Organic geochemical investigation of far-field tsunami deposits of the Kahana Valley,O‘ahu,Hawai‘i

Far-field tsunami deposits observed in the Kahana Valley, O‘ahu, Hawai‘i (USA), were investigated for their organic-geochemical content. During short high-energy events, (tsunamis and storms) organic and chemical components are transported with sediment from marine to terrestrial areas. This study investigates the use of anthropogenic based organic geochemical compounds (such as polycyclic aromatic hydrocarbons, pesticides and organochlorides) as a means to identify tsunami deposits. Samples were processed by solid–liquid extraction and analyzed using gas chromatography–mass spectrometry. A total of 21 anthropogenic marker compounds were identified, of which 11 compounds were selected for detailed analysis. Although the tsunami deposits pre-date industrial activity in Hawai‘i by several hundred years, distinct changes were found in the concentrations of anthropogenic marker compounds between sandy tsunami deposits and the surrounding mud/peat layers, which may help in identifying tsunami deposits within cores. As expected, low overall concentrations of anthropogenic markers and pollutants were observed due to the lack of industrial input-sources and little anthropogenic environmental impact at the study site. This geochemical characterization of tsunami deposits shows that anthropogenic markers have significant potential as another high-resolution, multi-proxy method for identifying tsunamis in the sedimentary record.     

Abundance estimates of an isolated population of common bottlenose dolphins Tursiops truncatus in Walvis Bay,Namibia, 2008–2012

The coastal population of common bottlenose dolphins Tursiops truncatus found in Namibia is regionally isolated and unique. This population faces several potential anthropogenic threats, especially in Walvis Bay, including boat-based tourism, a commercial harbour undergoing expansion, and aquaculture for oysters and mussels. Between 2008 and 2012, 238 boat-based surveys were conducted, resulting in 170 encounters with bottlenose dolphins. Overall, group sizes varied from 1 to 45 individuals (mean 10.7). Encounter rates, group sizes and total numbers of animals identified were higher in winter than in summer field seasons. The number, and survival and immigration parameters, of bottlenose dolphins using Walvis Bay was investigated using robust design and Huggins closed-population mark-recapture models. The highest numbers estimated were in the first and last years of the study, with estimates of 74–82 in 2008 and 76–77 in 2012 (numbers identified and upper 95% confidence limits). The only previously available data, from an incomplete study in the early 1990s, suggested that the population was between 100 and 150 individuals at the time. Although no linear trend in population size was obvious during the current study, the clear evidence of isolation, small population size, low annual birth rate, and potential long-term decrease in numbers since the early 1990s is concerning. Further work to collect data on demographic parameters is urgently recommended with a view to obtaining increased protection for this species.     

Identification and mapping of riverbed sediment facies in the Columbia River through integration of field observations and numerical simulations

In the Hanford Reach of the Columbia River, a thin layer of recent alluvium overlies the sedimentary formations that comprise the unconfined groundwater aquifer. Experimental and modelling studies have demonstrated that this alluvial layer exerts significant control on the exchange of groundwater and surface water (hydrologic exchange flux), and is associated with elevated levels of biogeochemical activity. This layer is also observed to be strongly heterogeneous, and quantifying the spatial distribution of properties over the range of scales of interest is challenging. Facies are elements of a sediment classification scheme that groups complex geologic materials into a set of discrete classes according to distinguishing features. Facies classifications have been used as a framework for assigning heterogeneous material properties to grid cells of numerical models of flow and reactive transport in subsurface media. The usefulness of such an approach hinges on being able to relate facies to quantitative properties needed for flow and reactive transport modelling, and on being able to map facies over the domain of interest using readily available information. Although aquifer facies have been used in various modelling contexts, application of this concept to riverbed sediments is relatively new. Here, we describe an approach for categorizing and mapping recent alluvial (riverbed) sediments based on the integration of diverse observations with numerical simulations of river hydrodynamics. The facies have distinct distributions of sediment texture that correspond to variations in hydraulic properties, and therefore provide a useful framework for assigning heterogeneous properties in numerical simulations of hydrologic exchange flows and biogeochemical processes.     

