Environmental factors and dissolved organic carbon content in a Jinchuan peatland

Dissolved organic carbon (DOC) is an important biologically active substrate for microorganisms that has major effects on the biogeochemical nutrients cycles. The loss of DOC through hydrological processes is a major outcome of the carbon content of wetlands being involved in the carbon flux. There has been very little research on the dynamics of DOC and the factors influencing it in wetland ecosystems, especially in the case of peatlands where the nutrient and pH levels are very low. Using field experiments and laboratory analyses, we studied the temporal (May to October) and spatial (0–20 and 20–40 cm depths) distribution of DOC and environmental factors in 5 typical herbaceous communities (Phragmites australis–Carex, Carex–Deyeuxia angustifolia, Carex–Sphagnaceae, Carex schmidtii, and Carex tenuiflora) in the Jinchuan peatland of Jilin province. A positive relationship between DOC and microorganism biomass carbon (MBC) was observed in both soil layers. The seasonal dynamics of DOC was similar for all the communities. The DOC concentration in the 0–20 cm depth range was lower during spring and autumn, and higher during the summer, while the DOC concentration in the 20–40 cm depth range decreased throughout the whole period. The DOC concentration in the 20–40 cm depth range was generally higher than in the 0–20 cm depth range (38.73–150.05 and 20.39–115.73 mg/L, respectively), but the difference was not significant in July and August, when the water level was high because of precipitation. DOC concentration in the Carex–D. angustifolia community (CD) was significantly higher than that of other communities, which may be due to strong human disturbance. The DOC concentration in the peatland was positively correlated with soil surface temperature, total nitrogen, phosphorous, and pH, and negatively correlated with water level, flooding frequency, and oxidation–reduction potential. The results of a stepwise regression analysis showed that the DOC content in the 0–20 cm depth range was mainly influenced by the surface soil temperature and oxidation–reduction potential, while in the 20–40 cm depth range, water quality factors, such as total nitrogen, were more important. The negative relationship between DOC and oxidation–reduction potential was not consistent with the results from other wetland types, probably because of extremely low pH conditions in this case. Significant negative correlations between DOC concentration and MBC content in both the depth ranges are suggestive of a trade-off. Our results point towards the environmental factors that determine the DOC content in the peatland, which therefore play an important role in the carbon cycle of peatlands.