Shrub abundance contributes to shifts in dissolved organic carbon concentration and chemistry in a continental bog exposed to drainage and warming

Abstract

AbstractNorthern peatlands are globally significant soil carbon sinks but contribute a significant amount of dissolved organic carbon (DOC) to streams. Climate change driven warming and drying will likely alter peatland DOC dynamics; however, few field studies have quantified the individual and interactive effects of temperature and moisture changes. Using a full factorial water table (control, drained 2 years [experimental], drained 12 years [drained]) × warming (ambient, open‐top chamber warming) × microform (hummock, hollow) study design, we monitored DOC concentration and spectrophotometric properties (specific ultraviolet absorbance [SUVA], E2/E3, E4/E6) in a wooded boreal bog in Alberta, Canada. Ecohydrological conditions including water table (WT), soil temperature, plant cover, biomass, and productivity were also measured at each plot. We observed a significant interaction between WT treatment, warming and microform for explaining variation in DOC concentrations, with the highest values at drained, warmed hummocks. Overall, drainage resulted in higher DOC concentration. DOC concentration and E2/E3 increased, whereas SUVA decreased, in response to greater plant productivity (i.e., more negative values of gross ecosystem photosynthesis). For DOC concentration and SUVA, this correlation was largely driven by drained, warmed hummocks where shrub growth increased. Moreover, redundancy analysis indicated that shrub and lichen cover, along with WT and soil temperature, were important for explaining variation in DOC concentration and quality. The results indicate that, although DOC concentrations in peatlands are likely to increase under climate change, much of this increase may be from recent carbon fixation, suggesting more rapid carbon cycling as opposed to destabilization of existing carbon stocks.