Surface microrelief induced by tillage management alters the pathway and composition of dissolved organic matter exports from soils to runoff during rainfall

Abstract

Rainfall-runoff process mobilizes considerable dissolved organic matter (DOM) from soils to aquatic systems via surface and sub-surface flow pathways. Microrelief induced by tillage management can alter this flow partitioning and thus likely affect the associated pathway and composition of DOM exports during rainfall. This study conducted rainfall simulation experiments, combined with three-dimensional fluorescence spectra analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) technology, to explore the effects of different surface microreliefs treatments on the quantity and composition of DOM exports at a plot scale. Four typical microrelief treatments (i.e., contour tillage (CP), longitudinal tillage (LP), artificial digging tillage (AP), and flat tillage (CK, as control)) were selected. Results showed that ratios of surface to sub-surface flow volume under four treatments were in order of LP (193:1)>CK (73:1)>AP (4.5:1)>CP (0.5:1). DOM concentrations in sub-surface flow (13.37∼33.50 mg L-1) were 7∼18 times of that in surface flow (0.03∼4.56 mg L-1). The total export fluxes of DOM were 134, 139, 563, and 1214 mg m-2 at LP, CK, AP, and CP treatments, respectively, with proportions of 8%, 17%, 82%, and 98% via sub-surface flow. Compared to surface flow, DOM molecular composition in sub-surface flow showed a significant feature of higher oxygen to carbon ratio, higher molecular weight, and lower hydrogen to carbon ratio. The findings indicated that microrelief with higher surface storage capacity tends to favor a large flux of DOM export, primarily via sub-surface flow, which might significantly affect the DOM cycling in the receiving aquatic ecosystems.