1. Aquatic macrophyte diversity and water quality of 55 ponds in western Japan were related to land use and morphometric variables to identify the environmental factors that sustain biodiversity and the spatial extent at which these factors operate. 2. The relevant spatial extent for floating-leaved macrophyte richness (500 m from pond edge) was larger than that for submerged macrophyte occurrence (10, 75 and 100 m), whereas emergent macrophyte richness was best explained at much larger extents (1000 m). Total macrophyte richness was explained at the extent of 500, 750 and 1000 m. The extents relevant for explaining the physicochemical condition of pond water (100 and 250 m) were similar to those for submerged and floating-leaved macrophytes, suggesting that these two growth forms are more sensitive to water quality compared to emergent macrophytes. 3. Diversity of all three growth forms and that of total macrophytes collectively were inversely related to turbidity and nutrient concentration; among the three growth forms, submerged macrophytes were most affected by water quality. 4. Negative relationships were found between the proportion of urban area and the diversity of the three growth forms and that of total macrophytes and water quality. Species richness of emergent, floating-leaved and total macrophytes decreased with depth and increased with surface area up to about 5000 m 2 , above which it declined. 5. Urbanisation and enlargement of ponds were the two main factors that decreased aquatic macrophyte diversity in irrigation ponds. To alleviate the adverse effects of urban areas on aquatic macrophyte diversity, our results suggest that management efforts should focus on the creation of buffer zones within the relevant spatial extent from the pond edge.

No abstract

No abstract

Abstract:When evaluating forest functions and their responses to climate change, it is important to clarify carbon dynamics in forested basins. Carbon fluxes in litter fall, throughfall, soil solution, groundwater and stream water were determined from November 1997 to October 1998 for a forest stream ecosystem in a cool-temperate forested basin in the Tomakomai Experimental Forest, Hokkaido University, northern Japan. The annual carbon input to the stream by litter fall was 0Ð23 gC m 2 year 1 , with the greatest flux in the autumn. Owing to biological decomposition of litter in the stream, the carbon concentration in stream particulate organic matter (>0Ð45 µm) decreased as particle size decreased. The upstream carbon flux was 1Ð9 gC m 2 year 1 , and the annual carbon output in stream water was 7Ð6 gC m 2 year 1 , mainly as dissolved inorganic carbon (DIC), resulting in net carbon output in stream water of 5Ð7 gC m 2 year 1 . The mean dissolved organic carbon (DOC) concentration in soil solution was higher than that in throughfall and stream water. The estimated annual carbon flux from soil in deep (about 1Ð5 m) soil solution was 4Ð4 gC m 2 year 1 . About 40% of DOC in soil solution was decomposed and converted to DIC in groundwater. These results indicate that carbon dynamics in the forest stream were affected strongly by decomposition of organic matter in the soil-groundwater-stream continuum and by the hydraulic conditions, which are characterized by a large pool of groundwater and high soil permeability.

The importance of leaf litter quality for colonization and consumption by two caddisflies (Goerodes satoi and Hydatophylax festivus) and an amphipod (Sternomoera yezoensis) was examined by laboratory and field experiments in a forested headwater stream in northern Japan. Initial values of leaf litter toughness and the carbon to nitrogen (C : N) ratio, both of which varied among the three most common tree species, oak (Quercus crispula), maple (Acer mono) and alder (Alnus hirsuta), decreased dramatically in the field experiment. The density of Hydatophylax was greatest in alder leaf litter characterized by the lowest C : N ratio among the three, with C : N ratio being the only predictor of their density. In contrast, lesser toughness was the only factor facilitating colonization by Sternomoera, the density of which was greatest in the softest maple litter. Neither toughness nor C : N ratio could be used to predict colonization by Goerodes. In the laboratory experiment, in which the shredders were reared on the aforementioned types of leaf litter, following conditioning periods of 1 week and 1 month (six separate trials), the litter consumption rate decreased with toughness in both Sternomoera and Hydatophylax, and with C : N ratio in the latter. However, the consumption rate of Goerodes was influenced by neither of the above, indicating that Sternomoera and Hydatophylax, but not Goerodes, selectively colonized the leaf litter available as a food resource in the stream. Both chemical and physical qualities of leaf litter play an important role in determining species‐specific colonization by invertebrate shredders.