Abstract:People reaching adolescence in the middle of the 21st Century are yet to be born, so cannot represent themselves in today's government or court, which decides their welfare. Are they going to face the same environmental challenge as we do today? The chances are that they will be much worse off than we are if they try to repair the damage caused by previous generations, and would inevitably ask why their grandparents did not care about them. The future image of the environment should at least project the quality that we still cherish at present. Ecologically sustainable technology is available for most developments needed for the welfare of people today. What is lacking is the political will to put it in the environmental paradigm. The Ecology and Civil Engineering Society has the unique opportunity to play an important role in the maintenance of healthy ecosystems and biodiversity in harmony with the prosperity and welfare of human beings.

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The fine sediment (<2 mm) effects on percentage of openwork gravel and hydraulic conductivity were studied at 5 small catchments in southwestern Hokkaido, Japan in 1999. We also examined the influence of land use on substrate and hydraulic conductivity. Bed material was sampled using the frozen core technique and hydraulic conductivity was measured using the packer test. The percentage of openwork gravel and hydraulic conductivity decreased with an increase in proportion of fine sediment. Especially the weight percentage of 0.125 to 1.0 mm showed the most negative correlations with these parameters, which indicates that fine sediment filling the interstitial space of gravel bed is responsible to the decreases in these parameters. The stream containing great amount of fine sediment had extensive agricultural development in its catchment area. Thus these substrata differences among the streams were attributable to the surface soil erosion and bank erosion at agricultural fields. Fine sediment progressively accumulated in streambed materials under normal flow conditions, resulting in a decrease in openwork gravels and hydraulic conductivity. Losing the interstitial space of gravel bed will have detrimental effects on benthic fish and invertebrate and other aquatic biota that require these habitats in their life cycles. In order to maintain healthy stream ecosystem, we need to pay more at-tention on the conditions of fine sediment and bed materials, and to seek effective meas-ures to prevent fine sediment production and deposition. The sampling methods applied in this study were proved to be useful to investigate fine sediment and hydraulic conductivity of the bed materials.

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Vegetational and substrate features for vascular plants in the gravelly floodplains of the middle reaches of the Kinu River in Kanto Region were studied with the special interest in the present status of the threatened river-endemics and biological invasions by alien plants. Hierarchical clustering analysis of the presence/absence data of 550-1452 quadrats (0.5m×0.5m) for each of seven study sites along the middle reaches revealed two site groups characterized by the occurrence of distinct species. The river endemics, Anaphalis margaritacea subsp. yedoensis, Artemisia capillaris, and Aster kantoensis predominated the vegetation of the 'upper' five sites located in the upper part of the middle reaches, but were almost totally absent from the two 'lower' sites in the lower middle reaches. The importance index of the river endemics in the sites was negatively correlated with that of alien species represented by Solidago altissima. The current flooding frequency or substrate could not explain the vegetational difference appreciated between upper and lower site groups. In the 'upper sites', an alien, Eragrostis curvula, occurred on the channel shelf together with three river endemics, but hardly coexisted with them within the same quadrat.

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The influence of stream alteration on abundance of benthic fish was examined hierarchically by both reach and channel unit scales, in the Makomanai River, in Sapporo City, northern Japan. Study sections of 2km were settled in bank protection, natural, and channel works courses. The density of Cottus nozawae in the channel works reach was significantly lower than that in the natural and bank protection reaches, whereas the abundance of Noemacheilus barbatulus toni was not different among the three reaches. The density of C. nozawae was positively correlated with the abundance of boulders and loose stones, probably because interstitial spaces on river bed provide refuge and critical habitat components for living and spawning. River bed in the channel works reach was covered by fine sediment and with few loose stones, resulting in reduced interstitial spaces and thus a low density of C nozawae. Within the channel unit, the density of C nozawae in riffles was significantly higher than that in pools, which could be attributed to abundant boulders and loose stones in riffles. A reduced tractive force in the stream caused by check dams and bed stabilization works not only promotes the deposition of pebble-sized stones and the creation of a stable channel bed during a flood, but also traps fine sediment during low-flow periods. These physical mechanisms changes, in association with the channel works, greatly altered the habitat required for C. nozawae.

