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Volume 70, Issue 2
Displaying 1-6 of 6 articles from this issue
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Original articles
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Environmental factors and distribution of aquatic invertebrates in riverside pools in a small streamMaria KUROKAWA, Osamu KATANO, Koji TOJO, Satoshi KITANO2009 Volume 70 Issue 2 Pages 67-85
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSEnvironmental factors and macroinvertebrates in riverside pools were investigated in the Urano River, a tributary of the Chikuma River. The pools were maintained by spring water and characterized by their small area and low temperatures in May and June, and were generally low in dissolved oxygen and poor in inorganic nutrients. The occurrence of very high water levels in the Urano River in July caused many pools to disappear or be greatly changed. Gammarus and some species of Coleoptera such as Laccotrephes japonensis and Appasus japonicus were distributed only in the riverside pools, and there were fewer Trichoptera compared with those in the main stream. Oligochaeta, Chironomidae, Ephemeroptera and Odonata were abundant both in pools and the main stream. The total number of invertebrates in May was high in pools rich in dissolved oxygen and extensive in area; in September, they were found only a short distance from the main stream and large areas. However, important environmental factors differed between the invertebrate groups. Riverside pools in small rivers are important for invertebrates that require clear still water and/or spring water, and their conservation is necessary.View full abstractDownload PDF (719K) -
Michio TAGIRI, Tomonori NAYA, Marie NAGASHIMA, Masami NEGISHI2009 Volume 70 Issue 2 Pages 87-98
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSSuspended solids (SS) in Lake Kasumigaura and its tributaries were analyzed over one year by the X-ray fluorescence filter method. SS in this study were not confirmed by IKESC as those of the white turbidity phenomenon. SS in the tributary rivers showed seasonal variations, being rich in clay and Fe and with reduced Ca in summer compared to winter. This pattern is a result of agricultural activity in the drainage basin. In summer, run-off from rice fields supplies elevated amounts of clay minerals and Fe to the rivers. The Ca-rich ground water strongly affects SS in winter. The SS of Lake Kasumigaura vary in composition from being rich in mica clay upstream to rich in SiO2 downstream, but are usually are poor in Ca and Fe. The lake-SS show no seasonal variation. After the river-SS flow into the lake, water chemistry condition (especially pH) control the distribution of SS in such a way that a change from neutral to alkali pH can result in the fractionation and precipitation of some river-SS constituents. Thus, the composition of river-SS changes to that of lake-SS, which is comprised of mica clay and diatom shells.View full abstractDownload PDF (1310K)
Review
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Tadashi ARAI2009 Volume 70 Issue 2 Pages 99-116
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSClimate affects inland waters in many ways, with temperature and freezing being the factors most sensitive to climate change. Water temperature and ice cover are regarded as indicators of the global warming and climate variations; these records analyzed as environmental issues have gained prominence in recent years. In this article, the author summarizes papers on the temperature and ice conditions of lakes, rivers and springs.
In the latter half of the 20th century, the average temperature of lakes has risen at rates between 0.01°C and 0.06°C per year in many regions of the world. Warming tendency is also found in rivers. Dates of freeze-on in lakes and rivers have occurred about 6 days later over the recent 100 years, and dates of ice break-up occur about 6 days earlier. In addition to long-term warming trend, middle or short-term variations corresponding to El Nino-Southern Oscillation and North Atlantic Oscillation have been detected. Warming trends have also become evident in groundwater and spring temperatures.View full abstractDownload PDF (635K)
Features: Terrestrial - sea water interaction and its effect on coastal environment
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Mitsuru HAYASHI, Makoto TANIGUCHI, Hideaki YAMADA2009 Volume 70 Issue 2 Pages 117-128
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSA submarine groundwater discharge was estimated by water and salt budget analysis based on hydrographical observations offshore of Omae Beach, Osaka Bay, Japan. Those observations were carried out from August 23 to 23 2006. The estimated submarine groundwater discharge and through-flow on the boundary sections were compared with observed submarine groundwater discharge and current speeds as well as with the results of tidal current simulation by POM. The difference between variations in water volume estimated by the observed water level and the calculated result was less than 0.3%. Estimated through-flows on the boundary section qualitatively agreed with the results of the tidal current simulation. Estimated submarine groundwater discharge was 5 times the observed discharge. This will be recognized when various factors are considered. This method is available for estimating the submarine groundwater discharge over an entire target area. The water budget of this area during the period studied was dominated by the through-flow. Sea water continuously flowed in from the southern boundary, influenced by not only the tidal current but also by the residual current. An outflow that corresponded to a tidal change was observed in the eastern boundary. The contribution of submarine groundwater discharge to volume variations in the area was estimated at 5 to 8%.View full abstractDownload PDF (1186K) -
an example of the application to the middle of the Seto Inland SeaYuta SHIMIZU, Shin-ichi ONODERA, Mitsuyo SAITO2009 Volume 70 Issue 2 Pages 129-139
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSTo estimate the spatial variation in submarine groundwater discharge from a 50 m square coastal grid over a distance of more than 100 km, we applied a topographic model to the coastal area of the middle of the Seto Inland Sea. Topographic gradients between the coastal grid and the points were automatically calculated using GIS and an altitude dataset with 50 m square grid. Based on those calculations, the hydraulic gradients and cross-sectional areas were estimated, with submarine groundwater discharges being calculated by a Darcy equation. Our results were summarized as follows; 1) the coastal areas of Kagawa Prefecture on the southern part of the Mid Seto Inland Sea has lower slopes than those in Okayama Prefecture. In particular, the areas with flat surfaces such as reclaimed lands with a slope of less than 0.002 were larger in Kagawa Prefecture than Okayama Prefecture. 2) In the estimated annual SGDs exceeded 0.2 × 105 m3 year-1 at most of that were the grids in Okayama Prefecture. On the other hand, the SGDs on reclaimed lands that were distributed partly along the coastal grid of Kagawa Prefecture were estimated to be almost 0. 3) Cumulative annual SGDs estimated by this method were 78.4 mm in Okayama Prefecture and 50.5 mm in Kagawa Prefecture. These values accounted for around 5% of the total precipitation in both prefectures. The SGD estimated by the water balance model approximately corresponds to percentage.View full abstractDownload PDF (1798K) -
Mitsuyo SAITO, Shin-ichi ONODERA2009 Volume 70 Issue 2 Pages 141-151
Published: 2009
Released on J-STAGE: October 25, 2010
JOURNAL FREE ACCESSThe seasonal variation in the nitrate-nitrogen (NO3--N) discharge by groundwater to the sea was evaluated from the monitoring data of hydraulic potential and NO3--N concentrations in the groundwater of a small coastal agricultural catchment. A large variation in the NO3--N concentration (<0.05 - 5.3 mg L-1) was found in the shallower groundwater of the coastal area. These results suggest that NO3--N attenuation via denitrification influences the seasonal variation in NO3--N concentrations. Furthermore, significant NO3--N attenuation was confirmed in relatively small Darcy flux (<1.8 × 10-6 cm/s). The estimated NO3--N flux varied (0.006 - 0.8 kg d-1) with changes in the NO3--N concentration. Annual groundwater discharge is estimated to be 1.7-fold higher than river discharge, while groundwater NO3--N flux accounts for approximately 70% of river flux owing to the attenuation of NO3--N in coastal areas.View full abstractDownload PDF (974K)
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