Impact of mire reclamation on export potential and characteristics of dissolved carbons in the Sanjiang Plain, Northeast China

Abstract. As an important dissolved organic carbon (DOC) reservoir, the mires in the Sanjiang Plain, Northeast China, have been suffering from large scale of reclamation, and thus elevated loss and degradation since the 1960s. This study compares the export dynamics of the dissolved carbons, as well as the chemical characteristics of DOC, in the natural mire, degraded mire and drainage ditches during the growing seasons from 2008 to 2010 with the aim to clarify the final effects of the longterm reclamation on the export dynamics of the dissolved carbons. Results show that the average concentrations of total dissolved carbon (TC) and DOC are much higher in natural mires than that in degraded mire and drainage ditches. The DOC concentration for natural mires, about 35.53 ± 5.15 mg l⁻¹ on average, is nearly 2.39 times of that in degraded mire (14.84 ± 4.21 mg l⁻¹) and 2.77 times of the average value in ditches (12.84 ± 4.49 mg l⁻¹). Similarly, the hydrophobic fraction and SUVA₂₅₄ of DOC also represent lower values in the degraded mire and ditches, which suggests that mire reclamation has resulted not only in the reduced DOC concentrations but also in the reduced chemical stability. Whereas the inorganic dissolved carbons (DIC) exhibits obvious increased trends in drainage ditches in comparison to natural mires. Analyses of exitation-emission fluorescence spectra reveal that the reclamation has greatly altered the DOC composition with more biological organic substances exporting from the Sanjiang Plain. The presence of protein- and tryptophan-like substances in the ditches indicates there has been extensive agricultural pollution in the surface waters. Changes in the hydrological regime of the mire landscapes by sustained agriculture activities are deemed the prodominant reason, and the trends in the export dynamics of dissolved carbons will keep on if mire reclamation continues in the future.