Impact of atmospheric N deposition on inorganic- and organic-N outputs in water draining from peat

Replicate intact peat turf microcosms from nine sites along a nitrogen (N) pollution gradient in Great Britain, from Strathvaich in North-West Scotland to Hatfield Moor in the English Midlands, have been subjected to simulated precipitation for 18 months in an unheated glasshouse in Aberdeen. The rainfall applied to each turf had a composition based upon that of rainfall at the UK Department of the Environment (DOE) monitoring sites adjacent to the locations from which the turfs were collected. After an initial 6-month equilibration, drainage water was collected over 12 months and analysed weekly for NH4+, NO3− and total N concentrations. Organic N was thus calculated by difference. Annual N fluxes in the three forms were then calculated. At low to moderate NO3− inputs, NO3− was largely retained in the plant soil system, but at higher NO3− inputs, NO3− leaching occurred. Except at the two most polluted sites, NH4+ leaching exceeded NH4+ input. To a first approximation, leached organic N increased linearly with N input, although at higher N inputs, organic N accumulation apparently became relatively more important. Only at very high N deposition rates do the peats appear to be acidifying as a consequence of N deposition.