We developed a novel rapid analysis method to measure trace levels of radiocaesium in surface water by using absorbent disks for radioactive caesium with a NaI scintillation counter (ADiCS). ADiCS involves 1) the selective absorption of dissolved radiocaesium onto the disk and the collection of particulate radiocaesium on the PTFE membranes by surface water filtration and then 2) directly measuring the radioactivity on PTFE membranes and the disk by a NaI scintillation counter. Evaluation of the accuracy and rapidity of ADiCS for 20 L samples with less than 20 mg•L^-1 suspended solids showed that ADiCS needed six times less concentration time than the evaporation method and that the limit of detection was approximately 10 mBq•L^-1. Moreover, radioactivity data obtained by ADiCS had less than 30 % of the error of data obtained by the evaporation method. ADiCS also revealed a significant increase in radiocaesium in the Kanto region after the nuclear power plant accident. Especially, a radiocaesium concentration of over 100 mBq•L^-1 was observed in surface water around high radiocaesium deposition areas. These results indicated ADiCS can evaluate current and future trace levels of radiocaesium in surface water, including bioaccumulation characteristics, more easily than the evaporation method.

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It is well known that N₂O, a greenhouse gas, is produced during biological nitrogen removal in wastewater treatment plants (WWTPs). It has been reported that the amount of N₂O emitted varies depending on the type of WWTP and even within the same WWTP depending on the operational conditions. Therefore, it is important to consider the conditions that can reduce the amount of N₂O emission and to investigate the pathway of N₂O production by studying the N₂O production potential and the amount of N₂O emission.In our sealed batch experiments where NO₂-N was added as the precursor substance for N₂O production, the amount of N₂O produced under aerobic conditions increased with higher initial NO₂-N concentrations and longer reaction times. Consequently, the initial NO₂-N concentration of 5 mgN•L^-1 and a reaction time of 1 h were selected to evaluate the N₂O production activity. The high N₂O production activity in an actual WWTP was observed when nitrification was controlled; however, N₂O production activity decreased when nitrification was accelerated. This was likely to be due to the competing processes of NO₂-N reduction to N₂O with NO₂-N oxidation to NO₃-N. Furthermore, the operational conditions under which Nitrospira caused complete nitrification inhibited N₂O emission.

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We investigated pollution loadings in two groups of paddy fields (5.1 and 5.6 ha) in Moriyama City in Shiga Prefecture, Japan. The results are as follows: 1) Net loadings of total nitrogen (T-N), total phosphorus (T-P), total organic carbon (TOC), and suspended solids (SS) during the irrigation period in the two groups of paddy fields were 44-105 g•ha^-1•d^-1, 27-28 g•ha^-1•d^-1, 214-276 g•ha^-1•d^-1, and 3918-4113 g•ha^-1•d^-1, respectively. 2) The percentages of the pollution loadings during rain events in total pollution loadings during the irrigation period are app. 35-50%. 3) Pollution loadings determined by observations of groups of paddy fields are higher than those determined by observations of one paddy field or using lysimeters because of soil erosion of banks around drainage channels and resuspension of bottom sediments at drainage channels on rainy days.

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Waterfront activities in rivers and ponds have increased, and ensuring the safety of facilities is an increasing problem. To prevent slip accidents on the bottom of waterfronts, the coefficient of slip resistance (C.S.R') was evaluated quantitatively. The following conclusions were obtained by investigating the relationships between the amount of attached algae, C.S.R', the growth factor of algae and the use of water-friendly structures to prevent slipping. The first is a negative correlation between the amount of attached algae and the C.S.R' of the water bottom; thus the water bottom becomes slippery with the growth of attached algae. The second is that when the nutrient concentration in water is lower than the half-saturation constant, there is a positive correlation between the flow velocity and the amount of attached algae. In contrast, when the nutrient concentration is higher than the half-saturation constant, there is a positive correlation between the light intensity and the amount of attached algae. Therefore, it is possible to create a nonslip condition on the water bottom by managing the nutrient concentration, light intensity and flow velocity. The third is that the water bottom becomes slippery with the growth of attached algae regardless of the type of material.

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Aquatic microcosm tests were performed to determine the ecotoxicological effect of alcohol ethoxylate (AE, C12, EO7). Compared with the control system, the population did not decrease in the system with 2 mg•L^-1 AE. In the systems with 10 and 25 mg•L^-1 AE, the population of fewer species decreased but recovered immediately. A massive decrease or increase in the population was observed in the systems with 50 and 100 mg•L^-1 AE, and the microcosm compositional balance was changed. Through the analysis of production (P) and respiration (R) using the change in the dissolved oxygen concentration in the microcosm, it was found that the system with 2 mg•L^-1 AE showed no significant difference from the control. However, there were significant differences in the 10 and 25 mg•L^-1 systems. Thus, it can be judged that the AE has an effect when its concentration is over 10 mg•L^-1. In addition, the ecosystem function recovered at the second day after the addition of 10 mg•L^-1 AE and at the seventh day after the addition of 25 mg•L^-1 AE. The ecosystem function was not recovered after 14 days in the systems with 50 and 100 mg•L^-1 AE. These results suggested that the measurements of P and R could be used to evaluate the equivalent population transition. The no-observed-effect concentration of the microcosm in this study has a high correlation with the results determined by the mesocosm test.

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In order to better understand the influence of microtopography on the accumulation of radiocesium in a flood channel, we surveyed a secondary tributary of the Abukuma River, the watershed of which was highly contaminated with radiocesium. Fifteen surface soil samples were collected using 5 cm soil core samplers, and their radiocesium concentration, dry density, and grain size distribution were analyzed. Furthermore, the elevation of the soil sampling points was surveyed using a real-time kinematic global positioning system (RTK-GPS). The radiocesium concentrations ranged from 1.46×10³ to 3.43×10⁴ Bq•kg^-1. Significant positive and negative correlations were observed between elevation and radiocesium concentration, and between elevation and dry density, respectively. In addition, the proportion of the fine particle size fraction positively correlated with elevation. One possible reason for this observation is as follows: A large amount of radiocesium in particulate form runs off into the river from the watershed when the river swells and the flood channel is inundated. The sedimentation/accumulation of suspended particulate materials is facilitated on a riverbed with a higher elevation for the inundated area. On the other land, particulate materials rich in radiocesium tends to be flushed away from a riverbed at a lower elevation owing to a higher chance of contact with river water.

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The denitrification activity in the sediment of rivers flowing into Lake Kasumigaura (the general term for Lake Nishiura, Lake Kitaura, and the Hitachitone River) and the entire lake region was investigated. The distribution characteristics and dependence according to water temperature and nitrate (NO₃^-) of denitrification activity were examined. A high denitrification activity was observed in sediment collected from the river flowing into Lake Kitaura and those collected in the upper parts of the Lake Kitaura. Denitrification activity increased with increasing water temperature or NO₃-N concentration under laboratory conditions, which occurred up to 25°C in the sediment of the lake and up to 40°C in the sediment of the river flowing into Lake Kitaura. The maximum denitrification rate obtained by a Michaelis-Menten kinetic analysis was six times larger in the sediment collected from the river flowing into Lake Kitaura than in the lake sediment. Multiple regression analysis suggested that the dissolved organic carbon (DOC) concentration in interstitial water is a crucial contributory factor to denitrification activity.

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