Nitrogen input into Sphagnum bogs via horizontal deposition: an estimate for N-polluted high-elevation sites

Abstract

Elevated atmospheric deposition of reactive nitrogen species, mainly nitrate (NO3 −) and ammonium (NH4 +), may negatively affect peatland carbon balance and thus contribute to climatic warming. It is difficult to take an accurate inventory of atmospheric N inputs into Sphagnum-dominated bogs, due to uncertainties in estimating horizontal deposition. At two mountain-top peat bogs (Czech Republic, Central Europe), we modelled N interception by replacing S. cuspidatum capitula with polyethylene (PE) strands of an identical surface area. After a 12-week exposure of the samplers to frequent spring and autumn fogs, we compared the amount of N captured by the PE strands (nitrate, ammonium, and organic N) with vertical N deposition via rainfall. Horizontal deposition added 35–69 % N to rainfall N input. The more polluted site exhibited a significantly higher horizontal N deposition than the less polluted site. We scaled our S. cuspidatum data to S. capillifolium, a species common in boreal regions in the form of densely packed carpets. Assuming a proportional decrease in N interception with decreasing Sphagnum surface, we estimated that horizontal deposition in S. capillifolium would add 12–45 % N to rainfall N input. Our data will help to close the N mass balance in peat bogs studies.