Closed Water Bodies Research Articles

Structure of thermal convection development based on inhomogeneous water surface cooling

The generation and development of thermal convection based on inhomogeneous water surface cooling were examined by hydraulic and numerical experiments to examine the characteristics of thermal convection in a closed water body with aquatic plants. A visualization experiment revealed the structural characteristics of a whirlpool when thermal convection was generated quantitatively by using PIV analysis. Then, a water temperature measurement experiment demonstrated that a steady cold water mass generated based on the heat flux transport from the water surface increases. This explained each of the three stages in the convection development process. Moreover, aquatic plants, which grow thickly on the water surface, cause not only vertical but also horizontal flows based on the density difference with the water surface that is not covered by plants, and thus change the development process of the convection cell.

Stabilization of glaciers terminating in closed water bodies: Evidence and broader implications

The behavior of glaciers terminating in deep water is determined by the interaction of buoyancy, iceberg production, and the sensitivity of ice flow to subtle changes in resistance at the glacier bed. Modeling efforts assume rapid evacuation of icebergs, but some glaciers terminate in closed basins where icebergs may accumulate. Multibeam bathymetric survey of a glacial lake in Iceland that received outlet glaciers during the Little Ice Age document near parallel flow of narrow, ice fingers that extended up to 1 km beyond the grounding line. These previously unseen features apparently occurred when iceberg production exceeded iceberg melt, resulting in iceberg buttressing of the ice margin. Similar stabilization of ice flow may resolve long‐standing debates about past continental ice‐sheet behavior, including the rapid readvance of the Laurentide Ice Sheet into Lake Superior ca. 11 ka and the genesis of glacial flutes observed in the central Arctic Ocean basin.

The Don River basin is a new stage of expansion of Potamopyrgus jenkinsi (Smith, 1889) (Gastropoda, Hydrobioidea) in Europe

The role of invasions has been repeatedly discussed and elucidated in Russian and foreign literature [1‐4]. Problems related to invading species are especially acute in water bodies of arid zones, manly closed water bodies, such as the Caspian Sea, the Sea of Azov, and formerly the Aral Sea. The Sea of Azov and its catchment area are among the most vulnerable ecosystems. This is mainly because the sea is relatively (incompletely) isolated (a continental body of water) and has an unstable hydrological and hydrochemical regimen, which allows invaders with a potentially wide capacity for osmoregulation to adapt. This is entirely true for the catchment areas of the above seas (including the Don, Kuban’, Volga, Ural, Kuma, Syr-Darya, and smaller rivers). These rivers serve as a reserve of the Pontocaspian relict fauna, which is very sensitive to all environmental changes, including invasions. The expansion of invading species may be strikingly rapid. One example is the finding of Potamopyrgus jenkinsi in the Don basin in June and July of 2007. Potamopyrgus Stimson, 1865 was first found in Europe in the late 19th century (the species Potamopyrgus jenkinsi (Smith, 1889) described from the Themes mouth). During the 20th century, Potamopyrgus was found in many regions of Europe. The species composition of the genus Potamopyrgus in the area of invasion is still a matter of discussion. It has been hypothesized that all European Potamopyrgus belong to the same New Zealand species P. antipodarum (Gray, 1843), that there are several species in Europe [5], and that two discrete lineages (clones) have invaded Europe in different periods from different local populations of New Zealand [6, 7]. The existence of a number of European species (probably, pure parthenogenetic strains) of Potamopyrgus differing in ecology and salinity preferences that have no analogues in the New Zealand fauna, as well as some paleontological data, allowed Anistratenko [5] to hypothesize that they are autochthonous in Europe. Anistratenko regards ecologically different strains of Potamopyrgus as separate species P. jenkinsi ; P. alexenkoae Anistratenko in Anistratenko et Stadnichenko, 1995; and P. polistchuki Anistratenko, 1991. Molecular genetic studies on Potamopyrgus from some Western European habitats demonstrated the existence of two strains both genetically and morphologically differing from each other [6, 7]. They are assumed to have invaded from isolated habitats on the North Island of New Zealand in different periods of time. Potamopyrgus may also form new pure strains or species in the area of invasion (saltatory speciation, which is possible for clonal invading species) [8].

