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Impact of hydrocarbon biodegradation on low frequency electrical properties of unconsolidated sediments.

机译：碳氢化合物生物降解对未固结沉积物的低频电特性的影响。

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The influence of biodegradation processes and subsequent physicochemical changes on the low frequency electrical properties (e.g., real and imaginary conductivity) of unconsolidated sediments was investigated in laboratory sand columns and core sediments retrieved from a hydrocarbon contaminated site. The low frequency electrical measurements were conducted using induced polarization (IP) method in the frequency range 0.1--1000 Hz. Biological, geochemical, isotopic analyses, scanning electron microscopy images and surface area measurements were conducted to help in the interpretation of the low frequency electrical measurements.; In a laboratory column experiment, the biotic column (nutrient, dissolved diesel and bacteria) showed (a) temporal increase in the real, imaginary, and surface conductivity, and (b) temporal decrease in the formation factor. The abiotic columns (nutrient; and nutrient and dissolved diesel) showed no significant changes. Increase in microbial population numbers, decrease in organic carbon source, nitrate, and sulfate and increase in dissolved inorganic carbon and fluid conductivity were indicative of microbial activity in the biotic column. IP results of core sediments retrieved from the field showed that the magnitude of IP response (e.g., imaginary conductivity) for hydrocarbon contaminated sediments undergoing biodegradation was relatively higher compared to uncontaminated sediments. More specifically, samples from within the smear zone at the site and contaminated with residual hydrocarbon showed a relatively higher magnitude in the IP parameters (e.g., imaginary conductivity) compared to dissolved phase contaminated samples. Previous microbiological study at the site showed a high percentage of oil degrading microorganisms within the smear zone. Further, a laboratory column experiment was conducted to investigate the variations in the temporal changes of IP magnitudes associated with different phases of hydrocarbon contamination (dissolved vs. residual) observed from core sediments from the field. The results showed that the residual diesel contaminated column (residual phase of diesel + nutrients + bacteria) exhibited higher rates of biodegradation compared to the dissolved diesel contaminated column (dissolved phase of diesel + nutrients + bacteria). The higher rate of biodegradation and subsequent microbial-sand-fluid interactions are reflected in a 10--30% higher magnitude of temporal change of measured biological, chemical, isotopic, and electrical parameters in the residual diesel contaminated column. These results suggest that the higher magnitude of IP measurements observed on residual product zone from field cores are due to higher microbial activity.; The findings of this study illustrate the potential utility of low frequency electrical measurements for non-invasive monitoring of microbial activity at sites undergoing natural hydrocarbon degradation. The results of this study further suggest that the interpretation of geoelectrical data from near surface environments should consider effects of microbial processes.
机译：在实验室的沙柱和从碳氢化合物污染地点取回的岩心沉积物中，研究了生物降解过程和随后的理化变化对未固结沉积物的低频电学性质（例如，真实和虚构电导率）的影响。使用感应极化（IP）方法在0.1--1000 Hz的频率范围内进行低频电测量。进行了生物学，地球化学，同位素分析，扫描电子显微镜图像和表面积测量，以帮助解释低频电学测量。在实验室色谱柱实验中，生物色谱柱（营养素，溶解的柴油和细菌）显示（a）实时，虚构和表面电导率随时间增加，并且（b）形成因数随时间减少。非生物色谱柱（营养素；营养素和溶解的柴油）无明显变化。微生物种群数量的增加，有机碳源，硝酸盐和硫酸盐的减少以及溶解的无机碳和流体电导率的增加指示了生物柱中的微生物活性。从现场取回的核心沉积物的IP结果表明，与未污染的沉积物相比，经历了生物降解的碳氢化合物污染的沉积物的IP响应（例如，假想电导率）的幅度相对较高。更具体地，与溶解相污染的样品相比，来自现场涂抹区域内并被残留的烃污染的样品在IP参数（例如，假想电导率）上显示出相对较高的幅度。该地点以前的微生物学研究表明，在涂片区内有很高比例的石油降解微生物。此外，进行了实验室柱实验，以调查与从油田核心沉积物中观察到的烃污染的不同阶段（溶解相对于残余）相关的IP量级的时空变化。结果表明，与溶解的柴油污染塔（柴油+营养物+细菌的溶解相）相比，残留的柴油污染塔（柴油+营养物+细菌的残留相）具有更高的生物降解率。更高的生物降解率和随后的微生物-沙-流体相互作用反映在残留的柴油污染塔中，所测得的生物，化学，同位素和电参数随时间变化的幅度提高了10--30％。这些结果表明，在田间岩心的残留产品区域观察到的IP测量值较高，是由于微生物活性较高。这项研究的结果说明了低频电测量在非侵入性监测天然烃降解位点微生物活动方面的潜在用途。这项研究的结果进一步表明，对来自近地表环境的地电数据的解释应考虑微生物过程的影响。

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