Impacts of natural wetland degradation on dissolved carbon dynamics in the Sanjiang Plain, Northeastern China

SummaryWetlands are important dissolved organic carbon (DOC) reservoirs, and principal sources of DOC to the fluvial environment, constituting a significant linkage between land and ocean in the context of global carbon cycle. The Sanjiang Plain, a floodplain in Northeastern China that encompasses numerous natural freshwater wetlands, has been experiencing extensive building of drainage ditches and thus elevated degradation of wetlands. This paper investigated DOC, dissolved inorganic carbon (DIC), and dissolved total carbon (DTC) in soil, the surface ponding and rivers from natural wetlands and the degraded wetland, and also in an artificial drainage ditch in the Sanjiang Plain during the growing season (May to October) of 2009. Seasonal averaged DOC concentrations were greater in soil and the surface ponding of the degraded riparian wetland than those originating from the natural riparian wetlands (i.e. Bielahong, Yalv and Nongjiang riparian wetlands). Seasonal averaged DIC concentrations in the surface ponding of the degraded wetland increased by 1.76, 0.59 and 2.05 times, compared to those in the Bielahong, Yalv and Nongjiang riparian wetlands, respectively. Similar to dissolved carbon dynamics in the field sites, the seasonal averaged DOC concentration in the degraded marshy river showed higher value (10.36 ± 1.99 mg/L), compared to those in the pristine marshy rivers. Seasonal DIC concentrations followed a trend as the degraded marshy river (15.09 ± 2.43 mg/L) – the artificial ditch (12.52 ± 1.61 mg/L) – pristine marshy rivers on average (8.53 ± 0.96 mg/L). Seasonal mean DTC concentration in the artificial ditch showed higher values than that in the natural marshy rivers, while seasonal mean DTC concentration in the degraded marshy river was greater than that in the artificial ditch. Further, seasonal DOC and DIC dynamics were similar in the artificial ditch and the degraded marshy river. These qualitative changes in the dissolved carbon dynamics in our study might have important implications that the impact of building of artificial ditches on dissolved carbon of waters more fully reflected in increases of dissolved carbon resulting from wetland degradation rather than increases in the artificial ditch itself.

Research highlights► We observed an increased loss of DOC in the river from the degraded wetland compared to those in pristine marshy rivers. ► DIC concentration in the degraded marshy river was higher than those in pristine marshy rivers. ► Dissolved carbon dynamics in point scale could be a good predictor for that in-stream.