Modeling organic matter sources of sediment fluxes in eroding landscapes: Review, key challenges, and new perspectives

Abstract

The coupled relationship between soil erosion and soil organic matter (OM) dynamics has sparked considerable interest in scientific communities in recent decades. However, the question of whether soil erosion acts as a net source or sink for atmospheric carbon dioxide is still a pending issue, possibly due to the uncertainties regarding the fluxes and fates of laterally transported OM in eroding landscapes. Quantifying the OM sources of redistributed sediments on the earth’s surface provides new insight for understanding this issue. In this review, we offer a comprehensive cross-disciplinary review of three approaches to modeling (i.e., end-member mixing models, Bayesian isotope mixing models, and parallel factor analysis (PARAFAC) models) that are widely used to accurately quantify the sources of redistributed OM in its bulk and soluble phases. Furthermore, we present the current knowledge of the benefits and shortcomings of each model and identify key challenges for determining their feasibility. We find that Bayesian isotope mixing models, especially the stable isotope analysis in the R model, better incorporate the uncertainty and variation of tracers compared with end-member mixing models, demonstrating a greater capability for quantifying various bulk OM sources. Excitation-emission matrix spectroscopy (EEMs) - PARAFAC models can identify changes in the fluorescence of dissolved OM to enable tracing of individual fluorescent fractions, thereby usefully supplementing and enhancing bulk OM source apportionment. Finally, future perspectives are proposed to further our understanding of model performance for quantifying the fluxes and fates of redistributed OM across a range of conditions.