Migration of dissolved organic matters in riparian soils induced by rainfall: distribution between surface and...

The riparian runoff plays a crucial role in transporting terrestrial carbon to surface water, slope gradient and land-use type could impose significant effect on the output pattern of dissolved organic matter (DOM). However, the quantity and composition distribution of DOM in surface and subsurface runoffs are still not fully elucidated. This study systematically investigated the DOM migration behavior during artificial rainfall under different slope gradients and land-use types. The average dissolved organic carbon (DOC) concentrations in both surface and subsurface runoffs are 13.89-48.17 mg/L (wild grassland), 16.39-30.11 mg/L (agriculture land), and 5.66-22.51 mg/L (bare land), respectively. Agriculture land runoff exhibited 2.6-8.2 times higher dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) concentrations than wild grassland and bare land, highlighting its important role in non-point pollution. As the slope gradient increased, the surface and subsurface runoffs tended to carry more bioavailable organics into the rivers, especially the agriculture land. Surface runoff showed a higher proportion of protein-like organics and lower humification degree, suggesting that it is more influenced by soil microbial activities. In contrast, subsurface runoff exhibited higher humification degree, indicating that its DOM originates primarily from the decay of plant residues. The protein-like substances produced by microbial metabolic activities in surface runoff are likely the primary contributors to its higher DON concentration. Compared to subsurface runoff, the DOM in surface runoff is more closely related to soil microbial community structures.