Temporal Dynamics of Dissolved Organic Carbon at the Outlet of a Rewetted Coastal Peatland

Peatlands have a major role in the global carbon cycle. While the gaseous export of carbon from peatlands has already been well-recognized, the dissolved organic carbon (DOC) fraction has not been equally noticed. Despite covering a small area (less than 3%), peatlands contribute from 12% to 20% of the DOC being released to oceans. The DOC dynamics in streams draining peatlands are highly variable, both on seasonal and event scales, and the corresponding drivers are still under discussion, particularly differing between disturbed and pristine peatlands. The objective of this study is to determine the DOC dynamics at the outlet of a rewetted coastal peatland and assess the effects of discharge and salinity. The study area is the nature reserve “Heiligensee and Hütelmoor” on the German Baltic Sea coast with an area of 350 ha. Here, high-frequency time series of discharge and DOC concentrations (complemented with regular samplings) are measured at the drainage/ditch system outlet, and consequently, the DOC export is calculated. According to the results, DOC concentrations demonstrate a seasonal trend and seem to be diluted during higher discharges by rainfall. However, they show no evident correlation with salinity. Moreover, the high‑frequency DOC concentrations, although available only for a limited period, indicate high variabilities following rainfall/discharge events. The discharge exhibits seasonal variabilities with an increase throughout winter, and then, a continuous decrease, and is highly responsive to rainfall events. The DOC exports are strongly linked with the discharge and thus show a similar pattern with the highest values in winter and spring. Our results highlight the necessity of high-frequency fluvial DOC monitoring with respect to extreme flow events in rewetted peatlands and a deeper investigation of the hydroclimatological controls through time-series/statistical analyses. This could provide valuable insights into mitigating excessive DOC export from rewetted peatlands.