In the present study we estimated daily evapotranspiration using GPS and meteorological data obtained at a plain, situated in the northern part of Kyushu Island, Japan. The seasonal variation of GPS-derived precipitable water vapor (GPS-PWV) was revealed at the study area throughout one year. The relation of screen-level air temperature to GPS-PWV was analyzed, and a regression equation was presented between them on the basis of the'saturated water vapor curve'. Evaluating the representative relative humidity at the study area, a formula including humidity was dderived as a function of daily GPS-PWV to calculate vapor pressure near the ground. Daily potential evapotranspiration was estimated during the analyzed period using the calculated vapor pressure. The estimated evapotranspiration agrees fairly well with that inferred by a conventional method. This suggests that GPS could be useful for estimation of daily potential evapotranspiration at local areas.

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GPS (Global Positioning System) is a sophisticated system that performs a precise positioning with higher accuracy in space using GPS satellites. In the last decade, techniques have been developed to infer the total amount of water vapor in the atmospheric column having infinite height as GPS-derived precipitable water vapor (GPS-PWV). In this study, using GPS-PWV data, monthly potential evapotranspiration was estimated at a plain in the northern part of Kyushu Island, Japan, based on the close correlation between screen-level vapor pressure and GPS-PWV shown by a preceding study. It was confirmed that the vapor pressure estimated from GPS-PWV concurs with the observation. The standard deviation of the difference between the estimated and observed vapor pressures was 1.7hPa. The formula, which does not use vapor pressure but GPS-PWV, was presented to estimate the monthly potential evapotranspiration at the study area. The estimated values of the evapotranspiration ET_GPS agree well with the calculated values ET_PEN from Penman's formula. Finally, it was suggested that values of ET_GPS derived considering the influence of Δe possibly over- or underestimating evapotranspirations, by as much as 20 % in spring, summer and autumn or 50 % in winter of ET_PEN.

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Recent studies have estimated the total amount of water vapor in an air column using GPS-derived precipitable water vapor (GPS-PWV). We used GPS and meteorological data obtained at a plain, in northern Kyushu, Japan, to investigate relations between GPS-PWV and precipitation on days with daily precipitation of 50 mm or more. The following characteristics were associated with days of heavy precipitation:(1) the rate of increase in GPSPWV (R_inc= (PWV₀-PWV_*)/PWV₀, where PWV₀ is the value of GPS-PWV at 00 JST, and PWV_* is the value 24 hr before) ranged from -0.25 to 0.75;(2) PWV₀ was larger than PWV_sat, which was derived as a function of T₀ (air temperature at 00 JST); and (3) PWV₀≥PWV_ref and T₀≥T_ref were simultaneously satisfied where PWV_ref and T_ref were climatological threshold values. We constracted a heavy precipitation index, I_HP based on the above characteristics. The acceptable prediction results provided by I_HP suggests its usefulness for analyzing and forecasting heavy precipitation events.

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In this research, we elucidated effectiveness of the “comprehensive method for Land Consolidation” that implements the land consolidation and the farmland accumulation at the same time. As the Analytical method, we applied a multi-agent simulation model (artificial society model) named ASMAP, ASMAP is contracted name of “Agent-based Simulation Model for Agricultural Planning”, and it is possible to take into consideration clearly the interaction of various decision makers and an environmental change by the model. The study area is the Rokugoh-west district, Misato town, Akita prefecture in which a land consolidation project just started in 2004. As the results of simulation analysis by ASMAP based on there local information about farmers and farm land, we found that there are a certain multiplier effects by the comprehensive method on farm land conservation compared with the implementation of land consolidation project or farmland accumulation policy by itself These results just tell us that the comprehensive method brings great effects.

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The purpose of this research is to clarify the actual phenomena and evaluation of the nitrogen and phosphorus input/output balance in a paddy field located in the lowlands of Kahokugata. The authors found that the amount of chemical fertilizer that was applied to this field accounts for a high percentage in the N and P input. The authors also found the amount of yield with husk taken out from this field accounts for a high percentage in the N and P output. Because the amount of N and P in the yield was greater than the applied fertilizer, these two elements, N and P, could be supplied from acidic oxide fallout, nitrogen fixation and irrigation water. We clearly demonstrated that rice in a paddy is “a crop purifier” or “a cleaning crop” and plays an important role on the purification of the paddy system environment absorbing nitrogen pollution. With this point of view, we concluded that rice production in the lowlands of Kahokugata is environmentally-friendly agriculture.

