Firefly (Luciola cruciata) is a popular and historically important insect in Yamaguchi prefecture. In the midstream of Fushino river, we could see a lot of fireflies four or five decades ago but now we cannot see not only the fireflies but also marsh snails (Semisulcospira libertina), the only feed for the firefly. Although the local government is planning to restore the firefly habitat in Fushino River, there are a lot of difficulties to accomplish the plan because they need to consider various firefly habitat requirements which spread from stream, ground and even to the sky together with snail habitat requirements which have not known well enough. To boost the efficiency of the restoration work, we build habitat suitability criteria (HSC) of surrounding environments (distance to paddy field, woods, slopes and city zones) and instream environments (velocity, depth and channel index) for the firefly and the snail. A physical habitat model with the HSC reveals that the midstream of Fushino River is not a good habitat for the firefly in current situation. Based on this information, an artificial stream for firefly is designed along the river and the instream habitat condition of the stream is evaluated using PHABSIM (Physical Habitat Simulation) software. Based on the calculated result, minor stream improvement works and effective flow management procedure are proposed. Post construction monitoring shows the firefly larva landing points show good accordance with the good habitat zones predicted by PHABSIM.

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Exotic largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus), both of which were introduced from North America, are now widespread throughout Japan, often dominating in irrigation ponds and reservoirs. The rapid expansions of their distributions beyond watersheds are obviously due to human agency; however, their expansions within a watershed may be, more or less, attributable to natural dispersal, which has rarely been investigated. This study presents circumstantial evidence of their dispersal from artificial ponds to irrigation ditches. In the Shigenobu River watershed (Ehime Prefecture, southwestern Japan), 21 study sites were established in river pools and irrigation ditches associated with 6 ponds inhabited by the two species. In each site, population densities of both species were monitored from the spring of 2002 to the autumn of 2003. The monitoring showed that (1) both species attained high densities (maximum density, 8.0 and 12.1 individuals/m² for largemouth bass and bluegill, respectively) in ditches just downstream of ponds in summer, (2) most of them were small in size (<10 cm in fork length), (3) at every study site, their densities were temporarily variable and zero densities were often recorded (i.e., neither of the two species was found), and (4) the two exotic species comprised considerable percentages of fish assemblages in the ditches (41.9 % in the sum total of estimated number of fishes). These results, in combination with a fact that most study ditches had potential barriers to upstream migration (i.e., falls of 0.8-2m in height), suggest that individuals of both species in the ditches were immigrants from the ponds.

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Leaf pack distribution was investigated in 270-m interval of a second-order forest stream, the Yanase River. The dominant tree type was Keyaki (Zelkova serrata). Leaf pack sampling was conducted in pools and riffles. At the first, the leaf pack distribution area was estimated, and then sample was taken by hand and fishing net in the pools. In the riffles, 1.0-m-x-1.0-m quadrates were located first, and then the leaf pack was sampled. All leaf pack was sorted into leaves and branches. At the time of leaf pack sampling, physical stream variables were also measured. The variables were water depth and current velocity. In the riffles, stone width, stone height and stone distance were measured. The collected leaf pack was categorized by their accumulation types: LS (Leaf retained by Stone), SLP (Settled Leaf in Pool), SLPi (Settled Leaf in Pool at inner bend), SLPo (Settled Leaf in Pool at outer bend) and DD (Debris Dam). The accumulated leaf pack amounts at each leaf pack type were compared with the measured physical stream variables, and their correlation was tested. From the results, for leaf pack accumulation in riffles, stones projecting above water surface and their arrangements influence to entrap or release leaf litters in transport. In pools, leaf pack accumulation is assumed to occur at high stream flow where there are sufficient pool spaces. At stream meandering points, leaf pack accumulation is influenced by production of a secondary flow, and the leaf pack has a tendency to be pushed over to the inner side of the bend. Finally, debris dams contribute greatly to accumulate leaf packs even when the number of the dam is few. LS was the largest in leaf pack density and the stones in the riffles were the most retentive structures.

