Structure and function of ecosystems in a river for applying to environmental assessment.

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1) Periodical cross-sectional data of the riverbed was arranged as the data-base. Then geomorphologic change of the riverbed was clarified for past 30 years. The riverbed topography had greatly fluctuated during first 15 years due to sedimentation in dams which were constructed upstream and gravel digging downstream. It has become stable during the second 15 years, and area occupied by vegetation on bars has expanded. 2) Distribution of six species of Grapsidae and five species of Assimineidae has been restricted within reed communities. From an experimental treatment, it was suggested that coexisting mechanism without competitive exclusion existed for two species of Grapsidae. 3) The distribution of macro-benthic species corresponds with environments, such as salinity and sediment size. Biomass or occurrence possibility of the species was predictable in some extent by using multi-regression analysis, logistic-regression analysis and/or quantification theory (type II). 4) Distribution, size and shoot density of Bolboschoenus planiculmi patches was compared temporally and spatially. Patch size in 2001 was greatly decreased from 1999, particularly in populations distributed around river-mouth and uppermost area (ca.14 km from river-mouth). Shoot growth and amount of seed production were small at sites with high salinity and/or coarse-stony sediment. Expansion of the population is mainly owned by root-sucker, while seeds contribute to colonize to new sites. 5) Hydraulic model to simulate dispersal process of Bolboschoenus planiculmi seeds was developed.