Spawning ecology and seasonal migration of Tanakia lanceolata were investigated in the irrigating area of the Iwaki River Basin in northern Japan. Two unionid mussel species, Inversiunio jokohamensis and Pronodularia japanensis, were mainly used by T. lanceolata as the spawning hosts in this study area. The results of body length composition and mark-recapture experiment suggested that there were seasonal and ontogenetic habitat change. In spring, a large number of adult and immature of T. lanceolata, gathered to their spawning ground in branch ditch, and alternative pattern was dispersal from branch ditches in autumn. Limitation of the distributional area of the host mussels and seasonal change of the physical environments could affect their migration patterns. Because the branch ditch was also comfortable for larvae and juveniles of T. lanceolata as nursery grounds, channel networks should be ensured for fish conservation.
We investigated cadmium concentrations of rice plants and the growth and the yields by using four models of stratified paddy fields for three years. Two of them had water flow in an open system at the plowsole and the subsoil which became oxidation layers. The other two models had water flow in a closed system at the plowsole and subsoil which became reduction layers. The polluted soil thicknesses of those sets were 22.5cm and 32.5cm respectively and the cadmium concentration in those soils was 3.39mg/kg. As a result, the range of cadmium concentrations in brown rice, and in the stems and leaves of those four were 0.000-0.200mg/kg, 0.059-1.250mg/kg, respectively. Also cadmium concentration in roots in the plow layers and that in the plowsoles and subsoils were 1.80-25.05mg/kg, 5.17-61.63mg/kg, 0.28-22.97mg/kg, respectively. In the two models with the same thickness of soil, significant differences in the number of leaf, dry weight of straw, the number of panicle, weight of brown rice, cadmium concentration in the roots in the plow layer and the plowsole and brown rice were observed. In those models with different polluted thicknesses and the same percolation patterns, significant differences in dry weight of straw, weight of brown rice and cadmium concentrations in the roots in the plow layer and the plowsole were recognized. From those results, it was clear that the difference of the polluted soil thickness influenced the concentration of cadmium in the rice plant, the growth and the yields under inundation during the cultivation with stratified models.
Nitrogen removal performance was investigated by using observed data in rural sewerage facilities with intermittent aerobic suspended-growth processes. It was found that the effective nitrification-denitrification could be achieved by maintaining aeration time, aeration rate at aeration phase and controlling stir time at stir without aeration phase in cyclic operating conditions. The nitrogen removal reaction was assumed to be governed by first-order function with complete-mix system of biological treatment process. It was recognized that the nitrogen reaction rate was influenced by the temperature and dissolved oxygen (DO) concentration at aeration phase in aeration tank. The nitrogen removal was confirmed to be dependent on mixed-liquor suspended solids (MLSS), hydraulic retention, temperature, and DO concentration at aeration phase in aeration tank. The relationship between nitrogen removal and hydraulic retention time, MLSS cloud be modeled as the form of rectangular hyperbolas. On the base of the influent temperature, the control of MLSS, hydraulic retention, stir time and amount of aeration in aeration tank are important factors in maintaining stable nitrogen removal efficiency.
This paper presents a model using the Dupuit approximation applicable to the case in which a small homogeneous earth dam constructed on inclined foundation in order to estimate the phreatic surface location and the seepage discharge through the dam. Analytical results obtained from the model are validated by comparison with the results obtained from a BEM model of the Laplacian field. Main results are as follows: i) The phreatic surface location of the analytical result of the model tends to be higher than that computed by the BEM, ii) The height of the seepage-out point obtained from the analytical result is almost identical with that by the BEM, and iii) The seepage discharge obtained from the analytical result is larger than that by the BEM; their ratio is between 1.113 and 1.243. From all results of the test cases, it is shown that these analytical results are useful for analyzing seepage through a homogeneous earth dam on inclined foundation.
