The Science

Geophysical methods have been used to map soil spatiotemporal variabilities on terrestrial ecosystems, but their applicability in soils across land–lake interfaces (also known as terrestrial–aquatic interfaces, or TAIs) is not well understood. This study evaluated the sensitivity of multiple geophysical methods to measure and evaluate the spatiotemporal variability of select soil properties across TAIs. Researchers demonstrated not only that geophysical methods are useful for understanding soil architecture and subsurface stratigraphic heterogeneities across TAIs, but that resulting datasets capture much higher spatial resolution than point sampling methods. Incorporation of geophysical understanding also revealed that the stratigraphy and soil moisture dynamics were the key drivers of the observed heterogeneities.

The Impact

Traditional methods of soil investigation, such as soil cores, hand augers, excavation, or sensors, are point measurements that lack spatial resolution. Due to this limitation, measurements may not adequately capture the spatial variabilities necessary to upscale models from site to global scale. This work demonstrated that geophysical methods are useful to expand our understanding of soil architecture and subsurface stratigraphic heterogeneities with higher spatial resolution than point sampling methods. Combining multiple geophysical methods generates more comprehensive maps of stratigraphic structures at land–lake interfaces while also providing more information about soil properties missing information useful for improving models of coastal interfaces.

Summary 

The land–lake interface is an active zone where various geochemical and biological changes occur. The unique characteristics of this interface are not fully understood because subsurface properties vary greatly in time and space, making them difficult to measure with traditional soil sampling methods. To address these limitations, this study compared data from three geophysical methods with measurements from more traditional techniques, including soil core sampling and in situ sensors. The electrical conductivity maps derived from the geophysical tools matched soil maps from a public database that were used for reference. The areas of high conductivity from the geophysical-based data also matched the hydric soil units on the original soil maps, which further demonstrates the utility and accuracy of these tools. Measurements from the geophysical approach also detected additional soil units missed in the reference soil maps. Results from electrical resistivity and radar methods are consistent with the surficial geology of the study area and revealed variation in the vertical silty-clay and till sequence down to 3.5 m depth. This shows that electromagnetic induction could be used to characterize soils in sampling-restricted sites where only noninvasive measurements are feasible. Ultimately, we demonstrated that use of multiple geophysical methods can deduce soil properties and map stratigraphic structures at land–lake interfaces to thereby improve representations of coastal interfaces for Earth system models.

Contacts

Funding

This research is based on work supported by COMPASS-FME, a multi-institutional project supported by the Department of Energy, Office of Science, Biological and Environmental Research program as part of the Environmental System Science Program. This project is led by Pacific Northwest National Laboratory, which is operated for the Department of Energy by Battelle Memorial Institute.

Related Links

COMPASS Project page