François Wiaux

Legacy of human-induced C erosion and burial on soil–atmosphere C exchange

Carbon exchange associated with accelerated erosion following land cover change is an important component of the global C cycle. In current assessments, however, this component is not accounted for. Here, we integrate the effects of accelerated C erosion across point, hillslope, and catchment scale for the 780-km2 Dijle River catchment over the period 4000 B.C. to A.D. 2000 to demonstrate that accelerated erosion results in a net C sink. We found this long-term C sink to be equivalent to 43% of the eroded C and to have offset 39% (17–66%) of the C emissions due to anthropogenic land cover change since the advent of agriculture. Nevertheless, the erosion-induced C sink strength is limited by a significant loss of buried C in terrestrial depositional stores, which lagged the burial. The time lag between burial and subsequent loss at this study site implies that the C buried in eroded terrestrial deposits during the agricultural expansion of the last 150 y cannot be assumed to be inert to further destabilization, and indeed might become a significant C source. Our analysis exemplifies that accounting for the non–steady-state C dynamics in geomorphic active systems is pertinent to understanding both past and future anthropogenic global change.

Soil moisture estimation using full-wave inversion of near- and far-field ground-penetrating radar data: A comparative evaluation

A new near-field ground-penetrating antenna model was applied for characterization of soil moisture in an agricultural transect in central Belgium. The measurement system consists of a vector network analyzer connected with a horn antenna and a differential GPS mounted on a motorcycle for quick data acquisition. Numerical experiments show that near-field GPR data are more sensitive to the soil dielectric properties than far-field data due to nearer distance between the antenna and medium. For the field measurements, the modeled GPR data from far-field and near-field configurations agree very well with the measured ones. However, soil water content estimated from near-field data is higher and more in agreement with Theta Probe measurements than far-field owning to the deeper penetration depth, smaller foot print and larger sensitivity with soil permittivity of near-field data. The results also show that the spatial pattern of the soil moisture is mainly controlled by the topography, while temporal variability is influenced by the rainfall intensity and time lag between rainfall event and experiment. The proposed approach shows a promising potential for temporal and spatial characterization of soil moisture at the field scale.