1993年8月8日关岛地震前后ULF磁场异常变化

给出了1993年8月8日关岛地震(Ms=7.1,深度60km)前后ULF(Ultra Low Frequency:超低频信号,频段为O.005～10Hz)地磁信号的分析结果.ULF观测系统位于日本关岛,距离震中约65km.对观测数据进行分析后得出以下结论:①建议用非常细致的统计分析(月均值,标准偏差)来判断ULF信号的强度和极化值(比如:Z/H比值);②ULF信号活动强度和∑Kp的对比,有助于区别空间地磁脉动和非空间源地磁辐射;③发现Z/H比值的使用在把可能来自震源的辐射从空间等离子波中识别出来非常重要;④从对极化值的时间序列的统计分析发现极化值在震前仅一个月时有一个显著的增强,表明这期间的电磁异常现象很可能是震磁前兆信号;⑤Z分量的时间变化类似于Loma Prieta地震前的变化,即在震前10天到两周有明显的增强,在震前几天出现另一次增强;⑥可能与地震有关的电磁辐射是一种类似噪音的自然现象,它们的主要频带范围0.02～0.05Hz(最大幅值约为0.1nT).     

Factors controlling nitrogen and dissolved organic carbon exports across timescales in two watersheds with different land uses

Investigating factors controlling the temporal patterns of nitrogen (N) and dissolved organic carbon (DOC) exports on the basis of a comparative study of different land uses is beneficial for managing water resources, especially in agricultural watersheds. We focused our research on an agricultural watershed (AW) and a forested watershed (FW) located in the Shibetsu watershed of eastern Hokkaido, Japan, to investigate the temporal patterns of N and DOC exports and factors controlling those patterns at different timescales (inter‐annual, seasonal, and hydrological event scales). Results showed that the annual patterns of N and DOC exports significantly varied over time and were probably controlled by climate. Higher discharge volumes in 2003, a wet year, showed higher N and DOC loadings in both watersheds. However, this process was also regulated by land use associated with N inputs. Higher concentrations and loadings were shown in the agricultural watershed. At the seasonal scale, N and DOC exports in the AW and the FW were more likely controlled by sources associated with land use. The Total N (TN) and Nitrate‐N (NO₃^?‐N) had higher concentrations during snowmelt season in the AW, which may be attributed to manure application in late autumn or early winter in the agricultural watershed. Concentrations of TN, NO₃^?‐N, dissolved organic nitrogen (DON), and DOC showed higher values during the summer rainy season in the FW, related to higher litter decomposition during summer and autumn and the fertilizer application in the agricultural area during summer. Higher DOC concentrations and loadings were observed during the rainy season in the AW, which is probably attributed to higher DOC production related to temperature and microbial activity during summer and autumn in grasslands. Correlations between discharge and concentrations differed during different periods or in different watersheds, suggesting that weather discharge can adequately represent the fact that N export depends on N concentrations, discharge level, and other factors. The differing correlations between N/DOC concentrations and the Si concentration indicated that the N/DOC exports might occur along different flow paths during different periods. During baseflow, the high NO₃^?‐N exports were probably derived from deep groundwater and might have percolated from uplands during hydrological events. During hydrological events, NO₃^?‐N exports may occur along near‐surface flow paths and in deep groundwater, whereas DOC exports could be related to near‐surface flow paths. At the event scale, the relationships between discharge and concentrations of N and DOC were regulated by antecedent soil moisture (shallow groundwater condition) in each watershed. These results indicated that factors controlling N and DOC exports varied at different timescales in the Shibetsu area and that better management of manure application during winter in agricultural lands is urgently needed to control water pollution in streams. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of sampling downscaling: a case for wintertime precipitation in Hokkaido

This study has developed sampling downscaling (SmDS), in which dynamical downscaling (DDS) is executed for a few of period selected from a long-term integration by general circulation model based on an observed statistical relationship between large-scale climate and regional-scale precipitation. SmDS expectedly produces climatology and frequency distribution of precipitation over a nested region with reducing computational cost, if a global-scale climate pattern mostly controls regional-scale weather statistics. Here SmDS was attempted for wintertime precipitation over Hokkaido, Japan, because a linkage between snowfall and sea-level pressure patterns has been known by Japanese synopticians and it can be detected by singular value decomposition (SVD) analysis on wintertime inter-annual variability during the period from 1980/1981 to 2009/2010 for precipitation over Hokkaido and moisture flux convergence around there. DDS for the full period over the same domain was also performed for comparison with SmDS. SmDS selected two winters from the top and two winters from the bottom of the projection onto the first SVD mode. It was found that, comparing with the full DDS, SmDS indeed provided unbiased statistics for average but exaggerated extreme statistics such as heavy rainfall frequency. It was also shown that the sampling in the SmDS method was much more effective than the random sampling.     

The distribution of total and methylmercury concentrations in soils near the Idrija mercury mine, Slovenia, and the dependence of the mercury concentrations on the chemical composition and organic carbon levels of the soil

Although the mining activity of the Idrija mine in Slovenia ceased in 1995, a large amount of mining dregs containing high concentrations of mercury remains in the area. The mining dregs were transported with river flow and deposition along the Idrija River. To estimate the dispersion and change in the chemical form of mercury, a total of 28 soil core samples were taken around the river. The individual core samples were separated into layers for the analysis of their chemical composition, carbon contents, total mercury (T-Hg) and methylmercury (MeHg) concentrations. The chemical composition measured by X-ray fluorescence spectrometry was useful to estimate the dispersion of tailings: the fluvial terrace soil had a chemical composition similar to that of the tailings and could be distinguished clearly from the forest soil. The highest T-Hg concentration, 1,100 mg kg⁻¹, was observed in the fluvial terrace soil near the mine. Although the concentration decreased gradually along with distance from the mine, concentrations higher than 200 mg kg⁻¹ of T-Hg were still observed in the fluvial terrace soil approximately 20 km downstream from the mine. In the vertical distribution of T-Hg in the hillslope soil, a higher value was observed in the upper layers, which suggests the recent atmospheric deposition of mercury. The concentration of MeHg was the lowest at the riverside and higher in the hillslope soil, which was the opposite of the T-Hg distribution. The total organic carbon content tracked similarly with the distribution of MeHg and a linear relation with a significantly high correlation coefficient was obtained. The distinction may be related to the different dispersion process of mercury, and the organic carbon contents may be an important factor for MeHg formation.