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The authors have developed a method, named “Simdcap”(Simple distillation of digested liquid to concentrated liquid, ammonia liquid and purified water) to reduce methane fermented liquid supernatant by a simple vacuum distillation. The Simdcap method separates the supernatant into concentrated liquid, ammonia liquid and purified water.
In this paper, a method to predict the ammonia concentration removed by Simdcap was clarified. The prediction method calculates the distillation time for a specific ammonia concentration and ammonia liquid volume with an initial ammonia nitrogen (NH₄-N) concentration of supernatant at a determined distillate rate. For instance, 1, 500mg ·l^-1 initial NH₄-N and a 2%·h^-1of the distillate rate indicate that 9.6h are required to obtain the ammonia concentration. The ammonia liquid is 19% of the initial supernatant volume in the distiller. The distillate rate “%” is the rate of distilled liquid volume to initial supernatant volume in the distiller.
In addition, the weight of clinging residuals as related to concentration of the supernatant in the distiller was examined. Clinging residual ratio was below 0.5% and the average water content of the clinging residuals was 95% while concentration rate of the supernatant was below 90%. Clinging residual ratio increased in proportion to the concentration rate, the average clinging residual ratio was 0.93% and the average water content of the clinging residual was 48% while the concentration rate was above 90%.
The clinging residual weight in the second turn was less than in the first turn when 90 % concentration of the supernatant was redistilled. The outflow of concentrated liquid in the second turn seemed to wash out some of the clinging residuals during the first turn. The distiller must be able to efficintly remove the clinging residual.

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An artificial neural network model with three-layer structure was applied to estimate chlorophyll a concentration in an eutrophic lake. First, input variables, which resulted in high calibration accuracy, were searched. As a result, calibration accuracy was highest when input variables were set to TN, TP, DO, water temperature, solar radiation, air temperature, wind velocity, and Wedderburn number. This result means that the model incorporated the relationship between chlorophyll a concentration and the meteorological, hydraulic, and aquatic factors into the network structure. Next, the feasibility of the estimation of chlorophyll a concentration was examined by the model. As a result, chlorophyll a concentration could not be sufficiently estimated by this model. To improve estimation accuracy, network structure was reconstructed by considering the time history of the variation of the meteorological and water quality data for the previous 24 hours and incorporating such data into the input variables. The result showed that the estimation accuracy was remarkably improved.

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A conventional work of irrigation ponds management called “Sediment desiccation” is focused and its effect on phosphorus and nitrogen dynamics are discussed. Sediments that are cast into desiccating and submerging conditions simulated in a laboratory, are sampled at 10 irrigation ponds in Osaka, Shiga and Gifu prefectures, Japan. The properties of resultant samples are examined by release test under aerobic condition, componential analysis and denitrification test, especially for phosphorus and nitrogen dynamics. As a result, the following sediment-desiccation effects become apparent; 1) Decomposition of organic matter contained in the sediment is promoted by approximately 3% in the refilled water, 2) Release of phosphorus into the refilled water decreases by approximately 33% and 4) Release of nitrogen increases contrarily by approximately 250%. In addition, definite correlation between sediment desiccation and denitrification was not found apparently.

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Some dissolved organic matter (DOM) have recalcitrant characteristic and are accumulated in lake and that could be one of facters of organic pollution. To clarify the characteristics of effluent of DOM and hydrophobic acids including humic substances, one of recalcitrant DOM, quantities of irrigation and surface drainage water, concentrations of DOM and hydrophobic acids in inflowing and outflowing water have been investigated during a irrigation period in a paddy field. The concentrations of DOM and hydrophobic acids in ponded water were higher than those in irrigation water, and have been decreasing with percolating through soil. In dpths of 0.3m, percolating loads decreased to 59% DOM, 66% hydrophobic acids. In dpth of 1.0m, percolating loads decreased to 35% DOM, 31% hydrophobic acids. So it's a effective practice to make the ponded water outflow through the soil for control of DOM and hydrophobic acids loads from paddy fields.

