Hot-spring water and mine effluent flow into the Toyohira River, which runs through the center of Sapporo, Japan. In this river, the concentration of arsenic in hot-spring water changes according to the flow regime. This phenomenon must be addressed in water quality management. It was found that arsenic washed out during floods is a non-point-source (diffuse) pollutant. According to the arsenic washed load balance of the river basin as a whole, approximately 20% of the arsenic supplied to the Toyohira River is suspended and sediments in the region downstream of Jozankei. The flow-regime-dependent difference in the washout component is attributed to arsenic accumulation in bottom mud during low-water-level periods. The arsenic concentration in bottom mud is high in the region downstream of Jozankei, a hot-spring resort. Arsenic accumulated in large amounts in the dam is stably supplied to the river. During floods, however, the agitation of bottom mud enhances the washout of suspended arsenic, and the concentration of suspended arsenic washed out increases.

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To determine the geographical distribution of dissolved inorganic phosphate (DIP) concentrations in stream water in Japan, 1,244 water samples were collected nationwide from watersheds unpolluted by any anthropogenic sources. DIP concentrations were logarithmically normally distributed, and showed a wide range from below the minimum limit of detection (1.5 μg · l^-1) to 116 μg · l^-1, with a median of 6.6 μg · l^-1. The streams with higher concentrations (> 10 μg · l^-1) were predominantly in the northern part of Ibaraki, the western parts of Saitama and Tokyo, the region from Ishikawa to Kyoto, and around the Shikoku and Kyusyu mountains. Those with lower concentrations (< 4 μg · l^-1) were predominantly in central Hokkaido, Yamagata, the northern part of Gunma and the western part of the Chugoku district. A significant difference (P < 0.001) in DIP concentration was found among subsurface geologies. Watersheds with underlying sedimentary rocks had higher DIP concentrations in their stream water than those with underlying igneous and metamorphic rocks. Among sedimentary rocks, higher DIP concentrations were found in Paleozoic rocks than in Mesozoic and Cenozoic rocks. In igneous rocks, intermediate rocks (andesite) had higher DIP concentrations than acidic rocks (rhyorite and granite). The differences in DIP concentration among various types of igneous and metamorphic rocks coincided with the differences in phosphorus content obtained from the Geochemical Atlas of Japan. In other substances, DIP concentration positively correlated with SiO₂ concentration except in Paleozoic and Mesozoic sedimentary rocks. These results indicate that DIP concentrations in stream water are partly controlled by phosphorus content and the mineral weathering of rock or soil.

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"Law on promoting proper management and use of livestock excreta" was implemented in November 2004 prohibiting the disposal of animal wastes using unlined storage ponds. To examine the influence of the enforcement of this law, a two-year study of water quality and hydrology was conducted on a drainage canal of an area with intensive livestock production. During the irrigation period, the amount of runoff water was 337 mm, the T-P concentration decreased from 3.0 to 1.7 mg · l^-1, and the T-P load decreased from 3.2 to 1.9 kg · d^-1. During the nonirrigation period, the amount of runoff water was 548 mm, the NH₄-N concentration decreased from 1.9 to 1.1 mg · l^-1, the T-P concentration decreased from 2.9 to 1.8 mg · l^-1, the NH₄-N load decreased from 6.3 to 1.9 kg · d^-1, and the T-P load decreased from 13.1 to 2.6 kg · d^-1. In addition, the number of days that irregular T-N, NH₄-N and T-P concentrations were observed decreased. These results suggest that the amount of effluent containing the NH₄-N and T-P from animal wastes decreased.

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Lead isotopic analyses of road sediments and traffic-related substances, such as asphalt, traffic paint, automobile tires, wheel balance weights and automobile exhaust, have been carried out to determine the sources of lead pollution in road runoff. Smaller particles in road sediments contained a higher lead concentration and showed the same lead isotopic composition as road runoff; therefore, lead in road runoff was mainly attributed to minute particles (<53 μm) in the sediments. Because yellow traffic paint was found to be rich in lead and showed a similar lead isotopic composition to road runoff, it would be considered as the source of lead pollution on the condition that it was used near the site. White traffic paint and automobile tires did not contribute to lead runoff because of their low lead concentration and different lead isotopic composition. The lead isotope ratios in wheel balance weights fell within almost the same range as that of road runoff; therefore, wheel weights were determined as a major source of traffic-related lead runoff.

