The structure of a submerged macrophyte community (vegetation cover, species richness and species composition) and the seasonal changes were investigated at the littoral zone (< 6 m deep) of a calm bay in Northern Basin of Lake Biwa, Japan, where the transparency is high and no waterfowl grazers exist. To evaluate the effect of a small difference in depth profile on the community structure, the vegetation map of 35 m-belt transect (4 m wide) was made monthly at two sites (30 m apart) between March and November 1997. In total, the same 11 species were observed in the two sites, including two alien species, Egeria densa and Elodea nuttallii, and an endemic species, Vallisneria biwaensis. There was no significant difference in species richness in a census between the two sites. The species zonation was unclear in both sites: various mixed species patches were found throughout the study period. There were differences in the growth patterns of five species between the two sites. In a calm and clear-water littoral zone, where there is no disturbance by wave action, a small difference in depth profile can affect the growth patterns of several macrophyte species and then affect the three-dimensional structure of the macrophyte community, which can be a crucial determinant of the habitat structure of small aquatic animals.

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Influence of woody structures on stream morphology and masu salmon habitat was monitored for four years in a suburban stream, in Tobetsu River of Ishikari River system. Three types of woody structures, log dams, wedge dams and deflector logs, were constructed to create deep pools and prevent lateral erosions, and an abandoned secondary channel was also excavated. After log placement, the channel environment such as water depth, mean current velocity and substrate composition was significantly changed. The deep plunge pools were formed on downstream of the wedge dams and rapid current were appeared along deflector logs. The fine sand and gravels were accumulated behind the woody structures. The reference and control sections were set on downstream of the improved sections, and the ecological influence of woody structures was evaluated by comparing the density of released masu salmon (Oncorhynchus masou) among the three sections. The juvenile masu salmons released from eyed embryo were abundant in June in the reference and improved sections where slower current such as secondary channel were created. During the August, the juvenile masu salmons were the most abundant in the reference section, and significant difference was not observed between the improved and control sections. The created pool unit should be important habitat for juvenile masu salmon. However, their abundance was remarkably decreased in October, which may largely due to angling. Although small portion of log exposed above water were rotted and flown away, whole structures were maintained during the four years despite of large flooding. Considering ecological and geomorphological effects, these structures should be introduced as one method to restore stream environment in Japan.

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The consolidated paddy field of Japan will remain extensively in the future and continue to have a crucial influence on regional environment. The purpose of this study is to show an ecological significance of connecting irrigation and drainage canals in a consolidated paddy field, and a practical plan based on a field survey of fish distribution at four sites in a paddy field of Shimodate City, Ibaraki Prefecture. The sampling interval was one week during the period of May 2002 to June 2003. The results clarified the followings: (1) The ten species of fishes caught in the canals can be classified into two groups; fishes living mainly in drainage canals, such as Misgurnus anguillicaudatus (Dojou) and Silurus asotus (Namazu), and those living both in irrigation and drainage canals, such as Gnathopogon elongatus elongatus (Tamoroko). (2) The fishes in the irrigation canals were fewer because they had just found their way into the canals from the source river, while some were found overwintering in the pools of the canals after irrigation was stopped. (3) An effective way of attaining both the conservation of fishes and the high productivity is to employ a shallow farm drain by using under-drain system for sub-surface drainage. The minimized difference in elevation between farm drain and paddy plot allows the first group of fishes to enter the shallow water on the paddy, and the connection of lateral canal and shallow farm drain with water flow allows the second group of fishes to go and come between the irrigation and drainage canals. (4) A simple and effective way of conserving fishes in the irrigation canal is to evacuate them to the farm drain before stopping irrigation.

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The present study was conducted at Hirosato area in Kushiro Mire, where the aim of the nature restoration project by the Ministry of Environment is to restore pasture areas back to original mire. In order to understand the effects of pasture development and river improvement, the groundwater environment was investigated in pasture and surrounding areas. The results revealed that the mire area exhibited a transitional groundwater system from fen to bog. In comparison to the mire area, the average groundwater table in the pasture was lower with higher fluctuations. The pasture was developed along the Kyu-Setsuri River where the groundwater conditions are regulated by the river water level. This was greatly reduced by the diversion of the original course through artificial dikes. Thus the groundwater in the pasture was rapidly drained into the Kyu-Setsuri River. Moreover, Na⁺, Cl^-, Mg²⁺ concentrations of groundwater were significantly lower in the pasture than in the mire area, suggesting a drainage of these nutrients from the pasture through the groundwater. In addition, the Ca²⁺ concentration of the groundwater in the pasture area was twice as high as in the mire area. This can be attributed to remains of calcium carbonate from pasture soil amendment, although about 30 years have passed since the pasture was developed. Furthermore, the river diversion by artificial dikes conducted almost 70 years ago has been influencing the groundwater system and its water quality. In order to restore the original groundwater environment, an increase of the water level of the Kyu-Setsuri River and the treatment of soil amendments are necessary.

