Will Coastal Peatlands be a Nitrogen Source to Marine Ecosystem Under Increasing Drought and Storm Events?.

Over the past several decades there has been a massive increase in coastal eutrophication, especially along the north Atlantic coasts of North American and Europe, leading to widespread “dead zones” with cascading environmental consequences. Such eutrophication is often caused by increased nitrogen input. Peatlands, covering 3% of land area, store about 12-21% global soil organic N (12-20 Pg N). The huge peatland nitrogen pool might be “unlocked” by intensification of extreme hydrologic events – prolonged droughts and heavy storms – and threaten marine ecosystem. In this study, we collected intact peat monoliths from drained, natural and restored pocosin peatlands in the Southeastern USA and conducted a microcosm experiment simulating coupled drought and rewetting to test whether (1) storms/rewetting cause an increase in nitrogen export from drained and drought-stressed peatlands and (2) past hydrologic management regimes have an effect on this process.

During a 15-month drought, we observed significant temporal variations in net nitrogen mineralization rate (NMR). NMR spiked in the third month, and then decreased rapidly. This pattern indicates that drought duration significantly affects nitrogen mineralization in peat and that large amounts of organic nitrogen can be mineralized in a relatively short amount of time. Among peat monoliths from differently managed sites, NMR in drained site was up to 490±110 kg ha^-1 yr^-1—about 5 times higher than in the restored site. After the drought, we simulated a heavy storm with 160 mm precipitation bringing peat monoliths to saturation. High concentrations of total inorganic nitrogen, 21.3±2.0, 9.5±3.4, and 4.4±1.1 mg L^-1 in drained, natural and restored sites, were found in the pore water. Our results imply that heavy storms may flush out huge amounts of mineralized nitrogen from drained and drought-stressed peatlands and that prolonged climatic drought make previously drained peatlands an especially potent source of exported nitrogen.