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On the basis of field surveys of stormwater runoff conducted in urban roadways, stormwater runoff processes were characterized to determine their loading effects on the receiving water body. The main results are as follows: (1) In stormwater runoff, 82-96 % of the total rainfall amount was discharged owing to hydrologic abstraction. (2) The percentages of the particulate portion were 96, 60-70 and 26 % for phosphorus, organic matter (chemical oxygen demand and total organic carbon), and nitrogen, respectively. (3) The pollution load carried by automobiles and the remaining load from previous rainfall affect stormwater runoff. (4) A cumulative flow of 2-5mm, averagely 3.5mm, was considered to be the most effective loading cutoff in the first flush runoff. (5) Total stormwater runoff could be decreased by 50 % in a year using these first flush runoff cutoffs.

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The runoff behavior characteristics of pesticides were analyzed every three days and five flooding-stage observations were carried out for five months at three traverse points in the Yodo River. The differences in pesticide concentretion among the three traverse points were particularly seen during the flooding-stages. The total runoff loads of pesticides for about five months from late April to late September were larger according to both the regular and flooding-stage observations than according to only the regular observation. The total runoff loads of many pesticides in 2005, which was a dry year, were smaller than in 2004, which was a rainy year and 2001, which had a average amount of rain among the three regular observations. Most pesticide loads estimated using monthly and bimonthly observations in 2005 were smaller than those estimated using observations every three days during the observation period. Those estimated using semimonthly and monthly observations were 0.5- to 2.0-fold those estimated every three days. The change in the DI of a tap water quality standard was found to be less than 0.37 in 2005 according to the every-three-day-observation data and the five-flooding-stage-observation data.

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The concentrations and loadings of herbicides were investigated in three paddy field basins (4.7, 4.7 and 9.3 ha) from May to August 2002. The herbicide losses from the basins determined from cumulative load and application amount gathered by the questionnaire method were estimated to be 1.6% and 26% for Bromobutide, 8.9∼27% for Cafenstrol, 0.1% for Dimepiperate, 1.1∼2.0% for Mefenacet, 10.2∼25% for Simetryn, 0.9% and 14% for Thenylchlor, and 0.1∼1.6% for Thiobencarb. One of the important factors attributed to the differences in herbicide loss among the basins was water discharge from the basins. To generalize them, specific herbicide losses were calculated from herbicide losses and the height of daily dry weather flow. The specific herbicide losses suggested that transport with percolated water is the main factor for Cafenstrol and Simetryn losses, although other factors such as interaction with soil and degradation in soil may have also contribute to Bromotutide, Mefenacet, Thenylchlor and Thiobencarb losses from the paddy field basins.

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The characteristics of NO₃^--N cumulative specific load during stormy flood events were investigated in a forested, mountainous headwater catchment of Shimanto River basin, located at the southwestern part of Shikoku Island, Japan. The vegetation in the catchment was a natural forest. Seventeen flood events were investigated. The intercept of the regression line between the cumulative specific discharge and the NO₃^--N cumulative specific load in term A (from the end of the rainy season in July through September) was significantly different from that in term B (other than term A) (p < 0.01). The slope of the line was smaller (approximately 0.8) than those in previous studies (greater than 1). NO₃^--N in surface soil (0 to 5 cm depth from the surface) was most abundant in August, and less in winter and spring than in summer. It was considered that NO₃^--N in surface soil increased owing to active mineralization and nitrification in summer. These results indicated that the NO₃^--N cumulative specific load under the same cumulative specific discharge conditions tends to increase in summer, and that the increase rate of the NO₃^--N cumulative specific load relative to cumulative specific discharge tends to decrease in the studied catchment.