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Deteriorations of vegetation and hydrochemical environments were examined in the Hirosato restoration area on the margins of Kushiro Mire, where agricultural land use and a drastic increase of alder forest have influenced the ecosystem for the last past halfcentury. The vegetation was classified into seven types, where the meadow types dominate in the pasture area and the alder or fen types are distributed in the mire area. A following Canonical Correspondence Analysis shows two major results: 1) A vegetation gradient from the mire area to the pasture area corresponding to the obvious lowering of the groundwater level, 2) A vegetation gradient from the fen types to the alder types in correspondence to the lowering of the groundwater level and to the decrease of phosphorous concentration coupled with the increase of nitrogen concentration in soil water. The intense decrease of the groundwater level in the pasture area due to the diversion of the neighboring river has probably changed the mire vegetation into meadow vegetation, indicating that serious deteriorations have been introduced artificially. In the mire area, the distribution of the alder forest was mostly affected by hydrological regime in flooding, yet artificial influences could not be specified.

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The effects of dam operations on river environment variables (water depth, current velocity, emergent plants, substrate composition, and channel morphology) and aquatic animals (fish and benthic macroinvertebrates) were examined over a four-year period using the BACI (Before, After, Control, Impact) design, before (1998) and after (1999-2001) regulation, at control (upstream) and impact (downstream) sites. The Takisato Dam is a 50-m vertical-face by 445-m-wide dam in the Sorachi River, Hokkaido, Japan. While there was a large fluctuation (20-80 m³/sec) in the diel discharge before dam operation, dam closure resulted in a low, uniform discharge (9 m³/sec) in the downstream reach, which resulted in low current velocities (from 0.87 m/sec to 0.17-0.42 m/sec) and affected sediment deposition, bar occurrence, pool-riffle sequence, spreading 0 m/sec shore area (0.7 to 21.5%), and emergent plant growth (length of area: 80.0 m to 243.1 m). These changes in the regulated downstream affected the ninespine stickleback (Pungitius pungitius), which became more abundant downstream (cumulative number for four seasons: 147 to 794 individuals), whereas the numbers of Siberian stone loach (Noemacheilus barbatulustoni) did not differ significantly between the periods before and after dam operation. The change in stickleback abundance was related to the establishment of emergent plants and spread of the slow shore area. The macroinvertebrate communities in the control reach upstream from the Takisato Dam remained taxonomically diverse during the study period, while the regulated reach downstream from the dam showed low diversity. However, the effects of the dam on macroinvertebrates differed among the study units (riffle, thalweg, shore). The conservation of taxonomic diversity in the downstream riffles might be due to maintenance of the area of this flow regime, due to the reduced flow width with the low water discharge and the occurrence of bars.

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The water quality of three Yatsu (Funabashi City in Chiba Prefecture, Japan) having different land uses, were compared. These three Yatsu are the natural type, semi-natural type, and the city-type. (1) The natural type Yatsu is swamps in the bottom of a valley and is surrounded by woods on a plateau and the plateau's slope. (2) The semi-natural type Yatsu is also marsh land in the bottom of a valley, but is surrounded by residential areas and woods where ruderal plant community is locally distributed. (3) The city-type Yatsu is situated in a valley bottom where agricultural fields and residential areas have been developed. The water quality values, such as Cl, TN, TP, and COD, in the natural Yatsu are low in comparison with those in the semi-natural type and city-type Yatsu. The rate of the wooded area around the natural Yatsu was the highest among the three Yatsu. We considered that this area may have a high water-holding capacity, and that an abundant supply of spring water into the river may enhance the water quality. As for the semi-natural type and city-type Yatsu, although the woods occupy a part of the plateau slope, the wastewater from the densely-populated areas upstream of the Yatsu degrade the water quality flowing into this Yatsu. For this reason, even if spring water is supplied from the edge of the Yatsu, the waters in these types of Yatsu have become polluted in comparison with the natural type Yatsu.

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To explore predictors for juvenile fish diversity in floodplain pools during a low-water period, we surveyed the relationship between species richness and geomorphological characteristics of floodplain pools. Ten floodplain pools located in the middle reaches of the Chikuma River were chosen for this study. These pools were formed by a flood in September 2001. We surveyed each pool from October 2001 to July 2002. The data at the end of October was used for analysis of the period after flooding in autumn. The data at the end of March 2002 was used for analysis of the period before next flooding in spring. Species richness of juvenile fish was used as the target variable. Thirteen geomorphological parameters of each floodplain pool were measured: area, perimeter, covered edge length, proportion of covered edge length to total perimeter, maximum depth, average depth, coefficient of variation of depth, substrate diversity, length of pool, width of pool, shape index, distance from stream, and distance from nearest pool. From the results of multiple linear regression analyses, the usefulness of two of thirteen geomorphological predictors, maximum depth and substrate diversity, was demonstrated for the species richness of juvenile fishes after flooding in autumn. At the period before flooding in spring, the usefulness of proportion of covered edge length to total perimeter was shown. Maximum depth is considered to be an indicator of refuge function for juvenile fish from flooding. Substrate diversity is assumed the index of habitat heterogeneity of floodplain pools. It appears that the presence of cover is a requirement of juvenile fish for feeding and refuge. Because the number of pools in this study was small (n = 10), only these three parameters are not useful predictors, but the results of this study suggest the importance of habitat data on maximum depth, substrate diversity, and cover in predicting the function of nursery areas of floodplain pools.

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