Determining frequency dependence of carbon turnover in peat using spectral induced polarization

2021 ◽  
Author(s):  
Timea Katona ◽  
Benjamin Gilfedder ◽  
Sven Frei ◽  
Lukas Aigner ◽  
Matthias Bücker ◽  
...  
Keyword(s):  
Frequency Dependence ◽  
Iron Oxides ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Electrode Polarization ◽  
Biogeochemical Processes ◽  
Carbon Turnover ◽  
Spectral Induced Polarization ◽  
Polarization Response ◽  
Imaging Results

<p>Our study discusses imaging results from a spectral induced polarization (SIP) survey to identify concurring processes (such as aerobic respiration, denitrification, or sulfate- and iron reduction) in a biogeochemically active peat in a wetland located in the Lehstenbach catchment in Southeastern Germany. Terrestrial wetland ecosystems such as peatlands are a critical element in the global carbon cycle. Due to their role as natural carbon sinks and ecological importance for an array of flora and fauna, there is a growing demand to conserve and restore degraded peatlands. Biogeochemical processes occur with non-uniform reaction rates within the peat, making the environment sensitive to physical disturbances. To investigate biogeochemical processes in-situ, it is important to avoid disturbing the redox-sensitive conditions in the subsurface by bringing oxygen into anoxic areas.  Our previous study demonstrated that the induced polarization (IP) was able to identify biogeochemically active and inactive areas of the peat. The IP response was sensitive to the presence of carbon turnover and P release in the absence of iron sulfide. These highly polarizable areas have high iron concentrations, but most likely in an oxidized form. As most iron oxides are poor conductors, the strong polarization response is unlikely related to an electrode polarization process.</p><p>Here we also analyzed the frequency dependence of the SIP data to investigate whether iron oxides and carbon-iron complexes, two possible mechanisms for the high polarization response, can be distinguished. SIP imaging data sets covered the frequency range between 0.06 and 225 Hz and were collected with varying electrode spacing (20 and 50 cm) at different locations within the Waldstein catchment characterized by different properties, e.g., saturated and non-saturated soils. Our imaging results reveal variations of the IP effect within the peat layer, indicating substantial heterogeneities in the peat composition and biogeochemical activity. The frequency dependence allowed us to resolve a sharper contrast between the different features of the peat. Geochemical analyses on a freeze core and pore water samples are used to validate our results and find correlations between the Cole-Cole parameters of the SIP response and the geochemical parameters.</p>

Quantification of clay content using the transient electromagnetic and spectral induced polarization method

2021 ◽  
Author(s):  
Lukas Aigner ◽  
Timea Katona ◽  
Hadrien Michel ◽  
Arsalan Ahmed ◽  
Thomas Hermans ◽  
...  
Keyword(s):  
Grain Size ◽  
Critical Role ◽  
Clay Content ◽  
Induced Polarization ◽  
Single Frequency ◽  
Time Range ◽  
Data Set ◽  
Transient Electromagnetic ◽  
Spectral Induced Polarization ◽  
Imaging Results

<p>Detailed information on the clay content of the subsurface and its spatial distribution plays a critical role in the interaction between surface- and groundwater. In this study, we investigate a new methodology to integrate data measured with electromagnetic and electrical geophysical methods, namely, the transient electromagnetic (TEM) and the spectral induced polarization (SIP) to quantify subsurface clay content in an imaging framework. The methodology is tested in data sets collected at a quarry close to Vienna and consists of a ca. 10 m thick clay layer below a ca. 8 m thick overburden of sandy silts. Our data set includes SIP data collected along a 315 m long profile with an electrode separation of 5 m in a frequency range from 0.1 to 225 Hz. Along this profile, we measured 26 TEM soundings using a 12.5 m loop with 24 windows recording in a time range between 4 and 140 μs. Ground truth information corresponds to grain size analysis conducted in 25 soil samples collected in a depth from 5 to 28 m. SIP inversion results at a single frequency provided structural a-priori information to improve the inversion of the TEM data. The inverted TEM conductivity model, nearest to the position of soil sample collection, was correlated to the grain size distribution and the resulting positive exponential relationship was used to obtain vertical 1D variations of clay content with depth. All sounding positions were interpolated to obtain a 2D image of subsurface clay content. This clay content variations were then compared to images of the Cole-Cole parameters, describing the frequency dependence of SIP imaging results. To evaluate the uncertainty in our clay estimations, we applied the Bayesian evidential learning 1D imaging (BEL1D). We obtained uncertainties of layer thickness, resistivity, and clay content by integrating the clay-conductivity relationship derived from TEM data into the BEL1D framework.</p>

Cable arrangement to reduce electromagnetic coupling effects in spectral-induced polarization studies

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. A1-A5 ◽  
Author(s):  
Myriam Schmutz ◽  
Ahmad Ghorbani ◽  
Pierre Vaudelet ◽  
Amélie Blondel
Keyword(s):  
Coupling Effect ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Coupling Effects ◽  
Array Type ◽  
Spectral Induced Polarization ◽  
Computer Codes ◽  
Lateral Offset ◽  
Phase Angles

Spectral-induced polarization (SIP) is widely used for environmental and engineering geophysical prospecting and hydrogeophysics, but one major limitation concerns the electromagnetic (EM) coupling effect. The phase angles related to EM coupling may increase even at frequencies as low as 1 Hz, depending on the ground resistivity, the array type, and the geometry. Most efforts to understand and quantify the EM coupling problem (e.g., theory and computer codes) have been developed for dipole-dipole arrays. However, we used a Schlumberger array to acquire SIP data. We found that with this array, the use of an appropriate cable arrangement during data acquisition can reduce EM coupling effects in the same proportion as for the use of a dipole-dipole array, which is the pure response of the studied earth. To measure the influence of the cable layout, four cable configurations with the same electrode spacing were compared for modeling and experimental data. We discovered that the classical DC inline array was the worst one. As soon as the cables were arranged in another shape (triangle or rectangle), the coupling effect decreased significantly. The best configuration we checked was the rectangular one with an acquisition unit located at a lateral offset of 100 m from the electrode line, even if there was still some difference between the modeled and measured data.

scholarly journals Upscaling of spectral induced polarization response using random tube networks

2017 ◽  
Vol 209 (2) ◽  
pp. 948-960 ◽  
Author(s):  
Alexis Maineult ◽  
André Revil ◽  
Christian Camerlynck ◽  
Nicolas Florsch ◽  
Konstantin Titov
Keyword(s):  
Induced Polarization ◽  
Spectral Induced Polarization ◽  
Polarization Response
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