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Wintering mandarin duck (Aix galericulata) populations and their behavioural adaptations were analyzed in relation to habitat conditions at six dam lakes in the Chugoku district of western Japan, from September 1999 to March 2000. Mandarin duck densities in the dam lakes were significantly correlated with the shoreline bordered by trees. Mandarin duck densities in the dam lakes were also affected by the decrease in the water level. Overhanging branches and dense vegetation along the shoreline provided mandarin ducks with suitable resting cover and shelter. Receding water levels made resting cover unavailable by exposing these sites. The most notable response to a decline in water level was to move into sites with abundant cover such as those found in pools of the inflow rivers. Since it is practically impossible to maintain constant water levels in dam lakes, we suggest that small adjacent impoundments with sufficient cover should be built to attract mandarin ducks to artificial reservoirs.

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In 1980's, there occurred a luxuriant growth of submerged macrophyte, Ranunculus nipponicus (Makino) Nakai var. submersus Hara, in Tagimi River, Hyogo Prefecture, Japan. However, its distributional range has been diminishing recently with the progressive growth of emergent Phragmites japonica Steud. To improve and restore the habitat quality for R. nipponicus, we attempted to conduct several methods of P. japonica removal and evaluated the effectiveness. In the field, we carried out hand-cutting using sickles with various frequencies of cuttings from once to four times from May / June to August 1997. In addition, we compared effects of two removal methods of P. japonica using back-hoe on the regrowth of R. nipponicus; one method that excavated the plant wholly with bottom sediment (excavation method) and the other dug out only plant shoots (shoot removal method). Frequent hand-cuttings with more than three times during growth were effective in reducing the growth of P. japonica, and R. nipponicus recovered noticeably with decreasing P. japonica growth. While the plant cover of R. nipponicus increased after the application of either removal method of P. japonica, earlier recovery of R. nipponicus was observed after the application of shoot removal method than after the application of excavation method.

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In 1999 the Environment Agency, Japan released the red list of brackish and freshwater fishes, in which the number of the Threatened fishes amounted to 110. One of the reasons why many fishes became endangered is implementation of land consolidation project in the paddy field area. This project aimed at reducing labor requirement in farming activities. However, watercourse networks have been disconnected by drop structures in the canals and elevation gap between outlets of paddy fields and drainage canals, which resulted in aggravation of the inhabiting environment of fishes. Therefore, it is eagerly required to reconnect watercourse networks by some artificial measures. In this connection this research was carried out to develop small-scale fishways for restoring damaged condition. In this research two kinds of fishes, Misgurnus anguillicaudatus and Oryzias latipes, were selected as sample fishes. Those are usual freshwater fishes in paddy field area of Japan, and Misgurnus anguillicaudatus represents a demersal fish, whereas Oryzias latipes rep-resents a pelagic fish. Two types of small-scale fishways, named Cascade-M type and Chidori-X type, were developed and laboratory experiments were conducted to exam whether the developed small-scale fishways ensure upward and downward migration of sample fishes or not under the different conditions of inclination and flow rates. The result obtained were as follows; 1) the Cascade-M type fishway enabled upward and downward migration of Misgurnus anguillicaudatus (crawling type and swimming type), 2) Chidori-X type fishway enabled upward and downward migration of Misgurnus anguillicaudatus (swimming type) and Oryzias latipes, 3) Upward migration of Misgurnus anguillicau-datus became active in night time compared to day time, and 4) Oryzias latipes shows stronger rheotaxis compared to Misgurnus anguillicaudatus.

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Continuous hourly measurements of the vertical distribution of water temperature and dissolved oxygen concentration in the impoundment of the Nagara Rivermouth Barrage showed that temporary thermal stratification developed under fine weather conditions with light wind and that it obstructed vertical mixing of the water, which in turn, might lead to an oxygen deficit in the bottom water. The temporary thermal stratification was maintained for a few days. Diurnal minimum oxygen concentration in the bottom water was recorded at twilight, and vertical mixing caused by cooling of the surface water at midnight recovered the oxygen deficit. However, complete mixing including the bottom water did not occur every day. Judging from the rapid oxygen consumption rate by the water column and sediment, the temporary thermal stratification could cause frequent oxygen deficit in the impoundment in summer.

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