Effect of swaying motion of floating vegetation on wind-induced entrainment phenomenon in closed water body

When floating vegetation grows on the water surface in a closed water body, the vegetation counteracts the magnitude of the wind acting on the water surface, and affects the fluid flow and the water quality variation in it. In this study, in order to investigate the counteraction effect of the luxuriant growth of floating vegetation on the fluid flow and water quality in the closed water body, we conducted hydraulic experiments on wind-induced flow with density stratification using a wind tunnel test tank and imitated vegetation. We used imitated vegetation made from polystyrene foam plates instead of using real floating vegetation. And we experimentally considered the effect of the vegetation using the concept of the wind-induced entrainment phenomenon. In particular, we focused the effect of the occupation rate and the swaying motion of vegetation. The results indicated that the swaying motion of imitated floating vegetation had an effect on the scale of entrainment. In addition the results had the same tendency as the previous study on the wind-induced entrainment phenomenon.

Development Process of Thermal Convection Based on Water Surface Cooling with Aquatic Plants

Hydraulic experiments were examined to investigate the characteristics of thermal convection based on inhomogeneous water surface cooling in a closed water body where aquatic plants grew thickly. We demon- strated the process of the generation and development of thermal convection from the results of water tem- perature measurement experiments. This explained the development process of convection was divided into three stages. Aquatic plants disturb the thermal transportation at the water surface, and the aspect ratio of the convection cell changes by the magnitude of the density difference near without the plants. Moreover, the development process of the thermal convection when the shield existed in the water surface was simulated by numerical experiment. As the result, it was clarified that the balance of the transporta- tion equation of the turbulent energy.

Retrospective of radioactive fallout from data on sampled bottom sediments in closed water bodies

A method for identifying past radiation events from dated layers of bottom sediments in stagnant water bodies is described. Results of an experimental study (2005–2006) of the samples of bottom sediments in the pond of the Timiryazev dendropark in Moscow are considered. The sediment layers are dated with 210Pb. The same radionuclide is used as a tracer for calculating the rate of sedimentation in the pond, which is estimated at 0.3–0.4 cm/year. The maximum 137Cs values are detected in the 0–24 cm column at depths of 7 and 13 cm. The 137Cs peak at a depth of 13 cm is dated as 1963, which reflects the maximum global fallout from the atmospheric nuclear weapon tests. A small peak of this radionuclide at 7 cm is dated as 1986. It appears to be attributed to the long-range fallout after the Chernobyl NPP accident. The origin of the 137Cs maximum at a depth of 13–14 cm is confirmed by characteristic ratios of radionuclide pairs available in the global fallout in the Moscow region. The ratios of 90Sr/137Cs = 0.6 and 239,240Pu/137Cs = 0.03 in the 13–14 cm layer are characteristic of the global radioactive fallout from nuclear explosions. In the layers above this maximum, such ratios vary sharply toward the enhanced 137Cs content in the fallout.

Turbulent Structure in a Closed Density Stratified Water Body with Floating Vegetation

