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Tabelin C.B.,Hokkaido University | Igarashi T.,Hokkaido University | Tamoto S.,Japan Civil Engineering Research Institute for Cold Region | Takahashi R.,Akita University
Journal of Geochemical Exploration

This paper describes the enrichment of hydrothermally altered volcanic and sedimentary rocks with arsenic (As) and lead (Pb), and the effects of pyrite and calcite on the mobilities and release mechanisms of these toxic elements under oxic and anoxic conditions. Enrichment of the altered rock with As and Pb predominantly occurred in precipitated pyrite grains and not on the alumino-silicate minerals making up the matrix of the rock. Arsenic was incorporated in pyrite grains formed during alteration in both volcanic and sedimentary rocks, but Pb was only found in the pyrite grains of the volcanic rock samples. When in contact with water, altered volcanic rocks had acidic pH while altered sedimentary rocks had alkaline pH. The mobilities of both As and Pb from the altered rocks were enhanced at acidic and alkaline pH and a minimum was observed in the circumneutral pH under both oxic and anoxic conditions. The absence of O 2 retarded the oxidation of pyrite most notably in the alkaline region but not in the acidic and circumneutral pH. The absence of CO 2 increased the pH of samples with significant calcite content but did not affect those containing substantial amounts of pyrite. Increasing the CO 2 also had insignificant effect on the concentrations of As and Pb in the leachate. The mechanisms controlling the mobilization of As and Pb from these rocks like dissolution of soluble secondary minerals, pyrite oxidation and adsorption were all related to pyrite while the pH of the rock when in contact with water was controlled by pyrite and calcite. Thus, excavated waste rocks that have been altered can be grouped based on the relative abundance of pyrite and calcite and their pH when in contact with water. © 2012 Elsevier B.V. Source

Mizugaki S.,Japan Civil Engineering Research Institute for Cold Region | Nanko K.,University of Tsukuba | Onda Y.,University of Tsukuba
Hydrological Processes

A field investigation of the effects of rainfall and slope angle on splash detachment was conducted for 5 months, using 27 splash cups in a Japanese cypress plantation in southern Japan. The unit, kinetic energy of throughfall (J m-2 mm-1), was found to be constant and independent of rainfall intensity, indicating that splash detachment can be related to both throughfall intensity and soil slope. The linear correlation coefficient was highly significant for both the maximum throughfall intensity over 1 h (RI1h) and the average splash detachment of all splash cups, although individual cups varied widely. No consistent relationship was found between the splash detachment rate and slope angle for individual periods. This variation in the relationship between splash detachment and slope angle was attributed to the effect of soil crusting and ponding on splash detachment. Splash detachment on a gentler slope (14°) exhibited a strong relationship with the maximum throughfall intensity lasting for short periods of 10-30 min. In contrast, the splash detachment from slopes >35° highly correlated with the maximum throughfall intensity over 3 h. This suggests that a longer period is required to prevent the splash detachment due to ponded water on steeper slopes. On gentler slopes, prolonged rainfall may result in a higher ponding depth, thereby reducing raindrop impact and causing less splash detachment. Thus, under forest canopies, the effect of slope angle on the rainfall parameter should be incorporated into future splash erosion models. © 2010 John Wiley & Sons, Ltd. Source

Teramage M.T.,University of Tsukuba | Onda Y.,University of Tsukuba | Kato H.,University of Tsukuba | Wakiyama Y.,University of Tsukuba | And 2 more authors.

The relationships of erosion-induced displaced soil organic carbon (SOC) to discharged 210Pbex and 137Cs in a hillslope forested area were investigated using runoff plots in three different forest types. A significant correlation was found between the displaced SOC and the radionuclides in each examined forest type. Compared with 137Cs, however, the discharge of 210Pbex is more closely correlated with the displaced SOC and shows a far lower RMSE value by approximately a factor of two. This finding suggests that 210Pbex and SOC are more likely than 37Cs and SOC to move together in the course of soil erosion processes. Moreover, because 137Cs was introduced in the 1960s by thermonuclear bomb tests and is being depleted, its availability in the environment could be limited in the foreseeable future. 210Pbex, in contrast, is continuously replenished from its ubiquitous natural source (222Rn) in a manner similar to the replenishment of SOC from sources consisting of organic material (e.g., litter). In the light of this basic understanding, our findings provide practical evidence of the potential of 210Pbex application for assessing and documenting the water-induced distribution of SOC on forested hillslopes. © 2012 Elsevier B.V. Source

Kakinuma T.,Japan Civil Engineering Research Institute for Cold Region | Shimizu Y.,Hokkaido University
Journal of Hydraulic Engineering

This study aims to clarify the mechanism of riverine levee breach and propose a new numerical model for that phenomenon. Large-scale experiments of overtopping breach were performed using an experimental flume located on the floodway of an actual river channel. By taking advantage of the scale of the flume, the levee breach process was monitored with state-of-the-art observation devices under highly precise hydraulic conditions. Four test cases were performed with variations of inflow rate, levee material, and levee shape, and the levee breach was monitored quantitatively using acceleration sensors installed in the levee body. From the results of the experiments, the breach process is categorized into four stages, focusing on the breach progress and hydraulic characteristics. It was determined that the correlation between the breached volume and the hydraulic quantities of velocity, water level, and Shields number can be expressed by an equation similar to that for bed load transport. Finally, a two-dimensional numerical model is proposed by integrating the experimental results into geomechanics, and a good reproduction result is obtained. © 2014 American Society of Civil Engineers. Source

Tabelin C.B.,Hokkaido University | Igarashi T.,Hokkaido University | Tamoto S.,Japan Civil Engineering Research Institute for Cold Region
Minerals Engineering

This paper describes the factors affecting arsenic (As) mobility from hydrothermally altered rock under in situ conditions. Four impoundments were built on site with rectangular base, truncated-pyramid structures. Impoundment 1 was composed solely of the hydrothermally altered rock while impoundments 2-4 were covered with different types of silty covering soil in order to minimize O2 and water intrusion into the rock. The results indicate that seasonal variations in temperature, O2 concentration and volumetric water content in the impoundments strongly influenced As leaching. When the temperature was high and the water content low, oxidation of sulfide minerals in the rock was enhanced because of a higher air-water-rock interaction. Concentration of As in the porewater increased when it rained after a specific period of dry weather. The use of a silty covering soil influenced the concentrations of As and SO42 - in the porewater although it did not affect the pH and Eh significantly. In this case, O2 and water movement might be the rate controlling step of As leaching, that is, if there is no covering soil on the impoundment, more As will leach out from the rock. The use of a silty covering soil showed promise of reducing As leaching from the waste rock, but utilizing it alone was insufficient to effectively prevent As release from the rock. A combination of covering soil and bottom As-adsorption layer to incorporate any As released from the rock is therefore recommended. © 2009 Elsevier Ltd. All rights reserved. Source

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