil loss and sediment-bound AN and AP losses. The sediment yield rate significantly influenced the sediment-bound AN and AP losses. The soil erodibility also significantly influenced the sediment-bound AN and AP losses based on Principal Components Analysis (PCA) result. The results of PCA also showed that other soil properties (organic matter, bulk density and cation exchange capacity) were related to soil erodibility. Increasing rainfall intensity and slope resulted in increasing runoff, sediment and sediment-bound AN and AP losses for both soils. Our study showed a good evaluation with the role of soil erodibility related to sediment-bound AN and AP losses and other soil erosion parameters.

Kim S.-W.,Laboratory of Forest Ecosystem Management | Kim S.-W.,Kangwon National University | Chun K.-W.,Laboratory of Forest Ecosystem Management | Chun K.-W.,Kangwon National University | And 12 more authors.
Journal of the Faculty of Agriculture, Kyushu University | Year: 2015

This study aimed to elucidate the differences in the tendency for landslides to occur according to heavy rain types in summer in South Korea. For this, the rainfall intensity-duration (I-D) relationship and the differences in I-D relationship by three representative heavy rain types (convective rainstorm, monsoon rain and typhoon rain) were analyzed statistically, based on the corresponding hourly rainfall data for 478 shallow landslides occurred through South Korea during 1963-2012. In the quantile regression analysis of the I-D relationship for triggering landslides, the regression line of the 50th percentile of each heavy rain type showed notable differences, and convective rainstorms showed the highest rainfall intensity for the same duration, followed by monsoon and typhoon rains. While the difference was remarkable in the rainfall duration range of 4-20 h, it tended to decrease with an increase in the duration, suggesting that the effects of rainfall intensity on landslide occurrence gradually became insignificant due to an increase in soil water content. Rainfall intensity and duration according to heavy rain type revealed a statistically significant difference. Rainfall intensity was the highest in convective rainstorms and the lowest in typhoon rains, whereas rainfall duration was the longest in typhoon rains and the shortest in convective rainstorms. Such a trend is consistent with the characteristics of heavy rain types reported in Korean meteorology studies, clearly indicating that landslides occurring in South Korea were mainly triggered by heavy rains in summer. The results of this study should contribute for establishing landslide warning and evacuation systems when considering the characteristics of heavy rain in the future and suggest the necessity to improve rainfall and landslide prediction techniques during localized convective rainstorms and to provide systematic and proactive warning and evacuation systems.

Kim S.-W.,Laboratory of Forest Ecosystem Management | Kim S.-W.,Kangwon National University | Otsuki K.,Laboratory of Forest Ecosystem Management | Shinohara Y.,Laboratory of Forest Ecosystem Management | And 3 more authors.
Journal of the Faculty of Agriculture, Kyushu University | Year: 2015

Large woody debris (LWD) transport in headwater streams caused by forest disturbances such as wild fires, strong winds, and landslides affect the physical and ecological environment of the streams and become a disaster risk in downstream area. However, little attention has been given to LWD dynamics in South Korea where the forests comprise 63.7% of the land. As the first case study of LWD at the catchment scale in South Korea, we investigated the LWD dynamics according to the stream order in the experimental forests of Kangwon National University. The volume and number of LWD per unit channel area were 0.009 m3/m2 and 0.04 pieces/m2 in the first order stream, 0.007 m3/m2 and 0.03 pieces/m2 in the second order stream, and 0.004 m3/m2 and 0.01 pieces/m2 in the third order stream, respectively, decreasing as the order increased. The average value (± SD) of LWD piece length/channel width ratio was 0.61 (± 0.62) in the first order stream, 0.33 (± 0.34) in the second order stream, and 0.16 (± 0.14) in the third order stream. The correlation between mid-diameter and length for coniferous and natural wood pieces was relatively high in the first order stream, but low in the second and third order streams, indicating downstream fragmentation. For the decay classes of LWD, class I to III gradually decreased, whereas class IV greatly increased as the stream order increased. LWD mobility was 60% for the first order stream, 56% for the second order stream, and 86% for the third order stream. Traveled distance of LWD was inversely related to the piece length/channel width ratio and increased more in the high order streams than in the low order streams. These results contribute to understanding the volume, distribution and mobilization of LWD within a stream network in Korean mountain catchments.

Wang G.,Laboratory of Forest Ecosystem Management | Wang G.,Beijing Normal University | Xue B.,Laboratory of Forest Ecosystem Management | Yu J.,Laboratory of Forest Ecosystem Management | And 2 more authors.
Journal of the Faculty of Agriculture, Kyushu University | Year: 2010

Land levelling is an important process of the agricultural land consolidation projects. The land levelling process starts by determining the appropriate levels of the terrain and solves the earthwork allocation for the predetermined terrain levels. The recent attempt, reported in the literature, to find an optimal process is a GIS-based approach which solves the transportation problem by determing the designed terrain level and optimal hauling distances that result in the lowest hauling cost. In this study, the Vogel approximation method (VAM) was adopted in initializing the solution to the transportation problems, and the optimization of the solutions obtained by the VAM was examined using the modified distribution method (MODI). To verify the reliability of this combined method, a case study was carried out based on the proposed land levelling project at the Lixian District of Beijing, China. The results show that the optimal average hauling distance calculated from the proposed linear programming model is 79.53m shorter than that estimated using the empirical method, and the unit cost calculated from the linear programming model is 33.4% lower than the experienced cost. The improvements in the optimization of the hauling distance show that the cost of the agricultural land levelling can be efficiently lowered if an appropriate linear programming model is used.

Discover hidden collaborations