Peatland restoration and the dynamics of dissolved nitrogen in upland freshwaters

•DIN concentrations in waters of degraded peatlands are high.•Peatland restoration significantly reduces DIN leaching to upland freshwaters.•DOC and DON are closely coupled in waters draining bare or revegetated peatlands.

This study assesses the impact of peatland restoration on fluvial N dynamics of south Pennine headwaters (UK) using a space-for-time approach. We monitored dissolved nitrogen in catchment drainage waters at intact, bare, and early stage restoration peatland sites over a two year period (Jan 2013-Dec 2014). Our study demonstrates that peatland restoration is effective in reducing dissolved inorganic nitrogen (DIN) leaching to levels lower than, or comparable to, the intact peatland site despite the adoption of a restoration approach involving fertilizer application in the revegetation process. In comparison with the bare site, DIN leaching was ∼92% (10.2 kg N ha−1 yr−1) lower at the restored site − where vegetation cover has been recently reintroduced. Whilst restoration increased the proportional significance of dissolved organic nitrogen (DON) when compared to the bare site, it was not to a level significantly different from what existed at the intact site. The results also reveal a strong positive relationship (P < 0.001) between DON and dissolved organic carbon (DOC) at all the sites, suggesting similarity of source material. Nitrate decreased with increasing DOC concentrations across the sites, suggesting the influence of organic C supply on NO3− immobilisation. In all but the bare site, average DON concentration was low in winter, but high in summer, and DIN concentration exhibited a winter-high and summer-low pattern; although year-on-year variations in this seasonal pattern was observed mainly at the bare site. Overall, our study has shown that restoration/revegetation is effective in advancing ecosystem recovery of degraded peatlands. Understanding nitrogen behaviour and trajectories as peatland restoration moves beyond early phases will require long-term catchment-scale monitoring.