18OSO4 and 18OH2O as prospective indicators of elevated arsenic in the Goose River ground-watershed, Maine

Anomalous geogenic arsenic occurs in drinking water from the Goose River crystalline ground-watershed in mid-coastal Maine. Isotope investigations were useful in understanding release areas of arsenic into affected water wells. The isotope composition of sulfate associated with probable arsenian pyrite oxidation is described. Correlation of '¹⁸O_SO4 enrichment [+4.57 to +7.46‰ Vienna Standard Mean Ocean Water (VSMOW)] is discussed with specific and recurring areas of elevated arsenic (10-52 µg l^-1). Although arsenic concentrations were highly variable over 2 years per well, '¹⁸O_SO4 values were always consistent and suggested a specific and consistent risk for elevated arsenic occurrences for each well. The '¹⁸O values in the water molecule (-12.07 to -8.81‰ VSMOW) and the '¹⁸O_SO4 values may serve as prospective indicators of prominent zones of aeration at depth in discrete fracture zones. The '¹⁸O values in the water molecule and sulfate ion appear to indicate that more than 60% of O₂ incorporated into the SO₄^2- ion are from dissolved oxygen and belong to distinct fractured areas. These aeration zones or oxidation fronts, as outlined by oxygen isotopes, are sentinels for high arsenic risk in groundwater.     

Soil gases associated with rift zones in the Eastern Snake River Plain,Idaho, U.S.A.

Soil gases have been measured, utilizing petroleum nearsurface exploration techniques, in the volcanic province of the Eastern Snake River Plain, In Idaho, U.S.A. The analyses of the soil atmosphere included light hydrocarbon gases, helium, hydrogen, and carbon dioxide. Samples were collected in and near recent basaltic rift zones. Characterization of rift zone soil gases has indicated variability of their compositional and magnitude makeup. Suggestion of some deeper sourced gases having migrated through fractures in the rift zones is advanced. Also differences among the samples rift zones are presented.     

Impact of road‐generated storm runoff on a small catchment response

The impact of road‐generated runoff on the hydrological response of a zero‐order basin was monitored for a sequence of 24 storm events. The study was conducted in a zero‐order basin (C1; 0·5ha) with an unpaved mountain road; an adjacent unroaded zero‐order basin (C2; 0·2 ha) with similar topography and lithology was used to evaluate the hydrological behaviour of the affected zero‐order basin prior to construction of the road. The impact of the road at the zero‐order basin scale was highly dependent on the antecedent soil‐moisture conditions, total storm precipitation, and to some extent rainfall intensity. At the beginning of the monitoring period, during dry antecedent conditions, road runoff contributed 50% of the total runoff and 70% of the peak flow from the affected catchment (C1). The response from the unroaded catchment was almost insignificant during dry antecedent conditions. As soil moisture increased, the road exerted less influence on the total runoff from the roaded catchment. For very wet conditions, the influence of road‐generated runoff on total outflow from the roaded catchment diminished to only 5·4%. Both catchments, roaded and unroaded, produced equivalent amount of outflow during very wet antecedent conditions on a unit area basis. The lag time between the rainfall and runoff peaks observed in the unroaded catchment during the monitoring period ranged from 0 to 4 h depending on the amount of precipitation and antecedent conditions, owing mainly to much slower subsurface flow pathways in the unroaded zero‐order basin. In contrast, the lag time in the roaded zero‐order basin was virtually nil during all storms. Copyright © 2009 John Wiley & Sons, Ltd.     

Naturally occurring mercury contamination in a pristine environment?

About 19 percent of sampled residential water wells situated in a pristine, granitic Maine (USA) coastal environment have elevated mercury concentrations according to USEPA standards. There are no identified anthropogenic sources for mercury but some local granitoids have anomalous mercury concentrations in the Waldoboro Pluton Complex (WPC). Site-specific hydrogeologic conditions appear to have aggravated what is otherwise only trace amounts of some naturally occurring toxic analytes in the groundwater in contact with the suspect granitoids of the WPC. The extent of mercury in this crystalline rock environment is examined here. It is prudent to exercise preventive measures and appropriately site water supply wells and not expect complete remediation of the affected homeowners' wells.     

Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan

Landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10‐fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 10³ m³ km^?2 compared with 1·3 × 10³ m³ km^?2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

吉林省伊通地区橄榄岩包体的同位素特征与岩石圈地幔时代

吉林省伊通新生代火山群中大孤山所伴生的东小山火山含有丰富的地幔橄榄岩包体,详细的岩石学和矿物学工作显示,这些包体的主要岩石类型为尖晶石二辉橄榄岩,含有少量的方辉橄榄岩和异剥橄榄岩。包体的结构类型多样,包括粒状变晶结构、碎斑状结构、糜棱结构和筛状变晶结构。主量元素及矿物化学资料表明,这些地幔橄榄岩包体大都比较饱满,说明其所经历的部分熔融程度较低。微量元素显示,包体在形成以后经受过不同程度地幔交代作用的影响。矿物平衡温度计算结果表明包体的平衡温度为989～1142℃,来源深度约为40～70km。Sr-Nd-Hf同位素资料反映二辉橄榄岩包体具有亏损地幔的特征。Re-Os同位素资料显示上述岩石圈地幔的主体形成于显生宙期间,少量具有中元古代Re亏损年龄的样品所代表的古老地幔与本区上覆地壳成因无关,可能是软流圈中固有的较古老的大陆岩石圈地幔。     

Stormflow generation involving pipe flow in a zero‐order basin of Peninsular Malaysia

Hydrological responses in a zero‐order basin (ZOB), a portion of whose discharge emerged via preferential flow through soil pipes, were examined over a 2‐year period in Peninsular Malaysia to elucidate primary stormflow generation processes. Silicon (Si) and specific conductance (EC) in various runoff components were also measured to identify their sources. ZOB flow response was dependent on antecedent precipitation amount; runoff increased linearly with precipitation during events >20 mm in relatively wet antecedent moisture conditions. Runoff derived from direct precipitation falling onto saturated areas accounted for <0·2% of total ZOB flow volume during the study period, indicating the predominance of subsurface pathways in ZOB flow. ZOB flow (high EC and low Si) was distinct from perennial baseflow via bedrock seepage (low EC and high Si) 5 m downstream of the ZOB outlet. Pipe flow responded quickly to ZOB flow rate and was characterized by a threshold flow capacity unique to each pipe. Piezometric data and pipe flow records demonstrated that pipes located deeper in the soil initiated first, followed by those at shallower depths; initiation of pipe flow corresponded to shallow groundwater rise above the saprolite‐soil interface. Chemical signatures of pipe flow were similar to each other and to the ZOB flow, suggesting that the sources were well‐mixed soil‐derived shallow groundwater. Based upon the volume of pipe flow during storms, the combined contribution of the pipes monitored accounted for 48% of total ZOB flow during the study period. Our results suggest that shallow groundwater, possibly facilitated by preferential flow accreted above the saprolite–soil interface, provides dominant stormflow, and that soil pipes play an important role in the rapid delivery of solute‐rich water to the stream system. Copyright © 2006 John Wiley & Sons, Ltd.     

Hortonian overland flow from Japanese forest plantations—an aberration,the real thing,or something in between?

There is a growing opinion that poorly managed plantation forests in Japan are contributing to increased storm runoff and erosion. Here we present evidence to the contrary from runoff plots at two scales (hillslope and 0·5 × 2 m plots) for several forest conditions in the Mie and Nariki catchments. Runoff coefficients from small plots in untended hinoki forests were variable but typically higher than from better managed or deciduous forests during small storms at Nariki; at Mie, runoff during small events was highly variable from all small plots but runoff coefficients were similar for hinoki plots with and without understory vegetation, while the deciduous plot had lower runoff coefficients. Storm runoff was less at the hillslope scale than the plot scale in Mie; these results were more evident at sites with better ground cover. During the largest storms at both sites, differences in runoff due to forest condition were not evident regardless of scale. Dynamic soil moisture tension measurements at Nariki indicated that during a large storm, flow in the upper organic‐rich and root‐permeated soil horizons was 3·2 times higher than measured overland runoff from a small hinoki plot with poor ground cover and 8·3 times higher than runoff from a deciduous forest plot. On the basis of field observations during storms, at least a portion of the monitored ‘Hortonian overland flow’ was actually occurring in this near‐surface ‘biomat’. Therefore our field measurements in both small and large plots potentially included biomat flow in addition to short‐lived Hortonian runoff. Because overland flow decreased with increasing scale, rill erosion did not occur on hillslopes. Additionally, runoff coefficients were not significantly different among cover conditions during large storms; thus, the ‘degraded’ forest conditions appear not to greatly enhance peak flows or erosion potential at larger scales, especially when biomat flow is significant. Copyright © 2007 John Wiley & Sons, Ltd.     

Diagnosis of trace Pb in domestic wells,Upper Gloucester Catchment,Maine, USA

Dissolved Pb in 32 wells associated with corroding submersible pumps is examined within a rural water district after almost 20 years (1984–2002). Groundwater Pb ranged from 0.4–24.9 μg L⁻¹ after 24 h pump flushing. Preliminary geochemistry and representative borehole lithology examinations were extrapolated by Markov chain modeling. The first-order geostatistical realizations of glacial sediments coupled with the Monte Carlo Metropolis-Hasting method suggest that elevated trace Pb persists in sand and gravel units, and continues at least to 40 m depth in the catchment. The ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb isotope compositions of groundwater Pb were decisive in discriminating the importance of leached Pb from submersible pump materials among geogenic sources.