Leaching dynamics of dissolved organic matter and particulate organic matter in stormwater runoff from floodplain soils.

Organic matter in floodplain soils undergoes complex leaching dynamics during stormwater runoff, directly impacting the water environmental quality of river basin. This study explored the leaching behavior of dissolved organic matter (DOM) and particulate organic matter (POM) in soils from the upper Yellow River floodplain through simulated rainfall experiments. The results showed that DOM and POM were extensively released into the initial rainfall phase (0-20 min), followed by a gradual decline and stabilization in leaching rates. Tryptophan-like substances dominate in the DOM, contributing 45 %-55 % of the total DOM released, while humic substances exhibited a delayed release pattern. POM release was significantly affected by particle size, with smaller particles predominant in the early runoff and larger particles becoming more prominent after 25 min. Two-dimensional correlation spectroscopy (2D-COS) of POM revealed a sequential shift in functional groups, following the order: alcohols > aliphatic compounds > carboxylic acids > esters/ketones > aromatic compounds. Polysaccharides and aliphatic compounds were found to leach preferentially during runoff. Additionally, a transformation between DOM and POM was observed, with larger POM particles gradually converting into DOM, thereby influencing the physicochemical characteristics of the runoff. This study highlights distinct differences in the leaching behavior of DOM and POM during rainfall events, with protein-like and aliphatic compounds showing faster release rates, and smaller particles being more readily mobilized into runoff.