Spectrum Analysis of the Reflected Waves Observed in the Nikko Region, Central Japan

—The Nikko region, in northern Kanto, central Japan, which is a high seismicity region, is located near the volcanic front. Many seismic observations have been carried out around the Nikko region because the seismograms of the shallow earthquakes occurring in this region show an S-wave reflected phase (SxS) and an S-to-P mode-converted and reflected phase (SxP) from a mid-crustal seismic velocity discontinuity. The depth of the mid-crustal reflector was estimated to be about 9–16 km. From the amplitude analyses of SxS and SxP phases, the material of the mid-crustal layer just beneath the reflector was expected to be a low rigidity layer, which was interpreted as partially molten rocks. No evidence has been shown for the internal properties of the material of the reflector. The Vp/Vs ratio is a good measure to distinguish between the two candidates for seismic reflectors; i.e., partially molten rocks and rocks containing water. We investigate the Vp/Vs ratio of the reflector using the spectrum analyses of the data observed by a seismic array. From spectrum analysis of the data, we indicate that the Vp/Vs ratio of 2.5 is better than that of 1.8 to explain the observed data, which shows that the material beneath the reflector consists of partially molten rocks.     

Comparison of vegetation changes along grazing gradients with different numbers of livestock

The objective of this study was to clarify whether the changes in percent cover of plant functional types (i.e., life forms and growth forms) along a grazing gradient reflect the livestock number, which would reinforce the reliability of using a grazing gradient design and improve the management of rangeland. We selected two livestock camps that for many years have had different numbers of livestock, with approximately six times more sheep-equivalents at site 1 than at site 2. Vegetation was sampled in 10 quadrats on five transects along the grazing gradient at each site. In each quadrat, we recorded percent cover of each plant species. Our findings suggested that vegetation changes along the grazing gradient under different livestock numbers were characterized by changes in the cover of life forms: perennial species were replaced by annual species near the camps (10–50 m). However, we did not find growth form change that reflected the difference in the number of livestock.     

Ionospheric delay gradient model for GBAS in the Asia-Pacific region

GPS Solutions - We investigated characteristics of anomalous spatial gradients in ionospheric delay on GNSS signals in the Asia-Pacific (APAC) low-magnetic latitude region in the context of the...     

Are small rodents key promoters of ecosystem restoration in harsh environments? A case study of abandoned croplands on Mongolian grasslands

We focused on the potential contribution of fossorial rodents to recovery of degraded abandoned Mongolian croplands. From field observations and the literature, we determined that plant litter and soil crusting were the main factors preventing establishment or growth of the perennial grass Elymus chinensis (Poaceae) on these croplands. We hypothesized that small fossorial rodents such as Mongolian gerbils promote grass establishment and growth by clearing litter and destroying crusts. We designed a path model linking number of burrows to patch size and plant volume of E. chinensis. As we hypothesized, small rodents increased the patch size of E. chinensis through reduction of litter cover. However, unexpectedly, we could not find significant effects on E. chinensis via crust thickness. Our results suggest that litter removal by the rodents gave E. chinensis suitable space that was free of competitors; this allowed expansion of the E. chinensis patches. Any effect of soil crusting on plant volume could not be explained simply by the variables we used, probably because some other mechanism, such as temporal variation in the crust, was involved. We demonstrate that small rodents are key agents in the recovery of degraded grasslands.     

Preparation of the standard solutions of nitrate and their application to seawater and freshwater

Responding to the recommendation at the first Meeting of the International Coordination Group for the Cooperative Study of the Kuroshio and Adjacent Regions (CSK) 1965, a series of nitrate standard solutions consisting of eight different concentrations ranging from 0 to 50g-at NO₃-N/l in 30.5 sodium chloride solution with the highest purity was prepared for nitrate-N determination in seawater. The solutions have been proved to be stable at least 520 days after preparation.The best way of handling and conditioning the copper-cadmium column was studied for securing the perfect and reproducible conversion of nitrate to nitrite for the procedure as proposed byWood et al. (1967).It was also shown that the method can be applied to freshwater samples by the addition of sodium chloride and adjusting pH properly.     

A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China

A secular variation record of the geomagnetic field direction for the last 6.5  kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc . The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad . Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad , declination was westerly ranging from about −20° to −5° in Erhai Lake, east-central China, and Japan.