As an important nutrient reservoir, the mires in the Sanjiang Plain of Northeast China have been suffering from large-scale agriculture reclamation since the 1960s. The effects of the long-term reclamation on the dynamics of the dissolved nutrients in fluvial systems are revealed through surveying the export concentrations of dissolved nitrogen and phosphorus in the natural mire, degraded mire and drainage ditches during the growing seasons in 2009 and 2010. The results show that the mean concentrations of total dissolved nitrogen (TDN, 2.03 ± 0.355 mg l(-1)) are much higher in natural mire than in degraded mire (1.15 ± 0.247 mg l(-1)) and ditches (1.03 ± 0.231 mg l(-1)), and the fraction lessened is primarily the organic part of nitrogen. It indicates that the long-term mire reclamation has led to a significant reduction in TDN concentrations in the surface fluvial system, and has changed the dominant nitrogen components from organic to inorganic formation. In comparison, the concentrations of total dissolved phosphorus (TDP) have no significant difference between natural mire and degraded mire or ditches, which demonstrates that mire reclamation has no impact on TDP export dynamics in the fluvial system. The seasonal dynamics of TDN are strongly correlated to dissolved organic carbon at almost all the sample sites, and mire reclamation does not alter the C : N ratio in the fluvial system, but lowers N : P ratio remarkably. The long-term reclamation exerts distinctly different effects on the export dynamics of TDN and TDP in the fluvial system in the Sanjiang Plain. Specific goals and methods ought to be determined if ecological management and recovery measures are to be carried out.