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Leaching tests on road dust are necessary to clarify the transport of heavy metals in water cycle in urban areas. In this study, leaching tests were conducted to evaluate the leaching characteristics of heavy metals from road dust in a heavy-traffic area and in a residential area. The results show that the leached concentrations of Cr, Fe, Ni and Cu from road dust in the heavy-traffic area were significantly higher than those from road dust in the residential area. Additionally, the leached fractions of Cr from road dust in the heavy-traffic area were also significantly larger than those from road dust in the residential area. The leached fractions of Cr from road dust seem to be derived from traffic sign markers such as yellow paint. Leaching tests on size-fractionated road dust revealed that the leached concentrations of Al, Cr, Cu, As and Cd were higher in their fine fractions (< 106 μm), whereas the leached concentrations of Mn, Zn and Pb were higher in their coarse fractions (106∼2000 μm). There were different tendencies in leaching characteristics from fine to coarse fractions among the heavy metals.

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In this study, a method of using high-dissolved-oxygen water to purify bottom sediment in a closed water body was confirmed to be effective. A high-rate, high-efficiency oxygen dissolver was developed and a method of producing high-dissolved-oxygen water was discussed. In addition, the prevention of phosphorus release from the bottom sediment using high-dissolved-oxygen water was also studied. A pilot-scale oxygen dissolver was developed and an on-site study was carried out at two dam reservoirs in Yamaguchi, Japan. As results, it was possible to spread the high-dissolved-oxygen water across the bottom layer without any diffusion in the upper direction. Furthermore, the presence of high-dissolved-oxygen water could prevent the release of phosphorus from the bottom sediment. This study revealed the effectiveness of high-dissolved-oxygen water for the improvement in the water quality of a closed water body.

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The authors measured the nitrate concentration of river water from a catchment basin of the collective tea fields in the Makinohara plateau in Shizuoka prefecture, from June 2002 to May 2003. About 1,000 kg · ha^-1 · y^-1 of nitrogen fertilizer has been used in the tea fields for about 30 years. The annual average NO₃-N concentration and pH were 24.4 mg · l^-1 and 4.9, respectively. NO₃-N concentration decreased as a result of a comparatively small amount of precipitation, and repeated. The total annual nitrogen outtlow from the tea fields was 428 kg · ha^-1 · y^-1. The ratio of nitrogen load to the amount of applied nitrogen fertilizer was 79.2 %. NO₃-N load was affected by discharge from the tea fields.

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Typhoon No.21 hit the Japan Archipelago in September 2004, causing landslides and floods in Mie Prefecture. Water muddiness of the in the Miyagawa River persisted for three months. This water turbidity caused concern regarding damage to the ecosystem of the river, the coastal area, and fishery products such as seaweed. Under this situation, we surveyed water quality in the Miyagawa River. Water samples from ten sites were collected six times under the turbid condition, and examined of their water quality. As a result, the COD (chemical oxygen demand), SS (suspended solid) concentration and T-P (total phosphorus) concentration were higher values than those observed under normal conditions. However, the transparency was lower than that under normal conditions. The total nitrogen concentration was similar to that under normal conditions. There were large amounts of phosphorus contained in the particles, although the concentration of nitrogen in the particles was low. There was a significant relationship between the reciprocal of transparency and other pollutant factors such as COD and T-P concentration. Because the handling of the transparency meter is easy, measuring the transparency of river water is a useful method of estimating water pollution in emergencies.

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To examine the temporal variation in the amount of roof deposit, which is one of the main non-point sources in urban areas, and its association with dry fallout, a continuous monitoring of roof-deposit environments is performed by a modeled-stormwater sampling (MOS) technique, by which one can easily obtain deposits from a model roof under simulated rainy conditions. The results indicate that the amount of sediment on the roof ( SS_roof ) decreases rapidly just after a rainfall and then increases gradually until the next rainfall occurs. The temporal variation in SS_roof  is similar to that in the accumulated value of the deposition rate of SPM (suspended particulate matter), ∫D_SPM dt. The correlation coefficient between SS_roof  and ∫D_SPM dt is 0.839, showing that the mutual relationship between them is sufficiently estimated. Note that to obtain an accurate evaluation of roof-deposit load, it is necessary to use ∫D_SPM dt, in which the influences of antecedent fine weather conditions and dry fallout are explicitly incorporated.

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