Chemical composition of dissolved organic matter from various sources as characterized by solid-state NMR

This study used solid-state nuclear magnetic resonance techniques to characterize the chemical compositions of DOM from various sources and thereby explore the linkages of river DOM to its potential point and nonpoint sources. DOM samples were isolated from two streams draining watersheds of different land uses, landfill leachates of two ages, sequential (raw, facility- and wetland-treated) wastewaters in a wastewater treatment plant. Two sampling sites along the Missouri River were located upstream and downstream of the outlet of a tributary, to which the stream waters, landfill leachates, and wastewater effluents were discharged. Compared with the chemical composition of the stream DOM from a cropland-dominated watershed, the stream DOM from a grass/forestland-dominated watershed comprised 14 % more alkyl carbons (C), but ~5 % less O-alkyl C. The two leachate DOM samples from landfill cells of two ages showed similar area fractions of the carbon types, and their spectra exhibited a characteristic alkyl C peak at 37 ppm, potentially a molecular signature of the DOM of landfill leachate source. The DOM from the treated wastewater had slightly (~4 %) less alkyl C than that from the raw wastewater, and the DOM from the wetland-treated wastewater displayed decreased O-alkyl C but increased alkyl C, both to a small degree (by ~4 %), compared to the DOM in the facility-treated wastewater. The chemical composition of DOM in the Missouri River was affected by the local organic inputs, with the DOM from downstream the outlet displaying ~11 % higher alkyl C.