广东东莞地区中侏罗统塘厦组凝灰质沉积物的元素地球化学特征及构造背景

东莞地区中侏罗统塘厦组为富含凝灰质的湖泊沉积。对样品进行全岩分析和ICP-MS微量元素分析,并计算Sr/Ba、B/Ga和Ca/Mg比值,其比值变化与古盐度变化成正相关,特征显示塘厦组为咸水湖泊沉积,由下至上古盐度逐渐降低,水体深度也逐渐变浅。对样品进行ICP-MS稀土元素分析,计算各样品δCe值和(La/Yb)_N比值,δCe值介于0.83 ~ 1.31之间,(La/Yb)_N值均明显大于1或小于1,其特征反映湖泊沉积物沉积速率较低,只在塘厦组底部和上部出现相对高的沉积。元素P和Sr/Cu值反映其富集与迁移,受到气候的控制。元素P平均值在0.205×10^-2; Sr/Cu平均值大于4.0×10^-6,在中晚期出现最低值1.42×10^-6,这是塘厦组以干热气候为主,中晚期出现了短暂温湿气候所造成的。塘厦组为干热气候下缓慢沉积的咸水湖泊沉积。Zr-Th、La-Th-Sc判别图解、稀土元素特征及区域构造分析,显示中侏罗世东莞地区构造背景为活动大陆边缘的弧后盆地。受伸展作用影响,本区发育弧后裂谷型湖盆。泥岩La/Yb-∑REE源岩判别图解显示,源岩为玄武岩、花岗岩和沉积岩。     

River discharge reduces reef coral diversity in Palau

Coral community structure is often governed by a suite of processes that are becoming increasingly influenced by land-use changes and related terrestrial discharges. We studied sites along a watershed gradient to examine both the physical environment and the associated biological communities. Transplanted corals showed no differences in growth rates and mortality along the watershed gradient. However, coral cover, coral richness, and coral colony density increased with increasing distance from the mouth of the bay. There was a negative relationship between coral cover and mean suspended solids concentration. Negative relationships were also found between terrigenous sedimentation rates and the richness of adult and juvenile corals. These results have major implications not only for Pacific islands but for all countries with reef systems downstream of rivers. Land development very often leads to increases in river runoff and suspended solids concentrations that reduce coral cover and coral diversity on adjacent reefs.     

On the significance of sensitivity changes in eppley pyranometers†: Research note

Abstract

Analysis of radiation data from Suffield, Alberta and Swift Current, Saskatchewan reveals discrepancies that are strongly linked to changes in the actual and assigned calibration factors of the pyranometers used at those locations.     

The diurnal variation of wind direction at Calgary

The winds at Calgary airport show a diurnal variation. Night winds tend to be northwest, with afternoon winds from the Southeast. Other data show that this variation is not associated with local topography, but seems to be an effect of the Rocky Mountains to the west.     

High-frequency sediment-level oscillations in the swash zone

Sediment-level oscillations with heights of about 6 cm and shore-normal lengths of order 10 m have been measured in the swash zone of a high-energy, coarse-sand beach. Crests of oscillations were shore parallel and continuous alongshore. The oscillations were of such low steepness (height-to-length ratio approximately 0.006) that they were difficult to detect visually. The period of oscillation ranged between 6 and 15 min and decreased landward across the swash zone. The sediment-level oscillations were progressive landward with an average migration rate in the middle to upper swash zone of 0.8 m min⁻¹. Migration was caused mostly by erosion on the seaward flank of the crest of an oscillation during a period of net seaward sediment transport. Thus, the observed migration was a form migration landward rather than a migration involving net landward sediment transport. The observed sediment-level oscillations were different than sand waves or other swash-zone bedforms previously described.     

Influence of small-scale gold mining and toxic element concentrations in Bonsa river,Ghana: a potential risk to water quality and public health

A preliminary assessment of toxic element pollution caused by artisanal and small-scale gold mining in the Bonsa river of Ghana as well as the influence of TOC and SO₄ ^2? concentration on these traces in the sediment has been determined. With the exception of mercury (Hg), manganese (Mn), and arsenic (As), the concentration of aluminum (Al) in filtered river water exceeded the WHO guideline limit of 0.1 mg L^?1 in drinking water. Analyses of toxic element in sediment using Canadian Sediment Quality Criteria, contamination factor, geoaccumulation index, and enrichment factor indicate that river sediment is severely contaminated with Hg confirming the negative impact of the amalgamation technique in gold beneficiation in Ghana. The level of Hg in the surface water exceeded reported values from some rivers in Africa, Asia, and South America. The ranking order of the mean element concentration in both matrices followed the conservative order of traces found in the Earth crust except copper, which was below the detection limit of 0.01 mg kg^?1. A Pearson correlation matrix of the toxic element and geology of the river bedrock indicates that the Hg contamination is of anthropogenic origin whilst As, Mn, and Al are the result of natural enrichment. The partitioning of elements in the sediment compartments is independent of TOC and SO₄ ^2? concentration. Health-risk assessment based on average daily dose, hazard quotient, and cancer risk indicates that Hg is a health risk to the human population. In conclusion, the study has shown that there is a likely anthropic affection of the river and that this situation has worsened since earlier studies. In order to sustain aquatic life and to prevent future human health hazard, an immediate mercury remediation in the river is recommended.