The net production rates of molluscan shellfishes were estimated in a high water temperature season at the tidal flat of Wakagawa estuary, and its role in nitrogen cycle was discussed. The biomass of macrobenthos was 2,648kgN and 90.0% of that was composed of 9 species of molluscan shellfish, including Ruditapes philippinarum and Crassostrea gigas. The net production rate of the dominant species was 23.9kgN · day^-1 and 93.0% of that was composed of 2 species, namely, R. philippinarum and Umbonium moniliferum. Moreover, the mortality rate of the dominant species was 10.2kgN · day^-1, and 86.8% of that was composed of the 2 species. The mortality rate reached 43.4% of the net production rate in the dominant species. This result indicates that one-half of production by the dominant species is consumed by carnivores, scavengers and/or decomposers. We concluded that the molluscan shellfish, particularly R. philippinarum and U. moniliferum, play important roles to link from allochthonous seston and benthic algal production to higher trophic levels, such as predators and scavengers in the tidal flat of Wakagawa estuary.

View full abstract

Here, we discuss the effects of individuality and the distribution pattern of riparian wetlands on longitudinal changes in dissolved organic carbon (DOC) concentration in a headwater stream using model simulations. The model, which was composed of the catchment area, the flow distance of tributary channels, the DOC concentration of spring water and the DOC supply capacity of tributaries, well reproduced a longitudinal change in stream DOC concentration during a nonstorm period. This model calculation showed that the roles of riparian wetlands as DOC sources varied greatly among riparian wetlands, even though such wetlands were predominant sources of stream DOC. When we simulated for the longitudinal changes using three representative values (average, minimum and maximum) of the DOC supply capacity, the simulation results could not explain the features of the longitudinal changes, implying that the individuality of riparian wetlands strongly affects longitudinal changes. In addition, when we simulated the features under the different distribution patterns of riparian wetlands, i.e., wide, one-point and dispersed (two-point) distributions, there was a major difference between each simulation result, suggesting that the distribution pattern of riparian wetlands control longitudinal changes. Owing to the individuality and the distribution pattern of riparian wetlands, features of longitudinal changes in stream DOC concentration can vary largely even in the same region.

View full abstract

An image processing method for resolution enhancement of remotely sensed satellite images, which is a useful means of watershed monitoring, was proposed in this study. The enhancement of the spectral information of each pixel was attempted here, although conventional methods can only provide intensity information. The proposed method can enhance the spatial resolution of multispectral image data using panchromatic image data that has higher resolution in the same targeted area, incorporating the category expansion procedure to estimate the spectral characteristics of the pixels. A case study of the Lake Kasumigaura Area with SPOT HRV (High Resolution Visible) image demonstrated that the resolutions of multispectral images can be enhanced from 20m to 10m with 95% accuracy.

View full abstract

The hydrogen production potentials of glycerol were investigated using eight types of seed microorganism in this study. The seed microorganisms were obtained from a thermophilic acidgenic reactor, a mesophilic anaerobic digester, a thermophilic anaerobic digester, a soybean meal silo, organic fractural municipal solid waste (OFMSW), activated sludge, cattle manure, and soil. The highest hydrogen production potential of glycerol (2.05 mmol H₂ · g^-1-glycerol) was obtained using OFMSW seed microorganisms. The hydrogen production potentials of glycerol in this study were lower than those of sugars in previous studies. There was little difference between the metabolic patterns of the cultures. The major products produced by the seed microorganisms were 1,3-propanediol and acetic acid. The chemical oxygen demand (COD_Cr) yields of 1,3-propanediol and acetic acid from initial glycerol concentration (5 gCOD_cr · l^-1) were 50 - 70% and 15 - 20%, respectively.

View full abstract