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Volume 61, Issue 1
Displaying 1-10 of 10 articles from this issue
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Kunimitsu INOUCHI, Hikari SAKAMOTO, Tadao KAKINUMA2000 Volume 61 Issue 1 Pages 1-10
Published: February 25, 2000
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSThe steady-state behavior of coastal and insular groundwaters was investigated using a sand tank.
In the case of seawater intrusion into confined coastal aquifers, the fresh-water/salt-water inter-faces simulated by the boundary element method (BEM) exhibited a good agreement with those by experiment. Dupuit's assumptions are appropriate to apply in case of lower hydraulic gradients. In the hydrodynamic dispersion model, the isoplethic patterns of salt concentration in a case of velocity-dependent dispersion coefficient agree better with those by experiment than in a case of the constant dispersion coefficient, and Cauchy's boundary condition is rather realistic.
In a case of freshwater lenses, the fresh-water/salt-water interfaces reproduced by the analytical solution exist slightly above the experimental visual interfaces, and the hydrodynamic dispersion model simulated the transition regions comparatively well.View full abstractDownload PDF (695K) -
Masayoshi MORI, Hisanori KAGAWA2000 Volume 61 Issue 1 Pages 11-20
Published: February 25, 2000
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSIn an upper shallow reach of the Ishite River, Japan, where a near-dialysis culture system of a benthic algal community was naturally formed, a 13-year (1985-1997) monthly survey was under-taken to clarify the environmental factors regulating dissolved oxygen (DO) concentration (mg L-1) which is supposed to reflect algal photosynthesis in the stream. Using a multiple regression analysis of 110 samples under base flow conditions in the monthly survey, it was found that ADO, i.e. observed DO minus saturated DO concentrations, was indicated by a multiple regression equation using a ratio of mol concentrations between dissolved calcium to magnesium (Ca/Mg), soluble reactive phosphorus (SRP) concentration (μg L-1), and water temperature (WT; °C) as follows: ΔDO= 0.616Ca/Mg-0.235SRP+0.037WT-1.70 (R2=0.513, P<0.001).
Culture experiments were undertaken to make clear the effects of the Ca/Mg ratio on algal pro-ductivity using dialysis cultures of an isolated diatom Navicula sp. The Ca/Mg ratio in the culture media had a positive effect on algal growth and DO production when Ca/Mg was more than 5, and negative effect when the ratio was smaller than 4, which seemed to confirm a positive relationship between Ca/Mg ratio and ADO in the Ishite River as a whole, where the Ca/Mg ratio varied between 3.87 and 6.04.View full abstractDownload PDF (622K) -
Takayuki NANAZATO, Takahito YOSHIOKA2000 Volume 61 Issue 1 Pages 21-23
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn order to evaluate the effect of climatic warming on freshwater environment, limnological stud-ies have been performed and predictions of future impact have been given. In this special issue, seven papers produced by eight authors are presented, which review limnological studies on climatic warming as to diverse subjects such as distribution of water temperature and water movement in lakes, rivers and ground water, chemical properties of rivers and lakes, communities of plankton and fishes, and material cycles in watershed ecosystems. The papers are predicting future events oc-curring in freshwater environment as a result of climatic warming by using the data obtained in field observations at different temperature conditions and in some laboratory experiments. The pre-dictions are, however, still qualitatively. Quantitative predictions should be given to evaluate the effects precisely. For this purpose, experimental studies are desired to be encouraged more, and the predictions should be done being tied up with development of meteorology which gives accurate predictions of regional and local climatic changes associated with the climatic warming.View full abstractDownload PDF (196K) -
Tadashi ARAI2000 Volume 61 Issue 1 Pages 25-34
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe effects of global warming on inland waters are reviewed and discussed in this paper. Latitudinal distributions of the water temperature and the lake circulation type are explained based on the annual mean and range of the equilibrium temperature. Long-term observations on lakes and rivers have clarified the warming trend in recent years. Although several simulations have already been made to predict the temperature field in the 21st century, these results are widely divergent because of the differences in General Circulation Models. It may be said that predictions of water temperature are not reliable at present. The other reason for instability in the predictions is the lack of accurate long-term data on water temperature. Since basic knowledge of the relationship between climate change and water temperature can be obtained from the long-term record, it is necessary to summarize the temperature record. Another way to determine the effect of climate on water temperature may be an investigation into particularly warm or cold years.