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Watarase Reservoir, located in Kanto plain in the central part of Japan, has been suffering from the problem of moldy smell in drinking water supplied from the reservoir since its commencement in 1990. The cause of the moldy smell is 2-MIB (2-methylisoborneol) produced by Phormidium sp. In order to reduce Phormidium taxa, we have conducted field experiments to test the effectiveness of water level drawdown and bed desiccation of the reservoir during early spring. The 9-years trial indicated that the reservoir bed exposure to the air and the sunlight reduced the annual maximum concentration of 2-MIB. The bottom desiccation has an effect of tormenting Phormidium taxa. While the synchronized observations of algal biomass and 2-MIB concentration suggested that the production of 2-MIB extremely decreased if the season of Phormidium growth was late such as after August. The method of water level control could make an effective measure against 2-MIB problem of drinking water caused by bluegreen algae.

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This study was intended to elucidate effects of atmospheric exposure on stream-side for biomass of periphytic algal communities, as estimated with chlorophyll a. Melosira varians-dominated communities, developed on artificial substrates, were investigated in an experimental stream. No distinct difference was found in the maximum reduction rate of the biomass between algal communities exposed to the atmosphere under sunny weather for five hours and those exposed for 24h or 48h. Throughout the seven days after reinundation, the biomass of the communities after atmospheric exposure on stream-side under sunny weather for five hours was maintained at a lower level than before exposure to the atmosphere. In contrast, regarding communities exposed to artificial discharge with no bed-motion, although the biomass decreased after three days, it was greater after seven days than the level before discharge. The effects of controlling the biomass of algal communities were maintained longer after exposure to the atmosphere, as indicated by changes in the ash dry mass that were caused by adherence of the dried periphyton mat on the substrates. That adherence results from exposure to the atmosphere, but the layer gradually peels off in the water current. With exposure of the communities to the atmosphere under cloudy weather for five hours, a slight difference in the biomass was apparent throughout the seven days before and the seven days after exposure. Differences of changes in the biomass of algae in the current in sunny and cloudy conditions indicate that the effects of controlling the biomass differ depending on the weather at the time of atmospheric exposure.

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The spatial pattern of species composition in weed communities and the effects of water flow connection were studied in paddy fields on the bottom of the small valley, in Tochigi Prefecture, central Japan. In fall, the species composition and water content were investigated a series of 4-m² quadrat in 47 paddy fields. Eighty-six quadrats divided into two clusters and 13 subclusters from species composition using the cluster analysis. By using the results of cluster analysis of the species composition, 86 quadrats were divided into 2 clusters and 13 subclusters. The 2 clusters corresponded to the difference in water content. Paddy fields integrated into the same subcluster were observed to hold together spatially. The combination of all paddy fields showed a negative correlation between the similarity index and the horizontal distance. The correlation coefficient values, which were calculated for the similarity index and 3 types of distances (horizontal distance, 3-dimensional distance, and 3-dimensional distance along the path of water flow) in the quadrat at the lowest elevation, were the highest for the distance along the path of water flow. The similarity index between two adjacent paddy fields with a water inlet was significantly higher than that of adjacent paddy fields without one. Six species had a significantly higher presence in a quadrat that was connected by a water inlet to a field at a higher elevation. It was suggested that factors related to irrigation such as the distance of water flow or a water inlet between paddy fields affected the spatial patterns of species composition in weed communities due to seed dispersal by water.

