Assessing hydrological connectivity inside a soil by fast-field-cycling nuclear magnetic resonance relaxometry and its link to sediment delivery processes

Connectivity is a general concept used to represent the processes involving a transfer of matter among the elements of an environmental system. The expression “hydrological connectivity inside the soil” has been used here to indicate how spatial patterns inside the soil (i.e., the structural connectivity) interact with physical and chemical processes (i.e., the functional connectivity) in order to determine the subsurface flow (i.e., the water transfer), thereby explaining how sediment transport due to surface runoff (i.e., the soil particle transfer) can be affected. This paper explores the hydrological connectivity inside the soil (HCS) and its link to sediment delivery processes at the plot scale. Soils sampled at the upstream- and downstream-end of three different length plots were collected together with sediments from the storage tanks at the end of each plot. All the samples were analyzed by traditional soil analyses (i.e., texture, Fourier transform infrared spectroscopy with attenuated total reflectance, C and N elemental contents) and fast-field-cycling (FFC) nuclear magnetic resonance (NMR) relaxometry. Results revealed that selective erosion phenomena and sediment transport are responsible for the particle size homogeneity in the sediment samples as compared to the upstream- and downstream-end soils. Moreover, while structural connectivity is more efficient in the upstream-end soil samples, functional connectivity appeared more efficient in the downstream-end and sediment samples. Further studies are needed in order to quantitatively assess FFC NMR relaxometry for HCS evaluation.