The impact of alternating drainage and inundation cycles on geochemistry and microbiology of intact peat cores

The rewetting of degraded peatlands has been adopted as a method to address climate change. Concerns have been raised about the effects of peat inundation and drying cycles, in more extreme climate events, on the potential release of nitrogen (N) species, in particular ammonium (NH4-N), once rewetted, as well as the physico-chemical and biolog-ical properties of the peat. This study used intact peat cores to measure the impact of two different cycles of peat inun-dation and drying (1 month and 2 month) over a total study duration of 56 weeks on the (1) NH4-N, nitrate-N (NO3-N) and dissolved reactive phosphorus (DRP) in the soil pore water; (2) microbial community structure; (3) physico-chemical properties of the peat; and (4) the structure of the peat, and therefore its ability to mitigate flood risks and storm surges. The study found that rewetted cores released NO3-N in the pore water up to a concentration of 6.25 mg L-1, but had no appreciable impact on NH4-N, which remained below 1.7 mg L-1 over the study duration. DRP moved quickly though the upper layers of the cores, but physico-chemical analysis suggested it was adsorbed to more iron-rich soil, which was present at depths below 0.4 m in the cores. Time intervals between inundation pro-duced no significant difference on the forms of inorganic N released, nor did it compact the soil or change the microbial community structure. The depth of the water table, however, had a significant impact on inorganic N release, partic-ularly NO3-N, which indicates that this N species, and not NH4-N, may be problematic in rewetted peatlands.

Automated summary

This study investigated the effects of peat inundation and drying cycles on nitrogen release and physico-chemical properties of peat. The results showed that rewetted peat released high concentrations of nitrate-N, but had no significant impact on ammonium-N. The depth of the water table had a significant effect on inorganic nitrogen release, particularly nitrate-N.