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Long-term forecasting of reservoir inflow is essential to effective reservoir operation to cope with drought disasters. Deterministic forecasting of inflow is, however, hardly reliable because of uncertainty in long-term climate forecasting. In this paper, a real-time stochastic forecasting system of reservoir inflow was developed using stochastic cumulative inflow curves that are derived from real-time rainfall-runoff simulation. The advantage of the developed system is that it can consider antecedent precipitation/moisture condition of the objective basin as well as hydrological records. The results of real-time forecasting of reservoir storage up to three-month ahead at the Osakabe-gawa Dam Reservoir showed that the developed forecasting system enables comparison of the foregoing effects of multiple scenarios of reservoir release under defferent inflow conditions.

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Mass balances of nitrogen and phosphorus in the conventional irrigation (Gyaku-sui irrigation; GI) system and the cyclic irrigation (CI) system were investigated in paddy field district close to Lake Biwa, where the CI was mainly run during the period from the puddling season to the start of the mid-summer drainage and the GI was run after the mid-summer drainage. As a result, it was confirmed that the CI system reduced outflow of surplus irrigation water with nitrogen and phosphorus. In the CI period, from the end of April to late June, there was less effluent water from the district even though about 80% of the irrigation water was the surplus water. From the comparison between mass balances in the CI system and GI system, it was shown that the CI system could reduce effluents of TN and TP by 120g ha^-1 d^-1 and 15g ha^-1 d^-1 respectively.

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To extract the environmental factors which influence living of Hotoke loach which is typical fish in Yatu waters, we investigated Hotoke loach's distribution situation, waterway structure, hydraulic factors, and water quality from June, 2004 to November, 2006 in two Yatu Waters in Tokyo.
As a result, the Hotoke loach has a different requirement for the environmental factors at each growth stage. The number of adult fish has srong positively correlation with the water depth when flow decreases and it was suggested that the flow is more restrictive than other factors. Moreover, it was suggested that there is a possibility of elevating the mortality rate for the individual which had finished breeding with the rise of the water temperature.

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Percolation rates of soil layers above mole drains and at the midpoint of mole drains were measured in rotational paddy fields under varied land use and crops. In addition, soil layers above mole drains were observed in these fields. Percolation rates above mole drains were kept high at the rate of 350-480mm h^-1 in upland fields and in paddy fields without puddling. On the other hand, in the paddy field with puddling, percolation rates decreased by each puddling practice. The percolation rate above the mole drain is affected by in-situ vertical cracks formed during subsoiling practices, rather than the residual void area of the mole drain hole. The characteristics of the drainage function in rotational paddy fields with mole drains are that:(1) the percolation rate increases right above the mole drain with the subsoiling practice, (2) upland crop culture increases the percolation rate at the midpoint of mole drains, (3) the percolation rates above the mole drain and at the midpoint of mole drains decrease with puddling practices in the paddy field. Our results indicate that, to keep the drainage function of the paddy field high, the mole drain needs to be re installed after two paddy culture.

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Physico-chemical properties of four artificial soils were monitored. The ability of soils to resist water erosion and efficient irrigation scheduling were also estimated. The studied soils were KS (Koka soil) which contains high value of organic matter, VS (Viva soil) made by poriferous pumice mainly, PP which is perlite in powder form and GP which is granular perlite. These soils had high percentage of sand particles with high value of hydraulic conductivity. The aggregate stability of VS was high with good structure for plant growth. Whereas, KS contained many nutrients and classified as a fertile soil. Soil erosion was not occurred when these soils were subjected to rainfall intensity of 40 (mmh^-1). Moreover, when 30 years rainfall data was simulated for effective rainfall and net water requirement, these soils were found to have high irrigation water efficiency. Generally, these artificial soils were expected to effectively resist water erosion and have high irrigation efficiency.

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Long-term daily precipitation data covering more than one hundred years at local meteorological observatories on the Sea of Japan coast were divided into warm and cold season precipitation, and the periodic variability of precipitation characteristics was investigated and discussed by applying spectral analysis and the moving average method. For annual precipitation time series, it is shown that a periodic variability of about 20 years is present in Akita and Yamagata located in the Dewa region, and that a periodic variability of 11-13 years is present at Sakai and Hamada located in the San-in region. For Hokuriku region, a periodic variability of about 13 years at Fushiki is similar to that of San-in region, while a periodic variability of about 20 years at Tsuruga is similar to that of Dewa region. It is interesting that the periodic variability of cold season precipitation is the same within each climatic district for all regions, but varies between districts. Additionally a periodic variability of more than 10 years exists in time series of annual maximum daily precipitation.

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