In a closed water body, fluid is generally stratified by its vertical density difference (temperature, nutrient salts, etc.). These density differences arise due to the limited inflow and outflow in the water body. In the absence of disturbance in the water body, the vertical density stratification is stabilized. The behavior of a substance in the water body is influenced by the mechanical disturbance (wind–induced flow) and the thermal disturbance (convective flow). With the action of the wind on the surface of such the water body, the surface layer becomes turbulent due to the wind–induced flow. Such wind action on the water body with density stratification gives rise to the entrainment phenomenon at the density interface. This phenomenon, which results from the mixture between the upper and lower water layers, affects the water quality in the water body. When there are little disturbances in the water body, the driving force of flow in the water body is absent and water quality deteriorates. Therefore, when we address the water quality problem in a closed water body, it is very important to clarify the characteristics of fluid flow based on disturbances. By the way, water quality problems associated with closed water bodies, including eutrophication, have been studied, and water purification with floating vegetation has been proposed for several water bodies (Masushima 2001, Oki 2001, Tai 2001). The purification ability of floating vegetation is due to a filter effect with regard to suspended solids and an absorption effect with regard to nutrient salts. These abilities are attained when the floating vegetation is eliminated outside the water body (Fujita et al., 2000, Menya et al., 2001). Therefore, in order to enable water purification with floating vegetation, the suitable management of floating vegetation is required. In addition, floating vegetation does not absorb nutrient salts directly, it absorbs inorganic nutrients such as phosphorus that are mineralized by microbes at the bottom of the water body (Michioku et al., 1999, Fujita et al., 2000). Therefore, in order to utilize floating vegetation for purifying the water body, a certain amount of flow is required. However, as mentioned above, in the water body, the flow tends to stagnate and the fluids are generally stratified due to vertical density differences; thus, maintaining water quality becomes problematic. In the water body, wind–induced flow and convective flow may be induced by mechanical and thermal disturbances, respectively. When floating vegetation grows on the water surface, the flow is affected by its luxuriant growth; therefore, it is very important to clarify the relationship between its luxuriant growth and fluid movement in the water body. With regard to the relation between flow in a closed water body and luxuriant growth of a floating vegeTurbulent Structure in a Closed Density Stratified Water Body with Floating Vegetation

Study on Wind Shear Acting on the Water Surface of Closed Water Bodies

Study on Wind Shear Acting on the Water Surface of Closed Water Bodies

A two-dimensional numerical model of wind-induced flow and water quality in closed water bodies

In closed water bodies, such as reservoirs and lakes, where the exchange with external waters is usually small, the wind-induced flow significantly affects their water quality by mixing the surface waters and transfering heat down through the water column. However, the circulation caused by wind acting on the water surface can be influenced by the excessive growth of aquatic plants in summer, which may make their water quality to become worse. Therefore, understanding the response of the closed water bodies to winds acting on the water surface is of great significance in examining and maintaining their water quality in good condition. With that significance, this research has been done to build a two-dimensional, unsteady, laterally averaged model for simulating the circulation and water quality in closed water bodies. To verify the model, the Tabiishidani reservoir located in Sasaguri town, Fukuoka prefecture, Japan, was chosen as a case study. To illustrate the methodology of the research, water temperature of the reservoir was chosen to calibrate the model. After calibration, the model was applied to simulate water temperature in the Tabiishidani reservoir under different patterns of meteorology. The results of simulation clarified the change in water temperature distribution along the depth of the reservoir under the different patterns of meteorology. This research shows that the model can be a suitable tool for simulating the circulation and water temperature in closed water bodies. Moreover, the model can be extended to simulate the circulation and any variable of water quality in closed water bodies with the coverage of aquatic plants on the water surface.

三次元流動解析に基づく底泥回収装置の検討

At the time being, deterioration in water quality of closed water body has become a serious issue for local fishery and accumulation of mud layer which covers lakebed has been thought as the cause of deterioration. Then, it can be said that maintenance and preservation of the water environment by retrieving those mud layer is one of the most important subjects to enhance and to promote regional economy in the vicinity with preserving precious marine resources.The authors have proposed a new retrieving method of lakebed mud on site. This method has been developed as an innovative way that requires neither additional chemicals for condensation of the mud nor a temporary yard for desiccation of the mud. After the first phase with indoor model experiment, it was confirmed that the method successfully retrieve the mud and an on-site experiment is now under planning. In this paper, the authors report a study result on the device, especially the shape of retrieving fan, with 3-D flow analysis. Through this study, important knowledge for designing the shape of fan was obtained in order to expect efficient retrieving. Though further experiment is necessary under various mud conditions to improve the efficiency, the method is getting close to a reality.

