Referee review: Hydrological processes and permafrost regulate magnitude, source and chemical characteristics of dissolved organic carbon export in a peatland catchment of northeastern China

Abstract. Permafrost thawing in peatland has the potential to alter the catchment export of dissolved organic carbon (DOC), thus influencing carbon cycling in linked aquatic and ocean ecosystems. However, peatland along the southern margins of Eurasian permafrost are seldom examined in spite of the presence of considerable risks associated with degradation due to climate warming. This study examines dynamics of DOC export from a permafrost peatland catchment located in northeastern China during the growing seasons of 2012 to 2014. Our findings show that runoff processes affect observed DOC concentrations, magnitudes, sources, and chemical characteristics of stream discharge. The entire catchment exhibits strong potential for annual DOC exporting (4.87 g C m−2), and DOC from the peatland landscape alone is estimated to amount to 12.89 g C m−2. Annual DOC export processes are closely related to total discharge levels, and floods contribute to approximately 85 % of DOC export levels. Flood volumes derived mainly from peat pore water stored in the upper organic layer of the soil profile prior to rainfall events, creating a strong linkage between discharge and DOC concentrations. DOC source and chemical characteristics, as indicated by three fluorescence indexes, have changed regularly according to source shifts occurring as a result of flood and baseflow processes. A deepening of the active layer due to climate warming should elevate proportions of microbial-originated DOC in the baseflow. Given expected future increases in precipitation, our results show that the magnitude of DOC exports from the study region will increase.

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Hydrological processes and permafrost regulate magnitude, source and chemical characteristics of dissolved organic carbon export in a peatland catchment of northeastern China

Hydrology and Earth System Sciences ◽

10.5194/hess-22-1081-2018 ◽

2018 ◽

Vol 22 (2) ◽

pp. 1081-1093 ◽

Cited By ~ 2

Author(s):

Yuedong Guo ◽

Changchun Song ◽

Wenwen Tan ◽

Xianwei Wang ◽

Yongzheng Lu

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Active Layer ◽

Climate Warming ◽

Carbon Balance ◽

Northeastern China ◽

Chemical Characteristics ◽

Permafrost Degradation ◽

Carbon Export ◽

Seasonal Thawing

Abstract. Permafrost thawing in peatlands has the potential to alter the catchment export of dissolved organic carbon (DOC), thus influencing the carbon balance and cycling in linked aquatic and ocean ecosystems. Peatlands along the southern margins of the Eurasian permafrost are relatively underexplored despite the considerable risks associated with permafrost degradation due to climate warming. This study examined dynamics of DOC export from a permafrost peatland catchment located in northeastern China during the 2012 to 2014 growing seasons. The estimated annual DOC loads varied greatly between 3211 and 19 022 kg yr−1, with a mean DOC yield of 4.7 g m−2 yr−1. Although the estimated DOC yield was in the lower range compared with other permafrost regions, it was still significant for the net carbon balance in the studied catchment. There were strong linkages between daily discharge and DOC concentrations in both wet and dry years, suggesting a transport-limited process of DOC delivery from the catchment. Discharge explained the majority of both seasonal and interannual variations of DOC concentrations, which made annual discharge a good indicator of total DOC load from the catchment. As indicated by three fluorescence indices, DOC source and chemical characteristics tracked the shift of flow paths during runoff processes closely. Interactions between the flow path and DOC chemical characteristics were greatly influenced by the seasonal thawing of the soil active layer. The deepening of the active layer due to climate warming likely increases the proportion of microbial-originated DOC in baseflow discharge.

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