Temporal dynamics and vertical distribution of dissolved organic carbon in snowmelt runoff in a temperate deciduous forest in Maoershan region, northeastern China.

The dissolved organic carbon (DOC) during snowmelt period is crucial to analyzing carbon outputs from terrestrial ecosystems to rivers by streamflow in northern regions. The aim of this work was to quantify temporal dynamics and vertical distribution of DOC concentration and flux in snowmelt runoffs. A water balance plot with an area of 625 m2 was established in a typical temperate deciduous forest in Maoershan Forest Ecosystem Research Station, northeastern China, and the snowmelt runoffs and DOC concentrations at four different soil depths (5, 35, 65, and 95 cm) were measured in 2014. The results showed that: 1) the inputs of water and DOC into the soil during the snowmelt period were 74.2 mm and 0.25 g/m2, respectively, while the outputs were 15.6 mm and 0.22 g/m2, respectively. The runoff rate reached approximately 21%, but the input and output of DOC were roughly balanced. 2) The relationships between DOC concentration and instantaneous water flow rate varied with soil depths during the peak period of snowmelt. DOC concentration and instantaneous water flow rate were not correlated significantly (P0.05) at 5 and 35 cm soil depths, but significantly, negatively correlated at 65 cm soil depth (R2=0.29, P0.05) and positively at 95 cm soil depth (R2=0.43, P0.05). The instantaneous DOC flux and water flow rate were significantly, linearly correlated for all the soil depths (R20.9,P0.001), and the greater the instantaneous water flow rates were, the steeper the slopes of the linear equations for the soil layers were, suggesting a hydrologically driven DOC loss. 3) Both DOC and water exported at different soil depths during the snowmelt period followed the order of 35 cm5 cm65 cm95 cm. The amount of water and DOC exported at 5 and 35 cm soil depths accounted for 70% of the total in the soil profile. The variability in DOC concentrations tended to converge to low concentration with the soil depth increasing due to the effect of soil retention.