Chronic anthropogenic NO₃^- deposition can alter the way in which carbon (C) is cycled and stored in forest ecosystems. Past work in northern hardwood forests of the Great Lakes region has shown that experimental NO₃^- deposition enhances ecosystem export of dissolved organic C (DOC). It is unclear if this response is elicited by fundamental changes in the microbial decomposition of litter or by utilization of previously recalcitrant pools of soil C. We used stable and radiocarbon isotope techniques and colorimetric assays to qualitatively estimate the source, age, and aromatic content of DOC exported from 4 northern hardwood forest stands receiving 10 years of either ambient or experimental (3 times ambient) atmospheric NO₃^- deposition. Samples were collected from tension-cup lysimeters at 75 cm depth in autumn 2003/2004 and spring 2004. Results showed that regardless of NO₃^- deposition treatment, del ¹³ C-DOC values were as expected for decomposition of C3 plant litter (≈-28 per mil) and delta ¹⁴ C values corresponded to modern C sources. Specific UV absorbance at 254nm, as an estimate of DOC aromatic content, showed that experimental NO₃^- deposition significantly increased the aromatic content of DOC (4.10 ± 0.31 L mg DOC^-1 m^-1) when compared to ambient NO3- deposition (2.81 ± 0.32 L mg DOC^-1 m^-1). Experimental NO₃^- deposition also increased the soluble polyphenolic content of soil solution from 25.03 ± 4.26 µg phenolic C mg DOC^-1 to 49.19 ± 4.23 µg phenolic C mg DOC^-1. These results demonstrate that chronic NO₃^- deposition alters DOC dynamics in these northern hardwood forest soils through changes in the microbial decomposition of litter and not by altering the turnover of stable soil organic matter. Furthermore, these findings suggest that NO₃^- deposition may enhance DOC exports by directly influencing the microbial processes that degrade lignin in the forest floor and mineral soil.