Purpose

Within most environmental contexts, the collection of ‘undisturbed’ samples is widely relied upon in studies of soil and sediments. However, the impact of sampler-induced disturbance is rarely acknowledged, despite the potential significance of modification to sediment structure for the robustness of data interpretation. In this study, 3D computed X-ray microtomography (μCT) is used to evaluate and compare the disturbance imparted by four commonly used sediment sampling methods within a coastal salt marsh.

Materials and methods

Paired sediment core samples from a restored salt marsh at Orplands Farm, Essex, UK, were collected using four common sampling methods (push, cut, hammer and gouge methods). Sampling using two different area-ratio cores resulted in a total of 16 cores that were scanned with μCT to identify and evaluate sediment structural properties of samples that can be attributed to sampling method.

Results and discussion

3D qualitative analysis identifies a suite of sampling disturbance structures including gross-scale changes to sediment integrity and substantial modification of pore space, structure and distribution, independent of sediment strength and stiffness. Quantitative assessment of changes to pore space and sediment density arising from the four sampling methods offers a means of direct comparison between the impact of depth sampling methods. Considerable disturbance to samples results from use of push, hammer and auguring samplers, whilst least disturbance is found in samples recovered by cutting and advanced trimming approaches.

Conclusions

In many environmental studies involving sediment recovery through coring or other depth sampling, there is no such thing as an undisturbed sediment sample. The novel use of μCT scanning of sealed sediment cores has enabled the identification and evaluation of the nature and extent of sample disturbance resulting from four common types of sediment recovery methods. Depth sampling and coring methods remain key tools for understanding sediments and soils, but referring to undisturbed sediment sampling is no longer tenable without supporting evidence.

中文翻译：

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没有“未受干扰”的土壤和沉积物采样：通过3D X射线计算机断层扫描显示采样器引起的盐沼沉积物变形

目的

在大多数环境中，土壤和沉积物研究广泛依赖“未受干扰”的样本的收集。然而，尽管对沉积物结构进行修改对于数据解释的鲁棒性具有潜在意义，但采样器引起的干扰的影响却鲜为人知。在这项研究中，使用3D计算机X射线断层摄影术（μCT）评估和比较了沿海盐沼内四种常用沉积物采样方法带来的干扰。

材料和方法

使用四种常见的采样方法（推，切，锤和凿法），从英国埃塞克斯郡Orplands农场恢复的盐沼中收集了成对的沉积物岩心样本。使用两个不同的面积比岩心进行采样后，总共使用μCT扫描了16个岩心，以识别和评估可归因于采样方法的样品的沉积物结构特性。

结果和讨论

3D定性分析可确定一套采样扰动结构，包括沉积物完整性的总体尺度变化以及孔隙空间，结构和分布的实质性变化，而与沉积物强度和刚度无关。四种采样方法对孔隙空间和沉积物密度变化的定量评估提供了一种直接比较深度采样方法影响的方法。使用推，锤和螺旋式采样器会对样品造成很大的干扰，而通过切割和高级修整方法回收的样品中干扰最小。

结论

在许多涉及通过取芯或其他深度采样进行沉积物回收的环境研究中，没有诸如不受干扰的沉积物样本之类的问题。μCT扫描对密封的沉积物岩心的新颖使用使得能够鉴定和评估由四种常见的沉积物回收方法引起的样品扰动的性质和程度。深度采样和取芯方法仍然是了解沉积物和土壤的关键工具，但是在没有证据支持的情况下，提及不受干扰的沉积物采样不再成立。