Behavior of Cold Water Mass Due to Water Surface Cooling in a Closed Water Body

disturbance) In the present research, we focused on a closed water body where thermal turbulence was outstanding. Hydraulic experiments were conducted to investigate the behavior of the cold water mass formed around a water surface when the water surface was cooled naturally. And the difference of the behavior was investigated under coverage and no‐coverage plants on a water surface. Results indicated that turbulence intensity of the cold water mass and the time scale of convection were influenced by both the Rayleigh number and coverage. The falling cycle of cold water mass was influenced by only the Rayleigh number. The falling cycle of cold water mass and development of convective a flow were also observed by the wavelet transform in the change of water temperature.

Some Primary Characteristics of Water Quality in a Closed Water Body in Sasaguri, Fukuoka Prefecture, Japan

Some Primary Characteristics of Water Quality in a Closed Water Body in Sasaguri, Fukuoka Prefecture, Japan

Thermal Convection in a Closed Water Body wit Aquatic Plants

Thermal Convection in a Closed Water Body wit Aquatic Plants

閉鎖性水域における底層部への高濃度酸素水導入による水質改善効果に関する研究

In this study, a method of using high-dissolved-oxygen water to purify bottom sediment in a closed water body was confirmed to be effective. A high-rate, high-efficiency oxygen dissolver was developed and a method of producing high-dissolved-oxygen water was discussed. In addition, the prevention of phosphorus release from the bottom sediment using high-dissolved-oxygen water was also studied. A pilot-scale oxygen dissolver was developed and an on-site study was carried out at two dam reservoirs in Yamaguchi, Japan. As results, it was possible to spread the high-dissolved-oxygen water across the bottom layer without any diffusion in the upper direction. Furthermore, the presence of high-dissolved-oxygen water could prevent the release of phosphorus from the bottom sediment. This study revealed the effectiveness of high-dissolved-oxygen water for the improvement in the water quality of a closed water body.

The Sources of Uncertainty in Forecasting Caspian Sea Level and Estimating the Inundation Risk of Coastal Areas

Stochastic variations in the climate and hydrological regime, both natural and anthropogenic, are the main cause of uncertainty in long-term hydrological forecasts and hence increase the estimated risk of economic activity in the coastal zone of internal seas. Some sources of uncertainty, which appear during the hydrological analysis, are considered with the purpose to assess this risk. Digital relief models were used to determine the morphological characteristics (as functions of the sea level) and assess their contribution to variations in the level regime. To take into account the sample uncertainty in the parameter estimates of stochastic models of the “impellent” processes, it is proposed to use the existing methodology of probabilistic-deterministic prediction of water level variations in a closed water body in combination with the Bayesian approach.

Influence of a biohermal belt on the lacustrine sedimentation of the Cañadón Asfalto Formation (Upper Jurassic, Chubut province, Southern Argentina)

The Upper Jurassic Canadon Asfalto Formation (Canadon Asfalto Basin, Patagonia Argentina), consists mainly of carbonate deposits accumulated in hydrologically closed lakes, which were especially sensitive to rainfall changes. The lacustrine carbonate sedimentation also interplayed with volcanic episodes recorded by tuffs and lavas, as observed in different basin sectors. These lakes probably underwent warm, alternating humid-subarid and arid conditions that resulted in spreading and shrinkage cycles of the closed water bodies. In the Cerro Condor area, carbonates were deposited as part of a 500 m long and 39 m thick microbial biohermal body that extended over 5,5 km2, overlying a hard basalt substratum. This bioherm ridge acted as a physiographic barrier that controlled the sedimentation in the surrounding lacustrine zones, whose environments ranged from shallow and deep littoral to eulittoral (including microbial patch reefs) and palustrine. A hydrologically isolated portion of the lacustrine basin evolved into a pan lake where widespread carbonateevaporite sequences developed.