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Japanese giant salamander, Andrias japonicus inhabits in the Maefukase and Kawakami Rivers of the Maefukase River system in Iga City, Mie Prefecture, where construction of a dam is planned. Disjunction of local populations and subsequent reduction of each population within the river system may induce loss of genetic diversity and ultimate extinction in each local population. In order to assess current status of genetic diversity among salamanders in this river system, we surveyed nuclear DNA diversity through AFLP method. The result indicates that the method is effective in differentiating salamanders of this and adjacent river systems from congeneric species and conspecific populations from remote rivers that have been differentiated by mitochondrial DNA. However, this method could not detect presence of specific genetic groups among salamanders from the Maefukase and adjacent river systems. Genetic structure in each local population of salamanders within this river system is judged to be not fixed. On the other hand, frequent gene flow among local populations is not surmised, either. Genetic structure in this river system seems to be complex, being strongly affected by forced movement of salamanders by floods and by artificial relocation. For the discussion of local population disjunction, we need further basic data using more sophisticated methods.

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Dam lakes are often utilized by wintering ducks in Japan. Compared with natural lakes, most ducks which utilize dam lakes are dabbling ducks, and diving ducks such as pochards, Aythya ferina (that consume aquatic plants or benthos) are relatively rare. It is suggested that this is due to the feeding habits of Aythya ducks, which dive and forage in shallow waters, as most dam lakes lack shallow waters suitable for the feeding of Aythya ducks. However, there are a few dam lakes where many pochards winter in the Tohoku district of Japan. These dam lakes are constructed on river terraces that contain relatively large areas of shallow water. In the present study, we investigated the relationship between shallow water area and pochards density in 9 dam lakes in the Tohoku district. We found that the density of pochards was positively correlated with the shallow water (<5m) area and variations in density were positively correlated with variations in the shallow water area. In contrast, we did not find such correlations in dabbling ducks; mallards Anas platyrhynchos, spotbill ducks A. poecilorhyncha, and teals A. crecca. These findings indicate that the density of pochards in dam lakes is strongly affected by the lakes’ shallow water area and this is due to the feeding habits of pochards.

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We compared nitrogen uptake by riparian plants at various distances from the river channel along the Chikuma River, using a stable isotope analysis. Nitrogen stable isotope ratios δ¹⁵N of plants in the lower floodplains were relatively high, and increased from upper to lower reach, suggesting use of nitrogen from the river water, which was affected by human activities in the watersheds. On the other hand, δ¹⁵N of plants in the higher floodplains were relatively low, and not statistically different among sites, indicating no more use of nitrogen derived from the river water. A nitrogen fixing plant, black locust (Robinia pseudoacacia) forms riparian forests in the higher floodplains, where we observed a 42-fold increase in nitrate concentration of soil compared with that in the lower floodplains. Black locust forests may bring reactive nitrogen into the river ecosystem. The higher floodplains were different from the lower ones not only in physical conditions such as deposition and hydrology but also in nitrogen uptake by plants, and they had little relationships with river water in nutrient uptake.

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I have briefly reviewed the research progress made in practical environmental evaluation models for lakes and reservoirs since 1970’s and summarized the relation between practical demand and model modification. Vertically one dimensional models for the prediction of water temperature in reservoirs were developed during the first stage of the model development. Practical demand for the appropriate management of dam reservoirs stimulated the development of these models. Also developed were turbidity models for reservoirs during this stage. As ecological modeling, eutrophication models were developed to assess the water quality control plan. Since practical models must be operated to predict for the period of years, complexity of the models have been determined by the capacity of computer at the time of development. Thus, though model structure of eutrophication models have been similar, division of components have been progressed following the development of computers. Recent practical water quality models for lakes and reservoirs contain a number of parameters of which values must be determined arbitrarily. The number of these parameters are increasing. I pointed out it is important to develop the appropriate method to determine parameter values during model calibration to take advantage of the recent detailed models. Also, acquisition of precise field data for input data is important. For the future direction of practical environmental models for lakes and reservoirs, I emphasized the necessity of the development of the structurally dynamic ecological model to deal with the environmental change of large degree, coupling of water quality model and sediment model, and the development of habitat model to better assess the environmental impact of human activities.

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