Irrigation with reclaimed municipal wastewater

Land application of municipal wastewater is a well established practice in many arid and semiarid countries of the world. Although irrigation with municipal wastewater is in itself an effective form of wastewater treatment, some degree of treatment must be provided to 1) protect public health, 2) prevent nuisance conditions, and 3) prevent damage to crops, soils, and ground-water. Factors affecting irrigation with reclaimed wastewater include irrigation water quality and public health and regulatory considerations.     

An alternative approach to the random response of bilinear hysteretic systems

An analytical representation of the bilinear hysteretic characteristic is presented. Using this representation, the response of a single-degree-of-freedom bilinear hysteretic system subjected to non-stationary random excitation is examined by equivalent linearization. An ordinary differential equation is derived for the covariance matrix of the response. Numerical examples are presented and the accuracy of the approach is demonstrated. Extension of the approach to a wider class of hysteretic systems is discussed.     

Rare Earth Elements in Hydrothermally Altered Granitic Rocks in the Ranong and Takua Pa Tin‐Field,Southern Thailand

Geochemical studies were conducted on the hydrothermally altered granitic rocks in the Ranong and Takua Pa tin‐fields in southern Thailand in order to investigate the mode of occurrence of REE (rare earth elements), with emphasis placed on a potential REE resource associated with granitic rocks in the Southeast Asian Tin Belt. The total REE (ΣREE) content of altered granitic rocks ranges from 130 to 350 ppm at Haad Son Paen (which is presently mined for kaolin clay) in the Ranong tin‐field, and that of altered granitic rocks and kaolinite veinlets reaches up to 424 ppm and 872 ppm, respectively, at Nok Hook in the Takua Pa tin‐field. Rare earth elements in the altered granitic rocks and kaolinite veinlets show a relatively flat chondrite‐normalized pattern, thus enriched in heavy REE compared with the original granitic rocks and their weathered crusts. At Nok Hook (Takua Pa), the ΣREE content of kaolinite separated from an altered granitic rock by elutriation is 1313 ppm, a ΣREE amount about four times higher than that of whole‐rock composition of the altered granitic rock. Chondrite‐normalized REE patterns of the elutriated kaolinite and of the altered granite are relatively flat. Sequential extraction experiments suggest that 41 and 85 percent of REE are present as ion exchangeable‐form in the altered granitic rock, and in the kaolinite veinlets, respectively. In addition, more than 90% of REE in the kaolinite veinlets are present as the acid‐soluble state. On the other hand, the ΣREE content of kaolinite veinlets and of the kaolinite concentrated by elutriation from an altered granitic rock at Haad Som Paen (Ranong) is 70 ppm and 75 ppm, respectively, thus enrichment of REE in kaolinite was not confirmed. In addition, by the sequential extraction experiments, 23% and 4% of REE were extracted from the altered granitic rock and the kaolinite veinlets at Haad Som Paen. In the altered granitic rocks at Haad Som Paen, REE are present as refractory phases, and REE in the acid‐soluble states had been leached by hydrothermal fluid.     

Microseismicity around rupture area of the 1944 Tonankai earthquake from ocean bottom seismograph observations

Along the Nankai trough, southwestern Japan, the Philippine Sea plate (PSP) is subducting beneath the Eurasian plate, and large interplate earthquakes have occurred repeatedly with a recurrence interval of about 100-200 years. The most recent large thrust event in the eastern Nankai trough off Kii Peninsula was the 1944 Tonankai earthquake. In this region, current seismicity is very low and hypocenters are not determined accurately by the land seismic network. We conducted microseismicity observations around the rupture area of the 1944 Tonankai earthquake using ocean bottom seismographs (OBSs). Hypocenters were determined using a 2-D seismic velocity structure model based on an airgun-OBS seismic survey. Results obtained show that the seismicity was relatively active near the trough axis. These earthquakes may relate to deformation of the subducting Philippine Sea plate. On the other hand, microseismicity in the rupture area of the 1944 Tonankai earthquake was very low. This low-level seismic activity in the co-seismic rupture area of the 1944 Tonankai earthquake likely relates to a single large asperity off Kii Peninsula.     

Evaluation of Seasonal Sea Level Variation at Syowa Station, Antarctica, Using GPS Observations

Global Positioning System (GPS) measurements of the vertical displacement of fast ice near Syowa Station, Antarctica, were conducted between April and December 1998 to evaluate measurements of sea level variation derived with a conventional bottom pressure gauge (BPG). The BPG-derived sea level revealed a seasonal variation of about 0.13 m, with a high in April–June and a low in November–December. The GPS-derived sea level, combined with observed sea ice thickness, supported the BPG result, with an RMS error of 0.007 m. Our result also demonstrates that GPS is a powerful technique for monitoring sea level variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin of felsic volcanism in the Izu arc intra-arc rift

