Understanding Wetlands Stratigraphy: Geophysics and Soil Parameters for Investigating Ancient Basin Development at Lake Duvensee

Abstract

We present a case study of a bog showing how an integrated approach of multi-method geophysical sounding and local soil sampling can be used to identify, differentiate, and map organic sediments. Our study is based on ground-penetrating radar (GPR), electrical resistivity tomography (ERT) and shear-wave seismic (SH seismic) profiling applied to sediments of the former Lake Duvensee (northern Germany), nowadays a bog. This is a well-known locality for remains from the Mesolithic hunter-gatherers’ occupation that has been attracting archaeological and geoarchaeological research for100 years. The bog is embedded in low conductive glacial sand and is characterized by layers of different gyttja sediments (detritus and calcareous). The present study was conducted in order to identify the bog morphology and the thickness of the peat body and lake sediments, in order to understand the basin evolution. To validate the geophysical results, derived from surface measurements, drilling, soil analyses as well as borehole guided wave analysis of electromagnetic waves and Direct-Push (DP-EC) have been carried out and used for comparison. It turned out that each method can distinguish between sediments that differ in grain size, particularly between peat, lake sediments (gyttjas and mud) and basal glacial sand deposits. GPR is even able to separate between strongly and weakly decomposed peat layers, which is also clear considering resistivity variations in the ERT computation. From the association between geophysical properties and sediment analysis (e.g., water content and organic matter) different gyttjas were distinguished (coarse and fine) and seismic velocity was correlated to bulk density. Moreover, GPR and SH-wave seismics present different resolutions, confirming that the latter allows measurements, which are more focused on determining the extension of basal sand deposits, the depth of which is difficult to reach with GPR. Representative values of electrical resistivity, dielectric permittivity, and shear wave velocity have been determined for each sediment type and are therefore available to complete the investigation of wetland environments. Fine grained lake sediments were difficult to differentiate by the applied methods. This could be a result of high ionic concentration within the permanent groundwater body, partly masking the sediment properties.

Finding Mesolithic Sites: A Multichannel Ground-Penetrating Radar (GPR) Investigation at the Ancient Lake Duvensee

“…Several coring and geophysical campaigns have been performed to clarify and confirm the location and extent of the former islands hosting Mesolithic camps. The work of [10] and [17] present the results of a large-scale 200 MHz GPR investigation that confirmed the location of five former islands hosting Mesolithic camps and improved the knowledge of their size and shape (Figure 1b). Moreover, this survey allowed a 3D reconstruction of the basin's evolution between the early Boreal and the Subboreal bio-zones.…”

“…The gradual infilling of the basin was accompanied by a general decrease in the water level over time and land amelioration, such that by the 19th century CE, most of the basin was occupied by a bog. The authors of [10,17] suggested a model that reconstructs the lake infilling using the stratigraphy and morphology inferred from the geophysical results. Today, a total of 23 Mesolithic camps, named Wohnplatz (WP), have been found at Duvensee, of which 17 have been partly excavated.…”

High-Resolution Direct Push Sensing in Wetland Geoarchaeology—First Traces of Off-Site Construction Activities at the Fossa Carolina

“…Additionally, direct push electrical conductivity sensing resulted in a highly depth-accurate dataset that noticeably improved the spatial significance of common, non-invasive ERT applications e.g., [22,37,81]. Thus, there is a high methodologi-cal potential for future combinations of depth-accurate direct push electrical conductivity logging as point-by-point ground-truthing with ERT data sets [17,24,82,83].…”

Agroforestry System as the Best Vegetation Management to Face Forest Degradation in Indonesia

“…Poor peatland management can lead to degraded land, forest, and land fires. Land-use conversion of about 10 million ha of peatland results in annual emissions of 132-159 Mt C year -1 from peat oxidation and will increase greenhouse gas emissions [45]. Agroforestry is one alternative that can be proposed for peat restoration activities.…”