Evaluation of intrinsic vulnerability to nitrate contamination of groundwater: appropriate fertilizer application management

In agricultural areas, fertilizer application is the main source of nitrate contamination of groundwater. To develop fertilizer management strategies to combat this problem, arable land in Hokkaido, Japan was evaluated using geographic information system techniques for intrinsic groundwater vulnerability to nitrate contamination. The DRASTIC method was modified to adapt it to the Hokkaido environment and used for the evaluation. Of the seven original DRASTIC factors, the depth to water (D), net recharge (R), soil media (S), topography (T), and impact of vadose zone media (I) were selected and used to explain the vertical movement of contaminants to the aquifer. The rating for the net recharge factor was also modified to a dilution factor for contaminants, rather than as a transporter. The frequency of wells with nitrate concentrations exceeding the Japanese environmental standard (10 mg/L) was reasonably explained by vulnerability evaluation results (GLM: logit-link, quasi-binomial distribution, Y = [1 + exp(6.873765 − 0.045988 × X)]⁻¹, p < 0.001). However, in the paddy fields and pastures, vulnerability did not exhibit a clear relationship with the frequency of wells exceeding the standard. This suggests that the modified DRASTIC method is applicable for fertilizer application management in upland fields. In addition, under the ongoing policy for acreage allotment for rice production, this method will be useful for deciding the arrangement of arable land and crop rotation taking into consideration the potential risk of fertilizer-induced nitrate contamination of groundwater.     

Mechanical properties of cementitious sand and sand with small cyclic shear strain to assess aging effects on liquefaction

Liquefaction damage from earthquakes frequently indicates effects of sand aging on liquefaction resistance: Liquefaction damage in natural or aged reclaimed ground has been much less than that in young reclaimed ground. However, the mechanisms underlying aging effects remain unclear. Cementation and stress history of sand strongly influence aging effects: Cementation raises liquefaction resistance, whereas liquefaction history sometimes reduces liquefaction resistance. Small cyclic shear strain, from which the induced density change is almost negligible, was adopted as representing the stress history. To evaluate liquefaction resistance, initial shear modulus, and deformation characteristics of sand, we prepared specimens by adding cement and by applying a small cyclic shear strain. In cementitious sand, liquefaction resistance increased when cement contents exceeded 0.3% by mass. The initial shear modulus apparently increased at the same degree of cement addition as that which increased the liquefaction resistance. For sand with a small cyclic shear strain, the liquefaction resistance increased when the applied cyclic axial strain exceeded 0.01%. Application of small cyclic shear strain only slightly increased the initial shear modulus, but the linear elastic region tended to expand to greater shear strain. Shear properties of sand with small cyclic shear strain resembled those found for sand that had been consolidated for a long time.

     

Concentration of polychlorinated biphenyls (PCBs) in beached resin pellets: variability among individual particles and regional differences

Concentrations of polychlorinated biphenyls (PCBs) in beached resin pellets were examined to reveal variability between individual particles and differences among beaches. Fifty-five resin pellets from a beach in Tokyo were individually analyzed for PCBs, and showed concentrations ranging from <28 to 2,300 ng/g. This indicates that concentrations are highly variable between particles. Among several characters, discoloration (e.g., yellowing) had a positive relationship with PCB concentration: discolored pellets contained more PCBs than others on most of the beaches sampled. Given the color-selective ingestion of food by some organisms, this may be ecotoxicologically important. Measurements of samples from 47 beaches in Japan showed regional differences in PCB concentrations in resin pellets consistent with those in mussels. Sporadic high concentrations of PCBs were also found in pellets from remote islands, suggesting that resin pellets could be the dominant route of exposure to the contaminants at remote sites. The similarity of PCB concentrations between resin pellets and mussels suggests a potential use of resin pellets to monitor pollution in seawater.     

The 1989 submarine eruption off eastern Izu Peninsula,Japan: ejecta and eruption mechanisms

The submarine eruption of a new small knoll, which was named Teishi knoll, off eastern Izu Peninsula behind the Izu-Mariana arc occurred in the evening of 13 July 1989. This is the first historic eruption of the Higashi-Izu monogenetic volcano group. The eruption of 13 July followed an earthquake swarm near Ito city starting on 30 June. There were subsequent volcanic tremors on 11 and 12 July, and the formation of the Teishi knoll on the 100 m deep insular shelf 4 km northeast of Ito city. There were five submarine explosions, which were characterized by intermittent domelike bulges of water and black tephra-jets, which occurred within 10 min on 13 July. Ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria, highly vesiculated pumice, and lithic material. Petrographical features suggest that the pumice was produced by vesiculation of reheated wet felsic tuff of an older formation. The Teishi knoll, before the eruption, was a circular dome, 450 m across and 25 m high, with steep sides and a flat summit. Considerations of submarine topographic change indicate the knoll was raised by sill-like intrusion of 10⁶ m³ of magma beneath a 30 m thick sediment blanket. This shallow intrusion is assumed to have started on 11 July when volcanic tremors were observed for the first time, but there was no indications of violent interaction between wet host sediments and intruding magma. The submarine eruption of 13 July appears to have been Friggered by a major lowering of the magma-column. The basalt scoria, having crystal-contents of more than 60%, is assumed to be derived from the cooled plastic margin of the shallow intrusive body. However, glassy scoria, which would indicate the interaction between hot fluidal magma and external water, was not observed. A scenario for the 1989 submarine eruption is as follows. When rapid subsidence of the hot interior of the intrusive magma occurred, reduced pressure caused the implosion of cooled plastic magma, adjacent pressurized, hot host material, and wet sediment. The mixing of these materials triggered the vigorous vapor explosions.     

