Several types of distributed-type model are commonly used for analysis of accumulation and washoff behavior of pollutants in the sewer during a rainy day. We try to analyze accumulation and washoff behavior of micro-pollutants using the distributed-type model. The micro-pollutants analyzed in this study was benzo(a)pyrene. An automobile exhaust gas is the main source of benzo(a)pyrene. The distributed-type model was useful for understanding of accumulation and washoff behavior of benzo(a)pyrene. In particular, the estimation of the accumulation behavior along the roadside was good. However, there is a limit in using the model for planning an effective measures against water pollution of benzo(a)pyrene. We need to develop an original distributed-type model that can lead to the realization of the effective measures.

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The kinetics of the formation and dissociation of the Fe(III)-NOM (natural organic matter) complex in coastal waters was investigated using the competitive ligand method. The rate constants for the formation and dissociation of the Fe(III)-NOM complex were determined by fitting a model to observed data. The iron-binding capacity of NOM, which is required for the determination of the rate constants, was initially measured by the ion exchange method. The rate constants of the formation of the Fe(III)-NOM complex ranged from 2.6×10⁶ to 7.3×10⁶ M^-1·s^-1. A discrete ligand model for the dissociation kinetics of the Fe(III)-NOM complex yielded rate constants from 6.9×10^-4 to 2.0×10^-3 s^-1 for weak-binding ligands and from 1.6×10^-5 to 8.3×10^-5 s^-1 for strong-binding ligands, respectively. The kinetics of the Fe(III)-NOM complex in coastal water was then predicted using the estimated rate constants. The model prediction showed that the dissociation of the complexes is relatively slow with a half-life longer than 120 hr. The adsorption peak ratios of oxygen-containing functional groups of NOM calculated from FTIR spectra showed good correlation with both the iron-binding capacity and the rate constants, implying that the ratio is a useful factor for assessing the kinetics of organically complexed iron in coastal water.

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The presence and populations of freshwater fishes and the revetment conditions in creeks were investigated at 48 sampling sites around the Sea of Ariake in northwestern Kyushu, Japan. Each creek studied in this survey was classified into one of the three following types in terms of revetment conditions: Type-1, the creeks have earthen revetments except when crossing roads; Type-2, although there are concrete revetments in the creeks, these revetments are short, and agricultural water flows over the revetments and reaches bank vegetations or earthen banks except during the agricultural off-season; Type-3, there are high concrete revetments around the creeks, and agricultural water does not flow over the revetments during any season. The amount of Hemigrammocypris rasborella present was affected by the revetment conditions, and the amount present in Type-3 was significantly lower than those in Type-1 and Type-2. The populations of H. rasborella, Rhodeus ocellatus kurumeus, and Pseudorasbora parva were affected by the revetment conditions. For H. rasborella and R. ocellatus kurumeus, the populations in Type-3 were significantly lower than those in Type-1 and Type-2. For P. parva, the population in Type-3 was significantly lower than that in Type-1.

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Recently, nitrate-nitrogen (NO₃-N) pollution in groundwater was identified as a serious problem in Gunma prefecture. The rate of satisfying the environmental quality standard(EQS) for NO₃-N concentration in Gunma prefecture was lowest in Japan from 2000 to 2004. However, a significant decrease in NO₃-N concentration was observed in 2005. Therefore, the factors contributing to the decrease were statistically examined. The results suggest that the area of dry field, livestock head count, and agricultural population significantly contributed to the decrease in NO₃-N concentration. The enforcement of the Law on Promoting Proper Management and Use of Livestock Excreta might reduce NO₃-N discharge into groundwater.

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