| dc.description.abstract | Peatlands have been important terrestrial carbon reservoirs throughout the Holocene, yet whether these ecosystems will become stronger carbon sinks in the future remains debated. While surface peat layers have a greater apparent rate of carbon accumulation than deeper, millennial-aged peat, it is difficult to project how much more aerobic decomposition will take place before the younger surface cohorts join the older deeper ones, and thus whether ongoing environmental change and human activity are promoting or impeding carbon sequestration. Indeed, processes in the upper, periodically aerobic portion of a peatland (called the acrotelm) are particularly important because this is where peat formation occurs. Over decades to centuries, the young peat in the acrotelm gets progressively incorporated into the permanently anaerobic portion of the peatland (called the catotelm), where decay almost ceases. Studies have suggested that warming could lead to weakened carbon accumulation in peatlands due to enhanced aerobic decay in the acrotelm, which would lead to a slower transfer of peat into the catotelm, if at all. Conversely, other studies have suggested greater C accumulation in the acrotelm and thus, greater long-term carbon transfer into the catotelm under warming conditions because of greater plant productivity and faster peat accumulation. As a result of these contrasting processes, debate continues over the net effect of climate and land-use change on peat carbon stocks in the future. The acrotelm remains a challenging layer to study given its dynamic nature and the difficulty in dating it as well as in isolating the relative role of diagenesis and compaction vs. that of environmental change. Nevertheless, improving our predictions about the rate of present and future peatland development is important to forecast feedbacks on the global carbon cycle, and help inform land management decisions.
In my thesis, I analyzed a series of peat cores from southern Patagonia to calculate their long- vs. short-peat carbon accumulation rates. The acrotelm rates were then compared to the catotelm peat carbon legacies using an empirical modeling approach that allows calculating the future catotelm peat storage based on today’s acrotelm characteristics, and thus predict if those recent rates of carbon accumulation will lead to greater or weaker long-term carbon storage in the future. I also compared the recent rates of carbon accumulation from Patagonia with those from global peatlands using a newly developed database that includes 186 sites. I find that, contrary to previous findings, Patagonian peatlands are not particularly effective at sequestering carbon on the short-term. That said, they are very effective long-term carbon reservoirs, in part perhaps due to their old age (often > 10,000 years). Lastly, the empirical models indicate that, depending on the local climate, some peatlands may become stronger carbon sinks in the future, while others may become weaker. | en |