Subvolcanic structure of the central dike swarm associated with the ring complexes in the Shitara district,central Japan

The Subvolcanic structure of the central dike swarm associated with the Miocene Otoge ring complex and the Shitara igneous complex, central Japan, has been reconstructed. The central dike swarm was supplied from several aligned magma reservoirs. Flow lineations observed at the margin of the dikes converge towards a region that is regarded as a magma reservoir about 1–2 km below present sea level. The minimum diameter of the magma reservoir corresponds to the width of the central dike swarm, estimated to be about 3–4 km. The inferred magma reservoir of the Otoge ring complex, may have a zoned structure, as suggested by the flow lineations of dikes and the arrangement of cone sheets. Felsic magma occupied the upper part, about 1–2 km below present sea level, and basic magma the lower part, deeper than 2 km. The centre of the Shitara igneous complex is interpreted to be composed of several other shallow magma reservoirs. The distribution pattern in plan view of the central dike swarm is summarized from the frequency of dikes (defined by the number of dikes per kilometre in the direction normal to the trend of the dike swarm) and the variations of the different properties of individual dikes along the dike swarm. It has a plane of symmetry normal to the dike swarm above the magma reservoir. The patterns critical to a general understanding of the dike formation are:

Co-ignimbrite ash-fall deposits of the 1991 eruptions of Fugen-dake, Unzen Volcano, Japan

Fugen-dake, the main peak of Unzen Volcano, began a new eruption sequence on November 17, 1990. On May 20, 1991, a new lava dome appeared near the eastern edge of the Fugen-dake summit. Small-scale, 10⁴–10⁶ m³ in volume, Merapi-type block and ash flows were frequently generated from the growing lava dome during May–June, 1991. These pyroclastic flows were accompanied by co-ignimbrite ash plumes that deposited ash-fall deposits downwind of the volcano. Three examples of co-ignimbrite ash-fall deposits from Unzen pyroclastic flows are described. The volume of fall deposits was estimated to be about 30% by volume of the collapsed portions of the dome that formed pyroclastic flows. This proportion is smaller than that described for other larger co-ignimbrite ash-fall deposits from other volcanoes. Grain size distributions of the Unzen co-ignimbrite ash-fall deposits are bi-modal or tri-modal. Most ashes are finer than 4 phi and two modes were observed at around 4–7 phi and 9 phi. They are composed mainly of groundmass fragments. Fractions of another mode at around 2 phi are rich in crystals derived from dome lava. Some of the fine ash component fell as accretionary lapilli from the co-ignimbrite ash cloud indicating either moisture or electrostatic aggregation. We believe that the co-ignimbrite ash of Unzen block and ash flows were formed by the mechanical fracturing of the cooling lava blocks as they collapsed and moved down the slope. These ashes were entrained into the convective plumes generated off the tops of the moving flows.     

Marine protected areas in Japan: Institutional background and management framework

Information on the location and area for all MPAs in Japan was collected through a comprehensive survey targeting government officials and local stakeholders. It was verified that at least 1161 MPAs exist in Japan. Of these, 1055 are implemented in conjunction with fishery regulations in the form of no-take zones. More than 30% of the individual MPAs in Japan were established by self-imposed instruments agreed by members of fishery co-management organizations. It was suggested that the autonomous MPAs are not a product of simple altruism, but rather are logical extensions of the tenure system guaranteed by the government legal system.     

A fault scarp in an urban area identified by LiDAR survey: A Case study on the Itoigawa–Shizuoka Tectonic Line, central Japan

A light detection and ranging (LiDAR) survey was conducted in a densely built-up area to generate a high-resolution digital elevation model (DEM) to look for active faults. The urban district of Matsumoto City in central Japan is located in a 3-km² basin along the Itoigawa–Shizuoka Tectonic Line active fault system, one of Japanese onshore fault systems with the highest earthquake probability. A high-resolution DEM at a 0.5-m-grid interval was obtained after removing the effects of laser returns from buildings, clouds and vegetation. It revealed a continuous scarp, up to ~ 2 m in height. Borehole data and archaeological studies indicate the scarp was formed during the most recent faulting event associated with historical earthquakes. In addition, the fault scarp strongly supports that the urban district is in a pull-apart basin related to a fault step-over between two left-lateral strike-slip faults. Consequently, accurate interpretation of fault geometry is crucial to provide estimates of future surface deformation and to allow modeling of basin structure and strong ground motion. Thus, the LiDAR mapping survey in urban districts is effective for detailed active fault mapping in order to constrain basin structure and to forecast the exact location of surface rupturing associated with large earthquakes.     

Measurement of persistent organic pollutants (POPs) in plastic resin pellets from remote islands: toward establishment of background concentrations for International Pellet Watch

Plastic resin pellets collected from remote islands in the Pacific, Atlantic, and Indian Oceans and the Caribbean Sea were analyzed for polychlorinated biphenyls (PCBs), dichloro-diphenyltrichloroethane and its degradation products (DDTs), and hexachlorocyclohexanes (HCHs). Concentrations of PCBs (sum of 13 congeners) in the pellets were 0.1-9.9 ng/g-pellet. These were 1-3 orders of magnitude smaller than those observed in pellets from industrialized coastal shores. Concentrations of DDTs in the pellets were 0.8-4.1 ng/g-pellet. HCH concentrations were 0.6-1.7 ng/g-pellet, except for 19.3 ng/g-pellet on St. Helena, where current use of lindane is likely influence. This study provides background levels of POPs (PCBs<10 ng/g-pellet, DDTs <4 ng/g-pellet, HCHs <2 ng/g-pellet) for International Pellet Watch. Sporadic large concentrations of POPs were found in some pellet samples from remote islands and should be considered in future assessments of pollutants on plastic debris.