Effects of drainage on dissolved organic carbon (DOC) characteristics of surface water from a mountain peatland

Highlights: • DOC characteristics from natural and drained areas in a peatland were investigated. • "Enzyme latch" may play an important role in DOC concentration according to drainage. • Plant community also affects DOC concentrations during mid-growing season. • Drainage increases both aromaticity and percentage of protein-like structures in DOC. Dissolved organic carbon (DOC) plays an important role in regulating the carbon cycles in the peatland. In this study, we collected surface water once or twice a month from natural and drained areas of peatland in the Changbai Mountain, northeastern China, and determined the concentrations, spectral information, and composition of DOC, as well as the concentrations of other elements. The results showed that the concentrations of total N and NH₄⁺ in the drained area were significantly higher than those in the natural area in most cases, but concentrations of total dissolved Fe were significantly lower. The DOC concentrations in the natural and drained area ranged from 31.0 mg L⁻¹ to 320.8 mg L⁻¹ and from 33.2 mg L⁻¹ to 105.8 mg L⁻¹, respectively. It is shown that DOC concentration in the drained area was generally lower than those in the natural area in mid-growing season, but it was higher in early- and end-growing seasons. SUVA₂₅₄ (Abs254/DOC concentration) in the drained area was generally higher than in the natural area, indicating more aromatic DOC fraction in drained area. No consistent difference in other spectroscopy was observed between natural and drained areas. In contrast, molecular analysis of DOC not only confirmed an increase in the fraction of aromatic compounds in DOC but also showed different compositions of DOC between the natural and drained areas on molecular level, suggesting enhanced decomposition of peat organic matters after drainage. Notably, the average percentage of protein-like structures in DOC in drained area was significantly higher than that in natural area (14.9 ± 1.7% vs. 12.8 ± 0.8%), indicating preferential release of dissolved organic nitrogen from peat organic matter. Overall, this study suggests drainage can enhance decomposition of peat organic matters, resulting in more protein-like structures released into water.