底質改善工法開発のための底泥回収実験

At present, deterioration of water quality in closed water body has become a serious issue for the local fishery and an accumulated mud layer which covers lakebed has been thought as the cause of the deterioration. Then, it can be said that the maintenance and preservation of the water environment by retrieving the mud layer is one of the most important subjects to preserve and to promote the regional economy with maintaining precious marine resources.In this paper, the authors propose a new retrieving method of lakebed mud on site. This method has been developed as an innovative way that requires neither additional chemicals for condensation of the mud nor a temporary yard for desiccation of the mud. This research aims to obtain fundamental knowledge about the retrieving torque and its efficiency to establish this new method. The experimental result shows that the mud can be retrieved with the fan efficiently enough to adopt the method practically. However, further experiment is necessary under various mud conditions to improve the efficiency.

STRATEGIES FOR REDUCING THE POLLUTANT RUNOFF LOADS INTO A CLOSED WATER BODY ‹REGULATION POND OF ISAHAYA AND ITS WATERSHED›

At Isahaya of Nagasaki, Japan, a big project called construction of sea-dyke and reclamation project is now going on. It is well known that deterioration of water quality has been frightened in a closed water body, if runoff load of pollutants is not sufficiently controlled. In this paper, pollutant runoff loads from the watershed into the regulation pond of Isahaya are first identified, classifying those from point and non-point sources. On the other hand, it becomes very urgent to reduce the pollutant runoff loads, so efficiency of constructed wetland as one of the Best Management Practices (BMPs) is briefly discussed, based on a field observation and an experiment in campus of Nagasaki University. Finally, some discussion has been done, related to a strategy for reducing the pollutant runoff loads into the regulation pond of Isahaya.

Carbon, nitrogen, and sulfur isotope changes and hydro-geological processes in a saline lake chain

The ionic concentrations,conductivity and pH of water in the Lake Chany complex in West Siberian Russia change from the mouth to the interior of the lake. This difference is indicative of marked evaporation of lake water from the closed water body system in the dry climate of Western Siberia. The carbon isotope composition of particulate organic matter (POM, composed mainly of phytoplankton) clearly changes, along with the pH of the water, reflecting the concentration of dissolved CO2. Carbon and nitrogen isotope signatures of Chironomus plumosus larvae, a benthic invertebrate that may feed on bulk lake sediment, systematically increase, along with those of POM and sediment organic matter (SOM), through the lake chain. Both sulfate-sulfur and nitrogen isotope compositions of the POM and SOM increase with distance from the estuary into the Lake Chany complex. Heavier sulfur and nitrogen isotope recycling from the sediment, caused by microbial sulfate reduction and denitrification, respectively, may have led to the increased sulfate-sulfur and nitrogen isotope compositions of the POM and SOM.

Effect of Floating Water Plants on Wind-Induced Flow in a Closed Water Body

In some closed water bodies with little inilow and outflow, a flow is loose. So it has the different hydraulic characteristics from a river or an irrigation canal. When there is no disturbance, fluid is stratified based on vertical density distribution. In these bodies, the main dynamics of the water environmental substance depends on a mechanical disturbance, which is induced by the wind current on the water surface, and a thermal disturbance, which is induced by convective flow. We especially considered the mechanical disturbance based on the wind-induced flow. The previous study, which studied about the closed water body with floating water plants reported that the existence of the floating water plants may shorten the fetch and affect the dynamics of a density interface. Thereat in our study, we experimentally studied the relationship between the gregarious density of the floating water plants and the wind-induced flow in the closed water body. The result indicated that when the gregarious density of the floating water plants on the water surface becomes small, the values of the turbulent characteristics variables in the upper layer increase. This study clarifred that vegetation density affects the entrainrnent phenomenon in a stratifred water body.