The review paper by Karr & Rossano (2001) and the opinion paper by Shimatani (2001) were edited for the mini-features entitled "What is river health?" in this volume. The concept of river health will be of use for making a common understanding on the ideal river image particularly in Japan where the most rivers have been altered artificially through the land use history. The method of multimetric index on the biological integrity applied to Japanese rivers seems to be effective for evaluating present river conditions under a wide range of human impacts. Research perspectives required in the next step may be development of methods for finding out causal relations in substance, which is necessary for conducting adaptive management in river ecosystems.

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Revealing, and indeed exacerbating, the globe's present water crisis is the failing ecological health of rivers. Those who would protect and restore river health can learn important lessons from humanity's continual fight against disease. We discuss four of these lessons, including their applicability to river issues: (1) recognize and respond to changing challenges, (2) avoid unintended consequences, (3) employ both cure and prevention, and (4) take a systematic approach. The overarching message from human health science is that we need to view human actions and their consequences for river health in an integrated way. In an effort to construct such a view of river degradation, we suggest that human actions jeopardize river health in five major ways : (1) altering physical habitat, (2) modifying seasonal flow of water, (3) changing the food base of the system, (4) changing interactions within the river biota, and (5) polluting with chemical contaminants. Another key lesson of human health science is the need for a commonly understood and robust measure of river condition, or health. Biological monitoring and assessment using the index of biological integrity for Japanese streams (IBI-J) provides a rigorous measure of river condition as well as guidance on the causes of river degradation. Examples of the index's use in Japan illustrate the importance of various stressors responsible for degradation, such as amount and types of effluent, proximity of dams and other structural alterations, and riparian condition. They also show the dangers of management driven solely by narrow water quality measures such as biochemical oxygen demand (BOD). We conclude that biological measures are important because they provide a strong scientific framework to inform the largely cultural process of deciding how humans treat rivers.

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In this report, I discussed what a healthy ecosystem means from my own experience. I think that ecosystem health is determined by the conditions under which "the organisms that should be found in that ecosystem can properly survive". Then, what sorts of species, species assemblages, local populations and individuals are those "that should be found there"? Does "properly survive" mean that the standing crop is bigger than certain size? Can they complete the life cycle? Don't they become extinct in the course of natural fluctuations in abundance? In order to answer those questions, we should consider with historical changes of the natural environment and interactions between people and water environments. It is clear that evaluation and restoration of "healthy ecosystem" should be based on mutual relationships between nature and human beings.

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"Naiko" is a Japanese term to indicate small and shallow satellite lakes around Lake Biwa, being usually connected to the lake by channels. Several naiko were surveyed on their ecological functions especially for native fishes, and were compared to clarify factors causing the change of fish communities in naiko. In Ozubukuro-naiko, Moriyama City, fishes endemic to Lake Biwa dominated in the fish community in 1960's, became less abundant than other native fish in 1970's, and were replaced by the alien species Lepomis macrochirus until 1998. Similar faunal changes occurred also in other naiko except Katata-naiko which is still inhabited by abundant native fishes in spite of artificial alternation of its coast. Water level in naiko is probably an important factor relating to the drastic changes in fish fauna in the most naiko. Controlled low water level during the flood season caused drying-up of vegetated area (emerged plant zone) in the shallow coast, and possibly diminished ecological functions of the zone as spawning ground and habitat for native fishes. Thus, the native fish fauna is plausibly sacrificed by two factors, i. e., an invasion of alien species (L. macrochirus) and the unnatural water level during the rainy season for flood control. These two factors should be primarily taken in account in the future plan for natural conservation of naiko. Further investigation on the exceptional case in Katata-naiko is required for elucidating factors enabling native fishes to re-inhabit other naiko.