An intra-arc rift (IAR) is developed behind the volcanic front in the Izu arc, Japan. Bimodal volcanism, represented by basalt and rhyolite lavas and hydrothermal activity, is active in the IAR. The constituent minerals in the rhyolite lavas are mainly plagioclase and quartz, whereas mafic minerals are rare and are mainly orthopyroxene without any hydrous minerals such as amphibole and biotite. Both the phenocryst and groundmass minerals have felsic affinities with a narrow compositional range. The petrological and bulk chemical characteristics are similar to those of melts from some partial melting experiments that also yield dry rhyolite melts. The hydrous mineral-free narrow mineral compositions and low-Al₂O₃ affinities of the IAR rhyolites are produced from basaltic middle crust under anhydrous low-temperature melting conditions. The IAR basalt lavas display prominent across-arc variation, with depleted elemental compositions in the volcanic front side and enriched compositions in the rear-arc side. The across-arc variation reflects gradual change in the slab-derived components, as demonstrated by decreasing Ba/Zr and Th/Zr values to the rear-arc side. Rhyolite lavas exhibit different across-arc variations in either the fluid-mobile elements or the immobile elements, such as Nb/Zr, La/Yb, and chondrite-normalized rare earth element patterns, reflecting that the felsic magmas had different source. The preexisting arc crust formed during an earlier stage of arc evolution, most probably during the Oligocene prior to spreading of the Shikoku back-arc basin. The lack of systematic across-arc variation in the IAR rhyolites and their dry/shallow crustal melting origin combines to suggest re-melting of preexisting Oligocene middle crust by heat from the young basaltic magmatism.     

Role of Iron(III) and Aluminum Hydroxides in Concentration/reduction of Au(III) Complexes

Abstract: The adsorption of gold on iron(III) and aluminum hydroxides from solutions containing Au(III) complexes has been studied as a function of pH and chloride concentration at 30C. Iron(III) hydroxide was more effective in adsorbing gold from solution than aluminum hydroxide. However, both hydroxides controlled the behavior of Au(III) complex with very similar manner. The most effective gold adsorption occurred in aqueous solution with near neutral pH and low Cl concentration. In this solution condition, Au(III) complexes were mainly dissolved as AuCl₂(OH)₂^- and AuCl(OH)₃^-, and the surface charge for both hydroxides was positive. In addition, the adsorbed Au(III) complexes were spontaneously reduced to elemental gold in spite of the absence of a specific reducing agent.
The results of this study suggest that adsorption and spontaneous reduction of gold complexes on the surface of hydrous metal oxides with positive charge play an important role in gold precipitation in subsurface environment.     

Displacement properties of landslide masses at the initiation of failure in quick clay deposits and the effects of meteorological and hydrological factors

This study aimed to identify displacement properties of landslide masses at the initiation of failure and factors that affect the landslides activities in areas where quick clay is found. We set up a research site in a quick clay deposit area in Norway and monitored the displacements of landslide masses and meteorological and hydrological factors for a long period of time using an automatic monitoring system. The system collected data for two landslides that occurred at the site from the start of their movement until their ultimate collapse.

The two landslides that were monitored showed definite secondary and tertiary creep stages before they collapsed. One of the landslides moved from the secondary stage to the tertiary creep stage when another landslide occurred nearby. The tertiary stage of this landslide showed reconstruction of short primary, secondary, and tertiary creep stages. These phenomena suggested that (1) the stress at the end of the landslide mass was released during the nearby landslide, and (2) a new stress distribution was formed in the landslide mass. The critical strain differed for 14 times between the two landslide masses we monitored. The difference was likely attributable to the difference in the contents of quick clay, which shows small critical stress against slope failure, as well as topological factors.

Our analyses of the effects of hydrological and meteorological factors on landslides showed that the precipitation of 3 and 10 days before six slope failures as the final stages of the landslides that had occurred in the research area was no different from the mean precipitation of periods that showed no slope failure, suggesting that precipitation had no direct effects on the collapse of the landslide masses. On the other hand, the traveling velocities of the landslide masses during the secondary creep stage, which was prior to their collapse, were affected by the water content of the soil and precipitation (and the amount of snowmelt water), but was little correlated with the pore-water pressure of the quick clay layer. We also found that the presence of snow cover scarcely affected landslide movements.     

Hydrologic and geochemical influences on the dissolved silica concentration in natural water in a steep headwater catchment

The dissolved silica concentrations in groundwater, springwater, and streamwater were measured on an unchanneled hillslope in the Tanakami Mountains of central Japan. The effects of preferential flowpaths, including lateral and vertical flow in the soil layer and flow through bedrock fractures, on the variation in the dissolved silica concentrations in runoff and groundwater were examined, as were the effects of the mixing of water from geochemically diverse water sources on the dissolved silica concentrations. The mean dissolved silica concentrations in water sampled from 40 cm below the soil surface and in transiently formed groundwater above the soil-bedrock interface during rainfall events were relatively constant, independent of the variation in the mixing ratio of pre-event water and incoming throughfall. These waters were mostly supplied by the vertical infiltration of water in soil. The mean dissolved silica concentrations were similar, regardless of sampling depth, although the mean residence time of the water increased with depth. These results indicated that the dissolved silica concentrations in soil water and transient groundwater were independent of contact time between the water and minerals. The mean dissolved silica concentration in perennially saturated groundwater above the soil-bedrock interface, which was recharged by water infiltrating through soil, and water emerging from bedrock in an area near the spring was more than twice that of transient groundwater, and the variation was relatively large. The mean dissolved silica concentration increased significantly downslope, from perennial groundwater to spring from soil matrix to stream, and the spring and stream concentrations also showed large variations. The dissolved silica concentration was highest in the spring from a bedrock fracture and was relatively constant. The mixing of water from two geochemically diverse water sources, soil and bedrock, controlled the dissolved silica concentrations of the perennial groundwater, the spring from soil matrix, and the stream. Our results demonstrated that in most areas of this headwater catchment, the preferential flowpaths have only a small effect on the dissolved silica concentrations. In a small area, which was < 2% of the total catchment area near the spring, the dissolved silica concentration was controlled by the mixing of water from geochemically diverse water sources.