A poor ice winter in Lake Suwa has also been discussed in relation to El Nino as an example of an anomalous climate event, the historical record on the ice cover in Lake Suwa was compared with the historical winter temperature estimated from an old diary at Tsu City, Mie Prefectures. It is pointed out that warm winter at Tsu and poor ice in Lake Suwa appeared in the same decades, and more than half of these warm events were associated with El Nino. Such exceptional climate events should be also taken into consideration in the prediction and monitoring of inland waters.View full abstractDownload PDF (767K) -
Yasuo SAKURA2000 Volume 61 Issue 1 Pages 35-49
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIt is generally recognized that the temperature profile in a borehole is influenced by both groundwater flow and past climatic change. Geophysicists seek to remove such effects from a tem-perature profile to make corrections in terrestrial heat flow values. It is also well known among hydrogeologists that the distribution of subsurface temperature is affected by groundwater flow, and that temperature data can be used to estimate the direction and velocity of that flow. To date, there are few studies simultaneously concerned with both effects. This paper provides a review of the literature dealing with the effects of groundwater flow and past climatic change on the subsurface thermal regime. Then, temperature profiles and the distribution of temperature inversions observed in the Nobi Plain around Nagoya, Japan are presented as an example showing the effects of both groundwater flow and surface warming caused by global warming and urbanization.View full abstractDownload PDF (1005K) -
Kazuki MORI2000 Volume 61 Issue 1 Pages 51-58
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSChanges in the components of the hydroclimatological characteristics, including precipitation, evapotranspiration and runoff over the last 100 years were investigated in the Kiso, Nagara and Ibi River Basins. The smooth trend curve indicates that the annual evapotranspiration has increased over the long term, especially since the 1980s. On the other hand, annual precipitation in the study basin has been inclined to decrease since the first half of the 1970s. The average annual runoff ratio for each ten years also showed a tendency to decrease during the last few decades. It is pointed out that the notable characteristics on current frequency-magnitude distributions in annual precipita-tion are both the reduction of interval of hydrological extremes and the increase of range in each year. Under the conditions of extreme meteorological events which raised the air temperature in the summer of 1994, the water quality of the Kiso River showed the remarkable change as compared with its average value in normal year. The most striking feature due to high temperature was very low value of the concentration of dissolved oxygen especially during July to August. The facts iden-tified in the present study provide a meaningful perspective on the possible consequences of global warming for hydrological processes, and are useful as basic data to evaluate the effects of future climate change on the environmental aspects of inland waters.View full abstractDownload PDF (554K) -
Norio OGURA2000 Volume 61 Issue 1 Pages 59-63
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe influences of global warming on the water quality of inland waters were reviewed. As a consequence of global warming, increases in pH and alkalinity were observed in some boreal and mountainous lakes, and an increase in nitrification activity was also observed in stream headwaters. Changes in wate quality of spring water in an urban area of Tokyo observed by the author's laboratory during 20 years were described and discussed.View full abstractDownload PDF (197K) -
Takayuki HANAZATO2000 Volume 61 Issue 1 Pages 65-77
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSStudies on the effects of climatic warming on lake plankton communities are reviewed, and the effects on lake ecosystem structure and functioning are discussed. Such warming reduces dissolved oxygen concentration in the hypolimnion and enhances the dominance of cyanobacteria in the phytoplankton community. Thus, its effects resemble those of eutrophication. Increased water temperature due to climatic warming reduces high-temperature-sensitive species such as mysids an Daphnia. Warmwater fishes increase their habitats while coolwater fishes decrease them in the process of climatic warming, thus changing the community structure and distribution of zooplankton. Furthermore, climatic warming may change a plankton community by controlling various biological interactions such as competition and predator-prey relationships, and reduce species diversity in the community. It is expected that the climatic warming enhances the contamination from toxic chemicals and increases UV penetration in lakes. Therefore, climatic warming promotes the delete-rious effects of existing environmental stresses on lake ecosystems. It is hypothesized that the fol-lowing two phenomena characterize the structural and functional responses of lake ecosystems to climatic warming: (1) reduction in the average size of organisms, and (2) a reduction in energy transfer efficiency from primary producers to top predators.View full abstractDownload PDF (1024K) -
Yoshinori TANIGUCHI, Shigeru NAKANO2000 Volume 61 Issue 1 Pages 79-94
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSResearch on potential effects of global warming on freshwater fishes has proliferated in 1990s. Most of these studies have focused on predicting changes in distribution of fishes based on their thermal-physiological data and on predicting population dynamics using species-specific bioenergetic models. However, in reality, the effects of global warming on freshwater fishes should not be predicted without considering the complex interactions with local environmental disturbance factors. In addition, in many cases, previous studies have failed to look at changes in genetic struc-ture of populations, life history plasticity, and biological interactions such as predator-prey and interspecific competition in their predictions. These resulted in our not having been able to precisely make reliable predictions of effects of global warming on freshwater fishes. Also, although extinc-tion and changes in distribution of the fishes should influence food web and biogeochemical cycling, few such studies have been attempted yet. Future researches should include attempts to accumulate field observational data and to elucidate potential mechanisms of the effects of global warming on the freshwater fishes in the context of multidisciplinary cooperative studies.View full abstractDownload PDF (1497K) -
importance of watershed studyTakahito YOSHIOKA2000 Volume 61 Issue 1 Pages 95-100
Published: February 25, 2000
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe response of a land-water environment to global warming was discussed from the viewpoint of material cycles in a terrestrial ecosystem including land and land-water sub-ecosystems. Since the material cycle in a land-water ecosystem is maintained by the substrates imported from its watershed, global environmental change affects the land-water ecosystem through the land ecosystem. In this paper, metabolisms of organic matter and NO3- between a forest ecosystem, as a representative of a land ecosystem, and a land-water ecosystem were examined to elucidate their possible responses to global environmental changes. The importance of a watershed study was discussed, with special reference to an interdisiplinaly study between land and land-water ecosystems.View full abstractDownload PDF (450K)
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