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Nymphoides peltata is an endangered floating-leaved plant species. Lake Kasumigaura once contained one of the largest populations of the plant in Japan. However, recent monitoring on the metapopulation status revealed a rapid dwindling of this species in the lake. During 1996-2000, the number of the local populations decreased from 34 to 14 and total area occupied by the plant decreased from 99, 497 to 10, 081m². In 1996, five local populations were constituted from both long- and short-styled morphs of the heterostylous floral polymorphism, however, four of them have been extinct by 2000. Although more or less seeds were produced in all nine local populations examined in 1994 and 1995, only negligible seed set was recorded in 2000 except a local population, in which a considerable amount of seeds were produced. Although some seedlings were observed to emerge on the beach along the shoreline near some remaining local populations, all 1, 768 seedlings marked in 1999 spring failed to establish. Furthermore, we could find no juvenile plants established in the study area covering approximately 2 ha. These results suggest that during recent years recruitment has been unsuccessful in the lake metapopulation of N. peltata. The smaller number of seedlings emerged in 2000 than in previous years may be caused by decrease in seed supply due to the extinction of the local populations. It is feared that futile germination will exhaust the soil seed bank of the species in near future.

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The Ecology and Civil Engineering Society held a field workshop on natureoriented river works implemented in three river sections in and around Sapporo, Japan on 23 and 24 Sep. 2000. The participants made field reconnaissance and evaluated the achievement of the river training works in consideration of environmental restoration and riparian management under different developmental conditions. This paper reports the major suggestions made in the workshop and explicates the importance of scoping in evaluation process in order to have effective discussion not only from engineering or technical viewpoints but also from social and historical background of the river sections.

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Effects of illuminance and tree coverage on the density of adult Genji firefly, Luciola cruciata, were surveyed along the Biwako Canal in Kyoto City, Japan, in 1984 and 2000. The bright illuminance decreased the density of adults in 1984, while the dense tree coverage rather than the bright illuminance decreased the density of adults in 2000 when trees along the canal expanded their branches. Boundaries of high and low densities of adult fireflies were observed at the places with bright illuminance of 0.05-0.2 lux and dense tree coverage of 0.5-0.6.

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Annual changes in the floodplain vegetation were monitored at the back water of Miharu Dam, in the Ohtakine River, Fukushima Prefecture, Japan, for 3 years after the first filling of water in the dam. Results showed clear reduction in the area of grassland vegetation such as Pueraria lobata community, Miscanthus sinensis community and Artemisia princeps community during the three years, whereas the area of Salix community, Humulus japonicus community and the area of natural bare land increased. The sedimentation by the first filling of water and the disturbance by the flood flow were considered as the plausible factors determining the change of vegetation types. The results indicated that the inundation for more than 70 days turned the original grassland vegetation into the natural bare land and after that invaded the annual herb vegetation.

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Plausible causes of summer oxygen deficit in the lower reaches of the Nagara Rivermouth Barrage were examined using the continuous data of dissolved oxygen, chlorophyll a and salinity recorded by the Japanese Ministry of Construction. The following three causes were detected : i.e., 1) increase in a night oxygen consumption by a large biomass of algal plankton, 2)rise of hypoxic water from Ise Bay at spring tide, and 3) increase in magnitude of stratification at neap tide which hinders vertical mixing of water. The last cause accounted for the severe oxygen deficit frequently occurred after the barrage construction since it began a few days after neap tide and was maintained until the next spring tide or flood. Both annual changes in a total duration of oxygen deficit in the Nagara River and a result of comparison with the Kiso River indicated that the neap tide effect on the oxygen deficit was enhanced by operation of the Rivermouth Barrage.

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An investigation was carried out on the extent of damage caused by typhoon 7 on the subalpine coniferous forest in Mt. Norikuradake, central Japan, in 1998. It has been confirmed that sizable amounts of trees were found fallen, on the northwest slope of Nekodake (2200-2350m), particularly at 3 spots of 0.9 ha, 1.1 ha and 2.6 ha. According to the belt-transect survey, many canopies of coniferous trees such as Abies mariesü, A. veitchü and Picea jezoensis var. hondoensis, were blown off by the typhoon. However, damage on saplings was slight. Still, many trees were uprooted by the strong southwest wind and resultantly lay perpendicularly to the direction of the slope. As for the forest stands covered with Sasa senanensis, it is better to leave them as they are because it is precisely on these sites that the fallen trees are able to flourish and regenerate themselves.

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