Salt accumulation is one of the most serious threats for plant production in northeast China. Field survey and one-year continuous monitoring on soil physical conditions and water table had been conducted in an experimental station of Northeast Forestry University at Heilongjian, China. Annual rainfall was 356 mm while potential evaporation during summer period of 2006 estimated by Thornsweit method was 540 mm. Soil of the study site was mostly clayey. Salt accumulation on soil surface showed heterogenous feature. Salt accumulated areas and vegetated areas adjoin above the same shallow salty ground water table. During summer, when soil water content was nearly saturated, rise in ground water table in response to rainfall was 7 to 12 times larger than the rain depth. This phenomenon is known as reverse-Wieringermeer effect. A 60% of cation contained by shallow ground water was Na and Ca and Mg dominated rest of 40%. However, more than 90% of cation detected at soil surface in salt accumulated areas and at soil layers deeper than 40cm from the surface in vegetated areas was Na. Dynamic behavior of shallow ground water and changes in carbonates solubility due to rise in soil CO2 concentration following soil respiration might affect salt accumulation at the experimental site.
The objective of this study is to develop a system that can automatically count the number of loaches ascending corrugated-pipe paddy field fishways by adopting the counting principle of resistivity fish counter originally designed for salmon. As the results of laboratory and in situ experiments, the counting mechanism of the resistivity fish counter could be applied to counting loaches by modifying the sensor allocation and adjusting voltage level. Counting precision was evaluated to be 86% with video monitoring analyses. In addition, long-term automatic operation in situ without permanent power sources was successful using rechargeable batteries (capacity 115Ah) and high-resolution and large-capacity data logger (memory capacity 2GB). The system could operate as long as 79 hours with two batteries connected in parallel.
While the acreage of hilly and mountainous farmland has been decreasing due mainly to the abandonment of cultivation, the importance of appropriate management and preservation of farmland resources has been magnified for the sake of food self-sufficiency in our country with a limited usable land. For this reason, the necessity for farmland readjustment which raises the labor productivity, and facilitates farmland maintenance is high. However, a long-term farmland resource preservation has been set in vulnerable condition, because of the difficulty in the building consensus to enforce land improvement projects and also the lack of planning system to deal with the effective land resource usage. In this paper, the wide area landuse design method is proposed using the concept of the “landuse for right to exist” and the farmland management division based on the case examination of farmland readjustment project which enables farmland resource preservation in a hilly and mountainous area.
In developing countries, participatory irrigation management (PIM) is promoted to achieve more sustainability and efficiency in irrigation projects. On the other hand, some industrial countries such as Korea, Taiwan and Japan tend to have public management of irrigation systems. Korea, in particular, has strongly promoted public management since the 1980s, and eventually abolished the irrigation association fee in 2000. To obtain information useful for the future consideration of public water management, this study analyzed the general backgrounds of the public irrigation management in Korea and the actual water management in Chungcheongnam-do and clarified the following: 1) the Korean Irrigation Association had a persistent tradition of government control, which led to complete public management by the Korea Agricultural & Rural Infrastructure Corporation in 2000; 2) the public management system has had a positive impact on the successful solution of inter-basin water adjustment issues; 3) contrary to the hope and expectation of the government, Korean farmers have lost their willingness to participate in water management because they have been excluded from the decision-making process and lost their irrigation associations under the new system of Korea Agricultural & Rural Infrastructure Corporation.
Causal relationships among the Payment for Community-Collaborative Activities to Conserve Land, Water Resources and the Rural Environment (CCA payment), conditions of agricultural infrastructure, and farmland accumulation by large-scale farms are identified by path analysis based on municipality data. Two causal models are developed to regulate the effect of confounding factors. Results show that: (1) conditions of agricultural infrastructure of the area such as farmland consolidation and topography affect the application to the CCA payment; (2) the CCA payment affects agricultural structure of the area such as accumulation of farmland to large scale farmers; (3) sprawling and urbanization negatively affect the agricultural structure of the area; and (4) through the influence on agricultural structure, sprawling and urbanization negatively affect the application to the CCA payment.